Luminescence Based Detection of Trinitrophenol and Aromatic Organophosphorous Pesticides Using a Coordination Polymer

J. Mex. Chem. Soc. 2017, 61(4),336-341 Article © 2017, Sociedad Química de México ISSN 1870-249X Luminescence Based Detection of Trinitrophenol and Aromatic Organophosphorous Pesticides Using a Coordination Polymer Rupinder Kaur,1 Manmohan Chhibber,1 Partha Mahata2 and Susheel K. Mittal*1 1 School of Chemistry & Biochemistry, Thapar University, Patiala-147004, India. Email: [email protected] 2 Department of Chemistry, Jadavpur University, Kolkata-700 032, India Email: [email protected] Received February 3rd, 2017; Accepted September 18th, 2017 Abstract: The fluorescent properties of a coordination polymer Resumen: Las propiedades fluorescentes del polímero de coordinación (CP), 1, were used as turn-on and turn-off detector for nitroaromatics (CP), 1, fueron utilizadas como detectores de encendido y apagado, para and organophosporus pesticides respectively. Compound 1 exhib- pesticidas nitroaromáticos y organofosforados, respectivamente. El its exceptionally high efficiency for the detection of 2,4,6-trinitro- compuesto 1 muestra una eficiencia extraordinariamente alta para la phenol (TNP) through luminescence quenching with a quenching detección del 2,4,6-trinitrofenol (TNP) utilizando la atenuación de la 5 -1 constant [KSV] value of 2.30 X 10 M , highest among the known luminiscencia , con un valor de la constante de atenuación [KSV] de 2.30 coordination polymers. Minimum detection limit achieved by the X 105 M-1, la más alta entre los polímeros de coordinación conocidos. proposed method was 43 ppb. This emission property of 1 was also El límite de detección obtenido para el método propuesto fue de 43 ppb. used successfully to detect triazophos and chlorpyrifos, aromatic or- La propiedad de emisión del compuesto 1 fue también utilizada exitósa- ganophosphorus pesticides, which enhanced the emission intensity mente para detectar el triazofos y cloropirifos, pesticidas órganofosfo- by 238% and a red shift of ~70 nm in case of former. Non aromatic rados aromáticos, los cuales incrementan la intensidad de emisión en un pesticides like malathion and acephate did not show any increase in 238% y un desplazamiento hacia el rojo de ~70 nm, para el primer com- the emission intensity. Minimum detection limits for triazophos and puesto. Los pesticidas no aromáticos como el malatión y el acefato no chlorpyrifos, aromatic organophosphorus pesticides, were 0.6 and mostraron un incremento en la intensidad de emisión. Los límites de 0.7 ppm respectively. detección para triazofos y cloropirifos, pesticidas órgano osforados aro- Key words: nitro-explosives; TNT; acetylcholinesterases; acetylcho- máticos, fueron de 0.6 and 0.7 ppm, respectivamente. line; molecular sensing; MOF Palabras clave: nitro-explosivos; TNT; acetilcolinesterasas; acetilco- lina; detección molecular; MOF Introduction has been reported that TNP is a much stronger explosive than 2,4,6-trinitro toluene commonly known as TNT[18]. Beside Being highly porous and crystalline, coordination polymers explosives, TNP is also used in glass, match sticks, fireworks, (CPs) belong to a better class of solids in comparison to the ze- dyes and in leather industry. [17, 19-20] TNP is also known to olites. Owing to the fact of unmatched structural diversity, tun- cause obnoxious effects on human heath such as irritation to ability and the possibility of post synthetic modification which skin, eyes and damage to the respiratory system. [21] There- generally lacks in zeolites, coordination polymers have been ex- fore, development of detection methodologies for TNP is of plored extensively during the last decade. Recently, CPs are be- immense significance for the safety and security of life. ing explored for their potential applications such as heterogenous Aromatic organophosphate pesticides are another class of catalysis,[1] gas storage,[2-3] drug delivery,[4-5] and molecular chemicals with a threat to the environment due to accumula- sensing [6-9]. These macromolecules can efficiently behave as tion in soil after use and their transfer to food chain via water, receptor and equally good signal transducer due to their porous grains, milk and poultry products. Chlorpyrifos and triazophos nature coupled along with luminescence properties, the foremost are two widely used aromatic organo phosphorous pesticides requirement to be developed into a good sensor. in many countries that have adverse effects on human health. The property of luminescence in CPs has become an ac- Their toxic nature can be realized from their ability to inhib- tive area of research due to its potential applications [10]. it acetylcholinesterases (AChE), an enzyme that causes rapid This is evident from geometrical hike in the number of reports hydrolysis of a neurotransmitter acetylcholine, thus preventing during the last few years related to the sensing of nitroaro- nerve impulses in human body causing neurological problems matics, the active components or by-products of explosives, [22]. Thus, there is a need to detect these compounds accurately [11-16] and important issues related to homeland security and and efficiently even in trace amounts. environment. TNP is a key energetic ingredient for the prepa- Current methods to detect explosives include trained ca- ration of landmines and improvised explosive devices. [17] It nines or sophisticated instruments, [23] such as ion mobility Luminescence Based Detection of Trinitrophenol and Aromatic Organophosphorous Pesticides Using a Coordination Polymer 337 spectrometry, [24] energy dispersive X-ray diffraction, [25] emission is due to the intra-ligand transitions (ᴫ*→n and ᴫ*→ plasma desorption mass spectrometry, [26] surface-enhanced ᴫ) of OBA ligands. Potential of 1 to detect trace amount of ni- Raman spectroscopy [27-29] and different imaging technolo- troaromatics was explored by incremental addition of analytes gies. [30] For pesticide detection commonly used techniques to its dispersed solution in water. are gas chromatography, [31-32] high performance liquid chromatography [33-34] and mass spectrometry. [35] Although these established methods are highly sensitive and accurate they suffer from a number of disadvantages such as high cost of instruments, complex functioning and lack of portability. The use of luminescence property of CPs for the detection of hazardous chemicals seems a logical alternate. [36] Recently, Kumar et al have reported two different CPs having Zn and Cd as metal centres to behave as sensitive detectors for nitro containing organophoshate pesticides. [37-38] Considering above advantages, we have used a two-dimensional Co-based CP, [Co(OBA)(H2O)2] [(OBA = 4,4’-oxybis(benzoate)], 1, prepared using an earlier reported protocol,[39] for the sensing of nitro explosives and pesticides. We found that all the nitroaromatics behave as fluorescence Fig.1: Two-dimensional layered structure where inter-layer hydrogen quenchers for CP,1, with TNP being the most efficient and bond interactions for CP,1. nitrobenzene being the least quencher. Organophoshate pesticides namely triazophos and chlorpyrifos, on the other hand, exhibited a turn-on luminescence behaviour. This is the first observation, to the best of our knowledge, where same CP has been used for the detection of nitro-explosives and aromatic organophosphate pesticides simultaneously through two different luminescence behaviours (turn-on and turn-off). In this article, we present the detailed studies of luminescence based detection behaviour of 1 for nitroaromatics and pesticides. Results and Discussion Synthesis, Characterization and Structure of CP Fig. 2: Emission spectra of 1 dispersed in water upon incremental ad- The coordination polymer, [Co(OBA)(H2O)2] [OBA= dition of 2,4,6-trinitrophenol solution (I = 255 nm). 4,4’-oxybis(benzoate)], 1 was synthesized using a convenient ex solvent evaporation method taking CoCl2.6H2O and 4,4’-oxybis (benzoic acid) as precursors and water as a solvent. The Fig. 2 shows gradual attenuation in luminescence intensity of crystal structure of as-synthesized CP was characterized with 1 with incremental addition of TNP. A final addition up to 20 the help of powder X-Ray diffraction technique (P-XRD) (Fig. M of TNP quenches the emission intensity of 1 to 84.5% of its S1). The diffraction pattern of the Co-MOF was found to be in initial intensity. Fig. 3 shows luminescence attenuation as low complete agreement with the simulated pattern generated from asµ 0.19 M which is equivalent to 43 ppb. These results clearly the single crystal data and with that of the earlier reported lit- mark 1 as one of highly sensitive detectors. erature.[39] The pattern shows two sharp and major peaks at Lowµ detection limit of TNP encouraged us to perform sim- 2Ɵ = 6.97º, 13.8º suggesting its highly crystalline nature and a ilar luminescence quenching titrations with other nitroaromat- multiplet ranging from 18.1º -21º. Briefly, the structure of CP,1, ics such as nitrobenzene, 4-nitrophenol, 4-nitrobenzoic acid, consists of Co2+ ions connected by the oxybis(benzoate) units 1, 3-dinitro benzene, 2,6-dinitro toluene, benzene and toluene forming a two-dimensional layered structure where inter-layer (ESI, Fig. S2-S8). The quenching efficiency (%) was estimated hydrogen bond interactions gives rise to supra-molecularly or- using formula (Io - I)/Io × 100, where Io is the fluorescence in- ganized three-dimensional structure as shown in fig. 1. tensity without the addition of analyte and I being the intensity after the addition of analyte. Fig. 4 shows the quenching effi- Nitroaromatic sensing ciency of all the analytes at 20 µM concentration. Quenching efficiency of 84.5 % with TNP is highest for 1 as compared to Compound 1 when dispersed in water exhibited a violet emis- other nitroaromatics, thus proving sensitivity for its detection. sion centred at 411 nm upon excitation at 255 nm. The observed Amongst others, the decreasing order of quenching efficiency 338 J. Mex. Chem. Soc. 2017, 61(3) Rupinder Kaur et al. was 2,6-dinitrotoluene (31.2%), 1,3-dinitrobenzene (18.8%), concentration are mainly due to static quenching, whereas the 4-nitrobenzoic acid (12.6%), 4-nitrophenol (8.15%) and ni- steep curves at higher concentration are presumably due to trobenzene (2 %).

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