Polymat Contributions

Proceedings Volume 1 Vol. 1 Pag.1

PHOSPHORUS DENDRIMERS: HYPERBRANCHED MACROMOLECULES FOR NANOSCIENCES

Anne-Marie Caminade1,2

1 CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France, E-mail: [email protected] 2 Université de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France

Dendrimers [1] are hyperbranched macromolecules, constituted of repetitive monomeric units as polymers, but they are never synthesized by polymerisation reactions. Dendrimers have a perfectly defined 3D structure, thanks to their step-by-step synthesis, layer after layer. Each time an additional layer of branching points is added, a new generation is created. Among the diverse types of dendrimers, phosphorus-containing dendrimers, in particular polyphosphorhydrazone dendrimers [2] occupy a special place, due to their numerous properties, as illustrated in Figure 1.

Figure 1. Chemical structure of a second generation polyphosphorhydrazone dendrimer. Properties and uses of this family of dendrimers, depending on the nature of the terminal groups R.

A few typical examples of these properties will be given below, concerning catalysis, nanomaterials, and biology/nanomedicine. Vol. 1 Pag.2

The use of dendrimers for catalysis concerns in general dendrimers having catalytic entities as terminal functions. The expected properties are an easy recovery, as the dendrimers have a larger size than the products and reagents, and possible synergistic effects, due to the proximity of the catalytic sites, which may afford better results than monomeric catalysts, for instance increased yields. In the case of phosphorus dendrimers, mainly positive dendritic effects [3] have been observed for the outcome of catalysis. The main types of ligands linked as terminal functions of phosphorus dendrimers and the metals used for their complexation are shown in Figure 2. These dendrimers have been used in most cases for catalyzing C-C couplings. The most salient features when using dendritic catalysts are: i) an easy recovery and re-use of the dendritic catalysts, up to 12 times by precipitation or by magnetic recovery [4], and even with an increased efficiency (yield) when entrapping Pd nanoparticles [5]; ii) an increased yield when the generation of the dendrimer increases, but using an identical number of catalytic sites (for instance 12 equivalents of monomeric catalyst compared with one equivalent of a first generation dendrimer, bearing 12 catalytic entities as terminal functions) [6]; an increased enantiomeric excess when the generation increases [7]; and the possibility to switch ON/OFF the catalytic activity by modifying the redox properties. [8]

Figure 2. Types of ligands used as terminal functions of phosphorus dendrimers for the complexation of different metals. The corresponding complexes have been used as catalysts, most generally for C-C couplings.

In the field of materials, dendrimers have been used either for creating new nanomaterials incorporating dendrimers, or for modifying at the nanoscale the surface of existing materials. Vol. 1 Pag.3

Mesoporous silica,[9] ordered titanium oxide clusters,[10] and rigid hydrogels [11] pertain to the first cases. Modified electrodes,[12] and elaboration of biological sensors [13] pertain to the second cases. Nanotubes [14,15] exclusively constituted of dendrimers have been also obtained thanks to electrostatic interactions between positively and negatively charged dendrimers. Most examples of polyphosphorhydrazone dendrimers used in the field of materials have as terminal functions those shown in Figure 3.

Figure 3. Selected examples of terminal functions of phosphorus dendrimers used for creating of modifying nanomaterials.

In the field of biology, the dendrimers need to be soluble in water.[16] Water-solubility of phosphorus dendrimers is afforded by the terminal groups; selected examples are shown in Figure 4. These dendrimers can be used for drug delivery, or as drugs by themselves. Phosphorus dendrimers ended by ammonium groups are useful for transfection experiments, to help negatively charged biological entities (DNA, RNA, plasmids, etc) to penetrate inside cells.[17] These dendrimers have also anti-prion activities,[18] including in vivo. [19] Negatively charged dendrimers (carboxylate terminal functions) interact with positively charged drugs, to facilitate their delivery. This includes drugs against HIV,[20] and to treat ocular diseases.[21] Drugs can be covalently linked to the surface of dendrimers, such as mannose derivatives, which prevent in vivo the acute inflammation of lungs.[22] However, some dendrimers can be drugs by themselves, it means that the functions of their surface have no special properties, but they become active when linked to the dendrimers. This is in particular the case of azabisphosphonic groups. The as functionalized dendrimers have many properties towards the human immune sytem.[23] In a study for a structure/activity relationship, many different phosphonic derivatives have been synthesized. The biological properties discovered include the multiplication of Natural Killer (NK) cells,[24] and anti- inflammatory properties against reumathoid arthritis,[25] and multiple sclerosis [26].

Figure 4. Selected examples of water-soluble terminal functions of phosphorus dendrimers used in the field of biology. Vol. 1 Pag.4

References [1] Caminade, A.-M.; Turrin, C.-O.; Laurent, R.; Ouali, A.; Delavaux-Nicot, B.; Editors, Dendrimers: Towards Catalytic, Material and Biomedical Uses. John Wiely & Sons Ltd.: Chichester, UK, 2011. [2] Launay, N.; Caminade, A. M.; Lahana, R.; Majoral, J. P. Angew. Chem. Int. Ed. Engl. 1994, 33, 1589-1592. [3] Caminade, A. M.; Ouali, A.; Laurent, R.; Turrin, C. O.; Majoral, J. P. Chem. Soc. Rev. 2015, 44, 3890-3899. [4] Keller, M.; Colliere, V.; Reiser, O.; Caminade, A. M.; Majoral, J. P.; Ouali, A. Angew. Chem. Int. Ed. 2013, 52, 3626-3629. [5] Badetti, E.; Caminade, A. M.; Majoral, J. P.; Moreno-Manas, M.; Sebastian, R. M. Langmuir 2008, 24, 2090-2101. [6] Ouali, A.; Laurent, R.; Caminade, A. M.; Majoral, J. P.; Taillefer, M. J. Am. Chem. Soc. 2006, 128, 15990-15991. [7] Garcia, L.; Roglans, A.; Laurent, R.; Majoral, J. P.; Pla-Quintana, A.; Caminade, A. M. Chem. Commun. 2012, 48, 9248-9250. [8] Neumann, P.; Dib, H.; Caminade, A. M.; Hey-Hawkins, E. Angew. Chem. Int. Ed. 2015, 54, 311- 314. [9] Turrin, C. O.; Maraval, V.; Caminade, A. M.; Majoral, J. P.; Mehdi, A.; Reye, C. Chem. Mater. 2000, 12, 3848-3856. [10] Soler-Illia, G.; Rozes, L.; Boggiano, M. K.; Sanchez, C.; Turrin, C. O.; Caminade, A. M.; Majoral, J. P. Angew. Chem. Int. Ed. 2000, 39, 4250-4254. [11] Marmillon, C.; Gauffre, F.; Gulik-Krzywicki, T.; Loup, C.; Caminade, A. M.; Majoral, J. P.; Vors, J. P.; Rump, E. Angew. Chem. Int. Ed. 2001, 40, 2626-2629. [12] Le Derf, F.; Levillain, E.; Trippe, G.; Gorgues, A.; Salle, M.; Sebastian, R. M.; Caminade, A. M.; Majoral, J. P. Angew. Chem. Int. Ed. 2001, 40, 224-227. [13] Le Berre, V.; Trevisiol, E.; Dagkessamanskaia, A.; Sokol, S.; Caminade, A. M.; Majoral, J. P.; Meunier, B.; Francois, J. Nucleic Acids Res. 2003, 31, 8. [14] Kim, D. H.; Karan, P.; Goring, P.; Leclaire, J.; Caminade, A. M.; Majoral, J. P.; Gosele, U.; Steinhart, M.; Knoll, W. Small 2005, 1, 99-102. [15] Caminade, A. M.; Majoral, J. P. Chem. Soc. Rev. 2010, 39, 2034-2047. [16] Caminade, A. M.; Hameau, A.; Majoral, J. P. Chem.-Eur. J. 2009, 15, 9270-9285. [17] Loup, C.; Zanta, M. A.; Caminade, A. M.; Majoral, J. P.; Meunier, B. Chem.-Eur. J. 1999, 5, 3644- 3650. [18] Ottaviani, M. F.; Mazzeo, R.; Cangiotti, M.; Fiorani, L.; Majoral, J. P.; Caminade, A. M.; Pedziwiatr, E.; Bryszewska, M.; Klajnert, B. Biomacromolecules 2010, 11, 3014-3021. [19] Solassol, J.; Crozet, C.; Perrier, V.; Leclaire, J.; Beranger, F.; Caminade, A. M.; Meunier, B.; Dormont, D.; Majoral, J. P.; Lehmann, S. J. Gen. Virol. 2004, 85, 1791-1799. [20] Blanzat, M.; Turrin, C. O.; Aubertin, A. M.; Couturier-Vidal, C.; Caminade, A. M.; Majoral, J. P.; Rico-Lattes, I.; Lattes, A. ChemBioChem 2005, 6, 2207-2213. [21] Spataro, G.; Malecaze, F.; Turrin, C. O.; Soler, V.; Duhayon, C.; Elena, P. P.; Majoral, J. P.; Caminade, A. M. Eur. J. Med. Chem. 2010, 45, 326-334. [22] Blattes, E.; Vercellone, A.; Eutamene, H.; Turrin, C. O.; Theodorou, V.; Majoral, J. P.; Caminade, A. M.; Prandi, J.; Nigou, J.; Puzo, G. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 8795-8800. [23] Caminade, A. M.; Fruchon, S.; Turrin, C. O.; Poupot, M.; Ouali, A.; Maraval, A.; Garzoni, M.; Maly, M.; Furer, V.; Kovalenko, V.; Majoral, J. P.; Pavan, G. M.; Poupot, R. Nature Comm. 2015, 6, 7722. [24] Griffe, L.; Poupot, M.; Marchand, P.; Maraval, A.; Turrin, C. O.; Rolland, O.; Metivier, P.; Bacquet, G.; Fournie, J. J.; Caminade, A. M.; Poupot, R.; Majoral, J. P. Angew. Chem. Int. Ed. 2007, 46 (14), 2523-2526. [25] Hayder, M.; Poupot, M.; Baron, M.; Nigon, D.; Turrin, C. O.; Caminade, A. M.; Majoral, J. P.; Eisenberg, R. A.; Fournie, J. J.; Cantagrel, A.; Poupot, R.; Davignon, J. L. Science Transl. Med. 2011, 3, 11. [26] Hayder, M.; Varilh, M.; Turrin, C. O.; Saoudi, A.; Caminade, A. M.; Poupot, R.; Liblau, R. S. Biomacromolecules 2015, 16, 3425-3433. Vol. 1 Pag.5

Enantioselective Catalysis with 3d Transition Metal Complexes: Chiral Pincers as Stereodirecting Ligands

Lutz H. Gade Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg

Meridionally coordinating chiral tridentate ligands, frequently referred to as “pincers”,1 provide the structural platform for the construction of efficient stereodirecting molecular environments. Whilst many of the known chiral systems of the “pincer” type perform relatively poorly in enantioselective catalysis due to certain lack of control of substrate orientation, the assembly from rigid heterocyclic units recently has given rise to several highly enantioselective catalysts.2 In particular five different classes of pincer ligands [Cbzbox (1),3 BOPA (2),4 Boxmi (3), BPI (4), and PyrrMeBOX (5), Figure 1] which contain a central anionic nitrogen σ-donor and two pendant lone pair donors from nitrogen atoms in oxazoline or pyridine rings have given rise to highly active and selective catalysts. The focus has been initially on the asymmetric Nozaki-Hiyama-Kishi coupling of aldehydes with halogenated hydrocarbons3,4 and, subsequently, on the development of Lewis acid catalysts involving an enantioselective electrophilic attack inter alia onto metal activated β-ketoesters and oxindoles. Increasingly, these stereodirecting ligands are being employed in other types of transformations, including hydrosilylations, cyclopropanations, and epoxidations, which will be reviewed in the final section of this overview.5 O Ph Ph R R1 N 2 N H NH N 1 H O N N O R O O N R2 N N R3 R1 R2 R3 O R 1 R 2 3 Cbzbox BOPA Boxmi

* R1 N N N R2 H O O NH N N R2 1 N N R * R R 4 5 BPI PyrrMeBOX

Figure 1. Chiral tridentate N^N^N pincer ligands discussed in this report.

Our work originally focused on the PyrrMeBox pincers 5 which we reported in 2003.6 However, after the development of an improved synthetic access to their protio-precursors,7 their applications have only recently begun to be explored, in particular in nickel catalysis involving one-electron redox steps.8 The chiral BPI derivatives 4 were found to be efficient stereodirecting ligands for Co catalysed hydrosilylations and cyclopropanations.9 Their use in enantioselective iron-catalyzed hydrosilylations of ketoned provided one of the first examples of its kind in 2008.9a More recently, we recently reported the synthesis of a new class of chiral N3 pincer ligands, bis(oxazolinylmethylidene)isoindolines (boxmi, 3), which are readily accessible in the modular three-step synthesis (starting from easily available phthalimides.10 Vol. 1 Pag.6

These ligands were were initially tested in the nickel(II)-catalyzed enantioselective fluorination of oxindoles and β-ketoesters yielding the corresponding products with enantioselectivities of up to >99% ee and high yields. Application of the chiral pincer ligands in the chromium-catalyzed enantioselective Nozaki-Hiyama-Kishi reaction of aldehydes gave the corresponding alcohols with a maximum enantioselectivity of 93 %.10 In a systematic study the highly enantioselective alkylation of β-ketoesters was achieved using boxmi-copper(II) catalysts. In particular, benzylic and allylic alcohols were employed to in situ prepare the corresponding iodides as the alkylating reagents without further purification. The primary chiral alkylation products were cyclized subsequently in a one-pot . procedure to generate spirolactones or bi-spirolactones by adding BF3 Et2O and in the presence of the copper catalyst.11 The corresponding Cu-catalyzed enantioselective alkylation of oxindoles was hampered by radical processes. In this case the use of zinc based catalysts gave the corresponding products in high yields and enantioselectivities.12 Furthermore, β-ketoester-substituted allylsilanes, were converted to spirolactones and bicyclic cyclopentanols with excellent enantioselectivities by subsequent treatment of the primary chiral allylation products (Scheme 1).11

Scheme 1. Stereoselective synthesis of allylsilanes and their subsequent transformations (L = Ph-boxmi)

Employing the chiral Cu-pincer systems developed for enantioselective alkylations described above, we extended the concept to include the asymmetric catalytic trifluoromethylation of β-ketoesters under mild conditions by using Togni’s electrophilic trifluoromethylating agent 3-Dimethyl-1-(trifluoromethyl)-1,2-benziodoxole. In this way a broad range of cyclic five-membered ring β-ketoesters were trifluoromethylated with excellent enantioselectivity (Scheme 2).13 Similar reactivity and enantioselectivity was also achieved in the corresponding enantioselective "electrophilic" trifluoromethylthiolations.14

Scheme 2. Enantioselective trifluoromethylation of five-membered ring β-ketoesters (L = Ph- boxmi).

Exploiting a similar strategy as for the enantioselective trifluoromethylation described above a highly enantioselective Fe-catalyzed azidation of β-ketoesters and oxindoles was developed by using a T-shaped iodine(III) compound as azido-transfer reagent (Scheme 3). In this way, an efficient protocol for enantioselective Fe-catalyzed azidation of cyclic β- ketoesters and 3-aryl oxindoles was achieved.15 Vol. 1 Pag.7

Scheme 3. Fe(boxmi)-catalyzed enantioselective azidation of cyclic β-ketoesters.

The cyclic β-ketoesters were converted to the corresponding products in high yields with up to 93% ee catalyzed by the combination of iron(II) chlorido complex and silver carboxylate. 3-Azido aryl oxindoles were obtained with up to 94% e.e. using the catalyst prepared by iron(II) propionate and ligand in situ. The α-Azido esters could be converted smoothly into α-amino ester by palladium-catalyzed hydrogenolysis, which may provide a useful method for the synthesis of highly substituted α-amino acid derivatives. On the other hand, copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), converted the α- azido esters into the corresponding triazoles in high yield.15 Using the boxmi ligand as stereodirecting pincer ligand, we developed iron(II) boxmi complexes as catalysts for the catalytic hydrosilylation of ketones, initially employing acetate complexes as precatalysts, which displayed a remarkable enantioselectivity but the usual low reactivity also found for other Fe acetate precatalysts. However, the corresponding alkyl or alkoxide precatalysts gave rise to highly active and enantioselective catalysts which match the top performers based on noble metals for the hydrosilylation of ketones (Scheme 4).16

a) [Fe] (5 mol%) (EtO)2MeSiH (2 equiv.), O toluene, -78 °C - rt, 6 h OH

R R' b) K2CO3/MeOH, rt, 1 h R R' 1 2

OH OH OH OH OH

Ph MeO 2a 2b 2c 2m 2n c. >95 %, 99 % ee c. >95 %, 98 % ee c. >95 %, 98 % ee c. >95 %, 99 % ee c. >95 %, 99 % ee OH OH OH OH OH

Pr

MeO2C F Br 2e 2f 2d 2o 2j c. >95 93 % ee c. >95 %, 99 % ee c. >95 %, 99 % ee a %, c. >95 %, 94 % ee c. >95 %, 94 % ee OH OH OH OH OH

n n C6H13 C11H23 tBu 2g 2h 2i 2k 2l c. >95 %, 99 % ee c. >95 %, 99 % ee c. 56 %, 73 % ee c. >95 %, 95 % ee c. >95 %, 99 % ee

Scheme 4. Substrate Scope of the Iron-catalyzed Hydrosilylation of Ketones This has led us to a systematic study of the mechanistic pathway(s) involved in the iron- catalyzed hydrosilylation of ketones as well as the activation pathway which converts the frequently employed carboxylate precatalysts to the catalytically active species. The proposed reaction mechanism is characterized by a rate-determining σ-bond metathesis of an alkoxide complex with the silane, subsequent coordination of the ketone to the iron hydride complex, and insertion of the ketone into the Fe−H bond to regenerate the alkoxide complex (Scheme 5).17 Vol. 1 Pag.8

O OH Fe(boxmi)OR*, (EtO)2MeSiH R R R' R' [LigFe-H] range > 95 % yield R: wide of and > 95 % ee (up to > 99 % ee) alkyl aryl substituents this work: precatalyst H activation FeLig O LigFe-OR' LigFe-OAc

R''

Scheme 5. Proposed mechanism of the Fe-catalyzed hydrosilylation of ketones.

References

(1) (a) D. Morales-Morales, C. M. Jensen, The Chemistry of Pincer Compounds, Elsevier, Amsterdam, 2007. (b) G. Van Koten, D. Milstein, Topics in Organometallic Chemistry, Vol 40, Springer, Heidelberg, 2013. (b) G. Van Koten, R. Gossage, Topics in Organometallic Chemistry, Vol 54, Springer, Heidelberg, 2013. (2) H. Nishiyama, Chem. Soc. Rev. 2007, 36, 1133 (3) T. Suzuki, A. Kinoshita, H. Kawada, M. Nakada, Synlett 2003, 570. (4) H. A. McManus, P. J. Guiry, J. Org. Chem. 2002, 67, 8566. (5) Q.-H. Deng, R. L. Melen, L. H. Gade, Acc. Chem. Res. 2014, 47, 3162. (6) C. Mazet, L. H. Gade, Chem. Eur. J. 2003, 9, 1759. (7) (a) F. Konrad, J. Lloret Fillol, H. Wadepohl, L. H. Gade, Inorg. Chem. 2009, 48, 8523. (b) F. Konrad, J. Lloret Fillol, C. Rettenmeier, H. Wadepohl, L. H. Gade, Eur. J. Inorg. Chem. 2009, 4950. (8) (a) C. Rettenmeier, H. Wadepohl, L. H. Gade, Chem. Eur. J. 2014, 20, 9657. (b) C. A. Rettenmeier, H. Wadepohl, L. H. Gade, Angew. Chem. Int. Ed. 2015, 54, 4880. (c) J. Wenz, C. A. Rettenmeier, H. Wadepohl, L. H. Gade, Chem. Commun 2016, 52, 202. (d) C. A. Rettenmeier, H. Wadepohl, L. H. Gade, Chem. Sci. 2016, 7, 3533. (9) (a) B. K. Langlotz, H. Wadepohl, L. H. Gade, Angew. Chem. Int. Ed. 2008, 47, 4670. (b) D. C. Sauer, H. Wadepohl, L. H. Gade, Inorg. Chem. 2012, 51, 12948. (10) Q.-H. Deng, H. Wadepohl, Lutz H. Gade, Chem. Eur. J. 2011, 17, 14922. (11) Q.-H. Deng, H. Wadepohl, L. H. Gade, J. Am. Chem. Soc. 2012, 134, 2946. (12) T. Bleith, Q.-H. Deng, H. Wadepohl, L. H. Gade, Angew. Chem. Int. Ed. 2016, 55, 7852. (13) Q.-H. Deng, H. Wadepohl, L. H. Gade, J. Am. Chem. Soc. 2012, 134, 10769. (14) Q.-H. Deng, C. Rettenmeier, H. Wadepohl, L. H. Gade, Chem. Eur. J. 2014, 20, 93. (15) Q.-H. Deng, T. Bleith, H. Wadepohl, L. H. Gade, J. Am. Chem. Soc. 2013, 135, 5356. (16) T. Bleith, H. Wadepohl, L. H. Gade, J. Am. Chem. Soc. 2015, 137, 2456. (17) T. Bleith, L. H. Gade, J. Am. Chem. Soc. 2016, 138, 4972. Vol. 1 Pag.9

STUDY OF PLASTICIZING EFFECT OF AGAVE SYRUP OF THERMOPLASTIC STARCH (TPS) BIOFILMS BY METHOD OF EXTRUSION AND CASTING

Casas-González M.R.,1*Rodríguez-González F.J.1

1Polymers Processing Department, Centro de Investigación en Química Aplicada, CP 25294, Saltillo, Coahuila, Mexico.

email: [email protected]

INTRODUCTION TPS has been considered a potential candidate for the development of edible biofilms due to their thermoplastic behavior (Mali et al., 2005). TPS biofilms can be obtained by different processing techniques such as casting (Maran, J.P et al., 2013) and extrusion method (Li, M. et al., 2011) where the starch is gelatinized and plasticized under high shear stress. TPS has been obtained from the disruption of starch granule in the presence of high-boiling point plasticizers (Bastioli 2001). The most commonly used plasticizer is glycerol (Fang et al., 2004). On the other hand, agave syrup is a source of sugars obtained after scraping stalks Agave salmiana. It is rich in sugars (such as maltose and fructose), dextrans and polysaccharides such as inulin, in addition to fructooligosacharides (FOS) also contains concentrations of maltooligosaccharides (Casas-Gonzalez, 2012) which can be used as plasticizers. The objective of this work was to compare the plasticizing action of agave syrup and glycerin in TPS biofilms prepared by extrusion and casting methods.

MATERIALS AND METHODS

Potato starch was acquired from Penford Food (France). Glycerol was purchased from Proquisa-Mexico, and agave syrup Agroindustries Faroc (Mexico). Films of potato starch were prepared by: 1) Casting. In a jacketed reactor, a suspension at 10% solids (starch + plasticizer) was gelatinized at 90°C for 30 min. The filmogenic solution was deposited on polystyrene plates and evaporated at 60°C for 16 h. Biofilms were formulated with agave syrup (TPSM) or glycerol (TPSG) in concentrations of 30, 35, 40% with respect to starch. 2) Extrusion. A suspension of starch-plasticizer-water was fed to the feeding zone of a twin-screw extruder ZSK30 (Werner & Pfleiderer) equipped with 9 heating zones at a rate of 3.5 k/h, 150 rpm and 90ºC (Tena-Salcido et al., 2008). TPS extruded films plasticized with glycerol (TPSGE) and agave syrup (TPSME) were stored in a desiccator before characterization. Water absorption and water solubility indexes (WAI and WSI, respectively) were determined by the method described by Anderson et al. (1969) and the relative loss of plasticizer (RLP) was calculated according to Casas- Gonzalez et al. (2014). The DMA measurements were performed using a TA- Instruments DMAQ800 equipment under multifrequency mode operation, from -150° to 150°C, at 5 °C/min, a frequency of 1Hz and amplitude of 20 µm used Dual Cantilever clamp. Vol. 1 Pag.10

RESULTS AND DISCUSSION Biofilms prepared by extrusion showed lower WAI values than those obtained by casting (Table 1). The decrease in WAI could be attributed to the alignment of starch molecules during both the pass through the die and the process of calendering. Rodriguez- Castellano (2013) mentions that increasing screw speed thermally damaged starch WAI reducing due to starch degradation. Moreover, TPSGE biofilms have WAI values higher than those of TPSME biofilms. WAI values of TPSGE tended to be higher because glycerol has better plasticizing action than sugars, as might be the case agave syrup (Van der Burgt, et al., 1996 and Mathew, A. P., et al., 2002).

Relative loss of Method Sample WAI (g/g) WSI (%) plasticizer (%) TPS-0 15.788 8.20 0 TPS-G30 16.085 17.10 38 TPS-G35 12.394 19.80 41 Casting TPS-G40 11.985 33.30 70 TPS-M30 12.194 19.10 44 TPS-M35 12.675 22.60 49 TPS-M40 14.679 26.40 54 Extrusion TPS-G30E 7.444 23.00 58 TPS-G35E 5.056 25.30 57 TPS-G40E 6.451 29.60 62 TPS-M30E 3.381 23.90 61 TPS-M35E 2.846 29.30 68 TPS-M40E 3.331 30.90 65 Table 1. Effect of type and concentration of plasticiser in TPS biofilms.

In the case of WSI, it was observed that biofilms obtained by casting have lower than those prepared by extrusion. It is probable that the depolymerization underwent by starch during the high-shear processing increased the soluble fraction of TPSE (Fakhouri, F. M. et al, 2013). On the other hand, WSI values were also dependent of the plasticizer content, thus the higher the concentration of plasticizer the greater the WSI values. Nemeth et al., (2010) reported that increasing the glycerol content in TPS films increased the dry matter content soluble in water. The LRP refers to the amount of plasticizer that reaches out of the biofilm in an aqueous medium, to find the equilibrium, resulting in 70% of PRL in biofilms TPSG- 40 (Table 1). However the TPS-M biofilms, have less PRL, having greater capacity plasticizer permanence in the polymer matrix. This is attributed to that agave syrup containing compounds of higher molecular weight (polymer-oligomers and monosaccharides) compared with glycerin (lower molecular weight) that interact with the starch, generate less free space that allow exists less migration plasticizer to the surface of the polymer matrix (Casas-Gonzalez, 2012), releasing only the low molecular weight compounds containing agave nectar and maintaining prebiotic FOS, inulin and dextrans in the polymer matrix. Vol. 1 Pag.11

Dynamic mechanical analysis (DMA)

The rheological properties of TPSG, TPSGE, and TPS-M TPS-ME biofilms are shown in Figure 1. G' values of TPSG and TPSGE biofilms showed two transitions: the first one at about -75°C corresponding to plasticizer-rich domains and the second at around 45ºC assigned to starch-rich domains (Rodriguez-Gonzalez, F. J., et al., 2004, Da Roz, Carvalho, Gandini, and Curvelo, 2006;. Khanh et al., 2015). Conversely, most of TPSM and TPSME biofilms showed just one transition at around 50°C which could be associated to starch-rich domains as observed in Figure 1b (Rodriguez-Gonzalez, F. J., et al., 2004).

Figure 1. Effect of glycerin content (a) and agave syrup (b) on the storage module TPS biofilms.

Some authors have related the maximum of loss modulus (log G”) to the glass transition temperature (Tg) of biofilms. The analysis of G” confirmed that TPSG and TPSGE biofilms have two thermal transitions and that both are dependent of glycerol content. As reported in the literature, the thermal transitions dropped as glycerol content increased. However, the first transition seemed to be less dependent on both the glycerol content and the process for preparing TPS biofilms than the second one (Fig. 2). Unexpectedly, G” values of TPSM and TPSME biofilms evidenced the presence of two thermal transitions. In the case of TPS-M biofilms, the first thermal transition increased from -40° to -28°C as the concentration of agave syrup decreased from 40 to 30%.

Figure 2. Effect of glycerin content (a) and agave syrup (b) on the loss module TPS biofilms. Vol. 1 Pag.12

The extrusion method is a good alternative for obtaining TPS-M biofilms as it provides a better mixing effect and distribution of plasticizer in biofilm formation. The biofilms TPS-GE starch-rich domains have more defined compared to TPS-G biofilms. Agave syrup has a greater effect of permanence within the polymer matrix to obtain lower loss of plasticizer that migrates to the surface while maintaining the high molecular weight compounds bonded to the biofilm (prebiotics) and releasing only low molecular weight sugars. The Tg of plasticized biofilms agave syrup increases with increasing concentration of plasticizer and decreases to be obtained by the extrusion method.

REFERENCES Anderson,R.A.,Conway,H.F.,Peplin ́ski,A.J.(1970).Gelatinization of corn grits by roll cooking, extrusioncooking and steaming. Starch 22, 130–135.Bastioli Catia. (2001). Global status of the production of biobased materials."Starch - Stärke 53(8):351-355.

Casas-González M.R., Rodríguez-González F.J. Contreras-Esquivel J.C., Andrade-Ramírez G. (2014) Estudio del efecto plastificante de la miel de agave y glicerina en la obtención de biopelículas de almidón termoplástico. Memorias del 37 Congreso Internacional de Metalurgia y Materiales. ISSN:2007-9540, 147-156.

Casas-González, M.R. (2012) Caracterización molecular de biopolímeros de aguamiel (Agave salmiana). Tesis Doctoral, Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila.

Da Róz, A., Carvalho, A. J. F., Gandini, A., & Curvelo, A. A. S. (2006). The effect of plasticizers on thermoplastic starch compositions obtained by melt processing. Carbohydrate Polymers, 63(3), 417– 424.

Fakhouri, F. M., Costa, D., Yamashita, F., Martelli, S. M., Jesus, R. C., Alganer, K., & Innocentini-Mei,L. H. (2013). Comparative study of processing methods for starch/gelatin films. Carbohydrate polymers, 95(2), 681-689.

Fang, J.M., et al., (2004).The chemical modification of a range of starches under aqueous reaction conditions. Carbohydrate Polymers, 55 p. 283–289.

Khanh Minh Dang, Rangrong Yoksan. (2015). Development of thermoplastic starch blown film by incorporating plasticized chitosan. Carbohydr. Polym. 115, 575-581.

Li, M., Liu, P., Zou, W., Yu, L., Xie, F., Pu, H., ... & Chen, L. (2011). Extrusion processing and characterization of edible starch films with different amylose contents. Journal of Food Engineering, 106(1), 95- 101.

Mali, S., Sakanaka, L. S., Yamashita, F., & Grossmann, M. V. E. (2005). Water sorption and mechanical properties of cassava starch films and their relation to plasticizing effect. Carbohydrate Polymers, 60, 283e289.

Maran, J. P., Sivakumar, V., Sridhar, R., & Immanuel, V. P. (2013). Development of model for mechanical properties of tapioca starch based edible films. Industrial Crops and Products, 42, 159-168. Vol. 1 Pag.13

Mathew, A. P., & Dufresne, A. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules, 3(5), 1101-1108.

Nemet, N. T., Soso, V. M., & Lazi_c, V. L. (2010). Effect of glycerol content and pH value of film- forming solution on the functional properties of protein-based edible films. Acta Periodica Technologica, (41), 1e203.

Rodríguez-Castellanos W., Martínez-Bustos F and Jiménez-Arévalo O. (2013). Functional properties of extruded and tubular films of sorghum starch-based glicerol and Yucca Schidigera extract. Industrial Crops and Products. 44, 405-412.

Rodriguez-Gonzalez, F. J., Ramsay, B. A., & Favis, B. D. (2004). Rheological and thermal properties of thermoplastic starch with high glycerol content. Carbohydrate Polymers, 58(2), 139-147.

Tena-Salcido, C., F. Rodríguez-González, et al. (2008). Effect of Morphology on the Biodegradation of Thermoplastic Starch in LDPE/TPS Blends." Polymer Bulletin 60(5): 677-688.

Van der Burgt, M. C., Van der Woude, M. E., & Janssen, L. P. B. M. (1996). The influence of plasticizer on extruded thermoplastic starch. Journal of Vinyl and Additive Technology, 2(2), 170-174. Vol. 1 Pag.14

AROMATIC QUANTIFICATION USING SS NMR SPECTROSCOPY FOR SOY-BASED FILLERS

Paula Watt, Toshikazu Miyoshi, Coleen Pugh

Department of Polymer Science, The University of Akron, [email protected]

INTRODUCTION Lighter weight composites are desirable for many markets, including automotive, aerospace and consumer goods. Glass-reinforced thermoset molding compounds use mineral fillers to reduce cost by displacing the more expensive resin matrix. Because these fillers are a significant portion of the compound and have typical densities of 2.5 g/cc, the density of the composite is greater than that of an unfilled system. Renewable biomass fillers have a density similar to that of the matrix resin, yielding compounds at the same volume reinforcement of glass with a 20-25% weight reduction, while maintaining the cost savings provided by matrix displacement. Thermal treatments of the biomass improve the hydrophobicity of the fillers, although cure inhibition problems can be induced [1]. This inhibition is attributed to aromatic species that form during the heat treatment [2]. Controlled thermal processing of soy biomass can yield fillers that do not interfere with the compound cure [3]. Quantification of filler characteristics to measure the level of thermal treatment are needed for quality assurance and process development. In previous studies, elemental analysis (EA) was used to characterize the extent of treatment [2], and solid state NMR (SS NMR) spectroscopy was used as a semi-quantitative means to measure the aromatic content of heat-treated biomass [4]. This paper correlates the SS NMR characterization of heat-treated soy fillers to EA results.

EXPERIMENTAL

A BRUKER AVANCE III 300 MHz NMR spectrometer was used to obtain solid-state 13C high speed magic-angle spinning (CPMAS) NMR spectra of filler samples at a resonance frequency of 75.6 MHz. A double resonance probe, at 13000 Hz spinning speed, with a 2 ms cross-polarization contact time and a pulse repetition rate of 2 s was employed. Figure 1 compares the 13C SS NMR spectra of soy hulls treated at increasingly high temperatures (from top to bottom) to that of untreated soy hulls (UTSH); the 204 °C and 249 °C samples were treated in a batch pilot process; the 288 °C and one 400 °C sample were treated in a continuous pilot process; and the other 400 °C was treated in a muffle oven [2]. All samples were dried under vacuum at 25 °C for two days and sealed for storage prior to testing.

1.2E+09

1.0E+09 UTSH 8.0E+08 204 °C ECP

6.0E+08 ? 249 °C ECP 4.0E+08 288 °C AGT/NCSU bench 2.0E+08 400 °C Muffle furnace 0.0E+00 200 150 100 50 0 ppm 400 °C AGT/NCSU pilot

Figure 1. 13C SS NMR spectra of untreated (UTSH) and heat treated soy hull fillers. Vol. 1 Pag.15

RESULTS AND DISCUSSION

As demonstrated in Figures 1 and 2, the resonances at 55 to 115 ppm corresponding to cellulose decrease and are eliminated with increasing heat treatment, while a broad aromatic resonance develops in the 95 to 160 ppm range. The aliphatic resonances in the region from 10 to 45 ppm, including those from the protein content, first increase relative to the cellulose resonances with treatment and then diminish at the most aggressive treatment level. The carboxyl resonances at 165 to 185 ppm also diminish with increasing treatment.

The resonances were integrated for the carboxyl, aromatic, cellulose and aliphatic content. Due to the high signal-to-noise ratio of the lower intensity resonances, the spectra were smoothed using a 10-point running average before the baseline was corrected and integrated. The cellulose resonances were integrated without smoothing to avoid distortion, since the random noise fluctuation had a minimal effect on their calculated values. The calculated integrals are plotted in Figure 2 as a function of heat treatment.

100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0%

Content 0.0% 288 °C 400 °C 400 °C UTSH 204 °C ECP 249 °C ECP AGT/NCSU Muffle AGT/NCSU bench furnace Pilot cellulose 89.7% 85.8% 69.8% 41.0% 0.0% 0.0% aliphatic 4.3% 5.8% 12.0% 19.4% 23.8% 6.9% carboxyl 6.0% 4.9% 4.3% 3.9% 2.0% 1.5% aromatic 0.0% 3.5% 14.0% 35.6% 74.2% 91.5%

Figure 2. Composition of untreated (UTSH) and heat-treated soy fillers calculated by 13C SS NMR spectroscopy.

Figure 3 presents the expanded baseline-corrected region for the cellulose resonances. As the intensity of the heat treatment increases, the cellulose resonances diminish and disappear entirely for the two most aggressive treatments.

3.5E+08 3.0E+08 UTSH 2.5E+08 204 °C ECP 2.0E+08 249 °C ECP 1.5E+08 288 °C AGT/NCSU bench 1.0E+08 400 °C Muffle furnace 5.0E+07 400 °C AGT/NCSU pilot 0.0E+00 105 85 65 45 ppm -5.0E+07

Figure 3. Baseline-adjusted 13C SS NMR spectra of the cellulose region of soy fillers. Vol. 1 Pag.16

Figure 4 presents the changes in the aliphatic region of the untreated and heat-treated soy hulls. The aliphatic content increases as less stable oxygenated species are liberated. The profile shift seen in the 400 °C muffle furnace sample indicates that the amount of CH3 chain ends increase relative to the CH2 groups as a result of thermally induced chain scission. In the most aggressively treated sample, the aliphatic content decreased significantly as ring formation of the aliphatic structures occurs. 3.50E+07 UTSH 3.00E+07 2.50E+07 204 °C ECP 2.00E+07 249 °C ECP 1.50E+07 288 °C AGT/NCSU bench 1.00E+07 400 °C Muffle furnace 5.00E+06 0.00E+00 400 °C AGT/NCSU pilot 60 50 40 30 20 10 0 ppm -5.00E+06

Figure 4. Baseline-adjusted aliphatic region of the 13C SS NMR spectra of untreated and heat-treated soy fillers. As shown in Figure 5, the carboxyl resonance decreases with increasing heat treatment, although some carbonyl species persist even in the most aggressively treated sample. The decrease in carbonyl content between the 204 °C and 249 °C treated ECP samples corresponds to accelerated carboxyl liberation in that range.

ppm

Figure 5. Baseline-adjusted carboxyl region of the 13C SS NMR spectra of untreated and heat-treated soy fillers. Finally, Figure 6 presents the increase in aromatic content as the heat treatments intensified. The fillers treated at up to 288 °C did not inhibit cure. The 400 °C treated filler, with much higher aromatic content, resulted in significant inhibition and a reduction in properties. 1.50E+08 UTSH 1.00E+08 204 °C ECP 249 °C ECP 5.00E+07 288 °C AGT/NCSU bench 0.00E+00 400 °C Muffle furnace 175 155 135 115 95 400 °C AGT/NCSU pilot ppm -5.00E+07

Figure 6. Baseline-adjusted aromatic region of the 13C SS NMR spectra of soy fillers. Vol. 1 Pag.17

Figure 7 plots the % aromatic content derived from the 13C SS NMR data as a function of the ratio of the moles of hydrogen plus oxygen and carbon from the EA data for the same sample set [4]. This figure confirms that the aromatic content correlates with the loss of oxygen and hydrogen; i.e. as the heat treatment becomes more aggressive, the oxygen and hydrogens in the biomass are liberated and aromatic rings form.

100 y = -43.642x + 112.55 80 R² = 0.986 60 40

% Aromatic % Aromatic 20 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 -20 (H+O)/C

Figure 7. Correlation of 13C SS NMR spectral data to EA data for the aromatic content of heat-treated soy hulls.

CONCLUSIONS

Both elemental analysis and 13C SS NMR spectroscopy can be used to measure the level of aromatic formation in biomass as a result of its heat treatment. With a correlation coefficient of 0.99, the data corresponding to the aromatic content of the soy hulls are in excellent agreement. The data from these characterization methods can assist in the development of optimal heat treatments, as well as provide a quality assurance measure of batch-to-batch repeatability. REFERENCES [1] Lee, R. “Reactions of Polyester Resins and the Effects of Lignin Fillers”, Composite Technology Inc. 2001, http://materialchemistry.com/DreamHC/Download/Polyester%20Reactions.pdf, downloaded 30 August 2016. [2] Watt, P.; Pugh, C. Studies to Determine Critical Characteristics of Thermally Treated Biomass Fillers Suitable for Thermoset Composites. Polymers from Renewable Resources. 2015, 6, 1-24. [3] Watt, P.; Pugh, C.; Rust, D. Soy-Based Fillers for Thermoset Composites; Robert Brentin, Soy- Based Chemicals and Materials, ACS Symposium Book Series, American Chemical Society, Washington DC, 2014, 265-298. [4] Sharma, R.; Wooten, J.; Baliag, V.; Lin, X.; Chan, W.; Hjaligol, R. Characterization of Chars from Pyrolysis of Lignin. Fuel 2004, 83, 1469-1482.

ACKNOWLEDGEMENTS We authors are thankful for funding by USB New Uses Grant #2456 & 1340-512-5275 under sub- contract from Premix, Inc. Vol. 1 Pag.18

PREPARATION AND CHARACTERIZATION OF ELECTRICALLY CONDUCTIVE POLYMER NANOCOMPOSITES WITH DIFFERENT CARBON NANOPARTICLES Víctor Cruz-Delgado1, Edson Peña-Cervantes1, José Perales-Rangel1, Marcelina Sánchez-Adame1, Fabián Chávez-Espinoza1, José Mata-Padilla1, Juan Martínez- Colunga1, Carlos Ávila-Orta1. 1Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo No. 140, Col. San José de los Cerritos, Saltillo, Coahuila. 25294. México. [email protected]

Abstract Polymer nanocomposites offer great expectations for new and unexpected applications due the possibility to change their behavior by the addition of nanoparticles, meanwhile retaining the flexibility and processability of plastics [1,2]. Carbon nanoparticles possess a combination of high electrical and thermal transport, low density and different morphology that makes it a good choice to reinforce plastics [3]. The possibility of electrical and thermal conduction in a polymer matrix with low amounts of the nanoparticles, brings opportunity for high demanding applications such as electrical conductors and heat exchangers [4,5]. In this work different carbon nanoparticles like: carbon nanotubes (CNT), modified carbon nanotubes (CNTM), graphene (G) and carbon black (CB) were selected to reinforce high density polyethylene (HDPE) at contents of 20% wt/wt by mean of ultrasound-assist extrusion [6] to obtain electrically conductive nanocomposites.

Keywords: Carbon nanoparticles, electrically conductive compounds, polymer nanocomposites.

Experimental. Materials High-density polyethylene (HDPE) with a MFI = 20 g/10 min, injection grade was used as polymer matrix. Carbon nanotubes (CNT) with an average O.D. = 30 nm, length 10 – 30 micron, purity ≥ 90wt% and SSA ≥ 110 m2/g, COOH functionalized CNT (CNTM) with an average O.D. = 20 nm, length 10 – 30 micron, purity ≥ 90wt% and SSA ≥ 200 m2/g, and graphene nanoplatelets (G) with an average thickness = 8 nm, 8-10 layers, average length < 2 micron and SSA ≥ 500 m2/g, were purchased to Cheap Tubes Inc, USA and were industrial grade. Carbon black Vulcan XC-72, average particle size = 15 nm, SSA ≥ 600 m2/g, purity ≥ 95% was acquired from Cabot, USA. Carbon nanoparticles were used without further purification.

Methodology A twin-screw extruder L/D: 40:1 Thermo Scientific 24-MC, was used to process all the samples, with a plain temperature profile of 220 °C and 100 rpm. Resin chips and powder, were feed to the extruder with the assistance of gravimetric feeders for each one at a rate of 5 and 1 kg/h respectively. The samples were extruded with the assistance of ultrasound waves [6] drive by a home made generator of variable amplitude and frequency in the range of 20 – 50 kHz and power of 500 W. Vol. 1 Pag.19

Characterization. Thermogravimetric analysis were carried out in a TGA, TA Instruments model Q500 at a heating rate of 10 °C/min with a flow of N2 of 50 ml/min. Electrical properties (permittivity and resistivity) were measured with a high precision LCR meter Keysight model E4980A, in the frequency range of 20 Hz to 1 MHz, 4 specimens were tested and the average value was reported. Tensile testing was conducted using a Universal Testing Machine, INSTRON 4301 model, at 5 mm/min using type V specimens in accordance with ASTM D 638 standard method. For the flexural properties evaluation, 2 X 0.5 inches strips were employed in accordance with ASTM D 790 standard method.

Results. Carbon nanoparticles prevent the thermal degradation of polyethylene resin at different extent as we can see in Figure 1. Nanocomposites with carbon black could enhance the thermal degradation resistance by up to 93 ºC and 36 ºC at the 5% and 50%, respectively. Nanocomposites with CNT, CNTM and G shown a similar tendency, which suggest that carbon nanoparticles are an effective filler to prevent the thermal degradation at elevated temperatures or during the processing by the common polymer processing methods.

Figure 1. Thermal degradation temperature for nanocomposites with different carbon nanoparticles.

Mechanical properties of polymer nanocomposites are shown in Figure 2. The flexural modulus of polymer nanocomposites exhibits an average increase up to 100% respect of PE resin, in this case graphene is the best reinforcing nanoparticle, this result could obey the 2D geometry of planar sheets of graphene that are homogeneously dispersed in the polyethylene matrix. Nanocomposites with CNT, CNTM and Carbon black shown similar values for flexural modulus, despite of presence of –COOH functional groups grafted on the surface of CNTM or the semi-spherical morphology of CB nanoparticles. The tensile stress is not increased notoriously with the addition of carbon nanoparticles, nevertheless for nanocomposites with CNTM the tensile stress is the lowest and suggest that the presence of –COOH functional groups in CNTM are no beneficial for the mechanical reinforcement. Vol. 1 Pag.20

Figure 2. Mechanical properties for nanocomposites with different carbon nanoparticles.

With the addition of carbon nanoparticles is possible to change the permittivity of a polymer and enhance their capacitive behavior, which means that this material could retain and release electrical charge during an event. The dielectric constant of nanocomposites with different carbon nanoparticles is shown in Figure 3. Polyethylene resin, exhibit a value of 3 and this value are linear over the entire range of frequency. Graphene nanocomposites shows a value of 10, and a linear response with the frequency. Nanocomposites with CNT, CNTM and CB exhibit an increase by 3 orders of magnitude, respect of polyethylene resin and their response is dependent the frequency, showing lower values at high frequencies.4

Figure 3. Dielectric constant as a function of frequency for nanocomposites with different carbon nanoparticles.

Polyethylene is considered the best electrical insulator; nevertheless with the addition of carbon nanoparticles this behavior was changed as shown in Figure 4. Polyethylene resin exhibit high resistance values at low frequencies, as the frequency increase polarization effects are present and diminishes their insulated behavior. Graphene nanocomposites shown a similar tendency like polyethylene resin, which corresponds with the lower values of permittivity observed above. Nanocomposites with CNT and CNTM exhibit a reduction up to 7 orders of magnitude in resistivity against polyethylene resin and a linear response. Vol. 1 Pag.21

Surprisingly, nanocomposites with CB show the lowest resistivity value around 1 Ω.m and a lineal response over the entire range of frequency. This value of electrical resistivity is close to electrical conductor and suggests their use in high demand applications like electrolytic and PEM fuel cells, and passive electronic components.

Figure 4. Electrical resistivity as a function of frequency for nanocomposites with different carbon nanoparticles.

Conclusions The thermal degradation of the nanocomposites has shown an increase up to 93 ºC and 36 ºC at 5% and 50% of degradation respect of the HDPE resin. Mechanical properties shown an average increase of 100% in flexural moduli, nevertheless tensile stress shown a little increase. Finally, permittivity measurements as a function of frequency in the range of 20 Hz – 1 MHz shown high values for nanocomposites in the following order CB, CNTM, CNT and G, which are in agree with the low values of resistivity. Due the good balance of properties for this polymer nanocomposites they will be used in the electronic/electric sector and for thermal conduction applications.

References.

[1] Prog. Polym. Sci. 2010, 35, 357 [2] Prog. Polym. Sci. 2010, 35, 1350 [3] Polymer 2015, 55, 642. [4] Prog. Polym. Sci. 2011, 36, 914 [5] Polymer 2002, 43, 2279 [6] J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 475

Acknowledgements We acknowledge the financial support from Fondo SENER/CONACYT under CeMIE-Sol program Project 207450/12. This work was financially (partially) supported by CONACYT through Project 250848 Laboratorio Nacional de Materiales Grafénicos for their support with the characterization of materials, and to Francisco Zendejo, Gilberto Hurtado and Rodrigo Cedillo for their assistance with processing and characterization of polymer nanocomposites. Vol. 1 Pag.22

Impact of process variables on the recovery of starch extracted from jicama González-Lemus LB 1, Calderón-Domínguez G 1*, Farrera- Rebollo RR 1, Güemes-Vera N 2, Chanona-Pérez JJ 1, Salgado- Cruz MP1 Martínez-Martínez V1. 1ENCB-IPN. Departamento de Ingeniería Bioquímica. Prolongación de Carpio y Plan de Ayala S/N, Casco de Santo Tomas, C.P. 11340, México, D. F. México. E-mail [email protected] 2ICAp-UAEH. Av. Universidad km 1. Rancho Universitario. Tulancingo, Hidalgo. C.P. 43600 México.

Abstract Jicama (Pachyrizus erosus) is a native crop from Mexico and Central America, and part of the genus Pachyrhizus, which includes other species such as jacatupé and ahipa. Previous studies show that this tuber is low in protein, inulin and fructo-oligosaccharides but has large amounts of starch. However, the values reported for this crop are variable and can be the result of the type used, growing conditions or the extraction method applied. On the other hand, it has not been found reports that mention or evaluate the percentage of extraction of jicama starch, so the objective of this work was to study the effect of different process conditions at the same time (freezing, sonication, and soaking in sodium metabisulfite) in the yield percentage of starch through response surfaces. A Box-benhken design was used, with three variables and three levels, and five central repetitions, with a total of 17 trials. The experimental design was significantly adjusted a quadratic model (P = 0.0183), with a coefficient of determination (R2 = 0.8745) and 0.7131 adjusted R. When evaluating variables applied to designing both the freezing time as sonication significantly affected the response (P <0.05) as well as the interaction between the time of freezing and sonication (P = 0.0256), while soaking time had no significant effect (P = 0.09184).

Figure 1. Effect of hydration time, freezing and sonication on the extraction of starch from jicama.

As for the combined and based on statistical analysis methods, it was observed that the starch yield is increased with respect to time of sonication or freezing, but independently, finding an antagonistic effect by combining the two or three variables , while the soak time had no significant effect. It is necessary to focus future research combining ultrasound and / or other mechanical process variable, which can be conducted to study its effect on the performance and properties of starch from various sources. Vol. 1 Pag.23

Introduction The legumes are plants of great importance worldwide, mainly because of its seeds, which are rich in proteins, which are the second most important crop after cereals. However, some legumes have tuberous roots, such as potatoes (Solanum tuberosum), jicama (Dioscorea rotundata) and cassava (Manihot utilissima)[1]. On the other hand, jicama (Pachyrizus erosus) is a native crop from Mexico and Central America, and part of the genus Pachyrhizus, which includes other species such as jacatupé and ahipa. This legume is considered that the only edible part is the root, which resembles a turnip [2]. In Mexico the main producers are Nayarit (56.995 tons.), Morelos (26.134 tons.) and Guanajuato (8,789 tons.) (SIAP, 2014). Most industrial starches are extracted from cereals and tuberous roots, but still, jicama starch has not yet been exploited for industrial applications [3]. Previous studies show that this tuber is low in protein, inulin and fructo-oligosaccharides but has large amounts of starch; but, the values reported for this crop are variable and can be the result of the type used, growing conditions or the extraction method applied [4]. However, it has not been found reports that mention or evaluate the percentage of extraction of jicama starch, so the objective of this work was to study the effect of different process conditions at the same time (freezing, sonication, and soaking in sodium metabisulfite) in the yield percentage of starch through response surfaces design.

Methods, Results and Discussion To perform the isolation of jicama starch was left of the methodology proposed by Novelo- Cen and Betancur-Ancona (2005). Jicama was peeled and cut into cubes of about 1cm on each side and were processed by grinding using a sodium bisulfite solution (1500 ppm) in a 1: 3, tuber: solution, respectively. After soaking time the suspension was placed in bags by sealing and subjecting the product to freezing and thawing. Once the suspension was completely thawed jicama and environmental conditions, it was placed in an ultrasonic bath (40W) for the required time. Then the bagasse fiber is filtered through fine mesh, making three washes with distilled water to achieve recover as much starch and remove impurities. The solution was allowed to precipitate for 2 hours and decanted cooling, resulting starch extracted in the background. Finally, the starch paste was dried in a convection oven for 12 hours at 45 ° C. The process extraction is carried out by a Box-benhken design using Design Expert v.9 software, with three variables and three levels, and five central repetitions, with a total of 17 trials (table 1).

Table 1. Intervals of operating conditions used in this test (soak time, sonication time and freeze time). Treatment Freezing Sonication Hydratation (days) (minutes) (minutes) 1 0 60 15 2 0 30 30 3 0 0 15 4 1 0 30 5 1 30 15 6 1 60 30 7 2 30 0 8 1 30 15 9 1 60 0 Vol. 1 Pag.24

10 1 30 15 11 2 60 15 12 2 0 15 13 1 30 15 14 2 30 30 15 1 0 0 16 0 30 0 17 1 30 15

The response variable was the starch yield percentage expressed on dry basis. The experimental design was significantly adjusted a quadratic model (P = 0.0183), with a coefficient of determination (R2 = 0.8745) and 0.7131 Adjusted R. This results show that both the freezing time as sonication significantly affected the response (P <0.05) as well as the interaction between the time of freezing and sonication (P = 0.0256), while soaking time had no significant effect on the recovery starch (P = 0.09184) (see Figure 1).

Conclusions As for the combined and based on statistical analysis methods, it was observed that the starch yield could be increased with respect to time of sonication or freezing, but independently, finding an antagonistic effect by combining the two variables, while the soak time had no significant effect. Depending on the results, the freeze-thaw step can be eliminated, as it represents greater time and cost of processes, leaving only the sonication and soaking bisulfite. It is necessary to focus future research combining ultrasound and / or other mechanical process variable, which can be conducted to study its effect on the performance and physical, rheological and functional properties of starch from tubers roots, but independently.

References [1] Melo E. A., Stamford T. L. M., Silva M. P. C., Krieger N., Stamford N. (2003). Functional properties of yam bean (Pachyrhizus erosus) starch. J. Bioresource Technology. 89, 103–106. [2]Ramos de la Peña A., Ring G., Noel T.R., Perker R., Cairns P., Findlay K. y Shewry P. R. (2002). Characterization of starch from Tubers of Yam Bean (Pachyrhizus ahipa). J. Agric. Food Chem. 50, 361-367. [3] Stevenson D., Janeb J. y Ingletta G. (2007). Characterisation of Jícama (Mexican Potato) (Pachyrhizus erosus L. Urban) Starch from Taproots Grown in USA and Mexico. Starch. 59, 132-140. [4] Zhu F. (2015). Composition structure, physicochemical properties, and modifications of cassava starch. Carbohydrate Polymers. 456-480.

Acknowledgements Thanks for financial support to the project IPN-SIP 20151383 and IPN Mexico COFAA. Vol. 1 Pag.25

CHARACTERIZATION OF CARBOHYDRATE-PROTEIN GELS USING DSC AND CONFOCAL MICROSCOPY

Hernández-Espinosa N., Salazar-Montoya J.A. y Ramos Ramírez E.G.*

Department of Biotechnology and Bioengineering. CINVESTAV-IPN. Mexico City, 073600. MEXICO. E-mail: [email protected] SUMMARY

During the last decade, it has increased the interest in exploring the gelling of aqueous solutions with a mix of carbohydrates and proteins, due to the functional properties of these biopolymers as food additives. The characterization of these mixtures is necessary for the development of new processing methods due to their ability to formation of structures with improved functional properties. It has been reported that gliadin (prolamin wheat) is capable of gelling at alkaline pH and temperature of 50 ˚C. Therefore, this work aimed to study the formation of gels from low methoxyl pectin (LMP) and gliadin to characterize its thermal properties and observe its distribution in the gels. Dispersions were prepared to LMP at 1 % and 0.5 % of gliadin, the latter stained with fast green following the methodology proposed by Beaulieu, 2001. Gel formation was induced by the addition of CaCl2. Differential Scanning Calorimetry (DSC) was performed weighing 8 mg of gel and heated from 20-350 °C, with a ramp 10 °C. Structure of the gels was performed using Confocal Microscopy Laser Leica equipment (diode type) and software Leica Application. The images were obtained with a 63x lens. LMP was able to form gels in presence of divalent ions Ca2+, gelling mechanism is described as "egg box" model. Confocal Microscopy showed gliadin dispersed in the gel with uniform distribution. Calorimetric studies showed a single peak near to 210 °C and ∆H= 1573 J/mol, having a different behavior with respect to the controls. The results showed that it is possible to design carbohydrate-protein gels with potential properties of interest, which could be useful in the industry of light foods enriched with wheat proteins.

Key words: Low Methoxyl Pectin (LMP), Gliadin, Confocal Microscopy, Differential Scanning Calorimetry (DSC).

INTRODUCTION

The gliadins are a source of protein storage in the wheat gluten and are essential for formation; they determine its viscous nature. In combination with glutenin, they provide significant viscoelastic properties to bread dough. The low methoxyl pectins (LMP) are obtain by modification of high methoxyl pectins (HMP) by controlled desterification reaction commonly carried out by a chemical method. LMPs have the ability to form gels without the presence of sugar, being an important advantage in the formulation of low calorie foods [5]. Carbohydrates-proteins complex arise from electrostatic interactions between oppositely charged macromolecules. These interactions induce the formation of different supramolecular entities, such as aggregation and complex coacervates [1]. The nature of complex carbohydrate-protein is determined by factors that affect the entropy of the system, like structure and molecular weight of the components. Gelation of these macromolecular complexes generally takes place by formation of new bonds between the two biopolymers, Vol. 1 Pag.26

polycation-polyanion electrostatic interactions and gel formation due to mutual exclusion of each component [4]. In these systems, favorable interactions occur between anionic polysaccharides and proteins found below their isoelectric point, which can cause increases the gelation temperature, melting temperature and gel strength, among others [4]. The concentrated dissolutions of two biopolymers (protein-protein, carbohydrate-protein or polysaccharide-polysaccharide) may be turbid and gradually separated into two translucent layers, each of which may contain some of the other component. However, before phase separation, compounds gels are obtained where the gelling biopolymer constitute a continuous phase network and the second is limited to form inclusions in the discontinuous phase [3]. Systems formed by various gelling agents can form gels fillers, mixed and complex [6]. In this research were proposed two techniques, confocal microscopy and differential scanning calorimetry for the characterization of carbohydrate-protein gels.

METHODOLOGY

LMP dispersions gliadin 1% and 0.5% were prepared, the latter with Fast Green FCF ™ stained adapting the methodology proposed by Beaulieu [2]. Gel formation was induced by the addition of CaCl2. The analysis by Differential Scanning Calorimetry (DSC) was performed weighing 8 mg gel, heated from 20 to 350 °C, with a ramp 10 °C. The structure of the gels was analyzed by using a computer Confocal Microscopy (Leica TCS laser (diode type) and Leica Application Software Ver. 2.4.1). The images were obtained with a 63x lens and scanned between 640 and 700 nm.

RESULTS

Confocal Microscopy The gels were prepared with varying thickness (≤ 140 microns) by placing them between a slide and coverslip, after obtaining the serial sections, for better structure observation of the gels and take gel micrographs. Using of Leica Application Software (Ver. 2.4.1) was possible to analyze the structure of experimental gels (LMP-gliadin). Figures 1 to 4 show the front and side face of a gel obtained by LMP and gliadin. Red dots (Figures 2 and 4) represent the fluorescence emitted by the chromophore bound to the protein; can also be seen that the protein is embedded in the three-dimensional gel network and distributed homogeneously (Figures 1 and 3). Figures in black and white (Figures 2 and 4) are a repeat of his counterpart in another format of design and red dots to gliadin immersed in the gel formed by the carbohydrate (black dots).

DSC (Differential Scanning Calorimetry). As a result of the comparative determination of the thermal properties of carbohydrate-protein gel and individual components (LMP and gliadin), in Figure 5 is showing the thermogram corresponding gel LMP-gliadin, which showed a different behavior of the presented controls (data not shown).The main peak suggests that it is a homogeneous mixture obtained under suitable processing conditions. The thermal peak was obtained near 210 °C and it was required a change energy (∆H= 1573 J/g). Vol. 1 Pag.27

1) 2)

Figures 1 and 2. Front view of LMP-gliadin gel.

3) 4)

Figures 3 and 4. Side view of LMP-gliadin gel.

Figure 5. Thermogram corresponding to LMP-gliadin gel. Vol. 1 Pag.28

CONCLUSIONS

With the proposed methodology it was achieved to obtain gels containing LMP-gliadin. The proteins were uniformly distributed in the three-dimensional polysaccharide network (LMP). The use of a chromophoric compound can permit to observe the morphology of the carbohydrate-protein gel by Confocal Microscopy. Also by the use of DSC analysis, we can determinate the changes in the thermal behavior of a mixed gel.

ACKNOWLEDGEMENTS

To CONACYT for the financial support number 211425 to N.H.E. For their technical support to Biol. M. P. Méndez Castrejón from Biotechnology and Bioengineering Department and to MSc. I. J. Galván Mendoza from LaNSE -CINVESTAV (Confocal microscopy).

REFERENCES

[1] Antonov, Y. A., Zhuravleva, I. L. Macromolecular complexes of BSA with gelatin. International Journal of Biological Macromolecules. (2012) 51 (3): 319-328. [2] Beaulieu M., Turgeon S. L., Doublier J. L. Rheology, texture and microstructure of whey proteins/low methoxyl pectins mixed gels with added calcium. International Dairy Journal, (2001) 11:961-967. [3] Chronakis, I. S., Kasapis, S., Abeysekera, R. Structural properties of gelatin-pectin gels. Part I: Effect of ethylene glycol. Food Hydrocolloids (1997) 11: 271-279. [4] Hua, Y. Gelling property of soy protein–gum mixtures. Food Hydrocolloids (2003) 17: 889- 894. [5] Sriamornsak Pornsak. Chemestry of pectin and its pharmaceutical uses: a review. Libre en la red. [6] Zasypkin, D. V., Braudo, E. E., Tolstoguzov, V. B. Multicomponent biopolymer gels. Food Hydrocolloids (1997) 11: 159-170. Vol. 1 Pag.29

STUDY OF THE CHARGE INTO THE PHYSICOCHEMICAL PROPERTIES OF A COMPOSITE MATERIAL Karina Abigail Hernández-Hernández, Javier Illescas*, María del Carmen Díaz- Nava, Claudia Muro-Urista

Instituto Tecnológico de Toluca, Av. Tecnológico S/N Col. Agrícola Bellavista, C.P. 52169, Metepec, Estado de México, México, *[email protected]

Introduction

The development of the adsorbent materials for water treatment is one of the most important research goals in the environmental field, within these materials are the polymer clay composites, consisting of a polymeric matrix material in which the disperse phase particles are clay; the physicochemical properties of the material will be influenced according to the different loads or dispersed clay content. The materials were synthesized in aqueous solution, noting that the ratio of acrylic acid/water and the crosslinking agent also play an important role in the structure and strength of materials. The synthesized materials were characterized by swelling limit tests, critical pH and pH reversibility also thermogravimetric analysis and infrared spectra were obtained.

Experimental

Composites were prepared according to the procedure used in the literature.1 In a test tube, known quantities of acrylic acid monomer (AAc, 2, 3 or 4 g) and benzoyl peroxide radical initiator (BPO), 1 wt-% referred to that of the monomer, were put together and mixed by means of an ultrasonic bath until the initiator was dissolved. Then, a certain amount of water was added to the mixture to give a total mass of 6 g and triethylene glycol dimethacrylate (TEGDMA) crosslinker agent was added, 0.4 wt-% referred to the amount of AAc monomer, and placed in an ultrasonic bath for 5 minutes until its complete dissolution. Next, solutions were placed in an oil bath for polymerization and the temperature was increased gradually from 318 to 338 K to avoid an autoacceleration process and an excessive bubbling in the polymer. The temperature program was: 318 K for one hour, 323 K for two hours, 328 K for three hours, 333 K for 4 hours and 338 K for 24 hours. After cooling to room temperature the synthesized polymers were washed in deionized water for a week to remove unreacted reagents. Finally, they were cut into small disks of 2 mm length (Fig. 1) and dried at room temperature for two days and put into a vacuum oven at 343 K for one week or until constant weight of the samples was reached.

Polymer clay composites of: (a) AAc/H O(2:1)/Clay 5 wt-%, Figure 1. 2 (b) AAc/H O(1:1)/Clay 5 wt-% and (c) AAc/H O(1:2)/Clay 5 wt-% 2 2 Vol. 1 Pag.30

Results and discussion

According to the Table 1 of swelling percentage, materials reach their equilibrium swelling around 8 h, with 400-500% water uptake. It is noteworthy, that the sample containing 1:2 AAc:H2O (w/w) had 1600% of water uptake. However, this sample was the one with the poorest mechanical properties.

Table 1. Swelling percentage of the polymer clay composites. Swelling (%) Time PAAc/H2O PAAc/H2O PAAc/H2O PAAc/H2O PAAc/H2O PAAc/H2O (min) (2:1)/Clay (1:1)/Clay (1:2)/Clay (2:1) (1:1) (1:2) 5 wt-% 5 wt-% 5 wt-% 0 0 0 0 0 0 0.00 5 54.14 34.24 61.15 42.10 47.23 50.00 10 69.34 63.73 78.06 53.65 69.02 67.58 20 102.76 112.88 125.90 74.77 86.42 98.48 30 123.20 146.44 150.36 88.31 106.12 127.27 60 227.07 216.27 245.32 126.29 158.70 192.27 90 305.80 267.46 282.01 156.31 204.97 245.76 120 348.34 322.03 320.14 186.19 247.04 300.76 180 417.96 386.10 394.60 231.47 314.53 393.18 240 426.52 442.71 462.23 259.76 356.98 473.64 360 438.67 516.27 514.75 300.66 426.20 607.12 480 441.16 566.10 547.48 323.90 466.54 721.21 1440 458.29 690.17 639.93 365.21 554.49 1240.91 2880 462.98 716.27 663.67 373.97 581.07 1584.85

TEGDMA was used in these samples as crosslinking agent, which gives better cohesion properties for the changes at different pH and increase the swelling percentage for all samples (with different AAc:H2O proportions). Figure 2 shows the pH critical value was found around 5.2 for materials without clay and 5.5 for materials with dispersed clay material.

Figure 2. pH critical value of the polymer clay composites in aqueous solution. Vol. 1 Pag.31

Figure 3 presents the reversibility of the extended and collapsed states for the composites PAAc and PAAc/clay at pH values above and below the critical pH value. Measurements were made for 8 h at pH = 2.2, and then for 8 h at pH = 7.

Figure 3. Reversibility at different pH values of the polymer clay composites in aqueous solution.

Spectra of PAAc hydrogel, clay and PAAc/clay composite with 5 wt-% content. PAAc hydrogel shows in the carbonyl stretching region, the characteristic stretching absorption band of the carbonyl group C=O appeared at 1700 cm-1. The stretching of C=O coupled with the bending OH neighboring carboxyl groups is responsible for the bands occurring at 1164 -1 -1 and 1241cm , and the bands corresponding to CH2 at 2961 and 1477cm .

Figure 4 shows the thermograms of the compounds synthesized in aqueous solution where a weight loss is observed from 513 to 573 K. In the next stage, PAAc dehydration occurs between 573 to 713 K. Then the decarboxylation of PAAc at 500 °C and finally in the last stage, around 823 K polymer degradation begins. Clay-containing composites were more stable since they started to lose weight at around 513 K while the PAAc begins at 473 K. Finally, in the composite of PAAc/H2O (2:1) with 5 wt-% clay-content, weight losses were minor compared with the other two materials.

Figure 4. Thermogravimetric analysis of the AAc/H2O/Polymer Clay composite Vol. 1 Pag.32

Conclusions

From these set of results, it can be said that both, the clay filler and the crosslinking agent, play an important role into the mechanical properties of the materials. As expected, they responded to pH variations, and the critical pH value was found between 5.2 and 5.5 depending on the clay content. This property of PAAc could find an eventual application in liquid effluents with different pH values. Also, the synthesized materials showed excellent reversible response to cyclical changes in pH. In addition, materials with a little dispersed clay content had better structural properties than those without the mineral structure.

References [1] N.M. Ranjha and U.F. Qureshi, Int. J. Pharm. Pharm Sci., 2014, 6, 400-410. [2] R. Srinivasan, Advances in Materials Science and Engineering, 2011, 17 pages. [3] S.S. Ray y M. Okamoto, Progress in Polymer Science, 2003, 28, 1539-1641. [4] E. I. Unuabonah, E. I. et al.; Appl. Clay Sci., 2014, 99, 83-92.

Acknowledgments Karina Abigail Hernández-Hernández is grateful to CONACyT for scholarship No. 573583. We are also thankful to CONACyT for project 3056 “Cátedras-CONACyT” and to Tecnológico Nacional de México (TecNM) for project 5646.15-P, for their financial support. Vol. 1 Pag.33

CHARACTERIZATION OF CHITOSAN MEMBRANES PROPERTIES AS A POTENTIAL MATERIAL FOR POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) REMOVAL IN WATER

A. Ozaeta-Galindo1, B. Rocha Gutiérrez1, F. I Torres Rojo1, G. Zaragoza Galán1, O. Solís Canto2, C. Soto Figueroa1, D. Y. Rodríguez Hernández1, L. Manjarrez Nevárez1

1Facultad de Ciencias Químicas, Universidad, Autónoma de Chihuahua, Av. Escorza #9000 col. Centro, C.P. 31000, Chihuahua, Chih., México, [email protected] 2Centro de Investigación en Materiales Avanzados (CIMAV S.C.), Chihuahua, Chih., México

I. Introduction

Human health and the environment have been threatened because of the exposure to synthetic chemicals. Some are classified as persistent organic pollutants (POPs). They are resistant to photolytic, chemical and biological degradation. Some of them include a wide range of substances, such as organochlorine pesticides and their metabolites, industrial chemicals and by-products [1].

Polycyclic aromatic hydrocarbons (PAHs), are the most common subclasses of POPs. They constitute a large group of organic compounds with two or more fused aromatic (benzene) rings, which may be presented in the environment by an incomplete combustion at high temperature of organic matter, or by processing of fossil fuels [2]. These compounds have carcinogenic, mutagenic and teratogenic properties. Additionally, PAHs are persistent in the environment due their chemical stability and biodegradation resistance [3]. For these reasons, it is very important to implement efficient technology for their removal.

The membrane processes are found at the highest vanguard level of separation technology, due to its efficiency. Materials are ones of the most important parameters for achieving at high percent of removal pollutant. Among various available film materials, considerable attention has been given to biopolymers of their surface properties and biodegradability. Chitosan is a polysaccharide, which is derived from chitin and is available from waste products in the shellfish industry. Its chemical, mechanical and antibacterial properties have been applied in removal applications. The functional properties of chitosan films are improved when chitosan is combined with other materials [4].

On the other hand, adsorbents are extensively used to remove contaminants, including PAHs, from wastewater. Activated carbon (AC) is a good adsorbent material, especially for non-polar compounds; PAHs adsorption on AC mainly depends on their textural properties Vol. 1 Pag.34

and oxygen functional groups at the periphery of carbon layers, which may be involved in adsorption mechanisms [5].

The present work was directed to synthesize composite membranes of chitosan /activated carbon and to obtain their morphologic and hydrophilic properties for their potential use in the removal PAHs from waste water.

II. Metodology

Membrane synthesis

Chitosan solutions (2%, w/v) were prepared by dispersing chitosan (sigma Aldrich, low molecular weight) in acetic solution (1%, v/v). Composite film base chitosan was prepared without activated carbon or 0.5%, 1.0% and with 1.5% of activated carbon provided from NORIT (Hidrodarco® R) by casting method. The casting solutions were spread over a glass dish. Precipitation by solvent evaporation was carried out at 60°C in an environmental chamber (Labnet I5211-DS) during 18 h. Then, the samples were immersed in sodium hydroxide solution bath in order to be removed from dish, washing thoroughly with pure water and finally were dried at 25°C for 48h before stored.

Morphology Characterization

Chitosan and composites films morphology were analyzed by atomic force microscopy (AFM) in a Multimode Nanoscope IVa, Veeco Instrument. Images were obtained in a tapping mode. Determination of root means square roughness was carried out with the WSxM software. Hydrophilic properties were attained by contact angle analysis through the sessile drop method using an FTA-32 goniometer, Firsttenangstrom.

III. Results

Roughness and surface hydrophilicity are the main parameters to control the membrane fouling and permeability characteristics. Incorporation of nanomaterials can also change the porosity and pore size of membranes, and subsequently, modify their water permeability and solute rejection.

Figure 1 shows the AFM micrographics of chitosan composite films with 0.5%, 1.0% and 1.5 activated carbon loads. The surface roughness (Rms) of chitosan film has been altered by activated carbon addition. Chitosan film presents the lower Rms value in relation with composites membrane (2.69 nm and 9 nm respectively). The increase of surface roughness of chitosan/AC in comparison to chitosan films is probably because of the low spread AC particles into polymeric matrix, as a result of their different polarity. However, this roughness modification will allow improving the low flux of chitosan film as consequence of its dense structure, because it will increase the contact area in the removal process. Furthermore, Salehi et al. 2012 reports that polar-no polar interaction between hydrophilic groups of chitosan and hydrophobic aromatic ring of carbon nanotubes causes formation of channels like wrinkles in the polymer matrix improving permeability through membrane [6]. Vol. 1 Pag.35

According AFM images, the synthesis film process and chitosan-AC interaction cause the AC disposition on the top surface membrane and by this hydrophobic character required for PAHs adsorption affinity. Therefore, this has been confirmed by contact angle results, where chitosan matrix increased its contact angle from 76° to 89° in accordance with the increasing AC loading from 0% at 1.5% (w/v) in the organic phase.

The changes of membrane structure, physicochemical property and mechanical resistance due to the presence of fillers materials rely on the good dispersion of filler in polymeric matrix, as well as good compatibility between them [7]. Efficient dispersion and homogeneity in chitosan film of AC particles was observed at relatively low loading (1%), providing more accessible active sites for sorption of organic pollutants on the surface film.

(a) (c)

(b) (d)

Figure 1. Topography images obtained by AFM of chitosan membranes (a), and composite chitosan/activated carbon membranes at different loads: (b) 0,5%; ( c) 1,0% and (d) 1,5%.

IV. Conclusion

Incorporation of activated carbon at low loading (1% w/v) in chitosan films, modifies the morphology and surface properties of this material in such a way that can be used in the PAHs removal from wastewater. Vol. 1 Pag.36

V. References

[1] Loos et al. EU-wide survey of polar organic persistent pollutants in European river waters. Environ. Pollut. (2009) 157, 561-568. [2] Samanta, S. K. et al. Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation. Trends Biotechnol. (2002) 20, 243-248. [3] Rubio-Clemente, et al. Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review Sci. Total Environ. (2014), 478, 201-225. [4] Salehi et al. A review on chitosan-based adsorptive membranes. Carbohydr. Polym. (2016)152 419-432. [5] Gong, Zongqiang, et al. Activated carbon adsorption of PAHs from vegetable oil used in soil remediation. J. Hazard. Mater. (2007) 143,372-378. [6] Salehi, E., et al. Novel chitosan/poly (vinyl) alcohol thin adsorptive membranes modified with amino functionalized multi-walled carbon nanotubes for Cu (II) removal from water: preparation, characterization, adsorption kinetics and thermodynamics. Sep. Purif. Technol. (2012) 89, 309-319. [7] Salehi E. el al. A review on chitosan-based adsorptive membranes. Carbohydr Polym. (2016) 152:419-32.

Acknowledgements The authors acknowledge the support of Universidad Autónoma de Chihuahua (UACH), Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio de nanotecnología and Óscar Solís Canto for technical support in sample analysis. Vol. 1 Pag.37

ARTIFICIAL WEATHERING OF POLYETHYLENE/MULTIWALL CARBON NANOTUBES AND POLYETHYLENE/COPPER NANOPARTICLES COMPOSITES PREPARED BY MEANS OF ULTRASOUND ASSISTED MELT EXTRUSION PROCESS. Juan G. Martínez-Colunga1, Lina Septien1, María C. Gonzalez-Cantú1, Juan F. Zendejo-Rodriguez1, Marcelina Sanchez-Adame1, Manuel Mata1, Víctor J. Cruz-Delgado1, Carlos A. Ávila-Orta1. 1Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo No. 140, Col. San José de los Cerritos, Saltillo, Coahuila. 25294. México. [email protected]

High density Polyethylene (HDPE) composites with high loadings of Multiwall Carbon Nanotubes (MWCNTs) and Cupper (Cu) nanoparticles were fabricated through ultrasound assisted melt extrusion technology. The present work shows the artificial weathering behavior of these polyethylene composites as a function of MWCNTs and Cu nanoparticles type with different contents (1, 2.5 and 5 w%). It was observed that the nanoparticle content has a significant effect on the nanocomposites elongation at break, mainly at higher particle contents. Nanocomposites were exposure to UV radiation into a QUV chamber for 1000 hr. The degraded samples were characterized by tensile properties. It was observed that the tensile strength and elongation at break of pristine HDPE decrease as a function of UV exposure time. It was established that MWCNTs composites had a better behavior during exposure to UV radiation than Cu composites. This was confirmed because the tensile properties of MWCNT composites did not show any significant changes after 1000 hours of exposure.

Keywords: High density polyethylene, carbon and cupper nanoparticles, composites, artificial weathering.

Introduction Copper (Cu) nanoparticles as well as multiple wall carbon nanotubes (MWCNTs) provide a very favorable mechanical polymer reinforcement, as well as an increase in the electrical and thermal conductivity [1-4]. But one of the problems in melt mixing is to obtain a good dispersion and homogenization of the nanoparticles in the polymer matrix. To solve this problem ultrasound was used to assist the extrusion process. Due to its properties nanocomposites are being used every day in a wide variety of applications and some of them are outdoors [4-6]. For this reason the present study aims to find the research work is to submit to artificial weathering for nanocomposites with nanoparticles of Cu and MWCNTs into HDPE.

Experimental. Materials High-density polyethylene (HDPE) with a MFI = 20 g/10 min Alathon H620. was used for obtain the masterbatch. High density polyethylene (HDPE) with a MFI: 0.08 g/10 min Total HP401N, was used for dilutions. Cu nanoparticles used have an average particle size 300nm, hemispherical morphology, purity 99.5%, SSA: 6 m2/g, supplier SkySpring Nanomaterials, Inc. USA. Multi-walled carbon nanotube (MWCNTs) was supplied by the Vol. 1 Pag.38

Alpha Nano Tech Co. Ltd., Incheon, Korea. Their diamater was 30–50 nm, and 5–15 micron in length.

Methodology Masterbatch preparation: A twin-screw extruder L/D: 40:1 Thermo Scientific 24-MC, was employed to process a masterbatches (HDPE/MWCNTs and HDPE/Cu), with a plain temperature profile of 230 °C and 100 rpm. Resin chips and powder of nanoparticles (MWCNTs or Cu), were feed to the extruder with the assistance of gravimetric feeders for each one at a rate of 5 and 1 kg/h respectively. The samples were extruded with the assistance of ultrasound waves [6] drive by a home-made generator of variable amplitude and frequency in the range of 20 – 50 kHz and power of 500 W. Nanocomposites dilutions preparation: A twin-screw extruder L/D: 40:1 Thermo Scientific 24- MC, was employed to process a nanocomposites dilutions, with a plain temperature profile of 230 °C and 100 rpm. Resin chips of HDPE with a MFI 0.08 g/10 min. and chips of masterbatch (HDPE/MWCNTs and HDPE/Cu) obtained nanomaterials with concentration of 0%, 1%, 2.5% and 5% of nanoparticles. Samples preparation: using chips of dilutions are prepared by compression molding test samples for the exposition to UV radiation and to determine tensile properties Artificial weathering:The weathering accelerated test was carried out using the cycle 1 described in ASTM G 154 (using UVA-340 lamps, 8 hours of UV radiation at 60°C and 4 hours of water condensation at 50°C). Samples were taken every 250 hours to accumulate 1000 hours of exposure.

Characterization. Tensile properties using ASTM D 638 for nanocomposites were measured before and after exposure into a QUV chamber in order to determine the changes of properties due to polymer degradation by the action of accelerated aging conditions.

Results. Tests conducted in the HDPE without particles gave base determine the behavior of the material in terms of its tensile strength and elongation at break. Therefore, we have a point of comparison to know if MWCNTs and Cu nanoparticles provide an improvement to the material.

0% conc 1% conc HDPE/Cu 2.5% conc 36 5% conc

32

28

24

20

16 tensile strenght (Mpa)

12

8 0 200 400 600 800 1000 Exposure time (hr) Vol. 1 Pag.39

Figure 1. Tensile strength of the nanocomposites HDPE/Cu with different concentration of Cu nanoparticles.

The behavior of the tensile strength of the nanocompounds of Cu and MWCNTs as a function of the exposure time in accelerated artificial weathering are show in the Figures 1 and 2. The best behavior for HDPE/Cu was found at 1% concentration followed by 2.5% and 5%. But the nanocomposite containing 1% shows the largest decrease in the tensile properties for a longer exposure time. It is also observed as the nanocomposite containing 5% copper no significant changes by exposure to UV radiation.

0% conc 32 1% conc 2.5% conc 5% conc 28

24

20

HDPE/MWCNTs 16 tensile strenght (Mpa) 12

8

0 200 400 600 800 1000 Exposure time (hr)

Figure 2. Tensile strength of the nanocomposites HDPE/MWCNTs with different concentration of nanotubes.

In nanocomposites with MWCNTs, the tensile strength showed the best behavior concentration 1% followed by 2.5% to 5%. Minor changes occurred in tensile behavior at any concentration and time of UV exposure.

In the nanocomposite with particles of Cu is observed that the elongation at break present at 1% concentration such behavior HDPE without nanoparticles. But the highest concentrations of Cu nanocomposites retained for longer exposure this elongation up to 750 hours. Nano composites that presented the lowest variation of the elongation at break as a function of exposure time were the ones with 5% concentration. Vol. 1 Pag.40

0% conc 1% conc 2.5% conc 800 HDPE/Cu 5% conc

600

400

200 Elongation at break (%)

0

0 200 400 600 800 1000 Exposure time (hr)

Figure 3. Elongation at break of nanocomposites HDPE/Cu with different concentration of Cu nanoparticles.

In nanocomposites with MWCNTs it is observed that the elongation at break is significantly affected by the concentration of MWCNTs. The exposure time had no significant effect in the elongation at break on these nanocomposites.

0% conc 1% conc HDPE/MWCNTs 2.5% conc 800 5% conc

600

400

200 Elongation at break (%)

0

0 200 400 600 800 1000 Exposure time (hr)

Figure 4. Elongation at break of nanocomposites HDPE/MWCNTs with different concentration of nanotubes.

Conclusions Cu nanoparticles strengthens HDPE at low concentrations and provide some protection to UV radiation at high concentrations. The MWCNTs exhibits excellent UV protection to HDPE contractions from 1%. Vol. 1 Pag.41

References.

Masoumeh N.S. et. al. J. Comp. Mat. July 29, 2015 0021998315597556.

Shuklaa A.K., et. al. 84, 2013 Pages 58–66.

[1] Comp. Sci. Tech. , 2007, 67, 3071 [2] J. Appl. Polym. Sci. 2004, 91, 2781 [3] Mat. Charac. 2013, 84, 58. [4] Comp. Part B: Eng. 2013, 55, 407 [5] J. Polym. Sci. part B 2012, 50, 963 [6] Polym. Degr Stab. 2013, 98, 2411

Acknowledgements We acknowledge the financial support from Fondo SENER/CONACYT under CeMIE-Sol program Project 207450/12. This work was financially (partially) supported by CONACYT through Project 250848 Laboratorio Nacional de Materiales Grafénicos. The funding for the trip for exposure this paper in the Polymat 2015 was supported by REDINMAPLAS. We thank its support with the characterization of materials, and to Francisco Zendejo, Gilberto Hurtado and Rodrigo Cedillo for their assistance with processing and characterization of polymer nanocomposites. Vol. 1 Pag.42

THERMAL, MECHANICAL AND ELECTRICAL BEHAVIOR OF POLYPROPYLENE/MULTIWALL CARBON NANOTUBES, POLYPROPYLENE/GRAPHENE AND POLYPROPYLENE/CARBON BLACK COMPOSITES PREPARED BY MEANS OF ULTRASOUND ASSISTED MELT EXTRUSION PROCESS

José M. Mata-Padilla, 1 Víctor J. Cruz-Delgado, 1 Janett A. Valdez-Garza, 1 Edson, Jesús L. Flores-Márquez, 1 Gilberto F. Hurtado-López, 1 Jesús G. Rodríguez, Velázquez, 1 Carlos A. Ávila-Orta, 1 Juan G. Martínez-Colunga.1 1 Centro de Investigación en Química Aplicada, Blvd. Ing. Enrique Reyna H. 140, Col. San José de los Cerritos, Saltillo, Coahuila, México, C.P. 25294. Email: [email protected]

The Thermal, Mechanical and Electrical behavior of Isotactic polypropylene (iPP) composites with high loadings of Multiwall Carbon Nanotubes (MWCNTs), graphene (G) and carbon black (CB) was studied by means of Melt Flow Index (MFI), Differential Scanning Calorimetry (DSC), Thermogravimetric Analyzer (TGA), tensile and flexural analysis, and surface conductivity and dielectric constant as a function of current frequency. The MFI of neat polypropylene decreased for all cases with the addition of each carbon nanoparticles. Additionally, the thermal properties indicated a nucleating effect on the iPP matrix where any nanoparticle was introduced, being the maximum effect for graphene nanoparticles. Conversely, the tensile properties showed a not significant change in the composites respect to the neat iPP, while the flexural module increased about three times with all carbon particles. It was also found that dielectric constant and surface conductivity behavior was a function of type of carbon nanoparticle, and in some cases of the current frequency.

Introduction The scientific and thecnological interest of polymer nanocomposites with carbon nanoparticles has increased in recent years due to the outstanding thermal [1], mechanical [2] and electrical [3] performance of these composites. In the case of polypropylene nanocomposites, there are reports about the fabrication of PP/MWCNT nanocomposites with low electrical percolation threshold and significantly enhanced mechanical properties [4] and PP/G nanocomposites with high thermal stability and enhanced mechanical properties [5]. Nonetheless, the high performance of these nanocomposites is highly dependent of an effective dispersion of carbon nanoparticles in the polymer matrix. To adress and solve this problem, the melt extrusion process assisted by ultrasound technology has been recently developed [6, 7]. In the particular case of our research group, an ultrasound, under variable frequency and amplitude, technology has been reported as a efficient alternative to disperse high loadings of carbon nanoparticles [8, 9]. However, the dispersion of carbon nanoparticles in polypropylene depends of different factors such as the nanoparticle type and the processing of nanocomposite (ultrasound frequence range, extrusion conditions, etc.). In the particular case of present work, the main aim was to study the thermal, mechanical and electric behavior of PP Vol. 1 Pag.43

nanocomposites with high content of carbon nanoparticles, varying the type of nanoparticle (MWCNT, G and CB) using constant extrusion and ultrasound conditions.

Experimental Polypropylene (Formolene 4111T from FORMOSA Plastics, USA, MFI= 35 g/10min) nanocomposites with high loading of MWCNTs (Cheaptubes USA, L/D= 100), Graphene (Cheaptubes USA, Thickness = 8 nm) and CB (VULCAN VXC-72, Cabot USA. size = 15 nm) were prepared by means of melt extrusion process (210°C, 100 RPM) assisted by variable ultrasound (15-50 KHz). The extruder was a twin screw extruder L/D: 40:1 from Thermo Scientific 24-MC. The thermal characterization of PP nanocomposites was realized by DSC (Q200 TA Instrument, 10 °C/min, N2 Atmosphere) and TGA (Q500 TA Instrument, 10 °C/min. N2 Atmosphere). The mechanical properties were evaluated in an INSTRON 4301 in accordance with ASTM D 638 (tensile properties) and ASTM D 790 (flexural properties). In addition, the electric properties (conductivity and capacitance) were evaluated using a High precision LCR meter Keysight model E4980A, in the frequency range of 20 Hz to 1 MHz.

Results and Discusion The first effect originated by the incorporation of high loadings of MWCNT, G and CB were observed on the melt flow index (MFI) of composites. The results of MFI were 45.0 g/10 min for the neat PP, 5.5 g/10min for PP/MWCNT, 10.2 for PP/G and 16.2 for PP/CB samples, respectively. These results indicated the high influence of carbon nanoparticles on the fluidity properties in accordance with previous works reported for similar systems [9]. The thermal properties (TGA and DSC) are reported in the Table 1. These results show that the carbon nanoparticles significantly increased the thermal stability of polymer matrix in about 15 °C at the 50% of degradation for the three carbon nanoparticles, similar to previously reported results [3, 5]. Additionally, it was observed an outstanding increase in the crystallization temperature for all nanocomposites, which has not been previously reported at high loadings of nanoparticles [4, 5]. However, there were not signifficant changes in the melting behavior of PP (Tm and ΔHm) when the carbon nanoparticles were incorporated.

Table 1. TGA and DSC results of Polypropylene Nanocomposites with high loadings of MWCNT, G and CB.

Sample Td, 5% Td, 50% Tm (°C) Tc (°C) ΔHm (J/g) ΔHc, (J/g)

Neat PP 373.5 437.6 168.4 110.9 94.1 97.3

PP/MWCNT 420.1 452.0 168.6 131.0 104.3 98.8 Vol. 1 Pag.44

PP/G 402.3 445.1 168.0 135.0 93.0 90.9

PP/CB 430.2 455.3 169.2 125.6 90.2 88.8

The effect of high loadings of MWCNT, G and CB on the tensile and flexural properties of polypropylene is shown in Table 2. These results clearly indicated that the effect of nanoparticles incorporation was significant, in the case of flexural modulus, respect to the neat polymer (about 300 %). This behavior has not been previously reported for similar nanocomposites systems [4, 5], However, the increase in the tensile modulus was limitated.

Table 2. Mechanical properties (Tensile and flexural modulus) of Polypropylene Nanocomposites with high loadings of MWCNT, G and CB.

Tensile Modulus Flexural Modulus Sample (MPa) (MPa)

Neat PP 34.9 288.6

PP/MWCNT 43.0 861.6

PP/G 42.1 980.3

PP/CB 44.2 913.0

The results of electric properties are displayed in Figure 1. The Figure 1a shows that the incorporation of high loadings MWCNT and G increased the electrical conductivity of polypropylene about 7.5 orders of magnitude in all the range of frequency, which was superior to similar systems obtained previously by means of solution mixing [3]. While, when the CB nanoparticles were incorporated, the PP/CB nanocomposite changed its behavior from static dissipative to semiconductor material [3, 9]. Vol. 1 Pag.45

Figure 1. Electric behavior (a) electric conductivity and (b) dielectric constant of PP nanocomposites with MWCNT, G and CB.

Conversely, the Figure 1b shows an increase in the dielectric constant for the PP/MWCNT, PP/G and PP/CB nanocomposites respect to the neat PP sample being higher the case of PP/G sample (about 3 order of magnitude). This behavior has been associated to the percolation phenomena [10]. The dielectric constant was practically constant in all the range of frequencies.

Conclusions This study showed that the introduction of carbon nanoparticles had a high influence on the thermal stability and thermal dissipation of the polypropylene matrix perhaps due to the better dispersion and distribution of nanoparticles in PP matrix when the ultrasound technology was applied. It was also observed that PP/G and PP/MWCNT nanocomposites showed the best flexural and electrical behavior due to a better interfacial interaction, while the electrical behavior of PP/CB nanocomposites was highly influenced by the current frequency, in the range of static dissipative or semiconductor material.

References [1] M. Norkhairunnisa, A. Azizan, M. Mariatti, H. Ismail and L.C. Sim, J. Compos. Mater. 2012, 46, 903-910. [2] M. El Achaby, F. E. Arrakhiz, S. Vaudreuil, A. el K. Qaiss, M. Bousmina, O. Fassi-Fehri, Polym. Compos. 2012, 33, 733–744. [3] C. A. Á vila-Orta, C. E. Raudry-López, M. V. Dávila-Rodríguez, Y. A. Aguirre-Figueroa, V. J. Cruz-Delgado, M. G. Neira-Velázquez, F. J. Medellín-Rodríguez, and B. S. Hsiao, Int. J. Polym. Mater. Polym. Biomater. 2013, 62, 635–641 [4] E. Logakis, E. Pollatos, Ch. Pandis, V. Peoglos, I. Zuburtikudis, C.G. Delides, A. Vatalis, M. Gjoka, E. Syskakis, K. Viras, P. Pissis, Compos. Sci. Technol. 2010, 70, 328–335 [5] P. Song, Z. Cao, Y. Cai, L. Zhao, Z. Fang, S. Fu, Polymer 2011, 52, 4001-4010. [6] A.I. Isayev, R. Kumar, T. M. Lewis, Polymer 2009, 5, 250–260. [7] J. M. Mata-Padilla, C. A. Ávila-Orta, F. J. Medellín-Rodríguez, E. Hernández-Hernández, R. M. Jiménez- Barrera, Víctor J. Cruz-Delgado, J. Valdéz-Garza, S. G. Solís-Rosales, A. Torres-Martínez, M. Lozano-Estrada, Enrique Díaz-Barriga Castro, J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 475–491. Vol. 1 Pag.46

[8] C.A. Ávila-Orta, J.G. Martínez-Colunga, D. Bueno-Baqués, C.E. Raudry-López, V.J. Cruz-Delgado, P. González- Morones, J.A. Valdéz-Garza, M.E. Esparza-Juárez, C.J. Espinoza-González, J.A. Rodríguez-González, Mx. Patent MX/a/2009/003842, 2014. [9] C A. Ávila-Orta, Z. V. Quiñones-Jurado, M. A. Waldo-Mendoza, E. A. Rivera-Paz, V. J. Cruz-Delgado, J. M. Mata-Padilla, P. González-Morones and R. F. Ziolo, Materials 2015, 8, 7900–7912 [10] A. B. Espinoza-Martínez, Carlos A. Ávila-Orta, V. J. Cruz-Delgado, F. J. Medellín-Rodríguez, Darío Bueno- Baqués, J. M. Mata-Padilla., J. Appl. Polym. Sci. 2015, 132, 41765.

Acknowledgements We acknowledge the financial support of this work from the SENER/CONACyT fund under CeMIE-Sol program, Project 12 “Desarrollo de Captadores, Sistemas Solares y Sistemas de Baja Temperatura con Materiales Novedosos para México”. This work was financially (partially) supported by Consejo Nacional de Ciencia y Tecnología (CONACYT) through Project 250848, we thank its support for the electrical characterization. Vol. 1 Pag.47

EFFECT OF LaPO4 REINFORCEMENT ON STRUCTURAL, THERMAL AND OPTICAL PROPERTIES OF PMMA D. Palma Ramírez1, M. A. Domínguez-Crespo1, A. M. Torres-Huerta1, D. Del Angel-López1 1 Instituto Politécnico Nacional (IPN). Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, CICATA-IPN Unidad Altamira. Carretera Tampico-Puerto Industrial, C.P. 89600 Altamira, Tamaulipas, México, [email protected] and [email protected]

Abstract. In this work, precipitation synthesis is used for obtaining lanthanum phosphate (LaPO4) particles and evaluate the possible application as UV absorber to increase the optical properties of poly(methyl methacrylate) (PMMA). In order to reach this goal, LaPO4 were dispersed during the polymerization of methyl methacrylate (MMA) and in commercial PMMA. Results indicate that LaPO4 can be potentially used to maintain the structural properties when PMMA is used in outdoor applications.

Introduction

PMMA exhibits good toughness at high and low temperatures and is one of the most commonly used thermoplastic polymers in outdoor applications. As a result of its amorphous structure, it allows 92 % of light passes through it and therefore, it is optically transparent [1]. PMMA has the disadvantage to be degraded under solar UV radiation (200-400 nm), this process starts with visible color changes and further leads to cracking and hazing [1]. In order to reduce those drawbacks, organic or inorganics UV absorbers such as titanium dioxide (TiO2), zinc oxide (ZnO) and cerium oxide (CeO2) can be incorporated [2]. Recently, rare earth phosphates have been proposed as UV absorber. In these systems, the UV light is absorbed and dissipated into a longer wavelength where the polymer degradation cannot takes place [3]. Lanthanum phosphate (LaPO4) has high temperature stability and chemical inertness [4] and it has not been well explored. The main of this work is to disperse LaPO4 into a commercial and synthesized PMMA and evaluate the structural, optical and thermal properties of the blends.

Experimental

LaPO4 particles were prepared by precipitation method using 0.036 M of lanthanum nitrate (LaNO3) and 0.036 M of tripolyphosphoric acid (H5P3O10). 50 mL of LaNO3 were added dropwise to 25 mL of H5P3O10 solution under stirring. H5P3O10 was previously prepared from the ion exchange of sodium tripolyphosphate (Na5P3O10). Deionized water was added to adjust a final volume of 100 mL and then, precipitate was washed with deionized water, centrifuged and dried at 100 °C. LaPO4 particles were heat treated at different temperatures for 4 h. LaPO4 particles were analyzed by Fourier Transform Infrared spectroscopy (FTIR, spectrum one Perkin Elmer spectrometer), X-ray diffraction (XRD, D8 Advance Bruker diffractometer), dynamic light scattering (DLS, ZEN5600 Malver Zetasizer NanoZSP) and fluorescence intensity measurements (LSM 700 Carl ZEISS Microscope). Vol. 1 Pag.48

Dispersion of particles into commercial PMMA. 0.1, 0.5 and 1 wt.% of LaPO4 particles were dissolved in 25 mL of chloroform with 3 g of PMMA pellets (Plexiglas V825) under sonication (2510 Branson) for 30 min.

In situ polymerization of particle dispersions in MMA. 0.1, 0.5 and 1 wt.% of LaPO4 particles were dissolved in 25 mL of chloroform under sonication for 30 min. 15 mL of methyl methacrylate and 0.5 mol wt.% of benzoyl peroxide were added and stirred for 1.5 h at 80 °C by mechanical stirring. Final solutions were cast in poly(propylene) molds and introduced in an oven for 24 hours at 80 °C. Polymers were characterized by FTIR and differential scanning calorimetry (DSC, Pyris 1 Perkin Elmer).

Results and discussion

FTIR spectra of LaPO4 presented in Figure 1 show the characteristics bands of PO4 groups. -1 The absorption bands at 1233-990 and 951 cm are due to P-O stretching in the ν3 vibration -1 region in the monoclinic LaPO4 [5]. Similarly, the bands located at 617, 577 and 563 cm are 3- attributed to bending of O=P-O and O-P-O of the PO4 groups in the ν4 vibration region [6]. XRD patterns in Figure 2 show the progress of the sintering process from room temperature to 700 °C. It can be seen that monoclinic structure of LaPO4 (PDF# 01-083-0651) is obtained by this facile method at room temperature. Additionally, high temperature heat treatment only produces the increase in peak intensities.

120 40 LaPO4 700 °C 110 LaPO LaPO4 35 4 100 30 90 563 LaPO 600 °C Dz = 2300 nm 80 4 25 70 PDI = 1.2 20 60 15 50 LaPO4 500 °C 40 617 Frequency 10 30 20 5 Transmittance (%) 951 LaPO4 400 °C 10 577 Intensity (a.u.) 0 0 1233-990 0 1000 2000 3000 4000 5000 1500 1350 1200 1050 900 750 600 -1 LaPO Diameter (nm) (132) 4 Wavenumber (cm ) (012) (402) (120) (103) (103) (200) (322) (212) (202) (101) (001) (212) (111) (110) (142) (124) (031) (023) (140) (241) (123) (340) (004)

20 30 40 50 60 70 2(°)

Figure 1. FTIR spectra of Figure 2. XRD patterns of the high Figure 3. Particle size LaPO4 temperature heat treatment of LaPO4 distribution of LaPO4

The particle size distribution (hydrodynamic diameter) measured from DLS is shown in Figure 3. It is observed that the particles display monodispersity (Polydispersity index (PDI) equal to 1.2) and an approximate size of about 2.5 µm. This fact clearly confirms that the precipitation method produces larger sizes than the microwave assisted hydrothermal method used to obtain rare earth phosphates [7]. However, the size is similar to those obtained from the precipitation of LaNO3 and orthophosphoric acid [8]. The luminescence spectra were acquired in order to evaluate whether the proposed LaPO4 powders were responsive to UV light. Figure 4 presents the emission spectra of LaPO4 samples. It is quite evident that this material has luminescent properties since it displays the emission in the visible range of the electromagnetic spectrum; specifically, in the 450-650 nm Vol. 1 Pag.49

range. Therefore, this feature can help to maintain the structural properties of polymers which are used outdoors and subjected to the UV light.

Commercial PMMA/1 wt.% of LaPO Synthesized PMMA/1 wt.% of LaPO 180 4 4

160 LaPO4 140

120

100 Commercial PMMA CH Synthesized PMMA CH 80 C-O group 60 C-O group Intensity (a.u.)

40 Transmittance (u.a.) CH3 Transmittance (u.a.) COCH COCH CH 3 20 CH CH 3 CH 3 C=O 3 CH C=O 0 C-O-C 3 C-O-C 400 450 500 550 600 650 700 2000 1800 1600 1400 1200 1000 800 2000 1800 1600 1400 1200 1000 800 -1 Emission wavelength (nm) Wavelength (cm-1) Wavenumber (cm )

Figure 4. Emission spectra Figure 5. FTIR spectra of Figure 6. UV-Visible spectra under 405 nm excitation selected commercial PMMA of selected synthesized PMMA/LaPO4 PMMA and PMMA/LaPO4

The addition of the LaPO4 either into commercial PMMA (Figure 5) or synthesized PMMA (Figure 6) does not generate new bands or shifting of bands in the FTIR bands spectra. Therefore, the spectra display the characteristic bands of PMMA as follows: 1723 cm-1 -1 -1 stretching of C=O, 1443 cm is the CH of CH3O group, 1210-1320 cm to the O-C stretching vibration, 1135 cm-1 is the C-O stretching, 1382 cm-1 and 750 cm-1 are the α-methyl group, -1 -1 -1 3440 cm , 985 cm is the C-O-CH3 rocking, 960-650 cm is bending of CH [9]. The effect of the incorporation of LaPO4 on the optical properties of PMMA was also observed by UV-Visible spectroscopy. Figure 7 and 8 display the transmittance in the UV- visible range for LaPO4 dispersion into commercial PMMA and synthesized PMMA, respectively. It can be seen that PMMA and PMMA/LaPO4 samples show UV absorption in the 180-400 nm range in all samples. Even, they are almost transparent to the visible light, it is important to mention that there was no control of the thickness of the polymer. Therefore, the transmittance percentage cannot be associated to the different wt.% addition of LaPO4. The unique differences between commercial and synthesized PMMA is observed in the UV region; π−π transition in the excited states of carbonyl group in PMMA is observed in commercial PMMA blends and not in synthesized PMMA [10]. This interesting feature might be probably due to the interaction between the carbonyl group and LaPO4.

Synthesized PMMA/0.1 wt.% LaPO4 Synthesized PMMA Table 1. Tg’s temperatures

LaPO4 Tg’s Tg’s content commercial synthesized (wt.%) PMMA PMMA Commercial PMMA (°C) (°C) Commercial PMMA/1 wt.% LaPO 4 0 65 108 Transmittance (a.u.) Transmittance (a.u.) Commercial PMMA/0.5 wt.% LaPO Synthesized PMMA/0.5 wt.% LaPO 4 4 0.1 86 110 Commercial PMMA/0.1 wt.% LaPO Synthesized PMMA/1 wt.% LaPO 4 4 0.5 98 112 200 300 400 500 600 700 200 300 400 500 600 700 1 99 115 Wavelength (nm) Wavelength (nm) Figure 7. UV-Visible spectra of Figure 8. UV-Visible spectra of commercial PMMA and synthesized PMMA and PMMA/LaPO4 PMMA/LaPO4 Vol. 1 Pag.50

It is observed that the glass transition temperature (Tg) of synthesized PMMA is higher than commercial PMMA. The addition of LaPO4 into commercial and synthesized PMMA increases Tg with increasing the amount of LaPO4 which is indicative of the reduction in mobility [11].

Conclusions

Luminescent LaPO4 particles of micrometer scale with monazite phase can be obtained by facile precipitation method at room temperature. XRD analysis confirmed that further thermal treatments do not alter the monoclinic structure. The addition of the particles into PMMA improves the thermal stability by increasing the Tg which can be of advantage for applications that require higher temperatures. Emission properties of LaPO4 corroborate that this systems can be potentially used as polymer fillers to maintain the structural properties and improve the thermal stability of the polymers.

References

[1] Rudko G, Kovalchuk A, Fediv V, Chen WM, Buyanova IA. Nanoscale Res. Lett. 2015, 10, 81. [2] Wiley. Processing and finishing of polymeric materials, Volume 2; John Wiley & Sons: Hoboken, New Jersey, 2012: p. 718. [3] Palma-Ramírez D.; Domínguez-Crespo M.A.; Torres-Huerta A.M.; Ramírez-Meneses E.; Rodríguez E.; Dorantes-Rosales H. and Cayetano-Castro H. Ceram. Int. 2016, 42(1, Part A), 774-788. [4] Wieczorek-Ciurowa K., Mechanochemical Synthesis of Metallic-Ceramic Composite Powders, in: M. Sopicka-Lizer (Eds.), High-Energy Ball Milling: Mechanochemical Processing of Nanopowders, Woodhead Publishing Ltd., 2010: p. 260. [5] Li G.; Li L.; Li M.; Song Y.; Haifeng Z.; Lianchun Z.; Xuechun X. and Shucai Gan. Mater. Chem. Phys.2012, 133(1), 263-268. [6] Zhou R.; Lv M. and Li X. Opt. Mater. 2016, 51, 89-93. [7] Nguyen Thanh H.; Nguyen Duc V.; Dinh Manh T.; Do Khanh T.; Nguyen Thanh B.; Train Kim A. and Le Quoc M. Rare Earths, 2011 , 29(12), 1170-1173. [8] Sujith S.S.; Arun Kumar S.L.; Mangalaraja R.V.; Peer Mohamed A. and Ananthakumar S., Ceram. Int. 2014, 40, 15121-15129. [9]Balamurugan, A.; Kannan S.; Selvaraj V. and Rajeswari S. Trends Biomater. Artif. Organs, 2004, 18 (1), 41-45. [10] El-Bashir, S.M.; Al-Harbi F.F.; Elburaih H.; Al-Faifi F. and Yahia I.S. Renewable Energy, 2016, 85, 928-938. [11]Rymma, S.; Filimon M.; Dannert R.; Elens P.; Sanctuary R. and Baller J. Nanotechnology, 2014, 25(42), 425704 (8pp).

Acknowledgements

D. Palma-Ramírez is grateful for her postgraduate scholarship to CONACYT, SIP-IPN and COFAA- IPN. The authors are also grateful for the financial support provided by CONACYT through the CB2009-132660 and CB2009-133618 projects and to IPN through the SIP 2015-0202, 2015- 0227, 2015-0205, SIP 2016-0541, SIP 2016-0542 and 2016-0543 projects and SNI-CONACYT. Vol. 1 Pag.51

LIFETIME PREDICTION AND DEGRADABILITY ON PET/PLA AND PET/CHITOSAN BLENDS

D. Palma Ramírez1, A. M. Torres-Huerta1, M. A. Domínguez-Crespo1, D. Del Angel-López1 1 Instituto Politécnico Nacional (IPN). Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, CICATA-IPN Unidad Altamira. Carretera Tampico-Puerto Industrial, C.P. 89600 Altamira, Tamaulipas, México, [email protected] and [email protected]

Abstract. Artificially accelerated weathering test (1200 h) was carried out in commercial poly(ethylene terephthalate) (PET) and recycled (R-PET) with poly(lactic acid) (PLA) or chitosan blends obtained by the extrusion process. Weak interactions between the biodegradable and polyester polymers were found. Lifetime prediction indicates that blends made from R- PET will decompose faster than from commercial PET. From overall samples, R-PET/ chitosan (95/5) and R-PET/PLA (85/15) were found to degrade faster than the others compositions after 45 and 54 years, respectively.

Introduction. The most favorable packaging material for soft drink bottles is PET, a kind of semi-crystalline, thermoplastic polyester with high strength and transparency properties. Unfortunately, most of these beverage bottles are used only once and then they are discarded, which inevitably creates serious resource waste. Consequently, the environmental problems (white pollution) is becoming more and more serious [1-2]. In order to solve this problem, one approach is to combine PET with materials preferentially from renewable resources such as chitosan and PLA to obtain a resistant material during their use and have degradable properties at the end of their useful life [3]. This implies the study of the structural, morphological and degradation properties as well as the lifetime prediction of the final blends. In this work, efforts have been made to evaluate the properties when selected ratios of poly(lactic acid) (PLA) and chitosan biopolymers are incorporated during the extrusion process into two matrixes: virgin PET and recycled PET (R-PET). Comparison between both type of blends and pure PET was made. Filaments were obtained and their structural, miscibility, thermal and morphological properties as well as their degradation under accelerated weathering were investigated to determine the feasibility of these blends.

Experimental. Different amounts of PLA (2002D NatureWorks) (5, 10 and 15 wt-%) or chitosan (1, 2.5 and 5 wt-%) with commercial PET (CLEARTUF®-MAX2) or R-PET (from discarded bottles) were hand mixed previous to extrusion process. Blends with filaments shape were obtained in a single-screw extruder (C.W. Brabender) with L/D ratio of 25:1 and four heating zones: feeding (225 °C), compression (237.5 °C), distribution (260 °C), and the extrusion die (225 °C). PET/PLA, R-PET/PLA, PET/chitosan and R-PET/chitosan blends were subjected to accelerated weathering (a.w.) test (QUV/Se, 313 nm and 0.63 W/m2) under UV (8 h, 60 °C)/condensation (4 h, 50 °C) cycles for a period of 1200 h. Weight loss percentage was used to estimate the degradation rate according to Eq. (1), where K is a constant of conversion units to mm/year, W is the weight loss (g), A is the area exposed (cm2), T is the time (h) and D is the density of the material (g cm−3). KW Degradation rate = ATD Eq. (1) Vol. 1 Pag.52

All blends were analyzed by Fourier Transform Infrared spectroscopy (FTIR, spectrum one Perkin Elmer spectrometer), differential scanning calorimetry (DSC) (Labsys Evo, Setaram) and scanning electron microscopy (SEM JEOL 6300).

Results and discussion Structural changes. FTIR spectra of PET/PLA, R-PET/PLA, PET/Chitosan and R- PET/Chitosan blends are shown in Figure 1a-f. For PET/PLA and R-PET/PLA, the band between 1768 cm-1 and 1670 cm-1 represents the carbonyl group of PET and PLA. The spectra show the main characteristics bands of PET as follows; at 1619-1510 cm-1 is the -1 -1 aromatic skeleton stretching, 1460–1341 cm is CH2 deformation, 1266–1102 cm is C(O)O −1 −1 stretching, 1018 cm is the 1,4 aromatic substitution, 963 cm is OCH2 stretching of ethylene glycol, 869 cm−1 is C-H deformation on an aromatic ring and 730 cm-1 is the band associated to the out of plane deformation of the two carbonyl substituents on the aromatic ring [4-7]. On the other hand, when PET and R-PET is blended with chitosan, there is no evidence of chitosan phase in the FTIR spectra due to the lower amounts used in the extrusion process. In this blends, there were no shift of the bands of any group in PET or R- PET either with PLA or chitosan. This confirms the no chemical interaction between both phases. a) PET/PLA 95/5 b) PET/chitosan 99/1 c) PET-PLA 95/5 PET/PLA 90/10 PET/chitosan 97.5/2.5

PET/PLA 85/15 PET/chitosan 95/5 PET-PLA 90/10 R-PET/PLA 95/5 CH C-O 2 R-PET/chitosan 99/1

R-PET/PLA 90/10 1,4 substitution R-PET/chitosan 97.5/2.5 PET-PLA 85/15 C-C O-CH2

Absorbance (a.u.) Absorbance C=O PET Absorbance (a.u.) Absorbance 1700 R-PET/PLA 85/15 Absorbance (a.u.) 1747 C=O(a) C-O C=O PET 1768-1670 PET signals R-PET/chitosan 95/5 C=O PLA

2000 1750 1500 1250 1000 750 3000 2500 2000 1500 1000 2000 1800 1600 1400 1200 1000 800 -1 -1 Wavenumber (cm-1) Wavenumber (cm ) Wavenumber (cm )

d) e) f) PET/chitosan 99/1 R-PET/PLA 95/5 PET/chitosan 99/1 ) a.u.

( PET/chitosan 97.5/2.5 PET/chitosan 97.5/2.5 R-PET/PLA 90/10

PET/chitosan 95/5 PET/chitosan 97.5/2.5 Absorbance (a.u.) Absorbance R-PET/PLA 85/15 Absorbance (a.u.) 1715 1715 1700 C-O 1746 C=O C-O 1746 1700 (a) C=O CH C=O (a) CH C=O(c) 2 (c) 2 2000 1800 1600 1400 1200 1000 800 2000 1800 1600 1400 1200 1000 800 -1 -1 2000 1800 1600 1400 1200 1000 800 Wavenumber (cm ) Wavenumber (cm ) Wavenumber (cm-1)

Figure 1. Spectra of a) PET/PLA and R-PET/PLA blends, b) PET/chitosan and R- PET/chitosan blends, c) PET/PLA blends after a.w. test, d) R-PET/PLA blends after a.w. test, e) PET/chitosan blends after a.w. test and f) R-PET/chitosan blends after a.w. test.

The spectra after accelerated weathering test show the structural changes in the bands produced by the temperature, UV light and humidity after 1200 h. For blends with PLA, C=O band is divided into different bands: 1700 cm-1 and 1747 cm-1 represent the photo-oxidation of the amorphous and crystalline chains, respectively [6,8]. Amorphous band is more defined Vol. 1 Pag.53

than crystalline because these regions are more susceptible to be degraded. In a similar way, PLA C=O band appears at higher wavenumber. Also, ester bonds at 1318 cm-1 and -1 -1 -1 1180 cm for PET and PLA and CH2 bands in PET at 1410 cm and 1340 cm become broad and weak after the process. Blends with chitosan spectra display weak bands showing the typical splitting of C=O signals. In blends of R-PET/chitosan, the shifting of crystalline- amorphous C=O is not observed indicating the degradation. Morphological changes. The surface morphologies of the exposed filaments of blends are compared in Figure 2. In all micrographs of blends, the damage caused by the UV light and humidity is evident. PET and R-PET/PLA blends are mainly composed of cracks which appear after the beginning of degradation by breaking of the C-O bonds of both polyesters [9]. On the other hand, PET and R-PET/Chitosan produces a similar damage but with smaller cracks that are due by the swelling of chitosan powders. Degradation rates and lifetime prediction. A relationship of 1000 h of accelerated weathering in QUV chamber equal to 1 year of natural weathering was used to evaluate the degradation rate and the lifetime prediction of final blends [10]. Figure 3 shows that the blends of R-PET/PLA or chitosan degrade faster than PET/PLA or chitosan blends; this is mainly due to the nature of the PET (recycled bottles). From all samples, the lifetime prediction indicates that R-PET/chitosan (95/5) and PLA (85/15) will decompose after 45 and 54 years of natural weathering, respectively.

R-PET/chitosan 95/5 45 years R-PET/chitosan 97.5/2.5 55 years R-PET/chitosan 99/1 56 years PET/chitosan 95/5 60 years PET/chitosan 97.5/2.5 93 years PET/chitosan 99/1 143 years R-PET/PLA 85/15 54 years Blends R-PET/PLA90/10 58 years R-PET/PLA 95/5 91 years PET/PLA 85/15 76 years PET/PLA90/10 103 years PET/PLA 95/5 107 years

0.0 1.0x10-3 2.0x10-3 3.0x10-3 4.0x10-3 Degradation rate (mm/year)

Figure 2. Surface morphologies of exposed Figure 3. Degradation rate of blends under surfaces of PET and R-PET/PLAPET and R- accelerated weathering PET/Chitosan, PET/PLA, R-PET/PLA, PET/Chitosan and blends after accelerated weathering test

Thermal properties. Table 1 displays the thermal properties of blends before and after being subjected to accelerated weathering. In general, PET, R-PET, PLA, PET/PLA, R- PET/PLA, PET/Chitosan and PET/Chitosan blends showed a decreasing in the melting (Tm) and crystallization (Tc) temperatures. The shifting of the Tc and Tm are mainly due to the disentangled and break of the chains. Mostly, shorter chains that are easily to move at lower temperatures are generated after the degradation [11]. Vol. 1 Pag.54

Table 1. Thermal properties of as-prepared blends before and after a.w. test Polymer Tm (°C) Tc (°C) Tm (°C) Tc (°C) As prepared After accelerated weathering PET 126, 243 201 248 170 R-PET 245 205 227, 245 156 PLA 161 126 150 120 PET/PLA 95/5 250 200 152, 243 205 PET/PLA 90/10 250 202 152, 242 202 PET/PLA 85/15 250 205 155, 244 200 R-PET/PLA 95/5 250, 158 198 152, 241 194 R-PET/PLA 90/10 250 201 152, 243 180 R-PET/PLA 85/15 250, 158 202 152, 239 180 PET/Chitosan 99/1 248 197 240 184 PET/Chitosan 97.5/2.5 249 197 242 191 PET/Chitosan 95/5 251 203 249 190 R-PET/Chitosan 99/1 248 208 241 - R-PET/Chitosan 97.5/2.5 250 207 - - R-PET/Chitosan 95/5 250 208 240 -

Conclusions. In this study, the effect of accelerated weathering on structural properties and lifetime prediction of PET, PLA and its blends showed how the degradation rate is improved when PLA or chitosan are added into the conventional matrix. Degradation of PET/chitosan favors more the scission of the chains compared to the PET/PLA blends. Thermal properties confirmed the modification of Tm and Tc after the degradation. Degradation leads to cracking along the surface exposed. The best performance was obtained for PET/chitosan polymer blend with a 95/5 weight ratio where an estimate time of about 45 years is required for its degradation.

References [1] Bach C.; Dauchy X. and Chagnon M-C. Water Res. 2012, 46(3), 571-583. [2] Zhang Y.; Guo W.; Zhang H. and Wu C. Polym. Degrad. Stab. 2009, 94, 1135-1141. [3] Lucas N.; Bienaime C.; Belloy C.; Queneudec M.; Silvestre F. and Nava-Saucedo J-E. Chemosphere, 2008 , 73(4), 429-442. [4] Garlota D. J. Polym. Environ. 2001, 9(2), 63-84. [5] Zhao Q.; Jia Z.; Li X. and Ye Z. Mater Des., 2010, 31, 4457–4460. [6] Andanson J.M. and Kazarian S.G. Macromol Symp, 2008, 265, 195–204. [7] Mai F.; Habibi Y.; Raquez J.M.; Dubois P.; Feller J.F. and T. Peijs, et al. Polymer, 2013, 54, 6818– 6823. [8] Zhang W.R.; Hinder S.J.; Smith R.; Lowe C. and Watts J.F. J Coat Technol Res, 2011, 8, 329-342. [9] Copinet A.; Bertrand C.; Govindin S.; Coma V. and Couturier Y. Chemosphere, 2004, 55, 763-773. [10] Wagner N. and Ramsey B. Technical Document by GSE Lining Technology, Inc., 2003. Houston, TX, USA. [11] Pasch H. and malik M. Advanced Separation Techniques for Polyolefins, 1st edition, Springer Laboratory, Springer International Publishing, Switzerland, 2014; pp. 42-43.

Acknowledgements D. Palma-Ramírez is grateful for her postgraduate fellowship to CONACYT, COFAA and SIP IPN. The authors are also grateful for the financial support provided by the CONACYT Research Fellowship- IPN-CICATA Altamira agreement, 2014-1905, IPN through the SIP 2016-0541, 2016-0542, 2016-0543 and 2016-1158 projects and SNI-CONACYT. The authors thank to ROMFER SA CV industries for their technical support. Vol. 1 Pag.55

EXTRACTION AND CHARACTERIZATION OF FOOD BIOPOLYMERS FROM BYPRODUCTS OF MANGO (Manguifera indica L.) Ramos-Ramirez, E. G., Sierra-López D., Pascual-Ramírez J., Salazar-Montoya J. A. Biotechnology and Bioengineering Department, CINVESTAV-IPN, Av. IPN 2508. Col. San Pedro Zacatenco. C.P. 07360, Mexico City, Mexico. Email: [email protected]

ABSTRACT

Due to its production volume and consumption rate, mango is one of the most important fruit crops in Mexico. The mango pulp is the only industrialized fraction, discarding major byproducts of mango processing like peels and seeds, which represent a serious disposal problem and contributing to water pollution and plagues. The aim of this study was the extraction and characterization of active biopolymers from seed and peel of mango Tommy Atkins variety. Samples were acquired during their commercial ripeness stage from a local market in Mexico City. The biopolymers fractions from peel and seed kernel (germ) were extracted and analyzed using Official Methods of AOAC and physicochemical methods. Results show that mango peel is an important source of raw fiber (19 %) and proteins (3 %), also soluble carbohydrates (68 %) in which we can find pectin. From seed kernels, it is possible to obtain starch (43 %), fat (12 %) and proteins (4 %), although this fraction did not have raw fiber nor pectin substances. Results show that pectin from peel was of high methoxyl and had low acetylation. It was not possible to determine the pectin fusion point due to its behavior of amorphous polymer, so a calcination point was greater than 220 °C. From the seed kernel was possible to isolate starch with high amylose and amylopectin. The information obtained in this work could contribute to the use of the byproducts of mango. Active biopolymers such as pectin and starch could give a value added to the crop and helping prevent waste production to the environment.

Key words: Biopolymers, mango peel, seed kernel, starch, pectin.

INTRODUCTION

Mango is one the most harvested fruits in Mexico. It has its origins in the Asian continent, specifically in the north area of India. It was distributed all throughout Southeast Asia and later on The Malay Archipelago. The Portuguese took it to the African Continent and later on to Brazil and from there it disseminated to the whole American Continent [1]. It belongs to the Anacardiaceae family, and the Manguifera genus, which includes 54 species, most of them, are small wild fruits, found in general in India. The specie Manguifera indica L. is the most commercial harvested worldwide and exist different varieties [2].

According to NOM-129-SCFI-1998 [3], the Indostan group include several varieties which fruits have a thick peel, fibrous pulp and a big seed. In Mexico, already to half of production of (1.7 million tons in 2015 according to SIAP [4]) belongs to Indostan group. Currently it is consumed mainly as a fresh fruit; leaving the peel and seed as waste [5], in this group, we have varieties as Haden, Tommy Atkins, Kent, Irwin, Keitt and Oro [6]. Vol. 1 Pag.56

The epicarp represents 10 to 20 % of the fruit, while the endocarp can make up to 30 % [7]. Process waste can result in 60 % of the fruits total weight, depending on the variety and ripeness stage. The most common use for the generated waste is cattle food. However, when disposed on residual waters, it affects its general quality and marine wildlife because of a rise in eutrophication [8]. There are some studies on the extraction of food additives using mango varieties of Asian and Indian, but there is no studies performed in Mexico. With this, the main objective of our study was the extraction and characterization of biopolymers from mango byproducts, because of the biopolymers extracted from the peel and seed could be important in the food industry.

MATERIALS AND METHODS

Mango fruits Tommy Atkins variety were purchased from a local market in Mexico City. The fruits in a commercial maturity state were separated into fractions: peel, pulp, and seed. In the seed kernel and peel was performed the proximal chemical analysis [9], the results indicated several components in greater proportion. The pectin was extracted from peel, while starch was isolated from the seed kernel. The characterization of the pectin included the determination of methoxylation [10] and acetylation [11] degree. The germ was used for the extraction of starch using the method of Kaur [12] with some modifications. In the starch isolated were analyzed total carbohydrates [13] and amylose/amylopectin relationship [14].

RESULTS AND DISCUSSION

Having made the manual separation of fractions, was obtained 11.5 % ± 2.11 of peel, pulp in this variety was 79.46 % ± 3.12, while for the seed was determined a value of 9.02 % ± 2.33. In Tommy Atkins variety was possible to obtain about 20 % of byproducts. The fruits with commercial maturity had a value of 17.22 °Bx ± 0.80 of total soluble solids, with an acidity of 0.03 % ± 0.01 quantified as a percentage of citric acid. After the characterization, the peels were separated into two groups. The first group was used for the proximal chemical analysis, while the second group was used for the pectin extraction. In the case of the seed, these were separated into his fractions in order to obtain the germ. The Figure 1 shown the fractions after the extraction process of the cotyledons.

Figure 1. Fractions of mango fruit after manual separation. a) Peel (pericarp), b) Seed (endocarp), c) Seed kernel (germ).

The result of the chemical characterization of the fractions is shown in Table 1. As can be seen, the peel of this fruit is rich in soluble carbohydrates, the ash and raw fiber found to be Vol. 1 Pag.57

significantly high in this fraction, possibly due to pectin content. From the cotyledons of the germ was determined that it is rich in soluble carbohydrates. The high content of soluble carbohydrates in all fractions indicate a high content of total sugars in the fruit.

Table 1. Proximal chemical analysis of the fractions of mango Tommy Atkins.

Soluble Ash Raw fiber carbohydrate % % % Peel 4.62±0.19 19.75±2.01 68.43±4.12 Pulp 2.12±0.02 4.70±0.95 89.06±3.21 Germ 2.53±0.10 4.07±0.08 76.58±4.86

Kratchanova [15] performed the quantifying of pectin in mango peel of Keitt variety. On the other hand, Kaur [12] report the presence of starch in the germ of mango Chausa, Totapuri, Kuppi, Langra and Dashehari. According to these authors and the data shown in Table 1 (related to the content of crude fiber and soluble carbohydrates) it can be assumed the presence of pectin in peel and starch in cotyledons of Tommy Atkins variety.

The peel pectin obtained was characterized as high methoxyl (94.81 % ± 0.9) and low acetylation (0.295 % ± 0.03) degree. It was not possible to determine the pectin fusion point due to its amorphous polymer behavior; its dehydration temperature was 125 °C, while the thermal calcination was detected at 245 °C. Einhorn-Stoll [16] determined the calcination temperature near to 250 °C for citrus pectin with different treatments.

Finally, the starch yield from cotyledons of mango Tommy Atkins was quantitated 26.74 % ± 1.28. Hassan [17] reported the presence of starch in four Nigerian varieties of mango, in a range of 52.8 % ±1.2 to 65.37 % ±1.11, depend on the variety. For Tommy Atkins variety in commercial maturity, the extracted starch represent an amount of amylose near to 26.61 %. Kawaljit and Seung-Taik [18] reported 28.8 % of amylose in starch of seeds of Chausa mango, as well as 33.6 % in starch from Kuppi mango seeds cultivated in South Korea.

CONCLUSIONS

The starch extracted from the Tommy Atkins seed kernel, in commercial maturity, present an amount of amylose near to 26.61 % similar to Asiatic varieties, representing a new option for their extraction. Pectin extracted from the peel was of high methoxylated and the calcination point near of 245 °C, represents a potential food additive useful at high temperature. The information obtained in this study could contribute to the use of the byproducts of mango (peel and seed kernel), since it was possible to extract and characterize pectin and starch biopolymers, which are of interest to the food industry.

AKNOWLEDGEMENTS

The authors are grateful to CONACYT for the scholarship granted to J.P.R. (219099) and for the technical support to Biol. M.P. Méndez Castrejón (chemical characterization) and to Ing. M. Márquez Robles (thermal analysis). Vol. 1 Pag.58

REFERENCES

[1] Samson J. A. Fruticultura tropical. Editorial Limusa. Primera edición. México. 1991. [2] Mora M. J., Gamboa P. J. y Elizondo M. R. Guía para el cultivo del mango. Ministerio de agricultura y ganadería. Costa Rica. 2002. [3] NOM-129-SCFI-1998. Información comercial – Etiquetado de productos agrícolas – Mango. México. Consultado en febrero de 2011. [4] SIAP. Servicio de Información Agroalimentaria y Pesquera. Cierre de la produccion agrícola por cultivo para 2015 en México. Disponible en http://www.siap.gob.mx/cierre-de-la-produccion-agricola- por-cultivo/ Consultado en Julio de 2015. [5] SAGARPA. Secretaría de Agricultura, ganadería, desarrollo rural, pesca y alimentación.Plan Rector Sistema Nacional Mango. Comité Sistema Producto Mango. México. 2005. [6] Sergent, E. El cultivo del mango (Manguifera indica L.). Botánica, manejo y comercialización. Universidad Central de Venezuela. Consejo de Desarrollo Científico y Humanístico. 1999. [7] Ferreira, S. Peralta, N. A. P., Rodríguez, A. G. P. Obtención y caracterización de pectina a partir de desechos industriales del mango (cáscara). Revisa colombiana de ciencias químico- farmacéuticas. 1995. [8] Assous M. T. M., El-Wahab A. E. S. and El-Waseif K. H. M. Effect of microwave power on quality parameter of pectin extracted from mango peel. Arab University Journal Agricultural Science. 2007. 15: 395-403. [9] AOAC. Official methods of analysis. Association of Official Analytical Chemists. Inc. Washington. E. U. 1995. [10] Schultz T. H. Determination of the degree of esterification of the ester methoxyl content of pectin by saponification and titration. Methods Carbohydrate Chemistry. 1965. 5 :189-194. [11] McComb E. A. and McCready M. M. Determination of acetyl in pectin and in acetylated carbohydrate polymers. Anal. Chem. 1957. 29(5):75-79. [12] Kaur, M., Singh N., Sandhu, K. and Guraya, H. S. Physicochemical, morphological, thermal, and rheological properties of starches separated from kernels of some Indian mango cultivars (Manguifera indica L.). Food Chemistry. 2004. 85: 131-140. [13] Dubois M., Gills K. A., Hamilton J. K. Rebers P. A. and Smith F. Colorimetric method for determination of sugar and related substances. Analytical chemistry. 1956. 28 (3): 350-356. [14] McGrance, S. J., Cornell, H. J. and Rix, C. J. A simple and rapid colorimetric method for the determination of amylose in starch products. Starch. 1998. 50: 58-63. [15] Kratchanova, M., Benemou, C., Kratchanov, C. On the pectic substances of mango fruits. Carbohydrate Polymers. 1991. 15: 271-282. [16] Einhorn-Stoll U., Hatakeyama, H. and Hatakeyama, T. Influence of pectin on water binding properties. Food Hydrocolloids. 2012. 27: 494-502. [17] Hassan L. G., Muhammad A. B., Aliyu R. U., Idris Z. M., Izuagie T., Umar K. J. and Sani N. A., Extraction and characterization of starches from four varieties of Manguifera indica seeds. Journal of Applied Chemistry. 2013. 3: 16-23. [18] Kawaljit, S. S. and Seungh-Taik, L. Structural characteristics and in vitro digestibility of mango kernel starches (Manguifera indica L). Food Chemistry. 2008. 107: 92-97.

Vol. 1 Pag.59

THE EFFECT OF ACCELERATED WEATHERING ON THE MECHANICAL BEHAVIOUR OF REINFORCED POLYPROPYLENE WITH COOPER NANOPARTICLES AND CARBON NANOTUBES

Janett Valdez-Garza1, Nuria Gonzalez-Angel1, Arturo Velazquez-de Jesús1, Concepcion Gonzalez-Cantú1, Manuel Mata-Padilla1, Víctor Cruz-Delgado1, Guillermo Martinez-Colunga1, Carlos Avila-Orta1. 1Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo No. 140, Col. San José de los Cerritos, Saltillo, Coahuila. 25294. México. [email protected]

Abstract The exposure of materials to the weather conditions like UV radiation, heat and humidity is a problem for the plastics industry that requires extending the lifetime of these materials. It is proposed to improve their properties by reinforcing them with nanoparticles [1,2]. For this purpose, polypropylene nanocomposites were prepared with copper nanoparticles and carbon nanotubes at different concentrations (0, 1, 2.5 and 5% wt/wt). The materials were exposed to UV radiation, humidity and heat. The mechanical strength was evaluated for an exposure time of up to 1000 hours. The tensile strength for nanocomposites is retained as the exposure time to ultraviolet radiation increases. This effect is noticeable after 250 hours exposure and is more evident for nanocomposites with carbon nanotubes. On the other hand, the elongation behavior for nanocomposites with copper nanoparticles exhibits a reduction from 250 hours of exposure for the different contents of nanoparticles, while nanocomposites with carbon nanotubes retain higher percentages of elongation greater than 100%, even with exposure times of 1000 hours.

Keywords: Carbon nanoparticles accelerated weathering, polymer nanocomposites.

Experimental. The extrusion process is most suitable and convenient method for homogeneous mixing of plastics with various additives. Two masterbatch were prepared with 20% wt/wt, of copper nanoparticles and CNT. Copper nanoparticles have an average size of 300 nm, purity 99.5% and SSA 6 m2/g, they were supplied by SkySpring Nanomaterials, Inc., USA, Industrial grade CNT (IGCNT) have an average diameter 20 nm, length 20 – 40 micron, SSA 220 m2/g, and were supplied by CheapTubes Inc, USA. Copper nanoparticles were coated with polyolefin wax to avoid oxidation and burning during handling, prior to mix with polymer resin.

Methodology A twin-screw extruder L/D: 40:1 Thermo Scientific 24-MC, was employed to process all the samples, with a plain temperature profile of 230 °C and 100 rpm. Resin chips and powder, were feed to the extruder with the assistance of gravimetric feeders for each one at a rate of 5 and 1 kg/h respectively. The samples were extruded with the assistance of ultrasound waves [3] provided by a home-made generator of variable amplitude and frequency in the range of 20 – 50 kHz and power of 500 W. Both masterbatches were diluted to reach 0, 1, 2.5 and 5% of nanoparticle concentration in the same equipment, without the use of ultrasound. Vol. 1 Pag.60

Characterization. For the accelerated weathering exposure of the samples a QUV chamber was used with a long wave (UVA) at 340 nm, a cyclic exposure consisting of 8 h of light/darkness and temperature between 50 -70 ºC, in accordance with ASTM G154 standard method. Time exposure was 0, 250, 500, 750 and 1000 h, 5 specimens were used for each exposure time. Tensile testing was conducted using a Universal Testing Machine, INSTRON model 4301, at 5 mm/min using type V specimens in accordance with ASTM D638 standard method.

Figure 1. Experimental route for the preparation of nanocomposites and exposure conditions for accelerated weathering.

Results. The tensile stress versus exposure time for nanocomposites at different concentrations of nanoparticles is shown in Figure 2. Polypropylene resin exhibit a noticeable reduction in mechanical properties after 250 hours of exposure and this effect is more evident as the time increases reached a value of 5 MPa after 1000 h. For nanocomposites with CNT it is possible to observe that mechanical properties are retained almost without change during the entire exposure time and this effect are homogeneous for all CNT concentrations, showing that the 1% is sufficient to protect the polymer against the UV light degradation.

Figure 2. Tensile stress versus exposure time for nanocomposites at different concentrations of nanoparticles. Vol. 1 Pag.61

For copper nanoparticles it is possible to observe a reduction in mechanical properties as the time exposure to UV light increase, and this is independent of the concentration of nanoparticles. This behavior suggests, that copper nanoparticles are not suitable for the protection of polymers against UV radiation.

Elongation at break is another important property in polymers and it is affected by the UV light in outdoor conditions, due that, is highly necessary to find alternative additives to protect plastics. In Figure 3, the elongation at break versus exposure time for nanocomposites at different concentrations of nanoparticles is shown. In accordance with the tensile stress behavior shown by the polypropylene resin, the elongation at break, decreases after 250 hours of exposure time, this means that material becomes fragile and brittle. Nanocomposites with 1 and 2% wt/wt of CNT present a monotonically reduction of elongation as the exposure time increases, and retain around 100% of elongation after 1000 hours of exposure to the UV light. The sample with 5% wt/wt of CNT shown lower elongation at begins of the test, and this property remains without change over the entire exposure time. On the other hand, nanocomposites with copper nanoparticles exhibit a noticeable reduction of elongation at break after than only 250 hours, which correspond with the tensile stress behavior shown above, therefore, copper nanoparticles are inappropriate for the weathering protection of plastics. These results show clearly that CNT are an effective additive to prevent the degradation of polypropylene by UV light, probably by the absorption of high- energy radicals involved in the photodegradation process.

Figure 3. Elongation at break versus exposure time for nanocomposites at different concentrations of nanoparticles.

Different reports in literature suggest that concentrations of CNT lower than 1% wt/wt promotes the photo-oxidation mechanisms in polyolefins by the increase of carbonyl index, and suggest a pro-degrading effect associated with a more homogenously dispersed carbon nanoparticles [4]. As the content of nanoparticles increases, CNT act as an effective and alternative UV stabilizer for polypropylene and polyethylene resins. In another study [5], the effectiveness of nanoparticles different to CNT was studied and concluded that silicon oxide (SiO2), nanoclays like montmorillonite (MMT) or organic modified montmorillonite (oMMT) are less effective to protect polymers against photo-induced degradation, as we can observe in the case of copper nanoparticles. Vol. 1 Pag.62

Conclusions The exposure to UV radiation affect the mechanical properties of polypropylene after only 250 hours and this tendency increases as the exposure time increases too. The addition of CNT in contents of 1, 2.5 or 5% wt/wt provides UV stabilization to polypropylene resin as observed by the retention of tensile strength and elongation at break in nanocomposites. Nevertheless, for nanocomposites with copper nanoparticles the photo-degradation phenomenon was observed after only 250 h, in similar manner to the neat polypropylene. From the above results, it is possible to conclude that CNT act as an effective and alternative UV stabilizer for polypropylene resins and to extend the shelf life of the polymer, besides to bring mechanical reinforcement, and the ability to conduct heat and electricity (unpublished results).

References.

[1] Prog. Polym. Sci. 2010, 35, 357 [2] Polym. Degrad. Stabil. 2010, 95, 1614 [3] J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 475 [4] Polym. Degrad. Stabil. 2011, 96, 151 [5] Polym. Degrad. Stabil. 2009, 94, 162

Acknowledgements We acknowledge the financial support from Fondo SENER/CONACYT under CeMIE-Sol program Project 207450/12. Authors thank Rodrigo Cedillo and Fabian Chavez by their assistance with processing of polymer nanocomposites. Vol. 1 Pag.63

ATRAZINE REMOTION FROM AQUEOUS SOLUTIONS WITH A POLYMER/CLAY COMPOSITE Alejandra Abigail Zúñiga-Pérez1,2, María del Carmen Díaz-Nava 1*, Javier Illescas1

1 Instituto Tecnológico de Toluca, Av. Tecnológico S/N Col. Agrícola Bellavista, C.P. 52169, Metepec, Estado de México, México. 2 Universidad Tecnológica del Valle de Toluca, Carretera del Departamento del D.F. km 7.5, Santa María Atarasquillo, Lerma, Estado de México, México. *[email protected]

Introduction The use of atrazine in agriculture has led to high levels of contamination in water systems and has been the subject of various investigations such as adsorption and degradation. These are the main natural attenuation mechanisms that control the migration of this herbicide in water and soil. Adsorption of atrazine depends on the texture and composition of soil, pH and principally the applied amount of herbicide. The adsorbent materials, such as clays, are of interest for their possible regeneration. They can withstand higher temperatures than activated carbon and can even regenerate in the absence of heat without reducing its lifetime. Another important feature is their mechanical strength which is higher than the activated carbon.

In this work, atrazine has been removed from aqueous solutions by using natural clay, which has been modified with HDTMA-Br by two different methods (A and B), incorporated into alginate beads with different clay contents.

Experimental Composites were prepared by two methods: A) 9.7 mL of hot deionized water were put into a beaker on a magnetic stirrer until it reaches 343 K. Then, 0.3 g of sodium alginate were added and stirred with a magnetic bar until dispersed. At that point, 0.1 g of modified or natural clay were placed and stirred until clay and alginate were totally mixed. After that, the mixture is placed in a syringe and added dropwise into a CaCl2 under stirring at constant temperature. Once the beads were synthesized, they were left in the same solution for 24 h. In method B) a certain amount of clay according to the desired load weight was dispersed in 50 mL of deionized water. The mixture was kept under constant stirring for 2 h. On the other side,1 g of sodium alginate was dissolved in deionized water at 333 K under constant stirring for 2 h. Then, alginate was added to the modified clay suspension, keeping constant stirring at 333 K for 2 h. The synthesized alginate/modified clay beads were collected dropwise with a syringe into a 0.01 M solution of CaCl2 where they were maintained under constant stirring until they were placed in the refrigerator for 24 h. Vol. 1 Pag.64

Adsorption of atrazine onto the clay-composites was performed in batch experiments as follows: 10 mL of atrazine solution was placed in contact with 500 mg of composite. During adsorption experiments, a vial containing an atrazine solution was stirred at 298 K and 100 rpm on a thermobath for 6 h.

Results and discussion The atrazine concentration present in aqueous solution was measured between 190-300 nm. It was observed that the maximum wavelength absorption for this herbicide in different aqueous solutions prepared with different concentrations was 222 nm as shown in Figure 1. Furthermore, this wavelength value was selected for measurement of atrazine in aqueous solutions with different concentrations and the calibration curve was constructed. Figure 2 shows the obtained graph.

Figure 1. Absorption spectra of Atrazine.

Figure 2. Calibration curve of Atrazine in aqueous solution.

Tables 1 and 2 summarize the obtained results for the removal of atrazine with two different clay-composites synthesized from methods A and B. As it can be seen, this percentage is similar for both composites synthesized by means of method A or B. Vol. 1 Pag.65

Table 1. Removal of atrazine (A) for 24 h with a natural clay-composite (NCC) or modified clay-composite (MCC) obtained from method A. Removal Weight Prom Cf Prom mg Atrazine/ g Sample DS Percentage DS (g) (mg/L) composite (mgA/gP) (%) NCC 24 h 0.1 5.2 0.0 22.0 0.12 0.001 1%wt MCC 0.1 5.1 0.1 25.5 0.13 0.015 2%wt MCC 0.1 5.1 0.1 36.0 0.23 0.010 5%wt

Table 2. Removal of atrazine (A) for 24 h with a natural clay-composite (NCC) or modified clay-composite (MCC) obtained from method B. Removal Prom mg Atrazine/ Weight Prom Cf Sample DS Percentage g composite DS (g) (mg/L) (%) (mgA/gP) NCC 0.217 3.9 0.9 0 0.05 0.021 2%wt MCC 0.213 2.3 0.1 5 0.13 0.014 2%wt MCC 24 h 0.208 1.9 0.1 22 0.15 0.005 4%wt MCC 0.220 1.9 0.1 23 0.14 0.010 6%wt MCC 0.210 2.0 0.4 22 0.15 0.004 8%wt

Finally, Figure 3 shows the zero load point which is the pH where the total charge of the particles from the surface of an adsorbent is zero. It is important to determine it, since this is a parameter that indicates the load of the material at different pH values. In our particular case, it shows that the zero load point of the alginate beads is approximately equal to 6.8. Vol. 1 Pag.66

Figure 3. pH vs. pHo of modified beads with 2 wt-% clay content. Conclusions From these set of results, it has been concluded that the efficiency for both polymer/clay composites (A or B) is similar for the atrazine removal. It has been observed that in synthesized beads with concentrations of 5 wt-% of modified clay, greater absorption values of the contaminant have been obtained. Finally, the adsorption capacity of atrazine in aqueous solutions for the synthesized polymer/clay composites was found between 0.12 and 0.23 mg atrazine/g material, depending on the clay content.

AcknowledgmentS We are thankful to CONACyT for the project 3056 “Cátedras-CONACyT” and to Tecnológico Nacional de México (TecNM) for the project 5646.15-P, for their financial support.

References

[1] E. I. Unuabonah, E. I. et al.; Appl. Clay Sci., 2014, 99, 83-92. [2] M. C. Díaz Nava et al.; J. Incl. Phenom. Macrocyc. Chem. 2012, 74, 67-75. [3] V. Golla et al.; J. Environm. Sci. Eng. 2012, 5, 955–961. [4] C. Salinas-Hernández et al.; Water Air Pollut. 2012, 223, 4959-4968. [5] M. C. Díaz-Nava et al.; J. Incl. Phenom. Macrocyc. Chem. 2005, 51, 231-240. Vol. 1 Pag.67

PLASMON-PHONON COUPLING IN MULTILAYER GRAPHENE ON POLAR SUBSTRATES

G. Gonzalez de la Cruz

Departamento de Fisica CINVESTAV-IPN, apartado postal 14-740, 07000 CDMX, Mexico, [email protected]

ABSTRACT

We investigated the effect of polar substrates on the collective excitations of a semi- infinite layered graphene structures within the self-consistent field approximation. The surface plasmon dispersion in semi-infinite stack of graphene layers is indeed modified via Coulomb interaction with polar substrate. At long wavelengths (q→0), these new surface-polaritons are situated above bulk plasmon band of the stack with an infinite number of layers, and they have a very long lifetime. However, at large momentum transfer the collective surface modes being sensitive to decay into a continuum plasmon band or by emitting an electron-hole pair excitation (Landau damping) due of the relativistic Dirac nature of charge carriers in graphene.

INTRODUCTION

Graphene, a two-dimensional (2D) crystal of carbon atoms arranged in a honeycomb lattice, owes its extraordinary optical and electronic properties to the presence of Dirac points in its band structure [1]. Graphene two-dimensional plasmons exhibit unique optoelectronic properties and enable extraordinary light-matter interactions. Many of the peculiarities of massless Dirac fermions in graphene are related to their collective excitations [2]. A plasmon is a collective mode of a charge-density oscillation in a free-carrier density, which is present in both classical and quantum plasmas. Studying the collective excitation in the electron gas has been among the very first theoretical quantum mechanically many-body problems studied in solid-state physics. Owing to the two- dimensional nature of the collective excitations, plasmons excited in graphene are confined much more strongly than those in conventionally noble metals. The strong linear and nonlinear interactions of massless Dirac fermions with light, together with the tunable conductivity and broadband response, make graphene an attractive material for atomically thin active devices operating at optically and therahertz frequencies with extremely high velocity. Graphene is an ideal material for the emerging field of plasmonics. References [3-8] focus on the recent progress of graphene plasmonics and its technological applications in different optoelectronic areas. Plasmon-phonon coupling has been observed experimentally for graphene on SiC (0001) [9] and theoretically investigated [10] solving Maxwell equations with appropriate boundary conditions at the interfaces between graphene-substrate system, and more recently the semiclassical Monte Carlo method was used to calculate the electron mobility in graphene on different substrates [11]. Recently, experiments have been performed to investigate the strong coupling between graphene plasmons and a Vol. 1 Pag.68

monolayer hexagonal boron nitride phonons, showing two clearly separated hybridized surface-plasmon-phonon-polariton modes that display an anticrossing behavior [12]. So far, the study on graphene collective modes has been mostly focused on plasmons in monolayer graphene, double layer sheets [13-14] and recently in hybrid relativistic/non-relativistic coupled two-dimensional electron layers [15-16]. The coupling of plasmons in a periodic multilayer graphene system, which is physically different from that in double-layer system, is also and important topic and it has been explored in several scientific papers [17-20]. In this paper, we investigate the role of oxide (semiconductor) substrates on the collective excitations (plasmons) in multilayer graphene. Our model provides a systematic description of an array composed of periodically stacked graphene layers with identical interlayer spacing coupling via surface charge density oscillations with the substrate optical surface phonons. The mode follows the graphene semi-infinite superlattice immersed in a material of background dielectric constant εs growth on a substrate with a dielectric constant ε0. We use such configuration to study the strong plasmon-phonon hybridization and explore new different spectral modes.

II Theoretical model

Here, we study the coupling between the two-dimensional semi-infinite superlattice graphene system and the substrate. The model system under consideration corresponding semi-infinite graphene electron layers separated a distance d is shown in Fig.1. The graphene electron layers system occupy a half-space z>∆+nd (n=0,1,2,3,…), of background dielectric constant εs. The substrate with dielectric constant ε0 occupies the space z<0.

Fig. 1

Within the self-consistent-field linear approximation theory (SCF) and assuming the relaxation time be infinite, each electron is assumed to move in the self-consistent field arising from the external field plus the induced field of all the electrons, then the electron density in the nth (n=0,1) graphene electron layer, ρn(q,ω) , in zero external field, is given by

ρn (q,ω) = ∑Vn,m (q)Πm (q,ω)ρm (q,ω) (1) m where

Vol. 1 Pag.69

V (q) = v e−q n −m d + αe−(n +m)d n,m q [] (2) is the interlayer Coulomb interaction and the second term proportional to

α = (ε −ε )/(ε +ε )e−2∆q , gives the modified Coulomb interaction between the two s 0 s 0 Dirac electron layers due to the image charge and Πn(q,ω) is the two-dimensional 2 polarizability for layer n calculated in Refs. [8], [9], and vq=2πe /εsq represents the two- dimensional Coulomb electron interaction. On the other hand, to describe surface modes, we make the assumption that ρ ω = − β ρ ω m (q, ) exp( m q) 0(q, ) for m>0, where β-1 is a decay length of the excitation away from the interface and we require that Reβ>0. Using the relation of ρm(q,ω) in Eq.(15), one finds

−β (m −n)d 2 vqΠ(q,ω)∑e Vnm (q) =1, vq = 2πe /ε sq (3) m The latter equation determines the value of the decay parameter β-1. It turns out to be an analytical result given as:

cosh(∆q) +ε sinh(∆q) exp(−βd) = r (4) cosh(d − ∆)d −ε r sinh(d − ∆)d

For a semi-infinite carrier layers the zeros of the dielectric function give the dispersion relation for the surface plasmon (SP) modes:

2 (1−ε r )sinh(qd) Ds(q,ω) = 2vqΠ(q,ω) − (5) [cosh∆q +ε r sinh∆q][cosh(d − ∆)d −ε r sinh(d − ∆)d]

In graphene semi-infinite superlattice on semiconducting substrates (Fig.1), it is easy to incorporate the coupling to optical phonons. One only has to replace the frequency- independent background dielectric constant ε0 by a frequency dependent

, where ωl and ωt are the longitudinal and transverse optical-phonon frequencies which are related with the dielectric constants by the Lyddane-Sachs-Teller relation and is the static (high frequency) dielectric function. By taking into account the frequency dependence of the dielectric function, we find the coupled bulk and surface plasmon spectrum for a graphene semi-infinite superlattice on polar substrate. In Fig. 2 we show the calculated coupled plasmon-phonon modes collective modes in graphene semi-infinite superlattice on polar substrate for two different distance from the first graphene layer to the substrate. In ordinary semiconductor superlattice, the plasmon-phonon mode coupling emerges above the continuum plasmon band and is unable to decay in plasmon band and a single electron-hole pair. However in multilayer graphene structures the hibridization of collective electron excitations with surface phonons in the substrate the coupled modes can decay into plasmons Fig 2a, or they are Landau damping Fig. 2b, this latter phenomenon is direct consequence of Vol. 1 Pag.70

the singular behavior in the graphene electron polarizability. Notice the plasmon like mode cannot exist due to the restriction on the decay of the evanescent electromagnetic field associated with the surface collective excitation, Eq.(4).

Fig. 2

CONCLUSIONS

In conclusion, we have analyzed the screening of plasmons in semi-infinite superlattice graphene on semiconducting and metallic substrates within the self-consistent field approximation. The hybridization between charge density collective excitations in multilayer grapheme structure and phonons on polar substrates, the energies of the collective modes can be significantly shifted and the resulted surface plasmon polaritons modes are long-lived collective excitations in the long wavelength limit. However these hybrid modes can decay into plasmon band or are Landau damping in the SPE continuum. This latter singular feature is a direct consequence of the electronic properties of graphene, in contrast with surface plasma excitations in conventional layered two-dimensional -electron gas which are not subject to Landau damping.

REFERENCES

[1] AHF Castro, F. Guinea, NMR Peres, KS Novoselov K and, AK Geim Rev. Mod. Phys. 81 109 (2009) [2] AN Grigorenko, M Polini and KS Novoselov, Nature Photonics 6 749 (2012) [3]S DasSarma, S Adam , EW Wang and E Rossi, Rev. Mod. Phys. 83 408 (2011) [4] L Ju, B Jeng, J Horng, C Girit, M Martin, Z Hao, HA Bechtel, X Liang, A Zettl , YR Shen and F Wang , Nature Nanotech. 6, 630 (2011) [5] W Zhu, ID Rukhlenko, LM Si and M Premaratne, Appl. Phy. Lett. 102, 121911 (2013) [6] YV Bludov, A Ferreira, NMR Peres and MI Vaselevskiy, Int. J. Mod. Phys. B 27 1341001 (2013) [7] T Otsuji, V Popov and V Ryzhii , J. Phys. D: Appl. Phys. 47 094006 (2014) [8] Y Cai, J Zhu and QH Liu, Appl. Phys. Lett. 106 043105 (2015) [11]R.J. Koch, T. Seyller and J.A. Schaefer, Phys. Rev. B 82 201413 (2010) Vol. 1 Pag.71

[12] Z.Y. Ong andM. Fischetti, Phys. Rev. B 86 165422 (2012) [13] VW Brar, M Jang, M Sherrot, S Kim, J Lopez, LB Kim, M Choi and H. Atwater, Nano Lett. 14 3876 (2014) [14] B Bunch, T Stauber, F Sols and F Guinea, New. J. Phys. 8 318 (2006) [15] EH Hwang and S Das Sarma , Phys. Rev.B, 80 205405 (2009) [16] SM Badalyan and FM Peeters, Phys. Rev.B, 85 195444 (2012) [17] RE Profumo, R Asgari, M Polini and AH MacDonald,Phys. Rev B 85 085443 (2012) [18] AC Balaram, JA Huatasoit and JK Jain, arXiv:1405-4014v2 (2014) [19] A Gamucci, D Spirito, M Carrega, B Karmakar, A Lombardo, M Bruna, AC Ferrari, LN Pfeiffer, KW West, M Polini and V Pellegrini, arXiv:1401.0902v1 (2014) [20] W Norimatsu and M Kusonoki, Semic. Sci. Technol. 29, 064009 (2014) [21] J Kim and G Lee, Appl. Phys. Lett. 107, 033104 (2015) [22] KWK Shung, Phys. Rev.B 34 979 (1986)

Acknowledgments: This work was financially partially supported by Conacyt

Vol. 1 Pag.72

Design and synthesis of new small molecules for electronic organics via direct hetero-arylation using ligand-less palladium catalyst

K. I. Moineau-Chane Ching1, C. Chen,1 D. Le Borgne,1 D. Hernandez Maldonado1.

1CNRS; LCC (Laboratoire de Chimie de Coordination); 205, route de Narbonne / Université de Toulouse; UPS, INP; LCC; 31077 Toulouse, France. [email protected]

INTRODUCTION

Organic photovoltaics have been intensively investigated for their advantages as low cost, low weight and their easy process on large flexible substrates. Much of the attention have been focused on the development of electron donor (D) polymer associated with electron acceptor (A) phenyl-C61-butryric acid methyl ester (PC61BM) or PC71BM. Recently, small molecules have confirmed to be as efficient as polymers with record power conversion efficiencies (PCEs) up to 10.08% [1] when used as D-materials and paired with PC71BM [1,2] or as A-materials to replace PCBM [3-4] reaching PCE near 8% with PTB7-Th [5]. Moreover they offer a better reproducibly, simpler synthesis and purification than polymers. The development of A-small molecules is a challenge because fullerene derivatives are expensive, difficult to purify, have a poor absorbance in UV-visible spectrum and their optoelectronic properties are hard to engineer. Therefore, we design and synthesize small molecules based on benzothiadiazole and thiophene moieties, owing to their potential capabilities in withdrawing and donating electron respectively. Particularly, we focused on developing a green coupling method, namely, direct heteroarylation[6] that requires neither toxic nor complicated to generate interesting intermediates, with low loading of ligand-less palladium-catalyst.

RESULTS AND DISCUSSION

The basic idea of this study is to provide small, as simple as possible molecules obtained after as few synthetic steps as possible, from commercially available raw materials. The need of two steps is believed to be the minimum reachable path, leading to the fewest waste production and lowest cost. 4,7-dibromobenzo-2,1,3-thiadiazole (diBrBz, molecule 1) acts here as the electrophile on both sides, in reaction with 2-thiophene carboxaldehyde (TCHO, molecule 2) which is found here to be exclusively 5-arylated, thus providing either D-A-D or A-D intermediates for building semi-conducting small molecules. For symmetrical D-A-D intermediate, the presence of two aldehyde functions at both extremities renders possible to elongate the molecule by a double Knoevenagel condensation leading to an A-D-A-D-A molecule, which is suitable for presenting semiconducting character associated with low band gap properties. For non-symmetrical A-D intermediate, the remaining bromine atom on Vol. 1 Pag.73

benzothiadiazole on one side allows to elongate the molecular structure by reaction with another D moiety that will constitute de core of the new D-A-D-A-D generated aldehyde flanked molecule. In the same manner as previously described, the presence of two aldehyde functions at both extremities of the D-A-D-A-D core renders possible to elongate the molecule by a double Knoevenagel condensation leading to an A-D-A-D-A-D-A molecule Among the available terminal electron-withdrawing groups, alkyl (R) cyanoacetate are often chosen.[7-9] Both octyl cyanoacetate (O) and 2-ethylhexyl (EH) cyanoacetate are very often chosen as the terminal groups because they confer a good solubility of the final molecule, promote self- organization in nanoaggregate structures, and contribute to enhanced photovoltaic performances.[10] Among the target molecules, we aim to synthesize symmetrical molecules such as Bz(T1CAR)2 or DTS[Bz(T1CAR)]2, in which “DTS” stands for dithienosilole central core and “CAR” for alkyl cyanoacetate end group. These target molecules are achievable in two to three steps only. Their benzothiadiazole precursors, either symmetrical Bz(T1CHO)2, or non- symmetrical Bz(T1CHO), are obtained from commercially available reagents, such as diBrBz, and TCHO via direct heteroarylation[6] as demonstrated here.

Symmetrical benzothiadiazole D-A-D intermediate

This symmetrical molecule is designed around a central acceptor fragment, the benzothiadiazole, and its synthesis has been developed using a green coupling method, the direct heteroarylation, that requires neither toxic nor complicated intermediates such as stanyl or boronyl derivatives.[6] Herein, the preparation of intermediate 3 has be achieved at low palladium-catalyst loading, without ligands, producing very few remaining toxic wastes (see Scheme 1).

Scheme 1: reaction scheme for synthesis of intermediate 3

This route proved to be reasonably efficient, with a reaction yield of 71% in isolated molecule when 2.2 equivalent of 2 are engaged for one equivalent of 1. Moreover, this reaction exhibits good green metrics (E-Factor = 143) and proceeds at low cost (evaluated cost of synthesized intermediate: 14 €/g).[11] It was possible to improve the reaction yield, and to decrease the amount of degradation products associated with side reactions experienced by 2. Indeed, the analysis and workup of the by-products revealed that non-reacted molecule 1 is totally recovered whereas the molecule 2 undergoes degradation products besides the desired one. For avoiding as much as possible the formation of wastes, the molecular ratio between 2 and 1 was lowered to 0.9, then 0.5 (instead of 2.2). The obtained values are gathered in Table 1. The reaction yield is improved, but with much worse green metrics. This is due to the fact that the non-reacted molecule 1 (when used in excess) is accounted in our calculations as a waste, thus this substantially contributes to the increase of the calculated value of the E-factor. Due to the fact that molecule 1 does not react by homocoupling reaction nor decomposes through any other degradation processes under these reaction conditions, it may possible to recycle it. Vol. 1 Pag.74

Thus, with optimized synthesis conditions, including the recycling of 1, it is feasible to synthesize 3 in quantitative yield with an E-factor approaching 143 g/g and a cost of around 14 €/g as reported for reaction conditions indicated in the first column of Table 1.

Table 1: Reaction yields, E-factors and costs calculated for the synthesis of 3 obtained via in decreasing the 2/1 ratios (r) r = 2.2 r = 0.9 r = 0.5

Yield (%) 71% 100% 100% E-factor (g/g) 143 226 408 Cost (€/g) 14 22 39

Non-symmetrical benzothiadiazole A-D intermediates

As for the symmetrical molecule, intermediate 4 (see structure below) was obtained via the same reaction path.

In that case, and for avoiding the diarylation, we tested different reaction conditions such as playing with the 2/1 ratio, the amount of catalyst and base, and various temperatures and time of reaction. It is worth to note that, once again, the non-reacted dibromobenzothiadiazole can be recovered, thus easily reused in the successive attempts. The best obtained result was a 35% yield in isolated product, which was obtained under the following condition: molar ratio 2/1 is 0.5, 1.5 equivalent of potassium acetate (KOAc) and 1 mol% catalyst palladium acetate (Pd(OAc)2 relative to compound 1, 6 mL of N,N-dimethylacetamide (DMA) and stirring at 105 °C for 21 h under argon atmosphere. Compared to the 30% yield of isolated product obtained via Suzuki coupling, direct C-H arylation appears to be slightly more efficient than traditional methods, and much greener.

CONCLUSION

In summary, direct heteroarylation arylation procedures with many different operating conditions were developed to obtain the di-arylated compound 3 and the mono-arylated compound 4. Whereas the yield in di-arylated compound 3 was reached up to 100%, the best yield in isolated mono-arylated compound 4 is 35%. Therefore, the direct arylation without ligand nor additive proved to be a nice efficient coupling protocol for the formation of new C-C bond. These intermediates can now be used in further reactions, such as directly Knoevenagel Vol. 1 Pag.75

condensation for compound 3 whereas the mono-arylated compound 4 will be coupled with stannyl-containing dithienosilole (DTS) derivatives to yield conjugated DTS-based small molecules for organic electronics applications. Works in this aim are in progress.

References [1] B. Kan, M. Li, Q. Zhang, F. Liu, X. Wan, Y. Wang, W. Ni, G. Long, X. Yang, H. Feng, Yi ., M. Zhang, F. Huang, Y. Cao, T. P. Russel, and Y. Chen, J. Am. Chem. Soc. 2015,137, 3886-3893. [2] D.H. Wang, A.K.K. Kyaw, V. Gupta, G.C. Bazan, and A.J. Heeger, Adv. Energy Mater. 2013, 3, 1161-1165. [3] J.D. Douglas, M.S. Chan, J.R. Niskala, O.P. Lee, A.T. Yiu, E.P. Young, and J.-M.. Fréchet, Adv. Mater. 2014, 26, 4313-4319. [4] L. Chen, L. Huang, D. Yang, S. Ma, X. Zhou, J. Zhang, G. Tu, and C. Li, J. Mater. Chem. A, 2014, 2, 2657-2662. [5] M. Li, Y. Liu, W. Ni, F. Liu, H. Feng, Y. Zhang, T. Liu, H. Zhang, X. Wan, B. Kan, Q. Zhang, T. P. Russell, and Y. Chen, J. Mater. Chem. A, 2016, 4, 10409-10413. [6] J. Roger, F. Požgan, and H. Doucet., Green Chem., 2009, 11, 425-432. [7] Y. Kim, C. E. Song, S.-J. Moon, and E. Lim, Chem. Commun., 2014, 50, 8235-8238. [8] J. Zhou, X. Wan, Y. Liu, G. Long, F. Wang, Z. Li, Y. Zuo, C. Li, and Y. ChenChem. Mat., 2011, 23, 4666-4668. [9] Y. Liu, X. Wan, F. Wang, J. Zhou, G. Long, J. Tian, J. You, Y. Yang, and Y. Chen, Adv. En. Mat., 2011, 1, 771-775. [10] K.-H. Kim, H. Yu, H. Kang, D.J. Kang, C.-H. Cho, H.-H. Cho, J.H. Oh, and B.J. Kim, J. Mater. Chem. A, 2013, 1, 14538-14547. [11]C. Chen, D. Hernández Maldonado, D. Le Borgne, F. Alary, B. Lonetti, B. Heinrich, B. Donnio and K.I. Moineau-Chane Ching, New J. Chem., 2016, DOI: 10.1039/C6NJ00847J.

Acknowledgements

The authors gratefully acknowledge financial support from French Region Midi-Pyrénées and IDEX Transversalité « dessine moi OPV », Consejo Nacional de Ciencia y Technologia (CONACyT, Mexico) and China Scholarship Council (China). This work has been also performed within the Framework of the French-Mexican International Laboratory (LIA-LCMMC) supported by CNRS and CONACyT.

Vol. 1 Pag.76

Microwave synthesis and characterization of a supramolecular βCD-based crosslinked network

Yareli Rojas-Aguirre1, Geovanni Sangabriel-Gordillo1, Israel González-Méndez1.

1Departamento de Farmacia, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, C.P. 04510, México D.F., México [email protected]

Abstract The synthesis of supramolecular networks using cyclodextrins as the crosslinking points is gaining attention because of their potential applications in a number of fields. In this work, we present the synthesis of a β-cyclodextrin (βCD) network with carbonyldiimidazole (CDI) as the crosslinking agent using microwave irradiation. This approach allowed obtaining the product in 45 minutes instead of the 8 h that takes the conventional synthesis. The physicochemical characterization confirmed the identity of the material, which showed, in addition, an improved host-guest complexation efficiency.

Introduction Cyclodextrins (CDs) are cone shaped cyclic oligosaccharides formed by glucopyranose units in which the outer surface is hydrophilic, while the cavity holds a hydrophobic microenvironment. Hence, CDs can host molecules of different nature resulting in the formation of inclusion complexes [1]. The synthesis of CD-based crosslinked networks is becoming popular in current research. In these systems, the CDs can act as the crosslinking points and interact with guest molecules simultaneously. The crosslinker, the reaction conditions and the stoichiometry will determine the degree of crosslinking, the characteristics of the mesh, the size and the shape of the system and, therefore, gels, polymer particles or continuous porous structures can be obtained [2]. Trotta and co-wokers have been pioneers in the synthesis of hypercrosslinked CD systems. Among them is the one called carbonate nanosponge, a crystalline nanometric structure, obtained from the reaction of βCD and CDI as the crosslinking agent [3]. Inspired by the work of Trotta and taking into account the potential applications of the βCD-based crosslinked networks, we consider that the generation of these materials rapidly with the possibilities to scale up their production is of great importance. In this sense, we herein present the synthesis and characterization of a βCD network with CDI as the crosslinking agent using microwave irradiation (βCD-CL-MW). In parallel, the crosslinked system using the conventional heating method was also synthesized (βCD-CL-H).

Materials and methods CDI, βCD, dimethylformamide (DMF) and ethanol were purchased from Sigma-Aldrich and used without further purification. Milli Q water was used for all the experiments. Vol. 1 Pag.77

βCD-CL-H was synthesized following the reported methods [4]. βCD-CL-MW was performed in an Anton-Parr Monowave 450 at 120°C and stirring rate of 500 rpm; the reaction was monitored through the integrated camera. Both, βCD-CL-H and βCD-CL-MW were prepared with a stoichiometric ratio βCD-CDI 1:4. The FTIR reflectance spectra were acquired in a Perkin Elmer Spectrum 400. The powder x-ray diffraction was carried out in a Bruker D8 Advance diffractometer using Cu ƙα (λ=1.5406 Å) radiation with 30 mA current and voltage of 35 kV. The SEM micrographs of the gold sputtered samples were taken in a Jeol JSM 5900LV in SEI mode, voltage of 20 kV, work distance of 11 mm and spot size of 22. To determine the complexation efficiency, an amount of phenolphthalein (Phen) was added to a suspension of the crosslinked systems, the samples were centrifuged and the free Phen was quantified in a UV-Vis spectrophotometer at 553 nm (Genesys 10UV Thermo).

Results Two βCD-based crosslinked structures were prepared. βCD-CL-H was obtained after 8 h, while βCD-CL-MW was produced in only 45 min. The systems were obtained as porous surface micrometric aggregates (Figure 1). The particle size was confirmed through their analysis in a zetasizer instrument (Malvern) and was found to be in the range of 4-5 µm.

Figure 1. SEM micrographs of A) βCD; B) βCD-CL-H and C) βCD-CL-MW

Both, βCD-CL-MW and βCD-CL-H, were characterized in order to confirm their identity. The IR spectra showed the characteristic band of carbonate group at 1750 cm-1 indicating the crosslinking between CDs through carbonate moieties in both cases (Figure 2B and 2C), whereas the IR spectrum of native βCD did not display this peak (Figure 2A). The diffraction pattern of βCD revealed the crystallinity of the native macrocyle, which is lost in some extent when is crosslinked. Interestingly, the degree of crystallinity in βCD-CL-MW seems to be higher than βCD-CL-H (Figure 3). Vol. 1 Pag.78

Figure 2. FTIR spectra of A) βCD; B) βCD-CL-H and C) βCD-CL-MW

Figure 3. X-ray diffractograms of A) βCD and B) crosslinked systems

Both, βCD-CL-MW and βCD-CL-H were incubated in the presence of Phen, a well known guest for the macrocyle. The crosslinked systems were more efficient forming complexes than βCD. This can be due to a cooperative effect that βCD rings have when they are close together [1] and because the guest molecules could also be trapped in the interstitial spaces in the crosslinked structure. It was found that the complexation ability and the impregnation volume of βCD-CL-MW material was higher than βCD-CL-H (Table 1). The latter was performed in order to indirectly know the porosity and the amount of water that can be taken by the material. These results show that besides the reduction of the reaction time, the microwave irradiation influences the crosslinking ratio and the order in which the macrocycles are packed to form the porous structure. This, in turn, will determine the entrapment capacity of the supramolecular materials and the further applications they could have. Vol. 1 Pag.79

Table 1. Specific features of the BCD crosslinked systems Reaction Yield Impregnation Complexation System time (%) volume (ml/g) efficiency (%) Native βCD ------0.53 68.4 βCD-CL-H 8 h 49 1.61 79.2 βCD-CL-MW 45 min 57 3.16 87.3

Conclusions Two βCD-based crosslinked systems were synthesized. As expected, the reduction in the reaction time when working in a microwave reactor decreased dramatically from 8 h to only 45 minutes. The microwave irradiation produced structures with an enhanced capacity to form inclusion complexes and to entrap water molecules than the same materials obtained by the conventional synthetic methods. These outcomes open the door to a fast production of materials with improved properties and to the possibilities for expanding their applications, which will be part of our future work.

References [1] Loftsson, T.; Duchêne, D. Int. J. Pharm. 2007, 329 (1-2), 1–11. [2] Concheiro, A.; Alvarez-Lorenzo, C. Adv. Drug Deliv. Rev. 2013, 65 (9), 1188–1203. [3] Cavalli, R.; Trotta, F.; Tumiatti, W. J. Incl. Phenom. Macrocycl. Chem. 2006, 56 (1-2), 209–213. [4] Lembo, D.; Swaminathan, S.; Donalisio, M.; Civra, A.; Pastero, L.; Aquilano, D.; Vavia, P.; Trotta, F.; Cavalli, R. Int. J. Pharm. 2013, 443 (1-2), 262–272.

Acknowledgment The authors thank Prof. Francisco Hernández-Luis for the technical assistance and facility of the Anton- Parr Microwave Reactor and Facultad de Química, UNAM for the financial support (PAIP 5000-9157). Vol. 1 Pag.80

SYNTHESIS AND CHARACTERIZATION OF MESO-SUBSTITUTED BORON DIPYRROMETHENES (BODIPY)

Gerardo Zaragoza-Galan1, E.A. García Mackintosh, D. Chávez-Flores, A. Camacho-Dávila, L. Manjarrez-Nevárez

1Universidad Autónoma de Chihuahua, Facultad de Ciencias Químicas. [email protected]

Abstract The synthesis of four meso-substituted Boron-Dipyrromethene derivatives (BODIPY; labelled 1, 2, 3, 4, respectively) using ‘’conventional’’ chemical methodologies (in presence of solvents) and mechanochemical methodologies (solvent-free) is reported.

OH

2) 4) Conventional Method CH Cl , Ar OH O 2 2 1) 3) R1,2,3,4 O + 1) TFA 1-2 drops, 2-12h N 2) DDQ 1 eq, 30min H O N N H 3) Et N 5eq, BF OEt 5eq, 0*C 3h 2 eq 1 eq 3 3 2 B N N F2 B R1= 4-Hydroxy-3-methoxybenzaldehyde Mechanochemical F2 R = 4-Hydroxybenzaldehyde N N N N 2 1) TFA 5 drops, 1min B R = 4-Methoxybenzaldehyde B 3 2) 2ml CH Cl DDQ 1 eq, 1 min F R = 1-Pyrenecarboxaldehyde 2 2, F2 2 4 3) Et N 3 ml,BF OEt 3ml,1 min 3 3 2 (Not isolated) (Not isolated)

1. Introduction 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dyes (abbreviated as BODIPY) are composed of two units of pyrrole which are connected by a methene in the 2-position and a boron atom coordinated by the N-heteroatom. BODIPY dyes are highly absorbent in the visible and ultraviolet spectrum, have high fluorescent quantum yields, thermic and photochemical stability and high solubility in organic solvents[1]. There are different synthetic routes to obtain BODIPY dyes[2], these differences are related to the need of obtaining symmetric or asymmetric compounds; to add substituents in different positions of the BODIPY core, and to reduce reaction times and solvent waste[3]. The simplest route to obtain meso-substituted dyes is by acid-catalyzed condensation of two pyrrole units with an aldehyde unit.

2. Experimental section 2.1 Reagents and instrumentation Commercially available reagents and solvents were purchased from Sigma-Aldrich, JT BAKER, Acros Organics and Golden Bell; and were used without further purification. 1H NMR 60MHz spectra was recorded using d-chloroform as internal standard with Eft-60 Anasazi Instruments spectrometer. UV-Vis measurements were performed on Lambda 25 Perkin Elmer spectrometer. 2.2 Synthesis 2.2.1 General procedure for conventional and mechanochemical synthesis of BODIPY dyes Conventional: A solution of pyrrole (2eq) and the desired aldehyde (1eq) was dissolved in 100mL of CH2Cl2, the system was purged with Argon in order to remove all the oxygen in the round flask; a drop of trifluoroacetic acid was added as an acid catalyst, and the mixture was stirred for 3-12 hours or until a TLC experiment revealed the total consumption of the Vol. 1 Pag.81

aldehyde. Then, 1 equivalent of DDQ was dissolved in 25mL of CH2Cl2 and was added dropwise; then the reaction mixture was stirred for 15-30min. Afterwards, Et3N and BF3OEt2 (3mL each) were slowly added under an ice bath. The reaction mixture was stirred for 3 hours. The crude mixture was then washed with water and a saturated K2CO3 solution, the organic phase was isolated and dried with Na2SO4. Purification was achieved by column chromatography in silica gel. 4-Fluoro-8-(4-hydroxy-phenyl)-4H-4a-aza-3a-azonia-4-bora-s-indacene; fluoride (2). Starting reagents were pyrrole (10 mmol, 0.67 g) and 4-hydroxybenzaldehyde (5 mmol, 0.61 g); oxidant was DDQ (5 mmol, 1.135 g). It was isolated as red/brown crystals. Reaction yield 10.0% (0.141 g, 0.00049 mol) UV-Vis (λ, nm): 497,370. 1H-NMR [60.0 MHz, DMSO-d6] (δ, ppm) 6.55 (m, 2H, H2), 6.91 (d, J=2.47Hz, H3), 7.02 (d, 2H, J=1.5Hz, H4), 7.39 (d, J=8Hz, H5), 7.89 (d, 2H, H1). 4-Fluoro-8-pyren-1-yl-4H-4a-aza-3a-azonia-4-bora-s-indacene; fluoride (4) Pyrrole (2 mmol, 0.134 g) and 1-Pyrenecarboxaldehyde (1 mmol, 0.23g); DDQ (1 mmol, 0.227 g) as oxidant. Product was isolated as cherry red crystals. Reaction yield 8.4% (0.035 -5 1 g, 8.36x10 mol). UV-Vis (λ,nm): 343,423,507. H-NMR [60.0 MHz, CDCl3] (δ, ppm): 8.10 (m, 9H, H4-5-6-7-8-9-10-11-12), 6.50, (d, J=6Hz, 6H, H-1-2-3). Mechanochemical: Pyrrole and aldehyde (2:1 eq), were added to a mortar. Five drops of trifluoroacetic acid were added and the mixture grinded with a pestle for 1 minute. Then, 1eq of DDQ was added slowly with 2mL of CH2Cl2; the mixture was grinded for 1min. After that 5mL of Et3N and BF3OEt2 were added and grinded for 1 minute. Reaction control by TLC was done at all the previous steps. The separation and purifying steps were the same as those of the conventional methodology. Compound 4 was synthetized via mechanochemical methods as previously described. Pyrrole (5 mmol, 0.335 g) and 1-Pyrenecarboxaldehyde (2.5 mmol, 0.575 g). DDQ (2.5 mmol, 0.567 g) as oxidant. Product was isolated as a red/brown powder. Reaction yield -5 1 3.2%. (0.031 g, 7.908x10 mol). UV-Vis (λ,nm): 340,424,507. H-NMR [60.0 MHz, CDCl3] (δ, ppm): 8.10 (m, 9H, H4-5-6-7-8-9-10-11-12), 6.50, (d, J=6Hz, 6H, H-1-2-3).

Table 1. Comparison between solvent and solvent-free methodologies. Reaction Steps

Condensation Oxidation Coordination

Solvent Solvent-Free Solvent Solvent-Free Solvent Solvent-Free

- Temperature control - Reaction - Reaction - Lower time: 2-12 h - Mitigate increase - Closed System reaction yields time: 1 min - Increase in in viscosity by (N2 atmosphere) and purity - Preparation viscosity makes - Preparation adding more time: 2 h grinding difficult. time: 15 min solvent - Highly pure - Can’t remove BODIPY dyes oxygen - Use of dry -Reaction time: - No solvents - Reaction time: solvents 1min 30min -Higher reaction - Reaction yields time: 1min

Reaction time: 3h Vol. 1 Pag.82

Figure 1. UV-Vis absorption spectrum for 2 and 4 dyes

3. Results and Discussion Table 1 describes a step-by-step comparison between the solvent and solvent-free methodologies used during this work. The conventional method was all-around the best route to obtain highly pure BODIPY dyes, the ability to maintain controlled atmosphere and replace all the oxygen present in the round flask with N2 is crucial to achieve the coordination between the boron and nitrogen. BODIPY dyes were characterized by 1H-NMR and UV-Vis spectrum were obtained. As shown in Figure 1, the UV-Vis spectrum of 2 and 4, were consistent with the typical BODIPY dye profile. Compound 2 showed a high absorption peak at 497 nm, which correspond to the S0-S1 transition; and a shoulder of high energy at 475 nm, which is caused by a 0-1 vibrational transition. The second important signal on the UV region was found at 370 nm and is attributed to a S0-S1 transition, since it lacks an additional chromophore to absorb in that region, this band is clearly observed. The molar extinction coefficient at the maximum absorption band (497 nm) was calculated with a value of 3806 M-1cm-1. Compound 4 presented two characteristic absorption bands: BODIPY and pyrene. For the BODIPY core, two bands were observed. One is an intense band at 507 nm, which corresponded to a S0-S1 transition and the other one is a slight shoulder at 480 nm, which is assigned to a 0-1 vibrational transition. Two additional intense and wide absorption bands were observed at around 343 nm, these ones are attributed to S0-Sn transitions in the pyrene unit that is attached to the meso-position of the BODIPY core. This result is evidence that the two moieties (BODIPY-Pyrene) have no electronic interaction at ground state since absorption at 343 nm is not clearly distorted by the presence of BODIPY unit. Optimization studies[4] demonstrate that the dihedral angle between the pyrene unit and the BODIPY core is 63̊, so that it not alters its planarity. Thus, the π-electronic clouds of both chromophores does not overlap and both system are independent of each other; this explain why in the UV- Vis absorption spectrum appears as the sum of the parts of BODIPY core and Pyrene typical absorption spectrums. The molar extinction coefficient at the maximum absorption band of the BODIPY core (507 nm), was calculated with a value of 136,413 M-1cm-1, which give us evidence that this dye is highly absorbent at this wavelength, this is important in applications such as sensitizers for solar cells. Vol. 1 Pag.83

BODIPY dye 1 could not be isolated; we believe that the conditions in the oxidation step were too severe for 4-Hydroxy-3-methoxybenzaldehyde, so the dipyrromethene was further oxidized to a quinone-like derivative. BODIPY dye 3 could not be isolated, however, an interesting result was observed in the conventional route. During the purification step, a highly fluorescent compound was isolated as purple crystals. UV-Vis absorption analysis revealed two important bands: a strong and sharp band around 420 nm, corresponding to a S0-S1 transition (Soret Band) and four small absorptions bands at around 550 nm (Q Bands); these correspond to a typical porphyrin absorption profile.

4. Conclusions BODIPY dyes 2 and 4 were successfully synthetized via conventional methodologies using CH2Cl2 as solvent; the reaction yields were 10.0% and 8.4%, respectively. 4 was the only dye that could be obtained via mechanochemical routes; the reaction yield was about 3.2%. The 1H NMR 60 MHz and UV-Vis spectra were obtained for all the isolated molecules. Also, the molar extinction coefficient for 2 and 4 was calculated with values of 3806 M-1cm-1 and 136413 M-1cm-1, respectively. During the analysis of the UV-Vis spectra, for compound 4, electronic interactions between the pyrene entity and the BODIPY core were not found, in the ground state. A comparison between solvent and solvent-free methodologies was done using reaction yields, reaction times, purity (as observed in a TLC experiment) and a variety of observations as criteria. Conventional methodologies proved to be more efficient than their mechanochemical counterpart.

References 1. Loudet A., Burgess K. (BODIPY dyes and their derivatives: Synthesis and Spectroscopic properties). Chem. Rev. 2007.107. 4891-4932 2. Lamarie P., Dzyuba S. (Expeditious, mechanochemical synthesis of BODIPY dyes). Beilstein Journal of Organic Chemistry. 2013. 9. 789-790. 3. Valeur B. (Molecular Fluorescence: Principles and Applications). Wiley-VCH. 2002.ISBN 3-527-29919-X 4. Dehaen W., Borggraeve W. (Synthesis and applications of reactive BODIPY dyes). Doctoral Thesis. Katholieke Universiteit. Faculty of Science. Netherlands. 2010. 3-8.

Acknowledgements

GZG thanks to National Science and Technology Minister (CB-2013-01 Project number 222847) and Public Education Minister (F-PROMEP-39/Rev-03) for financial support. Vol. 1 Pag.84

Behavior and Removal of Inclusions in a Funnel Mold in Thin Slab Continuous Casting. Use of Mathematical and Physical Simulations with the Aid of the Measured Vibrations with an Accelerometer. Gerardo Barrera C1, Hugo Arcos G2, Carlos Espinosa2, Guillermo Carreón G1. 1Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigación en Metalurgia y Materiales, Morelia, Mich., México, [email protected], [email protected] 2Graduate Students, Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigación en Metalurgia y Materiales, México, [email protected]

Abstract Up to date, there is little information available in the literature regarding the behavior of the inclusions, especially inside the funnel type mold. It has been found that the accelerometer is a transducer capable of relating the vibration with the behavior of the inclusions in the continuous casting mold. It was indicated that higher levels of vibration in the thin slab mold are greater than the removal of inclusions therein. Two nozzle designs, two depths of 22 and 34 cm, and three casting speed of 4, 5 and 6 m/min were simulated. In all cases, just 100 particles were simulated within the flowing liquid metal, because once the mathematical calculations or the processing time increases as the quantity of particles grow. These have previously been treated with a liquid, sensitive to the black light. All cases were also solved in the simulation software Fluent® where a slag layer, in which all the inclusions that reach it are trapped. The area near the nozzle has a greater concentration of particles, which is due to low speed or flow pattern change in said zone. These inclusions are eventually become stripped and trapped in the slag layer.

KEY WORDS: nozzle; mathematical and physical simulation; inclusions; slag; casting speed; accelerometer and continuous casting mold.

1. Introduction. The present research work is focused on analysis of the behavior of inclusions in a thin slab continuous cast mold, funnel type, and observation of the possibility to eliminate them. Physical and mathematical simulation is performed on the assumption with the redesign of a nozzle, which is currently used in a Mexican company (Ternium). By varying both the depth of it and the casting speeds, it was considered that greater removal of inclusions will possibly, becomes within the liquid steel and then they will be trapped in the layer of lubricant powder (slag).

2. Experimental Methodology. The experimental phase of this study was based on the analysis of the results of a previous mathematical modeling [1,6] both the nozzle and the mold for the continuous casting of thin slab funnel type. The main goal of this research work will focus on the physical modeling.

2.1. Physical Modeling A model of the mold and nozzle was designed based on the appropriate scale similarity criteria where liquid metal flow is simulated with water. If the water flow in the model is a realistic representation of the actual flow in the mold, it can be used to study various aspects of the flow into the mold, including. among others: Deformation of the free surface and surface turbulence, Viewing flow in different areas of the mold with a tracer, Transport, Vol. 1 Pag.85

flotation and simulation of inclusions, vorticity formation on the metal-slag interface and slag entrapment into the bosom of the liquid metal in the mold, Energy dissipation, etc. To study the behavior of the fluid flow, a physical model a 1/2 scale of the actual mold continuous casting of thin slab funnel-like clear acrylic 12 mm thick, was fabricated and a submerged entry nozzle SEN of complex geometry was manufactured in high density resin. The mold was designed to work with a speed of up 8 m/min, which is equivalent to 84.34 liters/min of water. 2.2. Vibration Monitoring The best way to visualize the performance of the continuous casting mold is monitoring it with transducers. The main purpose of this work, with the use of accelerometers, is to follow the evolution of the flow pattern generated on one of the thin mold walls, and also to correlate this pattern with the removal of inclusions in the mold in an indirect way. The accelerometer signals are digitized with a DAQ card. The accelerometer was placed at four different points. Programs were written in graphical programming environment, LabVIEWTM. A signal pattern is taken, and then natural noise of the system is subtracted numerically to the digitized transducer signal. An area under the curve is calculated with the signal depending on the conditions of the simulation. By this procedure, depending on the casting it will be the magnitude of the signal. 2.3. Inclusions Simulation Since the non-metallic inclusions in the liquid steel are lighter, they can float to the surface. For a range of sizes of inclusions reaching the continuous casting mold, it can be assumed that the inclusions float according to the Stokes velocity law.4) Using the relevant dimensionless numbers will reach to an equation in which the radius of the inclusion can be calculated with Eq. (1) and by substituting the values of Table I in this equation a relationship between the radius of the prototype inclusion and model inclusion, can be obtained from Eq. (2):

0.5 3.4 0.5 1− 1− ρinc, p  0.25 0.25 7.4 RRinc,, m = λ inc p  (1) R=λ RR= 2.5 (2) 1− ρ inc, m inc,, p inc p st 0.974 1− 1 Table I. Parameters for the calculation of model inclusions Density, of the Inclusion Density, of the prototype prototype inclusion model Water density inclusion Steel density radius (gr/cm3) (gr/cm3) (gr/cm3 (gr/cm3 µm 0.974 1 3.4 7.4 50-100 Using prototype inclusions ranging from 50 to 100 micros a calculation of the model inclusions was made based on Eq. (2). The reason why the range used is that one most likely to be eliminated but smaller, are almost impossible to remove. Also this fact has a nothing-significant effect on the quality of the slab. In table II the size distribution of the inclusions is shown. Table II. Physical model parameters Velocity Water Flow Inclusions Diameter (µm) Amount (m/min) (liters/min) of particles per gram 4 49 250/125 500 5 61.2 219/211 730 6 73.4 110/147 500 Vol. 1 Pag.86

2.4 Physical Simulation. The cast speed, flow of water, the diameter and the amount of the inclusions per gram are presented in Table II. Inclusions made with the acrylic material, which was subjected to grinding, classification and impregnation with penetrant inspection fluorescence dye. Several black light lamps were placed around the mold and in the discharge area of the nozzle to observe more clearly the injected inclusions. A digital camera to obtain images of the inclusions was used during its evolution into the mold and the slag, simulated with industrial oil. Because the amount of particles is huge, for the purpose of this research work it was arrived to the conclusion that in this model 0.01 grams was enough to be in the range of 14,000 to 40,000 [5] particles as in the industrial prototype. The depths in the model were 11 and 17 cm respectively. The inclusions must be previously prepared with a dispersant in order to avoid any agglomeration. Once the flow is leveled the particles are injected. In order to know the removal ratio, the inclusions are weighed and then a relationship is established with the injected ones. It was very important in this stage to wash the inclusions to remove any oil traces in order to eliminate any error in the final weight. Then is calculated the percentage of the removed inclusions. 2.5 Results and Discussion. The experimental results are analyzed in two stages; the analysis of the vibration measurements, and the inclusions removal in order to correlate the signals obtained with accelerometer and the behavior on the inclusions in the continuous casting funnel type mold. A relationship between the vibrations and the speed casting was found and there is a directly proportional relationship between the increases in the intensity of the vibrations of the mold, measured with an accelerometer. This can be translated as a greater intensity of the vibrations that occurs due to higher energy dissipation in the model. From the information obtained from the mathematical modeling phase, a comparison is made of how the fluid behaves in the walls of the model in Fig. 1. As it is expected for higher casting speed, there is an increased flow velocity in the mold walls that it can be translated as a greater intensity of the vibrations that occurs due to greater energy dissipation in the model.

Figure 1. Velocity profile at a line drawn at the mold narrow face and locations where the transducer was placed. Several graphs were done, some of the results are shown in Fig. 2, for a 200 s times, at three different casting speeds 4, 5 and 6 m/min and for both scales used in both; the physical simulation, superior part, as in the mathematical simulation, bottom part. Thus, being shown that the proposed transducer, accelerometer, not only can be used to detect changes in the flow pattern, which is translated in the detection of the oscillations created by the jets from the nozzle ports and that impacts the thin steel layer solidified, besides fluctuations in the steel-slag interface and in the prevention and correction of possible thread breakage. This might lead to a higher productivity of the continuous casting process and improved control of it. Also this can be taken as the start point to proof the relationship that exists between the Vol. 1 Pag.87

removals of inclusions and the intensity of vibrations, measured with the accelerometer. This shows that the accelerometer is a device capable of detecting, through its processed digital signal, the energy generated in the mold of continuous casting of thin slab and it can be correlated with the elimination or removal of inclusions in it. For experiments with casting speeds of 4, 5 and 6 m/min to a depth of 22 cm nozzle, some of the results are shown in Fig. 3 as percentage of removal of inclusions.

Figure 2. Intensity of vibrations and turbulent dissipation rate profile at a line drawn at the mold narrow face at a time of 200 s and locations where the transducer was placed for a) physical simulation and b) mathematical simulation.

Figure 3. Comparison of percentage of entrapment of inclusions, at 22 cm of deep, physical model Conclusions The mathematical and physical simulations as well as the vibration analysis have been proved to be very useful tools that can provide real and measurable values of the amount of energy in the mold and could be an indicative of how the inclusions are eliminated. It was found that the accelerometer could be a transducer capable of correlate the intensity of the vibrations with the behavior of inclusions in the continuous casting mold. Showing that at higher intensity of the vibration, the higher amount of inclusions could be eliminated. It also was found that the accelerometer could be used as a device to detect and prevent possible yarn breakage in the thin slab continuous casting machine. REFERENCES Vol. 1 Pag.88

1) H. Arcos and G. Barrera: Doctoral Work, No. 5, IIM, UMSNH, 2012, 1. 2) L. Zhang, S. Yang, K. Cai and B. G. Thomas: Metall. Mater. Trans. B, 38B, 2007, 63. 3) Y. Murakata, M. G. Sung, K. Sassa and S. Asai: ISIJ Int., 47, 2007, 663. 4) Y. Sahai and T. Emi: ISIJ Int., 36 (1996), 1166. 5) Q. Yuan, B. G. Thomas and S. P. Vanka: Metall. Mater. Trans. B, 35B, 2004, 703. 6) H. Arcos-Gutierrez, G. Barrera-Cardiel, J. de J. Barreto and S. Garcia-Hernandez: ISIJ Int. 2015 Vol. 1 Pag.89

Comparative analysis of the CO2 capture properties for pure, K- and Na-doped Li5AlO4. M. Teresa Flores-Martínez and Heriberto Pfeiffer Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, Del. Coyoacán, CP 04510 México, Ciudad de México., [email protected]

Introduction

CO2 is the main anthropogenic greenhouse gas in the atmosphere. One of the environment impacts of the large amount of CO2 in the atmosphere is the global warning and climate change.[1] Most efforts are focused mainly on reducing the amount of CO2 emitted to the atmosphere.[2] Recently, considerable high interest has been developed in the lithium-based ceramics and other alkaline elements due to their high CO2 absorption capacity at elevated temperatures. Among these ceramics, Li5AlO4 seems to be one of the best possible options as a CO2 capture material because of its high theoretical CO2 chemisorption capacity (15.9 mmol/g).[3] Previously, some works have reported the CO2 chemisorption process on Na- and K-doped lithium ceramics, where the capture processes are increased considerably, in comparison with their respective pristine ceramics. This behavior has been explained because lithium carbonate, formed during the CO2 chemisorption, forms an eutectic mixture with either potassium or sodium carbonates. Thus the ceramic surface is partially fused favoring the diffusion processes.[4,5] This work describes the CO2 chemisorption process in K− or Na−doped β−Li5AlO4 systems under different thermal conditions. Furthermore, different CO2 sorption kinetic studies were performed on K- or Na-doped lithium aluminates and the reaction mechanism was evaluated.

Experimental Details

β−Li5AlO4 was synthesized using a solid-state reaction that employs lithium oxide (Li2O) and gamma alumina (γ−Al2O3). It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption. Doped powders of β−Li5AlO4 were mechanically mixed with 10 wt% of potassium (K2CO3) or sodium (Na2CO3) carbonate. These samples were labeled as m−K−β−Li5AlO4 and m−Na−β−Li5AlO4, respectively. Additionally, Na− and K−doped β−Li5AlO4 samples were synthesized by a solid-state reaction, adding 10 wt% of potassium or sodium carbonate during the synthesis process. In these cases, the samples were labeled as s−K−β−Li5AlO4 and s−Na−β−Li5AlO4, respectively. To determine the CO2 chemisorption capacity, the Na and K−doped lithium aluminates were analyzed thermogravimetrically in the presence of dry CO2. Initially the samples were dynamically heated from room temperature up to 900 °C at 5 °C/min, subsequently the samples were tested isothermally at different temperatures (from 400 to 700 °C) under the presence of a CO2 flow (60 mL/min). For the isothermal experiments, the samples were heated up to the corresponding temperature under a N2 flow. Once the desired temperature was reached, the gas flow was switched from N2 to CO2.

Results and Discussion

The formation of β−Li5AlO4 was confirmed by X-ray powder diffraction (XRD, data not shown). The surface area of ceramics with and without K or Na doping was determined using Vol. 1 Pag.90

the BET model [6]. The obtained values were considerably low (>1 m2/g), thus, it was assumed that they had no influence on the CO2 capture. Initially the CO2 chemisorption capacities of Na- and K-doped β−Li5AlO4 were analyzed thermogravimetrically in the presence of a CO2 flux. Figure 1 shows the dynamic thermograms obtained for Na− and K−doped β−Li5AlO4, compared with the β−Li5AlO4 pristine. These thermograms show two different processes taking place in the materials. The first one is a superficial CO2 chemisorption process occurring between ~200 and ~400 °C. Then, when the temperature was increased (>500 °C), the diffusion processes were activated and the reaction continued through the bulk of the material, completing the CO2 chemisorption (Eqn (1)). Similar thermal trends have already been observed for other lithium ceramics [7−9]. Depending of the Na and K addition way, two different trends were observed.

Li5AlO4 (s) + 2 CO2 (g) 2 Li2CO3 (s) + LiAlO2 (s) (1)

170 β− Li5AlO4 β− 165 s-10K- Li5AlO4 m-10K-β−Li AlO 160 5 4 s-10Na-β−Li AlO 155 5 4 β− m-10Na- Li5AlO4 150 145 140 135 130

Weight (%) 125 120 115 110 105 100

100 200 300 400 500 600 700 800 900 Temperature (°C)

Figure 1. Comparative dynamic thermogravimetric analyses of Na- and K-containing β−Li5AlO4 samples with pure β−Li5AlO4 sample into a CO2 flux.

Then, in order to analyze and understand the K- and Na-doping effects in β−Li5AlO4, different and independent isothermal experiments were performed. The CO2 chemisorption of s−K−β−Li5AlO4 showed an exponential behavior between 400 and 500 °C (Figure 2). The eutectic mixtures should be produced at temperatures around to 550 °C, improving the CO2 diffusion-controlled chemisorption process. Additionally, it was possible to observe a double process occurring at 650 °C, the first one taking place during the first minutes, and the second one happening at longer times. This isothermal behavior is consistent with the observation of a double chemisorption mechanism mentioned above. Finally, the intercrystalline diffusion processes were activated at 700 °C, improving even more the CO2 chemisorption. After the qualitative analysis, the isotherms were fitted to a first-order reaction model with respect to Li5AlO4 (Eqn (1)). ln[Li5AlO4 ] = -kt (2) where k is the reaction rate constant, t is the time, and [Li5AlO4] is the molar concentration of the ceramic (Figure 3). Vol. 1 Pag.91

β− s-10K- Li5AlO4 170 700 °C 160 650 °C 150

140

Weight (%) 130 600 °C

120 550 °C

110 500 °C 450 °C 400 °C 100 0 20 40 60 80 100 120 140 160 180 Time (min)

Figure 2. CO2 isotherms of s−K−β−Li5AlO4 at different temperatures.

ln [Li5AlO4] =-k t 0.025 β− Li5AlO4 β− s-10K- Li5AlO4 β− 0.020 m-10K- Li5AlO4 β− s-10Na- Li5AlO4 β− m-10Na- Li5AlO4 0.015 ) -1

(s 0.010 k

0.005

0.000

400 450 500 550 600 650 700 Temperature (°C) Figure 3. Comparison of plots of k versus Temperature, for the data obtained at kinetic analysis, assuming a first-order reaction of Li5AlO4 for short times.

If the reaction is controlled by the interface movement from the surface inward it can be 1/3 described by the following equation: 1-(1-α) = kDt (3) where α is the molar fraction of Li2CO3 produced, t is time and kD is a constant which depends on the diffusion coefficient, particle size, and temperature (Figure 4).

Eyring's model, is typically used on heterogeneous reactions and solid−gas system to describe this kind of temperature dependence diffusion processes, then k and kD were to ‡ ‡ Eyring's model. ln(ki/T) = -(∆H /R)(1/T) + lnE + ∆S /R (4). Thus, by means of fit the data obtained to a linear model, the activation enthalpies (ΔH‡) were calculated for both different processes (Tables 1 and 2), for at least two temperature ‡ ranges. ΔH values for CO2 direct chemisorption are lower in K- and Na-containing samples compared to the β−Li5AlO4 pure sample. These values are higher for the kinetically controlled chemisorption processes. It means that the direct chemisorptions process is less dependent of temperature for doped samples than without doping. In the kinetically controlled chemisorption case it could be observed the opposite behavior. This implies that the direct chemisorption process is less temperature dependent than the chemisorption process kinetically controlled by diffusion processes. Vol. 1 Pag.92

α 1/3 kD t = 1-(1- ) β− Li5AlO4 β− s-10K- Li5AlO4 -5 1,0x10 β− m-10K- Li5AlO4 β− s-10Na- Li5AlO4 β− m-10Na- Li5AlO4 8,0x10-6

-6 ) 6,0x10 -1 (s

D k 4,0x10-6

2,0x10-6

0,0

400 450 500 550 600 650 700 Temperature (°C) Figure 4. Comparison of plots of k versus Temperature, for the data obtained at kinetic analysis, assuming a diffusion mechanism controlled by the interface movement from the surface inward.

Table 2. The activation enthalpies (ΔH‡) for Table 1. activation enthalpies (ΔH‡) for the diffusion mechanism controlled by the CO2 direct chemisorption interface movement from the surface inward Sample (450 - 650 °C) ΔH‡ (kJ/mol) Sample (400 - 550 °C) ΔH‡ (kJ/mol)

β−Li5AlO4 69.0 β−Li5AlO4 34.0 m-10K-β−Li5AlO4 48.5 m-10K-β−Li5AlO4 56.1 m-10Na-β−Li5AlO4 30.2 m-10Na-β−Li5AlO4 112.2 s-10K-β−Li5AlO4 66.2 s-10K-β−Li5AlO4 60.8 s-10Na-β−Li5AlO4 43.5 s-10Na-β−Li5AlO4 70.1

Conclusion It was observed that the Na and K-doped β−lithium aluminate, in the process of chemisorption of carbon dioxide at high temperatures, present an improvement in the CO2 capture process in the temperature range from 450 to 650 °C. However, the mechanically doped samples exhibit a great improvement in the CO2 capture temperature range from 500 to 650 °C. Thus, the possible application of each sample may depend on the temperature. Overall, the CO2 capture capacity from Na or K-doped β−Li5AlO4 is good considering their small surface area.

References [1] D´Alessandro D. M., Smit B., Long J. R. Angew. Chem. Int. Ed. 2010, 49, 2−27. [2] Qiang W., Luo J., Zhong Z., Borgna A. Energy Environ. Sci. 2011, 4, 42−55. [3] Ávalos-Rendón T., Lara V. H., Pfeiffer H. Ind. Eng. Chem. Res., 2012, 51, 2622−2630. [4] Olivares-Marín M., Drage T., Maroto-Valer M., Int. J. Greenhouse Gas Control 2010, 4, 623−629. [5] Seggiani M., Puccini M., Vitolo S., Int. J. Greenhouse Gas Control 2011, 5, 741−748. [6] Sing K. S. W., Everett D. H., Haul R. A. W., Moscou L., Pierotti R. A., Rouquerol J., Siemieniewska T. Pure & Appl. Chem. 1985,57, 603−619. [7] Mosqueda, H.A., Vazquez, C., Bosch, P. Pfeiffer, H. Chem. Mater. 2006, 18, 2307−2310. [8] Palacios-Romero, L.M., Pfeifer, H. Chem. Lett. 2008, 37, 862−863. [9] Durán-Muñoz, .F, Romero-Ibarra, I.C., Pfeiffer, H. J. Mater. Chem. A. 2013, 1, 3919−3925.

Acknowledgements This work was financially supported by PAPIIT and SENER-CONACYT. M. T. Flores-Martínez thanks PAPIIT and CONACYT for personal financial support. Vol. 1 Pag.93

Synthesis and characterization of Pr1-xCaxFeO3 (x = 0.1, 0.3 y 0.5) thin films and measurement of its electrical conductivity. T. Hernández, L. Madín, F. J. Garza Méndez

Universidad Autónoma de Nuevo León, Facultad de Ciencias Químicas Laboratorio de materiales I, CELAES, Ciudad Universitaria, Av. Pedro de Alba S/N, C.P. 66450, San Nicolás de los Garza, Nuevo León, México, Email: [email protected]

Abstract. In the past few years, a renewed interest has grown to study mixed perovskite oxides due to their potential for various applications such as catalysts, cathode materials in solid oxide fuel cells, magneto optics, solar cells and sensor materials. In this contribution Pr1-xCaxFeO3 (x = 0.1, 0.3 and 0.5) thin films with perovskite-type structure were prepared using a modified sol- gel spin-coating method and electric conductivity was evaluated as an indication of their potential use as gas sensor. The thermal decomposition of the precursors leads to the formation of Pr1-xCaxFeO3 thin film from a temperature of 650°C. The structural, morphological properties of the thin films were studied by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The measurement of electrical conductivity of Pr1-xCaxFeO3 thin films were studied in this work. The XRD analysis indicates the presence of Pr1-xCaxFeO3 in orthorhombic form in all the compositions. The topography and roughness of the coating was obtained by AFM, the morphology of the nanoparticles and the thickness of each composition around 190 nm were observed by SEM. The partial substitution of Ca in the structure increases the conductivity of the thin film.

Keywords: perovskite oxides, thin films, sol–gel, electric conductivity

Introduction. In the big cities with pollution, the presence of oxidizing gases and volatile organic compounds (VOCs) affect the ozone layer in the atmosphere, causing various disorders and diseases become a serious problem for human life [1]. This is one of the reasons why the gas sensors is an attractive area of research for the control of gas emissions in the automotive sector, industrial safety (detection of combustible gases such as propane, methane, hydrogen, etc.), domestic (CO alarms in homes, recreational vehicles), odor detection, leak detection (toxic gases), environmental control (monitoring air quality, ozone, etc.), smoke detectors, and many technologies that generally require the detection of gases in the atmosphere [2]. Among the different detection techniques employed to locate such harmful gases are solid state sensors due to their small size and ease of use [3]. In recent years it has given much importance to the conservation of the environment and has been clear increasing the use of green technologies that contribute to sustainable development of countries trend, and here is where the films of mixed oxides with type structure perovskite have acquired a very important role for the development of electronic devices. Perovskites have an ABO3 stoichiometry, one of the distinguishing characteristics of these compounds for other families of oxides is the wide variety of substitutions that can accept in their crystallographic structure, position A, in the centers of the cube, it can be occupied by ions metal as La3+, Nd3+, Pr3+ Ca2+, moreover, in the centers of the octahedra, sites B, can be occupied by small ions Co3+, Fe3+, consequently type perovskites are very versatile structures. The modifications in the microstructure, processing parameters and as well the concentration of the acceptor/donor dopant may vary the temperature coefficient of resistance and conductivity of the oxides ABO3 [4]. In literature you can find several methods of preparing perovskite films [5-7], in 2012, Nieto [8] prepared and characterized films of the system PrFe0.7Ni0.3O3 deposited on glass with the spin-coating technique, temperature for the crystalline phase was 650 ° C. It was observed that the homogeneity of the films is affected by the deposition rate and the concentration of polyvinylpyrrolidone which helps decrease cracks in the film. In 2014, Nieto [9] prepared semiconducting films Sm1-xCaxFe0.7Co0.3O3 (x = 0.0 - 0.3) on glass substrate using the sol-gel Vol. 1 Pag.94

method assisted by the spin-coating technique. The maximum sensitivity values were obtained for films with more calcium to 300 ° C reaching 100% response, these results showed that the properties of sensing films compared to CO and propane are improved by doping with Ca2+ in the site of Sm3+. In this context, the present research provides information on the synthesis and characterization of thin films of Pr1-xCaxFeO3 (x = 0.1, 0.3 y 0.5) and measuring its electrical conductivity and give a possible application as gas sensors

Experimental Section. Preparation of Pr1-xCaxFeO3 (x = 0.1, 0.3, 0.5) system. Stoichiometric amounts of Pr(NO3)3∙9H2O; Ca(NO3)3∙4H2O; Fe(NO3)3∙9H2O, Citric acid and ethylene glycol were weighed, these precursors were dissolved in 20 ml of polyvinylpyrrolidone (PVP) 10% prepared previously with constant stirring to homogenize the solution, then the mixture was placed in a sand bath at a temperature of 70 °C. Gel was obtained the resulting mixture, then with the aid of a syringe was deposited on the glass substrate using a conventional spin coater at a speed of 3000 rpm. substrates with the solution, are heated in an oven for 40 minutes at a temperature of 120 °C. Finally, the films are taken out and placed in a muffle furnace for 2 h at 650 °C (see Figure 1).

Figure 1. Outline of procedure

Characterization. The films were analyzed by X-ray diffraction (XRD) using a diffractometer for powder X-ray, the topography of the films was observed using atomic force microscopy (AFM), thickness was measured with a profilometer, the microstructure of the films obtained were analyzed by a scanning electron microscope (SEM), the current was measured with an amperemeter for measuring the conductivity of the films.

Results and discussion. The patterns of XRD low angle of the films Pr1-xCaxFeO3 (x= 0.1, 0.3 and 0.5) system at 650 °C synthesized are shown in Figure 2. It can be seen that all peaks higher intensity are indexed in comparison with the compound of Pr0.9Ca0.1FeO3. The results of AFM show that the films exhibit good homogeneity and does not vary significantly between sample to sample, because the samples were prepared in the same manner and were applied the same heat treatment to prevent superficial differences related to crystal growth due to temperature. It can be seen in the films obtained at 650 °C. agglomerates interconnected nanoparticles, the structure is composed of a porous lattice of islands, this behavior is characteristic of the perovskite. Ohm's law was used to measure the conductivity of the Vol. 1 Pag.95

material at room temperature, as we can see with increasing the amount of calcium in the sample exhibits better electrical properties

Figure 2. XRD patterns of the system Pr1-xCaxFeO3 (x = 0.1 - 0.5) at 650 °C by 2 h

Figure 3. The surface morphologies of films Pr1-xCaxFeO3 with a) x=0.1, b) x= 0.3, c) x=0.5 using AFM technique and surface morphology of film of Pr0.9Ca0.1FeO3 at different magnifications, a) 5000X, b) 20000x c) 50000X. using SEM technique.

Table 1. Data from films Pr1-xCaxFeO3 system (x = 0.1, 0.3 and 0.5) and the conductivity Vol. 1 Pag.96

Conclusions. The films Pr1-xCaxFeO3 (x = 0.1, 0.3, 0.5) with perovskite structure were synthesized without any impurities using citrate sol-gel method, homogenous films of approximately 190 nm thickness is obtained by depositing 1 ml of the precursor solution, at 3000 rpm spin velocity using the spin-coating technique and subsequent heat treatment at 650 °C for 2 hours. It is observed that as the amount of calcium in the sample has better electrical properties. By passing current through the films they present conductivity values so can be considered a material with potential use as gas sensor.

Acknowledgments. This study was carried out with financial support of UANL-PAICYT project IT 627-11.

References 1. Peñuelas J., y Lluisà, J., “Emisiones biogénicas de COVs y cambio global ¿Se defienden las plantas contra el cambio climático?”, Ecosistemas, 12 (2003) 1-7. 2. Rosovsky H., Narváez A., Borges G., González L., “Evolución del consumo per cápita en México. Salud Mental”; (1992) 35-4. 3. Seiyama T., Kato A., Fujiishi K., Nagatani M., “A new detector for gaseous components using semiconductive thin films”, Anal. Chem. 34 (1962) 1502–1503. 4. Ball J. M., Lee M. M., Hey A. & Snaith H. “Low-Temperature Processed Mesosuperstructured to Thin-Film Perovskite Solar Cells”. Energy Environ. Sci. 6, (2013).1739–1743. 5. Gao, P.-X. Shimpi, P. Gao, H. Liu, C. Guo, Y. Cai, W. Liao, K.-T. Wrobel, G. Zhang, Z. Ren, Z. Lin, H.-J. “Hierarchical assembly of multifunctional oxide-based composite nanostructures for energy and environmental applications”. International Journal of Molecular Sciences, 13, (2012) 7393-7423. 6. Bhargav K. K., Ram S., Labhsetwar Nitin, Majumder S. B. Correlation of carbón monoxide sensing and catalytic activity of pure and catión doped lanthanum iron oxide nano-crystals” Sensors and Actuators B 206 (2015) 389–398 7. Peng Song, Qi Wang, Zhongxi Yang “CO-sensing characteristics of La0.8Pb0.2Fe0.8Co0.2O3 perovskite films prepared by RF magnetrón sputtering” Physica E 41 (2009)1479–1483 8. Nieto M., “Preparación de películas de PrFe0.7Ni0.3O3 por la técnica spin-coating con polivinilpirrolidona (PVP) como aditivo de síntesis”, tesis licenciatura de química industrial, FCQ, Junio 2012 9. Nieto M., “Películas semiconductoras de Sm1-xCaxFe0.7Co0.3O3: preparación y estudio de sus propiedades sensoras de COVs”, tesis maestría en materiales, FCQ, Junio 2014 Vol. 1 Pag.97

NITRIC OXIDE (NO) DELIVERY FROM [RU(NO)] METAL COMPLEXES WITH SUBSTITUTED TERPYRIDINE LIGANDS

Pascal G. Lacroix1, Joëlle Akl1, Isabelle Malfant1, Isabelle Sasaki1 Patricia Vicendo2, Mireille Blanchard-Desce3, Norberto Farfán4, Rosa Santillán5 Valerii Bukhanko6, Zoïa Voitenko6

1LCC- CNRS 205 rte de Narbonne, 31077 Toulouse (France), [email protected] 2IMRCP-UPS 218 rte de Narbonne, 31062 Toulouse (France) 3ISM-CNRS 31 cours de la Libération, 33405 Talence (France) 4FQ-UNAM Ciudad Universitaria, 04510, México, D. F (México) 5CINVESTAV del IPN, México, D.F. Apdo. Postal 14-740, 07000, (México) 6Univ. T. Shevchenko, Volodymyrska Street 64, 01033 Kyiv (Ukraine)

From NO/ON switch to NO delivery

Our interest for ruthenium nitrosyl ([Ru(NO)]) complexes raised during a long research effort aimed at finding new nonlinear optical (NLO) switches induced at the molecular level by the action of an additional property [1,2], for instance by an optically induced isomerization [3]. However, to be fully convincing, this approach requires ensuring a high yield of isomerization in the solid state. Along this line, an exceptionally large yield of photo-switch was recently II reported on a crystal of [Ru (py)4Cl(NO)](PF6)2·1/2 H2O (Scheme 1), in which more than 92 % of the ruthenium-nitrosyl complexes can be successfully isomerized to ruthenium- isonitrosyl ([Ru(ON)]), bringing this optical material with intriguing switching capabilities [4]. 2+

N N Scheme 1 Cl Ru N O N N II 2+ [Ru (py)4Cl(NO)]

The last few years have witnessed an increasing interest for ruthenium-nitrosyl complexes. Indeed, the number of reports conducted from SciFinder on a literature survey at “ruthenium- nitrosyl” reveals that the number of publications on Ru(NO) has grown regularly since 1998. Interestingly, while 40 % of the entries are dedicated to “NO isomerization”, 60 % are dedicated to “NO release”!

As we became aware of various technological limitations in the design of such molecular NLO switches (in relation to temperature effects), we became gradually more interested in NO release, in relation to the numerous applications of nitric oxide in biology. Importantly, the action of NO strongly depends on its concentration (e.g. it favors cell proliferation at Vol. 1 Pag.98

concentration ranges around 10-9 mol.L-1 with potential application in tissues building and tissues healing, but it leads to scareless cell death at concentration around 10-9 mol.L-1 with potential application against cancer). [Ru(NO)] complexes have therefore emerged as especially promising because they are usually stable and well tolerated by the body and they can release the required amount of NO under irradiation, exclusively. Nevertheless II 2+ [Ru (py)4Cl(NO)] base species suffer from two inherent weaknesses for therapeutic applications: (i) the lability of the pyridine in biological media and, (ii) the need for an incident radiation in the λ = 300-500 nm range to release NO, however out of the therapeutic window of transparency of the tissues (λ = 600-1300 nm). To overpass these difficulties the more II + robust [Ru (R-terpy)Cl2(NO)] in which R-terpy is a substitute terpyridine (Scheme 2) has been preferred for this investigation. Furthermore, the two-photon absorption (TPA) techniques, in which 2 photons emitted at 800-1000 nm can be used instead of 1 photon at 400-500 nm, has been envisioned. There are additional advantages in using the TPA approach, such as the use of sub-pico laser pulses which provides no damages to the very little energy transferred to the cells, and the highly focalized effects allowing to work cell per cell without any collateral damages. Fluorene has been selected as the first promising R substituent (Scheme 2). It is indeed an electron-rich substituent which is usually engaged in charge transfer processes associated with large TPA capabilities.

1+ O 1+ Cl N N N R N Ru N O R N Ru Cl R = N N Cl Cl

II + II + trans(Cl,Cl)-[Ru (R-terpy)Cl2(NO)] cis(Cl,Cl)-[Ru (R-terpy)Cl2(NO)] fluorene

Scheme 2

II II trans(Cl,Cl)-[Ru (FT)Cl2(NO)](PF6), and cis(Cl,Cl)-[Ru (FT)Cl2(NO)](PF6)

The crystal structure of the resulting fluorenylterpyridine (FT) and related trans(Cl,Cl)- II + [Ru (FT)Cl2(NO)] complex is shown in Figure 1 [5]. The reduced torsion angle of 4.8° observed between the fluorene the terpyridine suggests that a significant charge transfer could take place from the fluorene to the withdrawing Ru-NO fragment.

II + Figure 1 Molecular crystal structures of FT (left) and trans(Cl,Cl)-[Ru (FT)Cl2(NO)] (right) showing the internal torsion angles and the path of fluorene to Ru(NO) intramolecular charge transfer. Vol. 1 Pag.99

This possibility is further confirmed by the electronic properties investigated experimentally (Figure 2) and computationally, by DFT (Figure 3). Both indicate the appearance of new transitions at low energy. The dominant HOMO → LUMO contributions in these transitions indicate a strong intramolecular charge transfer from the fluorene to the Ru-NO fragment.

II Figure 2 UV-visible spectra and absorption maxima for FT (left) and [Ru (TF)Cl2(NO)](PF6) (right). The cis(Cl,Cl) isomer is in blue, the trans(Cl,Cl) isomer is in red.

Figure 3 HOMO (bottom) and LUMO (top) frontier orbitals and related charge transfer II + capabilities of FT (left), trans(Cl,Cl)-[Ru (FT)Cl2(NO)] (center), and cis(Cl,Cl)- II + [Ru (FT)Cl2(NO)] (right).

The possibility for NO release has been tested by one-photon absorption (OPA) at 405 nm, for the cis and trans complexes in the presence of the Griess reagent , which leads to the appearance of a pink dye at λ = 520 nm, in the presence of free NO (Figure 4a). The quantum yield of photo-release is equal to 0.10 and 0.05 for the cis and trans derivatives, respectively. More importantly, the TPA induced NO release has been evidenced by irradiation at λ = 810 nm ((Figure 4b).

(a) (b) Figure 4 NO release monitored by Griess test: (a) UV-vis spectra with gradual appearance of pink dye under OPA irradiation at 405 nm; (b) NO release at the focal point under TPA irradiation at 810 nm. Vol. 1 Pag.100

Perspectives

The observation of TPA properties in the [Ru(NO)] complexes encourages the search for systems of enhanced capabilities. While the precise quantification of the molecular TPA parameter (“molecular cross-section” σ) leads to a set of numerous intricate parameters offering no chemical clue to guide the experimentalist, a two-level model, leads to a simplified picture relevant I the case of “push-pull” chromophores [6]:

16 ( ) = (Equation 1) 2 × 2 𝜋𝜋 𝑓𝑓 𝜇𝜇𝑒𝑒𝑒𝑒 − 𝜇𝜇𝑔𝑔𝑔𝑔 𝜎𝜎 2 Within this model, a restricted5ℏ number𝑐𝑐 Γ 𝐸𝐸 of accessible parameters for each g → e transition (intensity f, energy E and change in the dipole moment occurring during the transition µee – µgg) provide knowledge of the potential TPA response of the transition. We have therefore identified the targets shown in Figure 5 with their relative computed σ values.

Figure 5 Evolution of s values from equation 1, on the basis of possible substitutions performed on the FT ligand

References

[1] P.G. Lacroix, I. Malfant, J.A. Real, V. Rodriguez, Eur. J. Inorg. Chem. 2013, 615-627. [2] P.G. Lacroix, I. Malfant, Ch. Lepetit, Coord. Chem. Rev. 2016, 308, 381-394. [3] J. Akl, Ch. Billot, P.G. Lacroix, I. Sasaki, S. Mallet-Ladeira, I. Malfant, R. Arcos-Ramos, M. Romero, N. Farfan, New J. Chem. 2013, 37, 3518-3527. [4] B. Cormary, I. Malfant, M. Buron-Le Cointe, L. Toupet, B. Delley, D. Schaniel, N. Mockus, T. Woike, K. Fejfarova, V. Petricek, M. Dusek, Acta Crystallogr. Sect. B 2009, 65, 612-623. [5] J. Akl, I Sasaki, P.G. Lacroix, I. Malfant, S. Mallet-Ladeira, P. Vicendo, N. Farfán, R. Santillan Dalton Trans. 2014, 45, 12721-12733. [6] F. Terenziani, C. Katan, E. Badaeva, S. Tretiak, M. Blanchard-Desce, Adv. Mater. 2008, 20, 4641-4678.

Aknowledgements CONACyT, CNRS, ECOS-Nord action #M11P01, Campus-France and the French embassy in Kiev. Vol. 1 Pag.101

STUDY OF GRAIN REFINEMENT IN ALUMINUM ALLOYS BY ADDING AL-TI-C AS GRAIN REFINER.

G.A. Lara-Rodríguez*, N. A. Hernández-Zalasar, E-Hernández-Mecinas, O. Novelo-Peralta, I.A-Figueroa. Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Av. Universidad No 3000. Cd. Universitaria. C., A.P. 70-360, 04510 México D.F. México. E-mail: [email protected]

Abstract

In the present work, small addition of nanometric carbon was added in Al- Ti alloys, in order to obtain Al-Ti-0.25 C (in wt%) alloys. The alloys were prepared with an arc melting furnace and heat treated at 900°C for 30 min was carried out in order to produce Ti carbides. The alloy with the TiC was cast using the melt spinning technique in order to obtain melt-spun ribbons (25 m/s). The microstructural characterization was carried out using X, Ray diffraction (XRD), scanning electron microscopy (SEM). The Al-Ti-C was added to 1100 aluminum alloys, with the aim of obtaining grain refinement in cast ingot and then to study its effect over the aluminum-matrix microstructure.

Keywords: Al-Ti-C alloy; Rapid solidification; grain refinement Introductions In the last years, the aluminum-based alloys have been widely studied in order to improve their physical and mechanical properties. The Al-Ti-C compound has been considered as potential grain refinement for aluminum and their possible application as structural materials at high temperature [1-4]. This has been used as a grain refiner of aluminum and magnesium alloys. The Al-Ti-C alloy, exhibit particles of TiC, which are precursors of nucleation during solidification. In the present work, the effect of the addition of nanocarbon on the microstructure Al-Ti -C alloy was studied.

Experimental method A small addition of nanometric carbon was added to the Al-Ti binary alloy, Figure 2(a). The alloy was prepared with an arc melting furnace, and heat treated at 900°C for 30 min. This heat treatment was carried out in order to produce Ti carbides. After this, the alloy with the TiC was cast using the melt spinning technique in order to obtain ribbon shaped samples, Figure 2(b). These ribbons were prepared to investigate the effect of the small addition of nanometric carbon for both samples, i.e. melts spun ribbons and as-cast alloy. The speed of the cooper wheel was 25 m/s and the atmosphere used was argon. The microstructure of the rapidly solidified alloy was examined by means of scanning electron microscopy and X-ray diffraction. The spherical homogenous particles of the refined TiAl3 and TiC were observed within the melt spun ribbons. The as-cast microstructure of the alloy and melt spun ribbons were compared in terms of their size and shape of such TiAl3 and TiC compounds. The raw material used was the commercial aluminum 1100 alloy and 0.5 wt% of Al-Ti-C was added to Vol. 1 Pag.102

the melt. It is worth noting that the alloys were prepared in a graphite crucible using high frequency induction furnace. The molten alloys were finally cast into a cooper mold to produce ingots of 20 mm X 150 mm.

(a) (b) Free surface (c)

TiAl3

TiC α-Al

Contact wheel

Figure 1. a) SEM Micrographs nanometric carbon, b) Rapid solidification technique, c) Cross section melts spun ribbons.

Results and discussion

Figure 2. Shows that the XRD patterns of melt-spun ribbons are composed of the phases: α- Al, TiAl3, and TiC. The SEM microstructures of the Al-Ti-C melt-spun ribbons, Fig. 5, consist of needle shape morphology TiAl3, matrix a-Al and fine particles TiC embedded in α-Al, which is in agreement with the XRD results, Fig 1c.

Figure 2. XRD Melt spun ribbons.

Figure 3, show the macrostructure of melt aluminum 1100 and the alloy with the addition of Al-Ti-C. There, it was observed a columnar structure on pure aluminum cast ingot (Fig. 3a). On the other hand, Figure 3b, displays the macroestructure with small addition of Al-Ti-C. A significant differences have been observed on the microstructure. The microstructural features of the Al–Ti–C additions to master alloys showed a big impact on the grain refining efficiency, for the studied alloys. Vol. 1 Pag.103

(a) (b)

Figure 3. Micrographs of a) As cast pure 1100 aluminum alloys, b) 0.5% wt. Al-5Ti-0.25C grain refinement. From the above, it was also observed that there has been a slight decrement in the grain size. The macro grain size was minimized to some extent with this grain refiner; this is ascribed to concentration gradients in the liquid around the solidifying dendrites, which retard crystal growth. Besides, the release of the heat of fusion allowed the interior of the casting to undercool, forming new crystallites.

(a) (b)

Figure 4. SEM micrographs of microestructure of 1100 aluminium alloys: a) As cast pure 1100 aluminum alloys, b) Added 0.5% wt. Al-5Ti-0.25C grain refinement.

However, a significant decrement on the micro grain size was not observed. Figure 4 a-b shows the dendritic microestucture that was obtained. The grain size refinement was found to be rather poor, this could be attributed to the high amount of TiC particles which tended to agglomerate during the melting procces, leading to a poor nucleation efficiency. The mechanical properties of most cast alloys strongly depended on dendrite arm spacing (DAS). Further refinement may also lead to fine equiaxed structure [5].

Conclusions Al-Ti-0.25C (wt%) alloys do macrograin refine 1100 aluminum alloys. However, a rather poorly grain refinement on microstructure was found. It is possible, that high number of TiC particles agglomerated during the melting stage, leading to poor nucleation efficiency. More research to achieve grain size refining to improve mechanical properties of aluminum alloys Vol. 1 Pag.104

to develop new manufacturing process, like mechanical improvements in porous materials (metal foam) is needed.

Acknowledgements: This work done with the support of the UNAM-DGAPA-PAPIME Program No. PE103416. The authors are grateful to A. Tejeda, J.M. Garcia for the technical support

References [1] Zhonghua Zhang, Xiufang Bian, Zhenqing Wang, Xiangfa Liu, Yan Wang Microstructures and grain refinement performance of rapidly solidified Al–Ti–C master alloys. Journal of Alloys and Compounds 339, (2002), pp 180–188.

[2] P. S. Mohanty and J. E. Gruzleski, Mechanism of Grain refinement in aluminium. Acta metalltater. Vol. 43, No. 5, (1995),pp 2001-2012,.

[3] K. T. Kashyap and T. Chandrashekar, Effects and mechanisms of grain refinement in aluminium alloys, Bull. Mater. Sci. (2001), Vol. 24, No. 4pp. 345–353.

[4] Berker T. Gezer, Fatin Toptan, Sibel Daglilar, Isil Kerti, Production of Al-Ti-C grain refiners whit the addition of elemental carbon. Materials and Design. (2010), Vol 31, S30-S35,

[5] Bondan T. Sofyan, Daniel J. Kharistal, Lukfawan Trijati, Kaspar Purba, Ragil E. Susanto. Grain refinement of AA333 aluminium cast alloy by Al–Ti granulated flux. Materials and Design. (2010), Vol31, S36–S43. Vol. 1 Pag.105

SYNTHESIS AND CHARACTERIZATION OF SILVER NANOPARTICLES USING EICHHORNIA CRASSIPES

Silva-G., Angélica Mariel1, Martínez-G., M. Sonia Mireya1, Rosano-O. Genoveva2, Schabes-R. Pablo Samuel3

1 Instituto Tecnológico de Toluca. 2 Universidad Popular Autónoma del Estado de Puebla A.C. 3 Universidad Nacional Autónoma de México.

INTRODUCTION. In the nanomaterials field, nanoparticles are materials in size between 1- 100 nanometers in diameter. In this size range, these materials offer specific properties or different behaviors from the bulk material due to the number of edges, corners shapes, crystal structure, etc. [1]. The nanoparticles are not compounds with well defined bonds, they are clusters of stabilized atoms to avoid their agglomeration.

Metallic nanoparticles have been synthesized using different chemical, physical and biological methods [2], however, alternative green methods that using plant extracts has emerged as an easy and viable alternative to avoid toxic by-products or expensive production costs [3], furthermore, the plants extracts contain different constitutes like secondary metabolites or phenolic compounds, this last one are used for the biosynthesis of silver nanoparticles [4]. Therefore, in the present study, the synthesis of nanoparticles are using the water hyacinth (Eichhornia crassipes), which is an aquatic invasive plant, as reducing agent for silver nanoparticles in the quantum dots scale in acid condition and different plant section (roots, stems and leaves).

MATERIALS AND METHODS. For the AgNP synthesis, it was selected and collected 2m2 from water hyacinth from Chignahuapan lagoon located in Almoloya del Rio, State of Mexico. The plants were washed with water and separated in roots, stems and leaves and dried at room temperature. The water hyacinth sections were pulverized and washed with hydrochloric acid 0.1 N. For the synthesis, according to [5], 0.125 g of the biomass from each plant section was placed into polyethylene tubes. Subsequently deionized water, buffer solution pH 4 and metallic solution of silver nitrate were added. Between each addition, the tubes were exposed to ultrasonic bath during 15 minutes and centrifuged for 30 minutes. Finally, the biomass was separated from the solution by filtration. The silver nanoparticles formation was confirmed by UV-Vis spectroscopy at 200-800 nanometers and they were characterized by transmission electron microscopy (TEM) and high resolution (HRTEM).

RESULTS. In the synthesis, the plant solution was yellow-green color; however after addition of silver nitrate, the color was changed to brown. The formation of silver nanoparticles in aqueous solution was confirmed using UV-Vis spectroscopy (Figure 1). The analysis was shown an absorbance peak around 430 nanometers, which is the characteristic surface plasmon resonance for silver nanoparticles. Vol. 1 Pag.106

roots stems leaves Absorbance units

250 300 350 400 450 500 550 Wavelength (nm)

Figure 1. UV-Vis spectra of AgNP synthesized

With transmission electron microscopy, the silver nanoparticles images were analyzed in order to determine the shape, size distribution, structure and composition. With the leaves samples, were formed two different shapes: cuboctahedron and icosahedron (Figure 2)

m 5 nm Figure 2 HRTEM of a silver nanoparticles with a) cuboctahedron and b) icosahedron shapes. In the size distribution it was observed nanoparticles of 7.78 nanometers in diameter and 88.9% of total particles were in the quantum dots scale.

200

150

Frequency 100

50

0 5 10 20 30 40 50 60 Diameter (nm) Figure 3. AgNP leaves synthesized : a) micrography and b) size distribution.

With the interplanar spaces obtained from the Fourier Transform analysis, it was found only an silver oxide phase with two bravais lattice: hexagonal and triclinic (Figure 4).

a) (204) b) (121) 50° 105° 80° 25° (202) a) 50° 50° (004) (202) b)

2 nm

5 nm

Figure 4. FFT patrons of HRTEM in leaves samples of AgO structure and a) hexagonal and b) triclinic bravais lattice.

In the nanoparticles prepared with stems, the micrographs with HRTEM showed a cuboctahedron and cubic morphology. In the suspension the nanoparticles were stabilized without aggregation, with a mean of 13.9 nanometers. The silver nanoparticles does not Vol. 1 Pag.107

show a uniform diameter, however, the production of silver nanoparticles smaller than 20 nanometers was predominantly, but the quantum dots obtained were lower than leaves. According to the International tables for Crystallography, the particles were in silver oxide form with cubic and trigonal structure

In the synthesized nanoparticles using roots, icosahedral and cubic truncated shapes were identified. In the micrographs showed in the Figure 9, it was observed the 51.7% of the synthesized nanoparticles were in the quantum dots scale and their size distribution was consistent with the stems samples. Also, the nanoparticles were in AgO form with crystal systems hexagonal and triclinic.

DISCUSSION.

In this work the most important challenge was the study of the plant section influence, and it was observed under actual experimental conditions, with a real influence in the synthesized nanoparticles due to the plant section. With all sections were produced silver nanoparticles in quantum dots, but the higher percent was obtained using water hyacinth leaves with 88.9%, while using stems and roots in the synthesis, their size distribution was similar with high production of particles between 20 to 60 nanometers in diameter.

In UV-Vis spectroscopy, the most important change was in the nanoparticles synthesized with stems, and it has been associated with the highest production of particles between 20- 60 nm in comparison with roots and leaves, and as the diameter increases, the peak associated with the surface Plasmon resonance becomes more defined.

The change of color in the solutions was not immediately in some of them as occurs in the biosynthesis using pH in a basic scale. This condition has been associated with the pH influence during synthesis. With acid pH, an increase in the protons concentration occurs, and it reduces the oxidizing ability to replace electrons, increasing the particle size due the small particles collision.

On the other hand, the high resolution transmission electron microscopy analysis showed the single chemical form in the silver nanoparticles synthesized was silver oxide and the nanoparticles phase does not dependent from the water hyacinth section used during the biosynthesis process.

CONCLUSION.

The section used of water hyacinth in the biosynthesis of silver nanoparticles has not shown a real influence in the particles diameter. The smallest particles were founded while the green sections were used, and this may suggest that in these sections, the production of secondary metabolites increase as a mechanism of defense and adaptation to the environment.

The transmission electron microscopy and high resolution analysis showed silver nanoparticles in quantum dots as silver oxide phase, and the shape and structure were not dependent of the water hyacinth section. Vol. 1 Pag.108

References

[1] Gaillet S. & Rouanet J. (2015). “Silver nanoparticles: Their potential toxic effects after oral exposure and underlying mechanism”. Food and Chemical Toxicology, No. 77, pp. 58-63.

[2] Silva-de-Hoyos L., Sánchez V., Rico A., Vilchis A., Camacho M. y Avalos M. (2012). “Silver nanoparticles biosynthesized using Opuntia ficus aqueous extract” Superficies y Vacío, Vol. 25, No. 1, pp. 31-35.

[3] Rehab M. & Abuelmagd M. (2014). “Rapid Green Synthesis of Metal Nanoparticles using Pomegranate Polyphenols”. International Journal of sciences: Basic and Applied Research, Vol. 15, No. 1, pp. 57-65.

[4] Prusty A. & Parida P. (2014). “Green synthesis of Silver Nanoparticle Using Eichhornia and Study of in-vitro Antimicrobial Activity”. Scholars Academic Journal of Pharmacy, Vol. 3, No. 6, pp. 504-509.

[5] Rosano-Ortega G. (2009). “Síntesis de nanopartículas metálicas mediante un proceso autosustentado”. Tesis Doctoral, Facultad de Química, Universidad Autónoma del Estado de México. Vol. 1 Pag.109

PHOTOLUMINESCENCE AND STRUCTURE TREND IN MIXTURE OF ZNO AND CARBON NANOPARTICLES DURING MECHANICAL ACTIVATION

E. Velázquez Lozada1, T. Torchynska2, M. Kakazey3, M. Vlasova3

1SEPI – ESIME – Instituto Politécnico Nacional, Ciudad de México, [email protected] 2ESFM – Instituto Politécnico Nacional, México D. F. MEXICO 3CIICAp-Universidad Autónoma del Estado de Morelos, Cuernavaca, MEXICO

Introduction ZnO nanocrystals (NCs) with the native defects or different type dopants are the one of most popular new systems (1). ZnO NCs with a direct band gap (3.37 eV) and a high exciton binding energy (60 meV) at 300K promises numerous applications in optical and electronic devices (1, 2), such as: catalytic materials (3), solar cells (4), field emission cathodes (5, 6), luminescent materials (7) etc. Important electronic properties have been revealed in the nanocrystalline composites ZnO + xC recently, which permit improving the field emission properties of cathodes (5), engineering room-temperature ferromagnetism (8), modify luminescence properties (9), and to create the selective solar absorbed coatings (10). The creation of efficient electronic devices requires studying the emission nature and the mechanisms of defect generation in ZnO NCs. In present paper the transformation of photoluminescence (PL) and its temperature dependences have been investigated for the mixture of ZnO + 1.0% C NCs with the goal to study the nature of PL bands, the PL quenching mechanism, the radiative defect nature and the process of defect creation at mechanical processing (MP).

Experimental details ZnO NCs (99.5 % purity, Reasol; with the particle size of dZnO ~ 250 nm) and carbon nanoparticles (EPRUI Nanoparticles & Microspheres Co. Ltd.) were mixed. High resolution TEM images (performed earlier) have shown that the carbon nanoparticles are characterized by a spherical-like shape with an average diameter of dC ~ 50 nm. Mechanical processing (MP) of ZnO + xC mixtures with x = 1.0 % wt. was carried out in a Planetary Ball-Mill (PM 400/2, Retsch Inc.). The grinding chamber of 50 ml with the tungsten carbide balls (3 of 20 mm and 10 of 10 mm) were used. The weight ratio of balls to mixture powder equal to 28:1 has been used. MP was carried out with the rotation speed 400 rev/min for processing times (tMP) of: 1, 3, 9, 30, 90 and 390 min. The early X ray diffraction study has shown that the average ZnO NC sizes, estimated using Sherrer formula (11), decreases from 250 nm in an initial state down to 14 nm for tMP = 390 min. PL spectra were measured at 300K and the excitation by a He-Cd laser with a wavelength of 325 nm and a beam power of 46 mW using a PL setup on a base of spectrometer SPEX500 described in (12,13) in the temperature range of 10-300K. Vol. 1 Pag.110

Experimental results and discussion PL spectra of the ZnO + 1% C mixture at 300 K measured for the different MP times are shown in figure 1.

Figure 1. PL spectra of ZnO+1% C NCs at different moments of MP: (a) 1-1min, 2-3min, (b) 1-3min, 2-9min, 3-90min, 4-390min. It is clear that PL spectra are complex and can be represented as a set of PL bands. The PL spectrum measured after 1 min of MP can be decomposed on three PL bands with the peaks at: 3.14 eV (I), 2.42-2.50 eV (II) and 1.57 eV (III) (Fig.1a, curve 1). The UV and visible PL bands in ZnO NCs are attributed to the near-band-edge (NBE) (I) and defect related (II) emissions (14-18). NBE emission in ZnO NCs, as a rule, is related to the free or defect bound excitons with their phonon replicas, and/or the donor-acceptor pairs (14,15). It was shown earlier in (16,17) that free exciton emission or its replicas dominate in ZnO NC spectra at room temperature owing to the high free exciton binding energy (60 meV) at 300K and the fast decay of the PL intensities of bound exciton and donor-accepter pair emissions with increasing temperature in the range of 10-300K. Thus the high PL intensity and a small half width of 3.14 eV PL band in PL spectra of the ZnO + 1% C mixture at 300K permit assigning NBE emission to the LO phonon replicas of free exciton emission in ZnO NCs. The nature of IR PL band peaked at 1.57 eV (III) is not clear. Note that in our experiments (presented below) this PL band intensity varies by the same way as the PL intensity of 3.14 eV PL band. Thus we can attribute the IR PL band at 1.57 eV (III) to the second order diffraction peak of the 3.14 eV PL band (15-18). The PL intensity mentioned above PL bands decreases dramatically at MP and the new PL bands with peaks at 2.84 -2.95 eV, 2.10-2.20 eV and 1.42-1.47 eV appeared (Fig. 1b). The variation kinetics of the integrated PL intensities for all PL bands at MP are presented in figure 2. As it is clear there are two stages in this kinetics depending on the duration of MP process. Vol. 1 Pag.111

Figure 2. The variation of integrated PL intensities versus MP times for the PL bands:1 -3.14 eV, 2- 1.57 eV, 3-2.42 eV, 4-2.11 eV, 5-2.84 eV, 6-1.42 eV.

First stage. The PL intensity decreases upon the first MP stage (1-9 min) with nearly the same rates for the NBE and defect related PL bands. This effect can be assigned to the generation of non-radiative recombination centers (NR) at MP. The PL intensity is proportional to the quantum efficiency (η) of visible recombination (19). The increase of NR center concentrations stimulates the rise of NR recombination rate together with falling down the PL intensity at MP. Linear dependences of the PL intensity decay for the stage I, presented in logarithmic scales (Fig. 2), testify on the hyperbolic PL intensity variation versus time. Note that NR centers can be assigned to the dangling bonds on the surface of ZnO NCs created at crushing the individual ZnO nanoparticles at MP. Simultaneously, in the first MP stage the peak of defect related PL band (II) shifts to 2.11-2.25 eV and the new PL bands peaked at 2.84-2.95eV and 1.42-1.47 eV appear (Figures 1b). Second stage. The new PL bands with the peaks at 2.11-2.25 eV, 2.84-2.95 eV and 1.42- 1.47 eV dominate in the PL spectra of all samples after 9 min of MP (Figures 1b).The defects, responsible for the 2.11-2.25 eV PL band, can exist in the original ZnO NCs or their concentration can increase at MP as well. The IR PL band peaked at 1.42-1.47 eV is attributed to the second order diffraction peak of 2.84-2.95 eV PL band. The high energy PL band is characterized by the peak at 2.84-2.95 eV in the different samples of ZnO+1%C NC mixture.

Conclusion

The transformations of PL spectra and XRD diagrams in the ZnO NCs + 1%C mixture at mechanical processing have been investigated. Two stages of PL spectrum transformation have been revealed and discussed. It is shown that the first stage is connected with the quenching of PL intensities of all PL bands owing to the nonradiative center appearing at crushing the individual ZnO NCs and decreasing their sizes from 250 nm down to 14nm. The second stage of PL spectrum transformation at MP is connected with appearing the new 2.84-2.95 eV and 2.11-2.25 eV PL bands. Vol. 1 Pag.112

References [1] Zinc Oxide: Fundamentals, Materials and Device Technology. Hadis Morkoç and Ümit Özgur, 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [2] Ü . Özgür, Ya I Alivov, C. Liu, A. Teke, M A Reshchikov, S Doğan, V Avrutin, H Cho S-J, Morkoç J Appl Phys 98, 041301 (2005). [3] R Gurwitz , R Cohen, I Shalish: J Appl Phys 115, 033701 (2014). [4] Z Fan, J G Lu: J Nanosci Nanotechnol 5, 1561 (2005). [5] N Pan, H Xue, M Yu, X Cui, X Wang, J G Hou, J Huang: Nanotechnology 21, 225707 (2010). [6] Won Il Park, Jin Suk Kim, Gyu-Chul Yi, M. H. Bae and H.-J. Lee , Appl. Phys. Lett. 85, 5052 (2004). [7] M.A. Reshchikov,_, H. Morkoc, B. Nemeth, J. Nause, J. Xie, B. Hertog, A. Osinsky Physica B 401–402, 358 (2007). [8] H S Hsu, Y Tung, Y J Chen, M G Chen, J S Lee, S J Sun: phys status solidi (RRL) 5, 447 (2011). [9] Y Hu, H-J Chen: J Appl Phys 101, 124902 (2007). [10] G Katumba, L Olumekor, A Forbes, G Makiwa, B Mwakikunga: Sol Energy Mater Sol Cells 92, 1285 (2008). [11] H.P. Klug, L.E. Alexander, X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials, Wiley and Sons, NewYork, 1974. [12] T. V. Torchynska, M. Dybiec, S. Ostapenko, Phys. Rev. B. 72, 195341 (2005). [13] N. Korsunska, L. Khomenkova, M. K. Sheinkman, T. Stara, V. Yuhimchuk, T. V. Torchynska, A. Vivas Hernandez, J. Lumines., 115, 117 (2005). [14] A.B. Djurišic, A.M.C. Ng, X.Y. Chen. Progress in Quantum Electronics 34. 191 (2010). [15] T. V. Torchynska and B. El Filali, J. of Lumines. 149, 54 (2014). [16] A.I. Diaz Cano, B. El Filali, T.V. Torchynska, J.L. Casas Espinola, Physica E, 51, 24 (2013). [17] E. Velázquez Lozada, T.V. Torchynska, J. L. Casas Espinola, B. Perez Millan and L. Castañeda, Physica B, 453, 111 (2014), [18] A.I. Diaz Cano, B. El Falali, T.V. Torchynska, J.L. Casas Espinola, J. Phys. Chem. Solids,74, 431 (2013). [19] T.V. Torchynska, Physica E, 44, 56 (2011). Vol. 1 Pag.113

ALUMINUM CONCENTRATION AND SUBSTRATE TEMPERATURE ON THE PHYSICAL CHARACTERISTICS OF CHEMICAL SPRAYED ZNO:AL THIN SOLID FILMS

E. Velázquez Lozada1, L. Castañeda2, G. M. Camacho González3

1SEPI – ESIME – Instituto Politécnico Nacional, Ciudad de México, [email protected] 2ESIME – Instituto Politécnico Nacional, Ciudad de México. MEXICO 3ESIME – Instituto Politécnico Nacional, México D. F. 07738, México

Abstract Chemically sprayed aluminium-doped zinc oxide thin films (ZnO:Al) were deposited on soda- lime glass substrates starting from zinc pentanedionate and aluminium pentanedionate. The influence of both the dopant concentration in the starting solution and the substrate temperature on the composition, morphology, and transport properties of the ZnO:Al thin films were studied. The structure of all the ZnO:Al thin films was polycrystalline, and variation in the preferential growth with the aluminium content in the solution was observed: from an initial (002) growth in films with low Al content, switching to a predominance of (101) planes for heavily dopant regime. The crystallite size was found to decrease with doping concentration and range from 33 to 20 nm. First-order Raman scattering from ZnO:Al, all 4 C6v having the wurtzite structure . The assignments of the E2 mode in ZnO:Al differ from previous investigations. The film composition and the dopant concentration were determined by Auger Electron Spectroscopy (AES); these results showed that the films are almost stoichiometric ZnO. The optimum deposition conditions leading to conductive and transparent ZnO:Al thin films were also found. In this way a resistivity of 0.03 Ω-cm with a (002) preferential growth, were obtained in optimized ZnO:Al thin films.

Experimental details ZnO thin solid films were synthesized by the ultrasonic spray pyrolysis technique. The chemical preparation started from zinc acetate dehydrated (Zn(CH3CO2)2 , Sigma Aldrich 99.99 %) dissolved in 50 mL of acetic acid ([CH3CO2H] from Baker, 98%) to obtain a concentration of 2 M solution. Then, the aforesaid solution was dissolved with certain amounts of methanol ([CH3OH] from Baker, 98%) and deionized water to adjust the final concentration of the precursor to 0.1 M. The volume fraction of water in the solution was varied in the following way: 0.01, 0.05 and 0.15. In order to get the complete dissolution of the components, the solution was stirred for 20 minutes prior to spraying process. Alumina (Al2O3) substrates were cleaned prior to deposition. The cleaning process of the substrates is as follows: (i) sonication for five minutes in Extran® - Formaldehyde-free AP 33 (from Merck Millipore); followed by (ii) sonication for five minutes in trichloroethylene ([C2HCl3], J.T. Baker, 98 %) for degreasing the substrates; then (iii) sonication in methyl alcohol ([CH3OH], Aldrich, 98 %); (iv) sonication in acetone ([CH3COCH3], J.T. Baker, 98 %); and finally, (v) the substrates are dried under a flow of dry pure nitrogen (N2, PRAXAIR, 99.997 %). Vol. 1 Pag.114

Prior to deposition, interdigitated electrodes were deposited on the alumina substrates, by vacuum thermal evaporation of gold (wire, 0.5 mm diam., 99.99% Aldrich) through a metallic mask. A separation between the electrodes fingers of approximately 1.1 mm, with a thickness of 1.5 μm, was kept in order to get a maximum specific area (surface area/volume ratio), as shown on Figure 1. Afterwards, using ultrasonic spray pyrolysis, ZnO thin solid films were deposited through a stainless steel mask on the interdigitated electrodes.

Fig. 1 Schematic representation of the interdigitated electrodes that were deposited on the alumina substrates. Substrates were prepared by vacuum thermal evaporation of gold (scale in cm).

Then, for the deposition process, the substrates were placed on a molten tin bath. The cleaned substrate was preheated to 400ºC; this temperature was measured just below the substrate using a stainless steel jacket chromel-alumel thermocouple within an accuracy of ±1 °C. During deposition, pure N2 (from PRAXAIR, 99.997 %) was used as the precursor solution carrier and director gas, with flow rates of 3.5 and 0.5 L/min, respectively. The deposition system used in this work is equipped with a variable frequency piezoelectric transducer, which was set to 1.4 MHz and operated at 120 W. In the ultrasonic spray pyrolysis system, micrometric droplets are formed by the action of a beam of ultrasonic vibrations coming from the atomizer. The carrier gas transports and directs the formed spray droplets toward the surface of a hot substrate wherein the film growth takes place. By following these experimental conditions, the starting solutions were sprayed with a solution flow rate of 1 mL/min over the hot substrates. The experimental setup used for the fabrication of the samples in this work is schematically presented in Figure 2. Vol. 1 Pag.115

Fig.2 Experimental growth diagram.

References [1] K. Hyo-Joong, L. Jong-Heun: Sensor Actuat B-Chem.192( 2014) 607. [2] G. F. Fine, L. M. Cavanagh, A. Afonja and R. Binions: Sensors 10 (2010) 5469. [ 3] A. Wei, L. Pan, W. Huang: Mat. Sci. Eng. B-Solid. 176 [18] (2011) 1409. [4] A. Gonçalves, A. Pimentel, P. Barquinha, G. Gonçalves, L. Pereira, I. Ferreira, R. Martins: Appl. Phys A. 96 (2009) 197. [5] B. Fabbri, A. Gaiardo, A. Giberti, V. Guidi, C. Malagù, A. Martucci, M. Sturaro, G. Zonta, S. Gherardi, P. Bernardoni: Sensor Actuat B- Chem. ( 2015). [6] A. Forleo, L. Francioso, S. Capone , P. Siciliano, P. Lommens, Z. Hens: Sensor Actuat B-Chem. 146 ( 2010) 111. [7] Y. Wang, H. L. Wang, C.-Q. Liu, Y. Wang, S. Peng, W. P. Chai: Mater. Sci. Semicon. Proc. 15 (2012) 555. [8] O. D. Jayakumar and A. K. Tyagi: Int. J. Nanotechnol. 7 (2010) 1047. [9] M.A. Boukadhaba, A. Fouzri, V. Sallet, S.S. Hassani, G. Amiri, A. Lusson, M. Oumezzine: Superlattice Microst. 85 ( 2015) 820. [10] N.H. Sheeba, Sunil C. Vattappalam, J. Naduvath, P.V. Sreenivasand, M. Sunny, R. R. Philip: Chem. Phys. Lett. 635 (2015) 290. Vol. 1 Pag.116

TiO2 NANOPARTICLES SENSITIZED WITH MICROWAVE-AFFORDED Ru(II) COMPLEXES TO INVESTIGATE THE PHOTOPHYSICAL RESPONSE OF ANTENNA-COMPLEXES IN DSSC SOLAR CELLS

Jorge S. Gancheff1, Karolina Soca1, Florencia Luzardo1, Raúl Chiozzone1, Pablo A. Denis2, Paula Enciso3, M. Fernanda Cerdá3, Reza Dousti4, Andrea S. S. de Camargo4

1Cátedra de Química Inorgánica, Departamento Estrella Campos, Universidad de la República, Av. Gral Flores 2124, 11800 Montevideo, URUGUAY. E-mail: [email protected] 2Computational Nanotechnology, DETEMA, Universidad de la República, Montevideo, URUGUAY 3Laboratorio de Biomateriales, Facultad de Ciencias, Universidad de la República, Montevideo, URUGUAY 4São Carlos Physics Institute, University of São Paulo, São Carlos, SP 13566-590, Brazil

Abstract. The technology of converting sunlight into electricity has recently emerged as an important strategy aimed at achieving a sustainable diversification of the energy matrix in Uruguay and other South American countries. In this regard, photovoltaic devices appear quite attractive because they are noiseless, present no carbon dioxide emission, and require rather simple operation and maintenance, those of solid-state junction —usually made of silicon— being the most important ones. This technology, which is associated with important costs, has been challenged in the last few years by the development of a third-generation solar cells based on conducting polymers films and nanocrystalline oxides. The so-called dye- sensitized solar cells (DSSC) appear as a representative prototype of this family of photovoltaic devices. They combine the optical absorption and the charge separation processes by association of a sensitizer —as the light-absorbing material— with a wide band- gap semiconductor of nanocrystalline morphology.

Herein, photophysical investigations of a Ru(II) novel complex (synthetized by eco-friendly methods) of potential application as antenna in DSSC are presented. The studies cover the response of the isolated complex in the solid state and in solution. In order to have a clear picture of the influence of the sensitization process on the photophysical properties of complexes, absorption/photoluminescence studies of TiO2 (anatase) nanoparticles —also prepared by microwave-assisted reactions— sensitized with the Ru(II) complex are also included. To get deeper insight into the electronic features of all systems, DFT calculations at the B3LYP/LANL2DZ level of theory have also been conducted.

Vol. 1 Pag.117

The technology of converting sunlight into electricity has witnessed an enormous growth in the last few years. Solar cells have been used in different applications ranging from small consumer electronics to megawatt-scale power plants [1]. Direct use of solar radiation to produce electricity is perceived as an almost ideal way to employ nature´s renewable energy. Despite the significant development over the past decades, the high cost of solar cells remains a limiting factor for the massive implementation of solar electricity on a larger scale [2]. In contrast to conventional silicon- based semiconductor solar cells, the dye-sensitized solar cell (DSSC) technology, which comprises a photochemical solar cell, has emerged as an important alternative in the last few years. Since then, many scientists have focused on the development of new and most efficient dyes. One of the most important concerns with the synthesis of dyes for DSSCs is the use of harmful organic solvents. A solution to this drawback has been proposed by introducing a microwave-based synthetic approach employing eco-friendly solvents.

Herein, we present the synthesis and a spectroscopic investigation of a new Ru(II) complex of potential application in DSSC prepared by microwave-assisted reactions in water as a benign solvent. Then, TiO2 (anatase) nanoparticles, also synthetized by microwave irradiation, were sensitized with the Ru(II) complex to study the photophysical behavior of dyes in DSSC conditions. Theoretical (DFT and TD-DFT) calculations have also been performed to shed light into different electronic aspects of the isolated and the attached dye.

The reaction path used to prepare the new Ru(II) complex involved the use of [RuCl2(p-cymene)2]2 and cis-[RuCl2(dcbipy)2] as precursor. The microwave-assisted synthetic strategy employed to obtain [RuCl2(p-cymene)2]2 and cis-[RuCl2(dcbipy)2] allowed us to reproduce the results of Tönnenmann et al. [3], and Kristensen et al. [4], respectively. At the same time, it prompted us to implement the abovementioned strategy as a routine synthetic tool in our Inorganic Chemistry laboratory. Thus, we decide to prepared a new Ru(II) complex —potential antenna in DSSC— by using MW irradiation in water. The combination of cis-[RuCl2(dcbipy)2] and isonicotinic acid in inert atmosphere, led to the formation of cis-[Ru(dcbipy)2(ina)2]Cl2 (Ru-ina; Scheme 1). When the reaction proceeded in an oxidative atmosphere, we detected signals of metal oxidation (UV–VIS). The formation of the cis isomer was ensured by the use of a temperature above 170 °C, as stated by Kristensen et al. in preparing cis-[Ru(NCS)2(dcbipy)2] using MW tools [3].

Scheme 1. Microwave-assisted synthesis of Ru(II) complexes.

The Ru-ina complex was characterized by FT–IR and absorption/ photoluminescence spectroscopies. – The vibrational data show the asymmetric/symmetric bands for the carboxylic groups –CO2 at 1731, 1607, 1542, 1385 cm–1, and the characteristic pyridyl unit at 1385 cm–1. Two absorption bands were detected in the visible region centered at 489 nm (asymmetric band) and at 369 nm, both of them exhibiting almost equal intensity. Emission studies —exciting the complex with light of wavelength of 500 nm— lead to a band peaked at 550 nm. This result is in line with the behavior of the well-known and so-called N3-sensitizer (cis-[Ru(NCS)2(dcbipy)2]), which was taken (in this work) as a model. In this case, an emission band centered at 545 nm (exc = 480 nm) was observed. It is worth highlighting Vol. 1 Pag.118

that N3 was prepared by microwave irradiation (Scheme 1) according to the one made available by Kristensen et al. [4].

The microwave-assisted technique was also applied to prepare TiO2 nanoparticles (anatase) according to the protocol of Moura et al. [5], which were sensitized with the N3-model complex and with the new Ru(II)-complex. This process was accomplished by immersing the white nanoparticles in an ethanolic solution of the complex during 24 h in the absence of light. Pink nanoparticles were obtained, which indeed remained colored even after several washes with ethanol. This observation points to a covalent anchoring of the dye to the semiconductor. This result is not surprising since carboxylic groups are one of the most employed and effective anchoring groups of dyes in DSSC [6,7].

Luminescence investigations of the sensitized nanoparticles with the model dye (system N3@TiO2) revealed the presence of an absorption band at 530 nm, red-shifted (+30 nm) with respect to the free-complex. This result is in line, for instance, with the shift exhibited by N3 sensitizing Bi4Ti3O12 nanoparticles [8]. At the same time, the luminescence measurements show an emission band at 541 nm (exc = 500 nm), slightly blue-shifted (–4 nm) with respect to the free-dye. When the sensitization process involves Ru-ina, similar findings were obtained. The UV–VIS spectrum of (Ru-ina)@TiO2 (Fig. 1) exhibits two absorption bands a 315 nm and 502 nm, the last one being measured +13 nm with respect to the isolated dye.

– – – DFT and TD-DFT calculations were performed for cis-[RuX2(dcbipy)2] (X = NCS , Cl ) and for cis- 2+ [Ru(dcbipy)2(ina)2] [9]. In particular, TD-DFT emission calculations in the presence of EtOH as solvent have been carried out for cis-[Ru(Cl)2(dcbipy)2] [9]. This complex was used as an example to test the reliability of the theoretical tool in reproducing emission data and in doing that, to implement this theoretical tool in our Theoretical Chemistry Laboratory. While emission bands at 440 nm (exc of 340 nm) and at 540 nm (exc of 480 nm) have been experimentally detected for an ethanolic solution of cis-[Ru(Cl)2(dcbipy)2], two bands at 478 nm (exc of 396 nm) and at 527 nm (exc of 456 nm) have been calculated with B3LYP/LANL2DZ/C-PCM. These results evidenced that this simple methodology is reliable enough to study different electronic aspects of dyes —potential antenna in DSSC—, with a reasonable computational cost.

For Ru-ina, TD-DFT absorption data (Fig. 1) are available; no emission theoretical results were obtained so far. The simulated UV–VIS spectrum [9] in ethanol was in reasonable agreement with the experimental evidence. The excitations responsible for the band in the visible region involve starting MOs of mainly metallic character, while destination MOs are located on ligands (dcbipy and ina) (Fig. 1). These results helped us to infer the origin of the band experimentally observed at 502 nm for (Ru- ina)@TiO2 as metal-to-ligand charge transfer (MLCT). The band in the high-energy part of the spectrum (315 nm) seems to present the same origin (MLCT), with the electronic density moving from a metal-centered MO to a MO mainly located on the bipyridyl unit of the dcbipy anchoring ligands. It is worth mentioning that the sensitization process promoted an increase of the intensity of this band with respect to this band in the free-complex. As aforementioned, the contour of destination MO in the MLCT band at 315 nm displays charge delocalization on the bipyridyl unit of the dcbipy ligands. This finding suggests that the carboxyl groups, which act as a linkage group, are the ones located on the dcbipy ligands and not those of the ina ligand. To confirm this assumption, theoretical investigations of different electronic aspects of the Ru-ina@TiO2 system at the DFT level of theory are undertaken.

In conclusion, the microwave-assisted tool has been successfully employed in yielding model Ru(II) antenna-complexes in DSSC. At the same time, it has proven to be adequate and eco-friendly to prepare new Ru(II) compounds. In this line, the complex cis-[Ru(dcbipy)2(ina)2]Cl2 has been obtained and characterized. It has been used to sensitize the surface of TiO2 (anatase) nanoparticles, which have also been afforded by microwave techniques. Luminescence studies of the new Ru(II) complex Vol. 1 Pag.119

lead to results in line with the ones obtained for model complexes, which point out that the new complex present potential application as antenna in DSSC. The sensitization of the semiconductor surface does not significantly change the photophysical features of the attached dye. With assistance of theoretical (DFT) calculations, the sensitization of nanoparticles could be a reasonable model to study different electronic aspects of dyes in DSSC operative conditions.

Figure 1. TD-DFT result of (Ru-ina) (dashed line), and experimental UV–VIS spectrum of Ru-ina@TiO2 (solid line). Most important MOs involved in the origin of the simulated bands for Ru-ina are also included.

References [1] F. Dinçer; Renewable Sustainable Energy Rev. 2011, 15, 713. [2] B. Oregan, M. Grätzel; Nature 1991, 353, 737. [3] J. Tönnenmann, J. Risse, Z. Grote, R. Scopellitu, K. Severin; Eur. J . Inorg. Chem. 2013, 4558. [4] S. H. Kristensen, J. Toster, K. S. Iyer, C. L. Raston; New J. Chem. 2011, 35, 2752. [5] K. F. Moura, J. Maul, A. R. Albuquerque, G. P. Casali, E. Longo, D. Keyson, A. G. Souza, J. R. Sambrano, I. M G. Santos; J. Solid. St. Chem. 2014, 210, 171. [6] L. Zhang, J. M. Cole; ACS Appl. Mater. Interfaces 2015, 7, 3427. [7] A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson; Chem. Rev. 2010, 110, 6595. [8] Z. Chen, S. Li, W. Zhang, Int. J. Photoenergy 2011, 1155. [9] a) Geometry optimizations were performed at B3LYP/LANL2DZ level of theory. The nature of the stationary point was verified through a vibrational analysis (no imaginary frequencies at the minimum). The Time- Dependent DFT (TD-DFT) methodology was employed to calculate one hundred spin-allowed transitions in the gas phase and in the presence of the solvent (EtOH). The excitations responsible for the absorption bands were taken as exc in emission calculations, which were also conducted in the presence of the solvent. All effects of solvent were described by the conductor-like polarizable continuum model (C-PCM) [9b,c]. While all calculations have been conducted by using Gaussian09 (Rev. D.01) [6d], electronic UV-VIS spectra were simulated by means of the GausSum software [6e]; b) V. Barone M. Cossi; J. Phys. Chem. A 1998, 102, 1995; c) M. Cossi, N. Rega, G. Scalmani, V. Barone; J. Comput. Chem. 2003, 24, 669; d) M. J. Frisch et al. Gaussian Inc., Wallingford CT, 2009; e) N. M. O´Boyle, A. L. Tenderholt, K. M. Langner; J. Comp. Chem. 2008, 29, 839.

Acknowledgements

This work was supported by Agencia Nacional de Investigación e Innovación (ANII, Proy. FSE_1_2011_1_6156). We are also indebted to PEDECIBA-Química. A.S.S.C. would like to thank FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil) for the financial support (Cepid Project 2013/07793-6). Vol. 1 Pag.120

CCC-NHC Tantalum Bis(imido) Reactivity: Protonation or Rearrangement to a Mixed, Unsymmetrical CCC-N-Heterocylic Carbene/N-Heterocyclic Dicarbene (CCC-NHC-NHDC) Pincer Tantalum Bis(imido) Complex

T. Keith Hollis*1, T. Keith Hollis*1Theodore R. Helgert 1,2, Charles Edwin Webster1, Henry U. Valle,1,2 Allen G. Oliver3

1Department of Chemistry, Box 9573, Mississippi State University, Mississippi State, Mississippi 39762-9573, United States, [email protected] 2Department of Chemistry and Biochemistry, The University of Mississippi, University, MS 38677, United States 3Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States

Abstract: The coordination sphere of the reported (1,3-bis(3-butylimidazol-1-yl-2- idene)-2-phenylene) (tert-butylimido) CCC-NHC Ta (V) bis(imido) pincer complex 1 (Helgert, et. al. Organometallics, 2016, DOI: 10.1021/acs.organomet.6b00216) has been has been observed to spontaneously rearrange to yield X-ray quality crystals of a CCC- NHDC/NHC pincer Ta (V) bis(imido) complex (2). Over time CCC-NHC Ta (V) bis(imido) pincer complex 2 reacts with adventitious protons sources to form (BuCiCiCBu)Ta(V)(tert-butylamido)(tert-butylimido)iodo complex (4).

Introduction

The seminal work of Bertrand and Arduengo has shown that carbenes are not the transient intermediates chemists once believed, [1] but persistent and isolable carbon species. In particular, N-heterocyclic carbenes (NHCs) have become ever-present in late-transition-metal chemistry,[2] yet the study of early-transition-metal NHCs is still in its infancy.[1c] In particular, Ta NHC complexes are rare. Only eight Ta NHC complexes have been reported to date.[3] Due to the popularity of NHCs as ancillary ligands for new metal complexes, studies into NHC variants have become a new and expanding field of research.[4] One noteworthy NHC derivative is the imidazole-base-NHC bound to a metal via the backbone C-4 or C-5 carbons, known as a mesoionic carbene (MIC) or abnormal carbene. Crabtree reported the first MIC complex in 2001,[5] and the first free MIC was reported by Bertrand in 2009.[6] MICs/abnormal carbenes are interesting since they are better σ-donors than their C-2 bound NHC equivalents. The increased σ-donor ability is due to the presence of only one adjacent heteroatom, which decreases the inductive effect on the carbene.[7] Robinson has further expanded alternative binding by imidazole-based-NHCs with his recent report of imidazole ring containing simultaneous carbene centers at the C-2 and C-4 (or C-5) positions, known as the anionic N- heterocyclic dicarbene (NHDC).[8] Current research on NHDCs is primarily focused on mid-to-late-transition-metals NHDC complexes and the reaction of NHDCs with Vol. 1 Pag.121

small molecules such as BH3, CO2, SiCl4.[9] To date, only one report of early-transition- metal Sm and Y NHDC complexes, by Arnold, is found in the literature.[10] Chart 1. Imidazole based N-heterocyclic carbenes (Arduengo), meso-ionic carbenes or abnormal-N-heterocyclic carbenes (Bertrand), and Anionic N-heterocyclic dicarbenes (Robinson).

The pincer ligand architecture is a favorite motif for ligand design that has been research intensely since it was first reported in the 1970’s. This architecture offers a facile alteration of the metal center by modification of the donor groups prior to the synthesis of the complex. Manipulation of the pincer ligand after complexation has been reported and is often the deprotonation of a spacer group between donors.[11] Incorporation of NHC’s in pincer ligands has been of increasing interest and is an efficient route to synthesize stable early- transition-metal NHC complexes.[3a, 3c, 12] Pincer ligands containing NHDCs, nor the rearrangement of an NHC within a pincer ligand to an NHDC, have yet to be report. Thus we report, herein, the rearrangement of an NHC ligand to yield a CCC-NHC/NHDC pincer bis(imido) Ta complex and the reactivity of CCC-NHC pincer bis(imido) Ta complex with adventitious proton sources to form a new (BuCiCiCBu)Ta(V)(tert-butylamido)(tert- butylimido)iodo complex. Results and Discussion While investigating the synthesis of the recently reported CCC-NHC Ta bis(imido) complex,[3a] complex 1 was treated with excess lithium tert-butylamide in toluene at temperatures ranging from room temperature up to 80 °C (Scheme 1). In an effort to isolate solely the CCC-NHC Ta bis(imido) from the extraneous products, the crude material was washed with various hydrocarbon solvents (hexanes and pentane). Over time an extended period of time (2 month), crystals of a CCC-NHC/NHDC complex grew from the pentane washes. Despite numerous attempts to reproduce the exact experiment, a concise synthesis of NHDC complex 3 has yet to be found. Scheme 1. Synthesis of (1-(3-butylimidazol-1-yl-2-lithium-4-idene 3-(3-butylimidazol-1-yl-2-idene)-2-phenylene) bis(tert- butylimido)tantalum(V), 3.

excess Li t-BuNHLi N N N N N N Ta supernatant I N N N Bu N N Ta N Bu Bu months Ta N N Bu Bu t-BuN Bu t-BuN Nt-Bu NMe2 LiI

2 2 1 2 3 Molecular Structure Determination X-ray quality crystals of complex 3 grew from a saturated pentane solution 3 at room temperature. An ORTEP® plot of the molecular structure of complex 3 is presented in Figure 1-3 along with selected metric data. X-ray crystallographic data confirmed the tridentate bonding of the CCC-NHC and CCC-NHC/NHDC pincer ligand to the Ta(V) center in complexes 3. Complex 3 has distorted trigonal bipyramidal coordination due to the constraints of the pincer ligand. The NHC and NHDC ligands occupied coordination sites trans to each other and had a CNHC-Ta-CNHDC bond angle of 139.10(13)°. The Ta-CNHDC bond length was 2.277(4) Å. This unprecedented bond was comparable (-0.01 Å) to the other Ta- Vol. 1 Pag.122

CNHC bond length incorporated into a pincer ligand. At 2.286(4) Å, the Ta-CNHC was in agreement (±0.13 Å) with other known Ta-CNHC bond lengths.[3] The Ta-Caryl bond length was 2.282(5) Å, which was within 0.12 Å of other Ta pincer complexes with a similar aryl group flanked by neutral donors.[13] With a bond lengths of 1.866(4) Å and 1.825(4), the Ta- Nimido bonds were similar (±0.081 Å) to other reported Ta bis(imido) complexes.[14] At 117.67(19)°, the Nimido-Ta-Nimido was in similar to other Ta bis(imido).[14b] The C(7)-Li(7) bond length was 2.117 Å, analogous to the Li-CNHC bond length (-0.058 Å) of the free NHDC by Robinson.[8]

Figure 1. Molecular structure of complex 3 (1-(3-butylimidazol-1-yl-2-lithium-4-idene 3-(3- butylimidazol-1-yl-2-idene)-2-phenylene) bis(tert-butylimido)tantalum(V). Only one formula unit shown and the hydrogens have been omitted for clarity. Thermal ellipsoids are shown at 50% probability. Selected bond lengths (Å) and angles (°): Ta(1)-C(1), 2.281(4); Ta(1)- C(8), 2.277(4); Ta(1)-C(14), 2.286(4), Ta(1)-N(5), 1.869(3); Ta(1)-N(6), 1.826(3); C(8)- Ta(1)-C(14), 139.10(13); C(1)-Ta(1)-C(14), 69.50(14); C(8)-Ta(1)-C(1), 69.69(13); N(6)- Ta(1)-N(5), 117.68. Expanding the view of the crystal structure of 3 to include two formula units, illustrates the multiple interactions between the Li and NHDC carbons which bridges to form a dimer (Figure 2). The most notable interaction is between the NHDC carbon and the Li which has a length of 2.466 Å. The Li-CNHDC interaction length is larger than the Li-CNHDC length in Robinson’s free NHDC complex,[8] but smaller than the analogous K-CNHDC interaction in the Y NHC/NHDC dimmers reported by Arnold.[10] Furthermore, a Li-Nimido was observed between the two formula units in the dimer. The Li-Nimido interaction was 2.032 Å in length, similar to the Li-Nimido interactions in Wigley’s Ta bis(imido) complexes.[14a] This interaction explains the deviation between the Ta(1)-N(6)-C(25) bond angle (172.7(3)°) and Ta(1)-N(5)- C(21) bond angle 156.0(3)°. Figure 2. Dimeric view of 3 (hydrogens omitted for clarity).

Attempts to prepare the NHDC pincer In an effort to find a direct synthesis of NHDC pincer complex 3, the previously reported bis(imido) complex (2) was heated at elevated temperatures (Scheme 2). After heating the reaction for 1.4 days at 120 °C, signals consistent with a new CCC-NHC pincer complex were observed. These new signals increased in intensity as the heat was increased to 160 °C after 4 days and were the only signals observed after the reaction was heated at 160 °C for 13 days. The most obvious of these signals was a diastertopic multiplet at δ 4.07 corresponding to methylene group adjacent to the nitrogen of a new CCC-NHC pincer complex as illustrated in Figure 3. A new singlet at δ 1.61 with an integration of 9H was consistent with the a tert-butylimido ligand. Another singlet, with similar intensity (9H), at δ 0.86 suggested one of the tert-butylimido ligands of the starting material had transformed to a tert-butylamido ligand. This data, and the lack of a second set of butyl signals corresponding to the inequivalent butyl groups of NHDC complex 3, suggested that complex 3 was not formed. Rather, the bis(imido) complex reacts with adventitious water to form CCC-NHC Ta tert-butylamido, tert-buytlimido, iodo complex 4. Vol. 1 Pag.123

Scheme 2. Attempted preparation of the NHDC pincer complex.

Li N N N N heat N N Ta I N Bu N N N N N Ta Bu Bu days Ta N N Bu Bu t-BuN Bu t-BuN Nt-Bu HN LiI 2 2 2 4 3

t0

1.4 days, 120 °C

4 days, 160 °C

13 days, 160 °C

5.00 4.95 4.90 4.85 4.80 4.75 4.70 4.65 4.60 4.55 4.50 4.45 4.40 4.35 4.30 4.25 4.20 4.15 4.10 4.05 4.00 3.95 3.90 3.85 3.80 3.75 3. 3.65 3.6070 3.55 f1 (ppm)

Figure 3. 1H NMR spectra upon heating of 2 showing slow conversion to 4 due to adventitious water. In one attempt to grow crystals of bis(imido) complex 2, both tablet and needle crystals were observed. Apparently a source of adventitious protons was available, as upon solving the X-ray crystal data for the tablets the molecule was identified as imido/amido complex 4. The crystals were grown by layering a saturated THF solution with hexanes. An ORTEP plot of complex 4 is presented in Figure 2, along with select metric data. X-ray crystallographic analysis confirmed the tridentate binding of the ligand and the distorted octahedral geometry of complex 4. All data regarding the CCC-NHC pincer ligand (i.e. Ta- NHC bond lengths, Ta-aryl bond length, CNHC-Ta-CNHC bond angle, and CNHC-Ta-CNHC) were almost identical to the previously reported CCC-NHC Ta pincer complexes.[3a, 3c] The imido ligand of complex 4 has a bond length of 1.786(5) Å, which is longer than another reported Ta complexes containing a linear tert-butylimido ligand trans to a halogen. It is similar to other Ta imido complexes bearing a CCC- NHC pincer ligand.[3a, 15] The tert- butylamido ligand of complex 4 was comparable to other similar Ta tert-butylamido bond distances.[16] At 3.0769(4) Å, the Ta-I bond length is one of the longest Ta-I bond lengths reported.[3c, 16b, 17]

Figure 5. Molecular structure of (1,3-bis(3-butylimidazol-1-yl-2-idene)-2- phenylene)(tert-butylamido)(tert-butylimido)iodo tantalum(V) (4). Thermal ellipsoids are shown at 50% probability. Selected bond lengths (Å) and angles (deg): Ta(1)-C(7), 2.291(4); Ta(1)-C(14), 2.285(4); Ta(1)-C(1), 2.251(4); Ta(1)-N(6), 2.018(3); Ta(1)-N(5), 1.786(5); Ta(1)-I(1), 3.0769(4), C(14)-Ta(1)-C(7), 138.84(15); C(1)-Ta(1)-C(7), 69.51(14); C(1)- Ta(1)-C(14), 69.35(16).

Proposed Mechanism A plausible mechanism for the synthesis of the NHDC complex 2 is illustrated in Scheme 3. It was hypothesized that a backbone carbon of one of the C-2 NHC ligand in complex 2 is deprotonated by the excess lithium tert-butylamide to form intermediate NHDC complex a. The amine protonates C-2 of intermediate NHDC complex a, which produces a free MIC arm Vol. 1 Pag.124

in b. The free MIC rotates about the CAryl-NMIC bond to produce intermediate c. A bond is formed between C-5 of the free MIC intermediate and Ta producing d. Ta NHC/MIC intermediate d can be deprotonated at C-2 of the MIC ligand yielding NHC/NHDC pincer complex 3. Scheme 3. A reasonable initial hypothesis for the mechanism of the formation of 3.

H Li - Li N LiNR2 - R N H N N N 2 N N N N N Ta N N N N Bu Ta N Ta H N Bu N Ta t-BuN Nt-Bu Bu Bu Bu Bu Bu Li t-BuN Nt-Bu t-BuN Bu Nt-Bu t-BuN 2 a Nt-Bu R2NH b c - Li+

Li N N H N Bu LiNR2 N Ta N N Bu N Bu t-BuN Nt-Bu - HNR2 N Ta Bu t-BuN Nt-Bu 3 2 d Computational Results The geometry minimized energy (DFT-PBE/mod-LANL2DZ, 6-31G(d')) for the proposed intermediate a was found to be 12.8 kcal mol-1 higher in energy than the value computed for the monomer of 3. A direct transition state was located and found to have an unreasonably high energy (60 kcal mol-1). Therefore, it seems unlikely that the interconversion occurs in a single-step, direct pathway lending plausibility to the proposed multi-step path in Scheme 3.

Figure 6. Computed relative energies of a, TS, and the monomer of 3.

-1 a, 12.8 kcal mol-1 TS-a-3-monomer 3-monomer, 0 kcal mol 60 kcal mol-1

These three structures and their relative energies are illustrated in Figure 6. Conclusion In conclusion, novel bis(imido) Ta complexes bearing a CCC-NHC and CCC-NHC/NHDC pincer ligand were synthesized. Treatment of complex 2 with lithium tert-butylamide at elevated temperatures yielded CCC-NHC/NHDC pincer complex 3. Complex 3 is not only a rare example an X-ray crystallographically determined Ta NHC, but is also the first example of an X-ray crystallographically determined Ta NHDC complex and NHDC pincer complex. Exposure of bis(imido) complex 3 to adventitious proton sources yielded (BuCiCiCBu)Ta(V)(tert-butylamido)(tert-butylimido)iodo complex (4). References [1][a]A. J. Arduengo, R. L. Harlow, M. Kline, J. Am. Chem. Soc. 1991, 113, 361; [b]A. Igau, H. Grutzmacher, A. Baceiredo, G. Bertrand, J. Am. Chem. Soc. 1988, 110, 6463; [c]D. Bourissou, O. Guerret, F. P. Gabbai, G. Bertrand, Chem. Rev. 2000, 100, 39. [2]W. A. Herrmann, Angew. Chem., Int. Ed. 2002, 41, 1290. Vol. 1 Pag.125

[3][a]T. R. Helgert, X. Zhang, H. K. Box, J. A. Denny, H. U. Valle, A. G. Oliver, et al., Organometallics 2016; [b]L. P. Spencer, C. Beddie, M. B. Hall, M. D. Fryzuk, J. Am. Chem. Soc. 2006, 128, 12531; [c]T. R. Helgert, T. K. Hollis, A. G. Oliver, H. U. Valle, Y. Wu, C. E. Webster, Organometallics 2014, 33, 952. [4]R. H. Crabtree, Coord. Chem. Rev. 2013, 257, 755. [5]S. Grüdemann, A. Kovacevic, M. Albrecht, J. W. Faller, R. H. Crabtree, Chem. Commun. 2001, 2274. [6]E. Aldeco-Perez, A. J. Rosenthal, B. Donnadieu, P. Parameswaran, G. Frenking, G. Bertrand, Science 2009, 326, 556. [7]M. Heckenroth, A. Neels, M. G. Garnier, P. Aebi, A. W. Ehlers, M. Albrecht, Chem.—Eur. J. 2009, 15, 9375. [8]Y. Wang, Y. Xie, M. Y. Abraham, P. Wei, H. F. Schaefer, P. V. R. Schleyer, et al., J. Am. Chem. Soc. 2010, 132, 14370. [9][a]M. J. Bitzer, A. Pothig, C. Jandl, F. E. Kuhn, W. Baratta, Dalton Trans. 2015, 44, 11686; [b]Y. Wang, Y. Xie, P. Wei, H. F. Schaefer, G. H. Robinson, Dalton Trans. 2016, 45, 5941; [c]M. J. Bitzer, F. E. Kühn, W. Baratta, J. Catal. 2016, 338, 222; [d]Y. Wang, Y. Xie, M. Y. Abraham, P. Wei, H. F. Schaefer, P. V. R. Schleyer, et al., Organometallics 2011, 30, 1303; [e]Y. Wang, M. Y. Abraham, R. J. Gilliard, P. Wei, J. C. Smith, G. H. Robinson, Organometallics 2012, 31, 791; [f]R. A. Musgrave, R. S. P. Turbervill, M. Irwin, J. M. Goicoechea, Angew. Chem., Int. Ed. 2012, 51, 10832; [g]R. A. Musgrave, R. S. P. Turbervill, M. Irwin, R. Herchel, J. M. Goicoechea, Dalton Transactions 2014, 43, 4335; [h]J. B. Waters, R. S. P. Turbervill, J. M. Goicoechea, Organometallics 2013, 32, 5190; [i]M. Vogt, C. Wu, A. G. Oliver, C. J. Meyer, W. F. Schneider, B. L. Ashfeld, Chem. Commun. 2013, 49, 11527; [j]D. A. Valyaev, M. A. Uvarova, A. A. Grineva, V. Cesar, S. N. Nefedov, N. Lugan, Dalton Trans. 2016, 45, 11953; [k]C. Pranckevicius, D. W. Stephan, Chem. - Eur. J. 2014, 20, 6597. [10]P. L. Arnold, S. T. Liddle, Organometallics 2006, 25, 1485. [11][a]M. Vogt, O. Rivada-Wheelaghan, M. A. Iron, G. Leitus, Y. Diskin-Posner, L. J. W. Shimon, et al., Organometallics 2013, 32, 300; [b]E. Poverenov, D. Milstein, in Organometallic Pincer Chemistry, Eds. G. van Koten, D. Milstein, 2013, pp. 21-47 (Springer Berlin Heidelberg: Berlin, Heidelberg). [12][a]A. D. Ibrahim, K. Tokmic, M. R. Brennan, D. Kim, E. M. Matson, M. J. Nilges, et al., Dalton Trans. 2016, 45, 9805; [b]G. E. Martinez, C. Ocampo, Y. J. Park, A. R. Fout, J. Am. Chem. Soc. 2016, 138, 4290; [c]A. D. Ibrahim, S. W. Entsminger, L. Zhu, A. R. Fout, ACS Catal. 2016, 6, 3589; [d]W. D. Clark, K. N. Leigh, C. E. Webster, T. K. Hollis, Aust. J. Chem. 2016, 69, 573; [e]H. U. Valle, G. Akurathi, J. Cho, W. D. Clark, A. Chakraborty, T. K. Hollis, Aust. J. Chem. 2016, 69, 565; [f]S. W. Reilly, G. Akurathi, H. K. Box, H. U. Valle, T. K. Hollis, C. E. Webster, J. Organomet. Chem. 2016, 802, 32; [g]S. W. Reilly, C. E. Webster, T. K. Hollis, H. U. Valle, Dalton Trans. 2016, 45, 2823; [h]E. B. Bauer, G. T. S. Andavan, T. K. Hollis, R. J. Rubio, J. Cho, G. R. Kuchenbeiser, et al., Organic Letters 2008, 10, 1175; [i]J. Cho, T. K. Hollis, T. R. Helgert, E. J. Valente, Chem. Commun. 2008, 5001; [j]J. Cho, T. K. Hollis, E. J. Valente, J. M. Trate, Journal of Organometallic Chemistry 2011, 696, 373; [k]W. D. Clark, J. Cho, H. U. Valle, T. K. Hollis, E. J. Valente, J. Organomet. Chem. 2014, 751, 534; [l]T. R. Helgert, T. K. Hollis, E. J. Valente, Organometallics 2012, 31, 3002; [m]X. Zhang, A. M. Wright, N. J. DeYonker, T. K. Hollis, N. I. Hammer, C. E. Webster, et al., Organometallics 2012, 31, 1664; [n]M. Raynal, C. S. J. Cazin, C. Vallee, H. Olivier-Bourbigou, P. Braunstein, Chem. Commun. 2008, 0, 3983; [o]M. Raynal, R. Pattacini, C. S. J. Cazin, C. Vallée, H. l. n. Olivier- Bourbigou, P. Braunstein, Organometallics 2009, 28, 4028; [p]W. Zuo, P. Braunstein, Organometallics 2012, 31, 2606; [q]W. Zuo, P. Braunstein, Dalton Transactions 2012, 41, 636; [r]A. R. Chianese, M. J. Drance, K. H. Jensen, S. P. McCollom, N. Yusufova, S. E. Shaner, et al., Organometallics 2014, 33, 457; [s]A. R. Chianese, A. Mo, N. L. Lampland, R. L. Swartz, P. T. Bremer, Organometallics 2010, 29, 3019; [t]A. R. Chianese, S. E. Shaner, J. A. Tendler, D. M. Pudalov, D. Y. Shopov, D. Kim, et al., Organometallics 2012, 31, 7359; [u]S. M. M. Knapp, S. E. Shaner, D. Kim, D. Y. Shopov, J. A. Tendler, D. M. Pudalov, et al., Organometallics 2014, 33, 473; [v]Y.-M. Zhang, J.-Y. Shao, C.-J. Yao, Y.-W. Zhong, Dalton Trans. 2012, 41, 9280; [w]E. Peris, R. H. Crabtree, Coord. Chem. Rev. 2004, 248, 2239; [x]R. E. Andrew, L. Gonzalez-Sebastian, A. B. Chaplin, Dalton Trans. 2016, 45, 1299; [y]E. Peris, R. H. Crabtree, in The Chemistry of Pincer Compounds, (Ed. C. M. Jensen, 2007, pp. 107-124 (Elsevier Science B.V.: Amsterdam); [z]E. M. Matson, G. Espinosa Martinez, A. D. Ibrahim, B. J. Jackson, J. A. Bertke, A. R. Fout, Organometallics 2015, 34, 399. Vol. 1 Pag.126

[13][a]H. C. L. Abbenhuis, N. Faiken, D. M. Grove, J. T. B. H. Jastrzebski, H. Kooijman, P. Van Der Sluis, et al., J. Am. Chem. Soc. 1992, 114, 9773; [b]H. C. L. Abbenhuis, N. Feiken, H. F. Haarman, D. M. Grove, E. Horn, H. Kooijman, et al., Angew. Chem., Int. Ed. 1991, 30, 996. [14][a]T. C. Baldwin, S. R. Huber, M. A. Bruck, D. E. Wigley, Inorg. Chem. 1993, 32, 5682; [b]Y. W. Chao, P. A. Wexler, D. E. Wigley, Inorg. Chem. 1990, 29, 4592. [15]A. Merkoulov, S. Schmidt, K. Harms, J. Sundermeyer, Z. Anorg. Allg. Chem. 2005, 631, 1810. [16][a]R. E. Blake, D. M. Antonelli, L. M. Henling, W. P. Schaefer, K. I. Hardcastle, J. E. Bercaw, Organometallics 1998, 17, 718; [b]B. L. Yonke, A. J. Keane, P. Y. Zavalij, L. R. Sita, Organometallics 2012, 31, 345. [17][a]P. Bernieri, F. Calderazzo, U. Englert, G. Pampaloni, J. Organomet. Chem. 1998, 562, 61; [b]F. G. N. Cloke, P. B. Hitchcock, M. C. Kuchta, N. A. Morley-Smith, Polyhedron 2004, 23, 2625; [c]M. J. McGeary, A. S. Gamble, J. L. Templeton, Organometallics 1988, 7, 271; [d]F. Calderazzo, G. Pampaloni, G. Pelizzi, F. Vitali, Organometallics 1988, 7, 1083; [e]R. P. Hughes, S. M. Maddock, A. L. Rheingold, I. A. Guzei, Polyhedron 1998, 17, 1037; [f]T. W. Hayton, P. J. Daff, P. Legzdins, S. J. Rettig, B. O. Patrick, Inorg. Chem. 2002, 41, 4114; [g]T. W. Hayton, P. Legzdins, B. O. Patrick, Inorg. Chem. 2002, 41, 5388; [h]M. V. Barybin, W. W. Brennessel, B. E. Kucera, M. E. Minyaev, V. J. Sussman, V. G. Young, et al., J. Am. Chem. Soc. 2007, 129, 1141.

Acknowledgements: The National Science Foundation (OIA-1539035) is gratefully acknowledged for financial support. Vol. 1 Pag.127

Hydrogen bonds in Novel Pd(II) Coordination complexes containing fluorinated Schiff Bases. A Structural Study.

J. Roberto Pioquinto−Mendoza1, Marcos Flores-Álamo2, Rubén A. Toscano3 and David Morales-Morales3

1Facultad de Química, Universidad Autónoma de Yucatán, Calle 43 No. 613 x C 90, Col. Inalámbrica. C.P. 97069, Mérida, Yucatán, México. E-mail: [email protected] 2Facultad de Química (UNAM) Ed B Ave Universidad 3000, Coyoacán, CDMX, México. 3Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, C.P. 04510, CDMX, México. E-mail: [email protected]

Abstract. A series of novel fluorinated Schiff bases and their Pd(II) derivatives were synthesized and fully characterized by different analytical techiniques including, infrarred, elemental analysis, nuclear magnetic resonance and when possible by sigle crystal X-ray diffraction analysis. Due to the presence of –OH groups in the structures of the series of compounds, they exhibit intra- and/or intermolecular hydrogen bonds which are important for the stability of the lattice in the solid state and relevant for their study in crystal engineering. In addition to this important non-covalent interactions, compounds L3 and L4 also exhibited π-π stacking interactions of the phenolic and benzene rings.

Keywords Fluorinated Schiff Bases, Palladium (II) complexes, hydrogen bond interactions, supramolecular chemistry, crystal engineering, coordination chemistry.

Background Schiff bases are compounds that include on their structures the azomethine group. These species are known since the 19th century and have been widely studied due to their potential applications in many areas of chemistry, this being particularly true for homogeneous catalysis, mainly for their use as catalysts in Suzuki-Miyaura Couplings[1] as well as for their biological activity studies as antifungal[2], antimicrobial[3,4], antiviral and anticancer[5]. Thus, in this work we report a series of novel Schiff bases and their Pd(II) derivatives as well as their study in solid state to determine how “weak” interactions such as hydrogen bonds determine their molecular arrangements in the solid state.

Experimental section The Schiff Bases were synthesized by a traditional method i.e. the condensation reaction between 2,4-dihydroxybenzaldehyde and fluorinated anilines in an equimolar ratio using Na2SO4 as desiccant agent and a mixture of solvents methanol/toluene as reaction media, having a reaction time of 48 hours, after which the solvent was removed under reduced pressure affording a series of yellow microcrystalline powders, which then were further purified by recrystallization from a CH2Cl2/hexane solvent system (yields 90-97%). Scheme 1. Vol. 1 Pag.128

N Ph = N N

F F Ph F O N Methanol/ Toluene L1 L2 NH2 + Reflux Ph Na SO 2 4 N N HO OH 48 h HbO OHa F

F F3C CF3 F L3 L4 Scheme 1. Synthesis of fluorinated Schiff bases. Synthesis of Pd(II) Schiff base coordination complexes Coordination complexes were synthesized from the reactions between the synthesized fluorinated Schiff bases L1-L4 and [Pd(CH3COO)2] in a 2:1 molar ratio, in a solvent mixture of MeCN/acetone (1:1) as reaction media during 24 hours. After this time the solvent was removed under reduced pressure affording a series of yellow powders, which were then washed with n-hexane to produce microcrystalline yellow powders of complexes PdL1, PdL2, PdL3 and PdL4 in yields that go from 90 to 95% (Scheme 2). N Ph = N N

Ph N F F i) (CH3)2CO Ph F ii) Pd(CH CO ) / CH CN N 3 2 2 3 PdL1 PdL2 Pd O OHb HbO OHa HbO O N N N Ph F

F F3C CF3 F

PdL3 PdL4 Scheme 2. Synthesis of the Schiff base Pd(II) coordination complexes.

Results and discussion Infrared Spectroscopy. Fluorinated Schiff bases L1-L4 were characterized by infrared spectroscopy. In these spectra the bands due to the presence of the -OH functional groups were observed in the range of ν = 3238 to 3242 cm−1, while the signals due to the presence −1 of C=Nimine bonds were observed from ν = 1622 to 1630 cm . As expected, the very same signals on the coordination complexes PdL1-PdL4 reveal a shift to lower frequencies from those of the free ligands. Thus, bands due to the -OH groups span from ν = 3153 to 3210 −1 cm , while those bands corresponding to the C=Nimine are now observed between ν = 1589 and 1621 cm−1. This effect can be attributed to the metal coordination. Vol. 1 Pag.129

Nuclear Magnetic Resonance (NMR). In general, the 1H NMR spectra of the series of compounds show two signals for the -OH groups. One, located from δ = 13.36 to 12.97 ppm, assigned to the -OHa group and the second one observed between δ = 9.35 to 8.99 ppm which were assigned to the -OHb group. Signals attributable to the iminic group were observed about δ = 8.98 to 8.73 ppm for the free ligands; while a significant up field shift in the 1H NMR spectra is observed for the imine proton upon coordination to the Pd(II) center of about 1.0 ppm. This effect could be due to the shielding effect. On the other hand, in the 13C{1H} NMR spectra of the Pd(II) coordination complexes, the iminic carbon is more shielded than in the free ligand (about 2 ppm); this effect could be attributed to the formation of the six membered ring chelates.

X-ray Diffraction Crystals suitable for single crystal X-ray diffraction analysis of the Schiff bases L1, L3 and L4 and their Pd(II) derivatives PdL1, PdL3 and PdL4 were obtained from solutions of acetone and DMSO respectively. These analyses showed that for all the cases the lattices are stabilized by intermolecular hydrogen bonds, produced between the -OH and imine groups for free ligands and between the -OH and crystallization solvent molecules for the coordination complexes. All Pd(II) complexes crystalized in the P 21/c space group, exhibiting slightly distorted square planar geometries. Selected bond lengths and bond for the Pd(II) complexes PdL1, PdL3 and PdL4 are shown in Table 1.

Table 1. Selected bond lengths [Å] and angles [°] for PdL1, PdL3 and PdL4. Bond lengths in Å PdL1 PdL3 PdL4 Pd–N 2.0149 (19) 2.0157 (15) 2.0234 (18) Pd–O 1.9698 (16) 1.9689 (13) 1.9825 (14) Bond Angles in º O–Pd–N 91.64 (7) 91.92 (6) 92.02 (6) N–Pd–N 180.0 180.0 180.00 (8) O–Pd–O 180.0 180.00 (4) 180.00 (6)

Bond lengths for Pd–N ranged from 2.0149 to 2.0234 Å, while those for Pd–O are between 1.9689 to 1.9825 Å with bite angles closer to 90º. These values of bond lengths and angles are similar to other isostructural complexes previously described in the literature [1]. As a representative example, Figures 1 and 2 shown the molecular structures for L4 and its Pd(II) derivative PdL4 respectively. Vol. 1 Pag.130

Figure 1. Molecular structure for L4 Figure 2. Molecular structure for PdL4.

A quick view to the latter structure (PdL4) reveals the presence of two water molecules in the lattice. Thus, this complex forms a hydrogen bond network involving the O coordinated to Pd(II), the free OH group of the Schiff base ligand and the two water molecules (Figure 3 presents the graph set descriptor and Table 2 presents the corresponding bond lengths and angles). Parameters described in Table 2 are in good agreement with strong hydrogen bonds.

Figure 3. Hydrogen bond network in PdL4. Table 2. Hydrogen bonds in the crystal structure of PdL4. D-H...A d(D-H) d(H...A) d(D...A) <(D-H...A) O(2)-H(2D)...O(1W)#1 0.837(17) 1.761(18) 2.596(2) 176(3) O(1W)-H(1E)...O(2)#2 0.839(17) 2.00(2) 2.809(2) 161(3) O(1W)-H(1D)...O(1)#3 0.852(17) 1.920(18) 2.768(2) 174(3) Symmetry transformations used to generate equivalent atoms: #1 -x+2,y-1/2,-z+1/2 #2 -x+2,-y,-z+1 #3 -x+2,y+1/2,-z+3/2 Vol. 1 Pag.131

Conclusions A series of fluorinated Schiff bases and their corresponding Pd(II) coordination complexes were synthesized and unequivocally characterized. Analysis by single crystal X-ray diffraction experiments shown these compounds to exhibit intra- and intermolecular hydrogen bonds in the solid state, interactions that greatly benefit the structure of the lattice. These interactions where studied and a crystal engineering analysis produced which could be relevant for the development of new materials with potential applications in catalysis and other areas of chemistry. In all cases studied, the coordination complexes exhibited the Pd(II) center located into a slightly distorted squared planar geometry.

Acknowledgements We would like to thank Chem. Eng. Luis Velasco Ibarra, Dr. Francisco Javier Pérez Flores, Q. Eréndira García Ríos, M.Sc. Lucia del Carmen Márquez Alonso, M.Sc. Lucero Ríos Ruiz, M.Sc. Alejandra Núñez Pineda (CCIQS), Q. María de la Paz Orta Pérez and Q. Rocío Patiño-Maya for technical assistance. The financial support of this research by CONACYT (grant No. CB2010–154732) and PAPIIT (grants No. IN201711–3 and IN213214–3) is gratefully acknowledged.

References.

1 Kilic, A.; Kilinc, D.; Tas, E.; Yilmaz, I.; Durgun, M.; Ozdemir, I.; Yasar, S. J. Organomet. Chem. 2010, 695, 697–706 2 Shalini S.; Girija CR; Sathish C. D.; Venkatesha T. V. Chem. Sci. J. 2016, 7 122-126 3 Satheesh, C.E.; Raghavendra Kumar, P.; Sharma, P.; Lingaraju, K.; Palakshamurthy, B.S.; Raja Naika, H. Inorg. Chim. Acta 2016, 442, 1–9 4 da Silva, C. M.; da Silva, D. L.; Modolo, L. V.; Alves, R. B.; de Resende, M. A.; Martins, C. V. B.; de Fátima, A. J. Adv. Res. 2011, 2, 1–8. 5 Petrovic, V. P.; Zivanovic, M. N., Simijonovic, D.; Dorovic, J.; Petrovic, Z. D.; Markovic, S. D. RSC Adv., 2015, 5, 86274–86281 Vol. 1 Pag.132

Polymeric supports for heterogenization of zirconocene aluminohydrides. Zertuche-Martínez, Sergio A., 1 Peralta Rodríguez, René D., 1 Pérez Camacho, Odilia.1 1Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo 140, Col. San José de los Cerritos Saltillo, C.P 25294, Coahuila, México.

Abstract. Functionalized polymer particles prepared with commercial polymerizable surfactants (anionic Hitenol BC and non-ionic Noigen RN) by miniemulsion polymerization, have been used as carriers of catalytic species in the polymerization and copolymerization of olefins and alpha olefins, producing homogeneous copolymers. In this work, particles of crosslinked poly (styrene - acrylic acid - divinylbencene) P(S-AA-DVB) were prepared by miniemulsion polymerization, and used as organic supports for metallocene derivatives, for the polymerization and copolymerization of ethylene and 1-hexene in "slurry". The particles in the polymer latex were characterized by dynamic light scattering (DLS), to determine the average particles diameter and Z potential. The crosslinked polymers were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The dried polymer particles were used to support zirconocene aluminohydrides catalysts. The supported catalysts, (nBuCp)2ZrH3AlH2 / MAO / P(S-DVB-AA) containing neutral or ionic groups from the polymeric surfactants and the AA, were tested and compared as catalytic systems, in the homopolymerization of ethylene and copolymerization of ethylene and 1- hexene. The polyolefins obtained with the new catalytic systems were characterized by 13C nuclear magnetic resonance spectroscopy (NMR), DSC, gel permeation chromatography (GPC) and SEM. The catalytic activity of each supported system was also determined.

Introduction In recent decades, there has been considerable progress in the polymerization of olefins. In order to improve the morphology of polyethylene and polyethylene-alfa-olefin copolymers, and to have an alternative to silica supports traditionally used to immobilize metallocenes, organic supports based on polymers have been studied. Polystyrene based supports crosslinked with divinyl benzene and functionalized with acrylic acid and polymeric surfactants containing a number of ethylene oxide units in their hydrophilic chain were used. The supported metallocene interacts directly or indirectly with these groups, by electrostatic interactions, where it ionizes and forms active species. [1]

Experimental section The terpolymers P(S-DVB-AA), were synthesized from styrene, divinylbenzene and acrylic acid, with a molar ratio of (92:5:3) using polymerizable surfactant Hitenol BC with different chain length of ethylene oxide (10, 30) and molar ratio of (94:5:1) and non-ionic Noigen RN30, by miniemulsion polymerization. A pre-emulsion was formed by mixing in a flat bottom flask, an aqueous phase (formed by water and surfactant) and an oil phase (monomers, hexadecane, initiator) under agitation (1000 rpm). The resulting pre-emulsion was subjected to the action of ultrasound (Sonics 500 W, 81 % power), under cooling to avoid undesirable polymerization, for 3 min, and the flask and contents were transferred to a heating bath. Then the polymerization was carried out at 72 °C with magnetic stirring (400 rpm) for 16 hours. [2] Lattices obtained were analyzed by dynamic light scattering (DLS). Finally, lattices were purified by dialysis, and lyophilized. The dry polymer was characterized by scanning electron microscopy (SEM) and Differential Scanning Calorimetry (DSC). The particles of dried latex were immersed in toluene and the suspension was sonicated for 30 min in an ultrasonic bath (40 W). Then 20 ml of 15 wt% MAO solution in toluene at 0 °C were added, and the mixture was stirred for 12 hours at room temperature. Subsequently, Vol. 1 Pag.133

the solid was washed five times with 20 ml of toluene, removing excess MAO, and the particles were dried for 6 h under vacuum. Particles modified with MAO P(S-DVB-AA / MAO) were re-suspended in 20 ml of toluene, the -3 solution was cooled to 0 °C, and aluminohydride (n-BuCp)2ZrH3AlH2 (2.48 X 10 mol) solution in toluene was added. The mixture was stirred at room temperature for 12 h, and then the particles were washed five times with 20 ml of toluene, and dried at room temperature for 6 h under high vacuum. The supported catalyst was tested in the "slurry" polymerization and copolymerization of ethylene and 1-hexene at 70 °C and 289 kPa (42 psi) of ethylene pressure. Iso-octane was used as the solvent with different ratios of MAO. [3] Polymers and copolymers obtained were characterized by Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance (NMR) 13C, DSC and SEM.

Results The P(S-AA-DVB) lattices obtained by the method of miniemulsion polymerization, showed high monomers conversions and stability, with average particles diameter of 61.9 ± 2 nm and 54.5 ± 3 nm for Hitenol BC10 and 30, respectively, and average diameters of 151 ± 8 nm for Noigen RN30 (Table 1). Differences in particle sizes were attributed to the ionic character of the Hitenol BC surfactants, where its sulfonate termination can interact with chains of ethylene oxide, and the hydrophobic part of the molecule with the nonyl chain of the additional surfactant, generating smaller particles. [4] The Z potential values of miniemulsions prepared with different polymerizable surfactants are shown in Table 1, in which we see that for Hitenol BC 10 and 30, the values obtained were ~ -50mV (millivolts) while for the surfactant Noigen RN30 ~ -20 mV. The lattices prepared with ionic surfactants showed good stability, due to its negative charge, whereas the ones prepared with the nonionic surfactant, showed higher values of Z potential, so that coagulation of the polymer particles can occur. [5] The results of the glass transition temperatures (Tg) obtained for each of the particles, are shown in Table 1, where it can be seen that the Hitenol BC series and Noigen RN30 have a Tg adequate to carry out the polymerization of ethylene in slurry at 70 °C.

Table 1. Characteristics of the particles obtained with the different surfactants by miniemulsion polymerization. AA Conversion Z Potential DP DLS DP SEM Surfactant Tg (°C) (%) (%) (mV) (nm) (nm) Hitenol BC30 3 91.32 (-) 47.9 ± 2 61.9 ± 2 59.06 ± 2 113.05 ± 3 Hitenol BC10 3 91.54 (-) 53.4 ± 3 54.5 ± 3 54.02 ± 1 113.57 ± 3 Noigen RN30 1 92.35 (-) 20.7 ± 2 150.9 ± 8 84.26 ± 11 89.46 ± 1

The polymer particles obtained after purifying and drying the lattices were dispersed in toluene, modified with MAO and subsequently with the zirconocene aluminohydride [6] (figure 1), to be used as catalysts for the polymerization and copolymerization of ethylene and 1-hexene in "slurry".

O O n-Bu O O n-Bu Al O H Zr H O Al Al H H H Al H H Al H H P(S-DVB-AA) Zr

Figure 1. Schematic representation of the supported zirconocene aluminohydride. Vol. 1 Pag.134

Figure 2a shows the SEM micrograph of the particles obtained using the polimerizable surfactant Hitenol BC30, where the spherical morphology of the particles can be compared with the average particle size obtained by DLS (Table 1). Polymer particles obtained with Hitenol BC series do not have significant difference between the two measurement techniques (> 3nm). However in the case of the particles obtained with the surfactant Noigen RN, a big change in Dp (<60 nm) can be seen. This is attributed to less strong steric interactions between particles with nonionic surfactant, leading to the formation of small domains in the particle containing AA, and to the separation in droplets, to stabilize in a more favorable manner. [2] Figure 2b shows the SEM micrographs of polyethylene obtained with heterogeneous catalysts in organic supports, which shows reproducibility of the nearly spherical morphology (agglomerates) from polymeric supports, with an increase in size of ~ 200 times.

Figure 2. SEM of a) Particles of P(S-DVB-AA), obtained with Hitenol BC30, b) HDPE obtained with the catalytic system supported on this P(S-DVB-AA) particles.

The new catalytic systems showed activities, from 1,300 to 2,600 kg PE/(mol Zr * h). The molecular weights of the homopolymers (HDPE) obtained (R- 1, 3, 5 in Table 2), were higher than 74,000 g/mol, additionally molar mass dispersities (Đ) were lower than 2.1, while for PE- HEX (R- 2, 4 and 6 in table 2), where 1-hexene was used as comonomer, the activities decreased from 13 to 20 %, compared to homopolymerizations, due to the longer chain size of 1-hexene, its incorporation could slow down the rate of incorporation of ethylene monomer, however, molecular weights remained between 82,000 g/mol to 66,000 g/mol, with Đ from 3.18 to 1.85. As far as the melting temperatures and percent crystallinity of the polymers, as expected, the copolymers (PE-HEX) exhibited lower melting temperatures (Tm = 126 °C) and lower crystallinity compared with HDPE (Tm = 133 °C) due to the presence of short chain branches (four carbons) in the polyethylene backbone.

Table 2. Polymerization results and polyethylenes characterization. Activity Tm Cristalinity Mw R* Surfactant (kg PE / Comonomer Đ (°C) (%) (g/mol) (mol Zr* h) 1 Hitenol BC30 2669.41 - 133.28 70.82 1.82 74800 2 Hitenol BC30 1304.19 1-HEXENE 126.42 47.82 3.18 82600 3 Hitenol BC10 2407.92 - 133.05 68.55 1.6 94700 4 Hitenol BC10 2102.71 1-HEXENE 126.29 69.31 2.59 66700 5 Noigen RN30 2045.40 - 132.83 68.72 2.08 107800 6 Noigen RN30 1641.72 1-HEXENE 125.55 57.85 1.85 75500 R* Reaction identification.

Figure 3 shows the 13C NMR spectrum of the polymer obtained in experiment R-2, where peaks correspond to tertiary carbons, observed at 35 ppm and the carbons of the branches (1-4) from the incorporation of 1-hexene in the polymer chain. According to the results Vol. 1 Pag.135

obtained by NMR, the comonomer incorporation was calculated as low as 0.08 to 0.43 % mol, but significantly enough to modify the properties of the polymer. [7]

Figure 3. 13C NMR spectrum in tetra-chloroethane / Tol-d8 of the copolymer obtained in R.2, Table 2.

Conclusions The aluminohydride zirconocenes heterogenized on polymeric supports, showed high catalytic activities in the synthesis of HDPE and LLDPE (PE-HEX) with values between 1,300 and 2,660 kg PE/(mol Zr * h), with high molecular weights and narrow dispersities (Đ~ 2.3), characteristic of PE prepared with metallocene systems.

References [1] Bianchini, D., Stedile, F. C. & Dos Santos, J. H. Z. Appl. Catal. A Gen. (2004) 261, 57–67. [2] Musyanovych, A., Rossmanith, R., Tontsch, C. & Landfester, K. Langmuir. (2007) 23, 5367–5376. [3] Villasana Salvador, C. I. (Centro de Investigación en Química Aplicada, 2013). [4] Atta, A. M., Dyab, A. K. F. & Al-Lohedan, H. A. J. Surfactants Deterg. (2013) 16, 343–355. [5] Conde, Kosegarten, C. E. & Munguía Jiménez, M. T. Temas Sel. Ing. Aliment. (2012) 2, 1–18. [6] Li, K., Dai, C. & Kuo, C. Catal. Commun. (2007) 8, 1209–1213. [7] Rojas de Gáscue, B. et al. Polymer (Guildf). (2002) 43, 2151–2159.

Acknowledgements The authors would like to thank the financial support of CONACYT for 167901 and 168472 projects, and the fellowship of Sergio Zertuche for graduate studies (M. Sc.) at CIQA and also thank Maricela García, Víctor Comparán and Gladis Cortez for technical support. Vol. 1 Pag.136

Rotaxanes, Fulvalenes and Catenanes: Optimization of Photosynthesis by Nanocomposites

Luis Alberto Lightbourn Rojas1, Luis Amarillas Bueno1, Rubén León Chan3

1Instituto de Investigación Lightbourn, A.C, E-mail: [email protected]

Global warming is predicted to have a negative impact on plant growth due to the damaging effect of high temperatures on plant development. Solar radiation (electromagnetic radiation) is one of the most important factors that influences the growth and development of plants, and is involved in many important processes such as photosynthesis, phototropism, photomorphogenesis, opening stomata, temperature of plant and soil [1].

The most heat-sensitive component of the photosynthetic apparatus; some studies suggest that the high temperature increases the membrane fluidity in chloroplast thylakoids, limiting carbon assimilation, the ATP generation and causing damage to photosystems, particularly the D1 protein of the photosynthetic machinery that is damaged due to generation of reactive oxygen species [2]. The UV radiation can inhibit photosynthesis by altering gene expression and by damaging the parts of the photosynthetic machinery [3].

The high energy of UV radiation is particularly damaging to the light collector complex II (LHCII), the PSII reaction center and PSI acceptor. However, most of the studies have demonstrated that PSII is more sensitive to UV radiation in comparison to PSI; this is due to the chemical changes which produces the UV radiation on amino acids with double bonds of the PSII proteins [4].

Plants alter their metabolism in various ways in response to elevated temperatures and exposure to UV radiation. The ability of plants of responding to strong irradiation by the synthesis and accumulation of the compounds selectively absorbing in the UV, in most cases is overcome by intense solar radiation. Therefore, the exogenous application of photoprotective compounds, could be providing a reliable long-term protection against photodamage [5].

Efficient use of solar energy for photosynthesis is important for plant growth and survival, especially in low and high light environments. Nanotechnology and nanoscience are attracting and promising disciplines of applied science that integrate a broad range of topics related to optimize light absorption for photosynthesis while avoiding damage (Perrine). In regard, mechanically interlocked structures such as fulvalene, rotaxane and catenane provide a novel backbone for constructing functional materials with unique structural characteristics. Therefore, we have developed a new plant nutrition technology, based on fulvalene, rotaxane and catenane compounds [6]. The fulvalene, rotaxane and catenane are molecules whose structure changes when exposed to sunlight, and can remain stable in that form indefinitely. It increases the uptake, Vol. 1 Pag.137

storage and availability of monochromatic ray at 563 nm. Foliar application of these compounds can prevent the growth inhibition and thylakoid membrane photodamage caused by solar radiation. Then, when a stimulus — a catalyst, a small temperature change, a flash of light — it can quickly snap back to its other form, releasing its stored energy in a burst of heat. These molecules are foliar applied to allow for maximum absorption and optimizers photosynthesis by helping to capture light energy efficiently and reduce photodamage.

The fulvalene, rotaxane and catenane applied by foliar absorption and involves an innovation in signaling and synchronization cell, because provide continuity in photosynthetic energy uptake and transfer, due to that clusters absorb and store energy. Furthermore, owing of these clusters not interrupt the metabolism on account of darkness, there are no delays in the formation and maintenance of plant tissue which means the total dejection of metabolic delays and consequences translated into structural failures, metabolic, energetic and homeostatic that directly affect the quantity and quality of biomass [7].

References [1] Bita CE, Gerats T. 2013. Plant tolerance to high temperature in a changing environment: Scientific fundamentals and production of heat stress-tolerant crops. Frontiers in Plant Science 4: 1-18. [2] Allakhverdiev S, Kreslavski V, Klimov V, Los D, Carpentier R, Mohanty P. 2008. Heat stress: An overview of molecular responses in photosynthesis. Photosynthesis research 98:541–50. [3] Smith KW, Gao W, Steltzer H. 2009. Current and future impacts of ultraviolet radiation on the terrestrial carbon balance. Front Earth Sci China 3:34–41. [4] Kristoffersen AS, Hamre B, Frette Ø, Erga SR. 2016. Chlorophyll a fluorescence lifetime reveals reversible UV-induced photosynthetic activity in the green algae Tetraselmis. European Biophysics Journal 45: 259–268. [5] Ramakrishna A, Ravishankar GA. 2011. Influence of abiotic stress signals on secondary metabolites in plants. Plant Signaling and Behavior 6: 1720-1731. [6] Perrine Z, Negi S, Sayre RT. 2012. Optimization of photosynthetic light energy utilization by microalgae. Algal Research 1:134–142. [7] Lightbourn R L A, 2011. Descripción de la Innovación del Grupo Hyper. In: Modelo Bioteksa de Gestión de Tecnología e Innovación I + D + i = 2i. ISBN:978-0-9833321-7-6.

Acknowledgements We would like to thank all those who have been involved with the development of this work. ISSN 2448-590X / la Dr. de 2016. Autor, Copilco, de Exclusivo Exclusivo de editor uso Materiales, octubre en de Derecho Derecho 20 postura del del la publicados siempre y cuando Investigaciones Investigaciones (55)56224581, y (55)56224500 Tel. modificación, Nacional Nacional Reserva Reserva de Derechos al textos aquí última los la de Peláez. Peláez. de el Instituto necesariamente necesariamente reflejan número, Instituto de parcial por no Monroy Peláez, Avenida Universidad 3000, Col. este de total o Marel otorgado otorgado los autores por producción la . . 04510, Ciudad de México, fecha D.F., D.F., a través del Instituto de Investigaciones en Materiales, Avenida Universidad la última actualización .

autoriza C.P García, Dra. Betsabé de Se Rivera opiniones expresadas 04-2015-110313532900-203, 04-2015-110313532900-203, POLYMAT CONTRIBUTIONS, Año 1, No. 1, enero-diciembre 2016, es una publicación anual editada por por editada anual publicación una es 2016, enero-diciembre 1, No. 1, Año CONTRIBUTIONS, POLYMAT www.iim.unam.mx/polymatcontributions, www.iim.unam.mx/polymatcontributions, Ernesto [email protected]. Rivera García, Dra. Betsabé Marel Monroy Editores responsables: Dr. 3000, Col. Copilco, Del. Coyoacán, C.P. 04510, Ciudad de México, México, de Ciudad 04510, C.P. 3000, Coyoacán, Del. Col. Copilco, la Universidad Nacional Autónoma de 04510, México, México, Ciudad Universitaria, Delegación Coyoacán, C.P. No. ISSN 2448-590X Responsable se notifique al editor se notifique al Ernesto Del. Coyoacán, Las publicación.