DOCSLIB.ORG

Addition of Sulfenic Acids to Monosubstituted Acetylenes: A

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Addition of Sulfenic Acids to Monosubstituted Acetylenes: A Addition of Sulfenic Acids to Monosubstituted Acetylenes: a Theoretical and Experimental Study Alessandro Contini, Maria Chiara Aversa, Anna Barattucci, Paola Bonaccorsi To cite this version: Alessandro Contini, Maria Chiara Aversa, Anna Barattucci, Paola Bonaccorsi. Addition of Sulfenic Acids to Monosubstituted Acetylenes: a Theoretical and Experimental Study. Journal of Physical Organic Chemistry, Wiley, 2009, 22 (11), pp.1048-n/a. 10.1002/poc.1557. hal-00477799 HAL Id: hal-00477799 https://hal.archives-ouvertes.fr/hal-00477799 Submitted on 30 Apr 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Journal of Physical Organic Chemistry Addition of Sulfenic Acids to Monosubstituted Acetylenes: a Theoretical and Experimental Study For Peer Review Journal: Journal of Physical Organic Chemistry Manuscript ID: POC-08-0252.R2 Wiley - Manuscript type: Research Article Date Submitted by the 02-Mar-2009 Author: Complete List of Authors: Contini, Alessandro; Università degli Studi di Milano, Istituto di Chimica Organica Aversa, Maria; Università degli Studi di Messina, Dipartimento di Chimica organica e biologica Barattucci, Anna; Università degli Studi di Messina, Dipartimento di Chimica organica e biologica Bonaccorsi, Paola; Università degli Studi di Messina, Dipartimento di Chimica organica e biologica Keywords: syn-Addition, DFT, HSAB principle, Regioselectivity, Sulfenic acids http://mc.manuscriptcentral.com/poc Page 1 of 36 Journal of Physical Organic Chemistry 1 2 3 4 Addition of Sulfenic Acids to Monosubstituted 5 6 7 8 9 Acetylenes: a Theoretical and Experimental Study 10 11 12 13 Maria Chiara Aversa, 1,3 Anna Barattucci, 1,3 Paola Bonaccorsi 1,3 and Alessandro Contini 2,3 * 14 15 16 1 17 Dipartimento di Chimica organica e biologica, Università degli Studi di Messina, Salita Sperone 31 18 For Peer Review 19 (vill. S. Agata), 98166 Messina, Italy 20 21 22 2 Istituto di Chimica organica “A. Marchesini”, Facoltà di Farmacia, Università degli Studi di Milano, 23 24 25 Via Venezian 21, 20133 Milano, Italy. 26 27 28 3 Centro Interuniversitario di Ricerca sulle Reazioni Pericicliche e Sintesi di Sistemi Etero e 29 30 31 Carbociclici 32 33 34 [email protected] 35 36 37 Tel. +390250314480 38 39 40 Fax +390250314476 41 42 43 44 45 Abstract 46 47 48 49 50 The reaction of benzenesulfenic acid, generated in situ by thermal decomposition of 3- 51 52 53 (phenylsulfinyl)propanenitrile, with monosubstituted acetylenes was experimentally and theoretically 54 55 investigated at the DFT level using the MPW1B95 density functional. A computational model based on 56 57 the Hard Soft Acid Base (HSAB) principle was evaluated for its ability to qualitatively and 58 59 60 http://mc.manuscriptcentral.com/poc 1 Journal of Physical Organic Chemistry Page 2 of 36 quantitatively predict the regioselectivity, while kinetics and thermodynamics of the reaction were 1 2 3 studied through the analysis of the reaction paths leading to the possible regioisomers. 4 5 6 7 Introduction 8 9 The importance of sulfenic acids RSOH as transient intermediates in biological processes is widely 10 11 recognized. Oxidation of thiol groups in living systems and much of the chemistry of the penicillin 12 13 [1] 14 sulfoxides have been considered to involve sulfenic acids. Unfortunately, most of them are too 15 16 unstable to be isolated and, for this reason, much of the knowledge of their reactions has been derived 17 18 indirectly through the rationalizationFor Peer of the final products.Review In particular, the syn -addition of sulfenic 19 20 21 acids to carbon-carbon triple bonds provides an easy way to obtain vinyl sulfoxides in mild conditions 22 23 and with some regioselectivity, and this reaction has found several applications in organic synthesis.[2] 24 25 Some theoretical works concerning the chemistry of sulfenic acids were carried out, most of them 26 27 28 dealing with the mechanism of the sulfoxide thermolysis, through the combination of theoretical 29 30 calculations with instrumental analysis.[3] Another computational study compared the syn-elimination 31 32 from corresponding amine oxides, sulfoxides, and phosphine oxides, showing that the elimination from 33 34 35 an amine oxide occurs with the lowest activation barrier, with the sulfoxide being the intermediate 36 37 case. [4] Other works were found dealing with the mechanism of sulfoxide reduction by thiols,[5] with the 38 39 rearrangement of H SO to give sulfenic acid HSOH,[6] or studying the acidity of several inorganic sulfur 40 2 41 [7] 42 oxoacids. Concerning the syn -addition of sulfenic acids to carbon-carbon multiple bonds (Scheme 1) 43 44 the generally accepted reaction mechanism is concerted and, when the sulfenic acid is trapped by a 45 46 monosubstituted unsaturated compound, the product is usually the one in which the partial positive 47 48 49 charge deriving from H approach to the multiple bond is better stabilized at the TS level, thus the 50 51 Markovnikov or anti-Markovnikov products for electron-donor (ED) or electron-withdrawing (EW) 52 53 substituents. [8] 54 55 56 57 58 59 60 http://mc.manuscriptcentral.com/poc 2 Page 3 of 36 Journal of Physical Organic Chemistry H ED H 1 O O O H 2 S S S 3 R R R 4 ED ED 5 6 Markovnikov 7 H 8 EW H O O O H 9 EW S S S 10 R R R EW 11 12 anti-Markovnikov 13 14 Scheme 1. 15 16 17 18 For Peer Review 19 To our knowledge, the syn -addition reaction of sulfenic acid to carbon-carbon triple bonds has never 20 21 been subjected to a systematic computational study. In particular, we were interested in rationalizing the 22 23 role of the alkyne substituent in governing the regiochemical outcome as well as in identifying some 24 25 26 reliable computational models able to predict the regiochemistry. Starting from the excellent work of 27 28 Jenks and coworkers, [3d] we have optimized a DFT based approach to study the addition between 29 30 benzenesulfenic acid and alkynes. Indeed, within the DFT framework, the development of a simple 31 32 33 theoretical model for the qualitative and semi-quantitative prediction of the addition regiochemistry has 34 35 been also possible through the HSAB principle,[9] thus assisting in rationalizing the role of the alkyne 36 37 substituent. Moreover, the computational analysis of the reaction paths leading to the different 38 39 40 regioisomers and the comparison of theoretical and experimental results have provided new and 41 42 interesting insights into the mechanism, kinetics and thermodynamics of the sulfenic acid syn -addition 43 44 reactions. 45 46 47 Results and Discussion 48 49 Experimental test set. Some representative examples for evaluating the regiochemistry of the addition 50 51 were planned in order to cover the main electronic and steric features of the alkyne substituent (Scheme 52 53 54 2). Thus, acetylenes bearing an aromatic strong or weak ED group ( 3a and 3b respectively), a phenyl 55 56 substituent ( 3c ), an aromatic strong EW group ( 3d ), an aliphatic EW group ( 3e ), and a sterically 57 58 59 encumbered weak ED group ( 3f ) were reacted with benzenesulfenic acid, generated in situ through the 60 http://mc.manuscriptcentral.com/poc 3 Journal of Physical Organic Chemistry Page 4 of 36 thermal decomposition of 3-(phenylsulfinyl)propanenitrile ( 1) (alkyne/ 1 molar ratio 6:1). Sulfenic acid 1 2 [10] 3 precursor 1 has been obtained in two simple steps from benzenethiol. The reactions were conducted 4 5 both in toluene and in acetonitrile at their reflux temperature in order to evaluate solvent influences in 6 7 governing the regiochemical outcome. Yields have been almost quantitative in all the cases. 8 9 10 11 12 R O R R 13 ∆ 3 S S H + 14 Ph CN i or ii Ph O 15 Ph S Ph S 16 1 2 4O 5 O 17 18 Fori: toluene Peerii: CHReviewCN 19 3 20 alkyne R 4/5 time (min) 4/5 time (min) 21 3a p-CH3OC6H4 100:0 25 100:0 420 22 3b p-CH3C6H4 100:0 30 99:1 480 23 3c Ph 100:0 30 99:1 510 24 3d p-NO2C6H4 90:10 35 90:10 600 25 3e COOCH3 30:70 70 25:75 900 26 3f TMS 0:100 70 0:100 1020 27 28 29 Scheme 2 (Reaction time and products obtained by the addition of sulfenic acid 2 to alkynes 3). 30 31 32 33 34 Results reported in Scheme 2 suggest that the solvent plays no relevant action in ruling the 35 36 37 regiochemistry, because an apolar solvent such as toluene and a polar aprotic solvent such as acetonitrile 38 39 lead essentially to the same regioisomeric ratio. The main observed change concerns the reaction time, 40 41 much shorter when the addition is conducted in toluene (from 25 to 70 min for 3a and 3e ,f, 42 43 44 respectively). Bearing in mind that the reaction is conducted at reflux, the observed differences in 45 46 reaction kinetics are probably due to the higher boiling point of toluene, and not to specific solvent 47 48 effects. It should also be noted that, as suggested by calculation results extensively discussed later on, in 49 50 51 most cases the reaction rate limiting step seems to be the decomposition of 1 to give benzenesulfenic 52 53 acid 2, with the evident exception of alkyne 3f whose addition to 2 results as the rate limiting step.
Load more

Recommended publications
  • Kimia Reaksi Anorganik
    12/22/2011 Kimia Reaksi Anorganik 2nd Mid-Semester Topics Yuniar Ponco Prananto • Frontier Orbitals (2 sks) • HSAB Application (5 sks) • Heterogeneous Acid Base Reaction (2 sks) • Reduction and Oxidation (12 sks): - Extraction of the Elements - Reduction Potential - Redox Stability in Water - Diagrammatic Presentation of Potential Data Frontier Orbitals …..summary Huheey, J.E., Keiter, E.A., and Keiter, R.L., 1993, Inorganic • Frontier orbitals, which are HOMO (highest occupied Chemistry, Principles of Structure and Reactivity , 4 th molecular orbital ) and LUMO (lowest unoccupied molecular ed., Harper Collins College Publisher, New York orbital ), has been focused nearly since the beginning of Miessler, D. L. and Tarr, D. A., 2004, Inorganic Chemistry , HSAB theory. 3rd ed., Prentice Hall International, USA • Koopman’s theorem , the energy of HOMO → the Atkins, P., Overton, T., Rourke, J., Shriver, D. F., Weller, M., ionization energy, while the energy of LUMO → the and Amstrong, F., 2009, Shriver and Atkins’ Inorganic electron affinity for a closed-shell spesies, in which both th Chemistry , 5 ed., Oxford University Press, UK orbitals are involved in the electronegativity and HSAB Gary Wulfsberg, 2000, Inorganic Chemistry , University relationships. Science Book, California, USA • Hard species → have a large HOMO – LUMO gap • Soft species → have a small HOMO – LUMO gap. [email protected] 1 12/22/2011 Frontier orbitals is the HOMO (filled or partly filled) and the LUMO (completely or partly vacant) of a MOLECULAR ENTITY. HOMO is the highest-energy molecular orbital of an atom or molecule containing an electron. Most likely the first orbital, from which an atom will lose an electron.
    [Show full text]
  • Predicting Metal Interactions with a Novel Quantitative Ion Character -Activity Relationship (QICAR) Approach
    W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 2002 Predicting metal interactions with a novel quantitative ion character -activity relationship (QICAR) approach David R. Ownby College of William and Mary - Virginia Institute of Marine Science Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Environmental Sciences Commons, and the Toxicology Commons Recommended Citation Ownby, David R., "Predicting metal interactions with a novel quantitative ion character -activity relationship (QICAR) approach" (2002). Dissertations, Theses, and Masters Projects. Paper 1539616800. https://dx.doi.org/doi:10.25773/v5-w1nf-pb08 This Dissertation is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. Reproduced with with permission permission of the of copyright the copyright owner. owner.Further reproductionFurther reproduction prohibited without prohibited permission. without permission. PREDICTING METAL INTERACTIONS WITH A NOVEL QUANTITATIVE ION CHARACTER-ACTIVITY RELATIONSHIP (QICAR) APPROACH A Dissertation Presented to The Faculty of the School of Marine Science The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Doctor of Philosophy by David R. Ownby 2002 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPROVAL SHEET This dissertation is submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy David R. Ownby^' Approved, May 2002 / r , V v t ( n i t Michael C.
    [Show full text]
  • The Hard-Soft Acid-Base Principle in Enzymatic Catalysis: Dual Reactivity of Phosphoenolpyruvate YAN LI and JEREMY N
    Proc. Natl. Acad. Sci. USA Vol. 93, pp. 4612-4616, May 1996 Biochemistry The hard-soft acid-base principle in enzymatic catalysis: Dual reactivity of phosphoenolpyruvate YAN LI AND JEREMY N. S. EVANSt Department of Biochemistry and Biophysics, Washington State University, Pullman, WA 99164-4660 Communicated by R. G. Pearson, University of California, Santa Barbara, CA, January 11, 1996 (received for review October 9, 1995) ABSTRACT In this paper, the chemical reactivity of C3 of Fukui function f(r) (9) is one such quantity that is related to phosphoenolpyruvate (PEP) has been analyzed in terms of the electronic density in the frontier molecular orbitals and density functional theory quantified through quantum chem- thus determines the chemical selectivity (10). For a chemical istry calculations. PEP is involved in a number of important reaction, a Taylor series expansion can be performed up to enzymatic reactions, in which its C3 atom behaves like a base. second order by energy perturbation methods within the In three different enzymatic reactions analyzed here, C3 framework of density functional theory (11). The energy sometimes behaves like a soft base and sometimes behaves like change for a molecule will be, to second order in the changes a hard base in terms ofthe hard-soft acid-base principle. This AN and Av(r): dual nature of C3 of PEP was found to be related to the conformational change of the molecule. This leads to a ( aE\- aE testable hypothesis: that PEP adopts particular conforma- AE = AN + tions in the enzyme-substrate complexes of different PEP- aN\ vN,(r) a v (r) N Av (r)dr using enzymes, and that the enzymes control the reactivity through controlling the dihedral angle between the carboxy- _E - l( d2E late and the C=C double bond of PEP.
    [Show full text]
  • Effect of Some Electron Donor and Electron Acceptor Groups on Stability of Complexes According to the Principle of HSAB
    ISSN: 1304-7981 Number: 4 , Year: 2014, Pages: 82-89 http://jnrs.gop.edu.tr Received: 31.01.2014 Editors-in-Chief: Naim Çağman Accepted: 19.03.2014 Area Editor: Yakup Budak Effect of Some Electron Donor and Electron Acceptor Groups on Stability of Complexes According to the Principle of HSAB Savaş Kayaa,1 ([email protected]) Sultan Erkan Karipera ([email protected]) Ayhan Ungördüa ([email protected]) Cemal Kayaa ([email protected]) aChemistry Department, Faculty of Science, Cumhuriyet University, 58100, Sivas, TURKEY Abstract – Chemical hardness is an important feature of substances. Lewis acids and bases have been classified to considering the chemical hardness concept and HSAB (Hard and Soft Acid- base) Principle has been demonstrated by Pearson. HSAB principle is an extremely useful qualitative theory that enables predictions of what adducts will form in a complex mixture of potential Lewis acids and bases. Furthermore, Keywords – HSAB, Pyrithione, chemical hardness is associated with chemical reactivity of molecules. In DFT, Chemical hardness, this study, effect of the chemical hardness in complexes formation was Coordination complexes investigated. For this purpose, complexes with Ca2+, Zn2+, Mg2+, Cu2+ ions of pyrithione (PT) ligand and its derivatives were studied. All calculations were made using the Gaussian 09, Revision B.01 program. The obtained geometries were further optimized at the b3lyp/ 6-31g (d,p) level using Gaussian package. In complex formation reactions, reaction energy (ΔE) has been calculated. 1. Introduction Chemical hardness fundamentally signifies the resistance toward the deformation or polarization of electron cloud of the atoms, ions, or molecules [1]. Chemical hardness is one of extremely useful conceptual constructs of chemistry and physics.
    [Show full text]
  • Hard and Soft Acids and Bases 1965- Ralph Pearson Introduced the Hard-Soft-Acid-Base (HSAB) Principle
    380 Hard and Soft Acids and Bases 1965- Ralph Pearson introduced the hard-soft-acid-base (HSAB) principle. “Hard acids prefer to coordinate the hard bases and soft acids to soft bases” This very simple concept was used by Pearson to rationalize a variety of chemical information. 1983 – the qualitative definition of HSAB was converted to a quantitative one by using the idea of polarizability. A less polarizable atom or ion is “hard” and a more easily polarized atom or ion is “soft” 381 The Quantitative Definition of hardness: The average of ionization N = (I.P. – E.A.) /2 potential and electron affinity Actually, the electronegativity, X, of a neutral species is the same X = (I.P. – E.A.) /2 One can relate n (hardness) to the gap between the HOMO and LUMO: E (energy) 2n = (ELUMO - EHOMO) HOMO and LUMO orbitals (molecules) or simply highest occupied and lowest unoccupied orbitals in atoms participate in the bonding more than any other levels. (The lower the energy of the HOMO and the higher the energy of the LUMO, the more stable the species is thermodynamically) The greater the n value - the more hard the species is. 382 Basically, HSAB theory endeavors to help one decide if AB + A’B’ AB’ + A’B goes to the left or the right A= and Acid B = Base Hard and Soft Acids and Bases Hard acid: High positive charge Small size Not easily polarizable Hard base: Low polarizability High electronegativity Not easily oxidized Soft acid: Low positive charge Large size; easily oxidized Highly polarizable Soft base: High polarizability Diffuse donor orbital Low electronegativity Easily oxidized 383 Hard acids prefer to bind to hard bases and soft acids prefer to bind to soft bases.
    [Show full text]
  • Medical Therapy of Patients Contaminated with Radioactive Cesium Or Iodine
    Roskilde University Medical Therapy of Patients Contaminated with Radioactive Cesium or Iodine Aaseth, Jan; Nurchi, Valeria Marina; Andersen, Ole Published in: Biomolecules DOI: 10.3390/biom9120856 Publication date: 2019 Document Version Publisher's PDF, also known as Version of record Citation for published version (APA): Aaseth, J., Nurchi, V. M., & Andersen, O. (2019). Medical Therapy of Patients Contaminated with Radioactive Cesium or Iodine. Biomolecules, 9(12), [856]. https://doi.org/10.3390/biom9120856 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal. Take down policy If you believe that this document breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 30. Sep. 2021 biomolecules Review Medical Therapy of Patients Contaminated with Radioactive Cesium or Iodine Jan Aaseth 1,2,* , Valeria Marina Nurchi 3 and Ole Andersen 4 1 Research Department, Innlandet Hospital Trust,
    [Show full text]
  • A Map of the Inorganic Ternary Metal Nitrides
    A Map of the Inorganic Ternary Metal Nitrides Wenhao Sun1, Christopher Bartel2, Elisabetta Arca3, Sage Bauers3, Bethany Matthews4, Bernardo Orvañanos5, Bor-Rong Chen,6 Michael F. Toney,6 Laura T. Schelhas,6 William Tumas3, Janet Tate,4 Andriy Zakutayev3, Stephan Lany3, Aaron Holder2,3, Gerbrand Ceder1,7 1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 2 Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA 3 National Renewable Energy Laboratory, Golden, Colorado 80401, USA 4 Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA 5 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 6 SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. 7 Department of Materials Science and Engineering, UC Berkeley, Berkeley, California 94720, USA Corresponding Authors: [email protected], [email protected] Abstract: Exploratory synthesis in novel chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation—from which we experimentally realized 7 new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity, and covalency of solid-state bonding from the DFT- computed electron density, we reveal the complex interplay between chemistry, composition, and electronic structure in governing large-scale stability trends in ternary nitride materials.
    [Show full text]
  • The Reaction of Platinum Triamine Complex with Different DNA and Protein Complexes
    Western Kentucky University TopSCHOLAR® Honors College Capstone Experience/Thesis Projects Honors College at WKU Spring 5-16-2014 The Reaction of Platinum Triamine Complex with Different DNA and Protein Complexes Morgan Gruner Western Kentucky University, [email protected] Follow this and additional works at: https://digitalcommons.wku.edu/stu_hon_theses Part of the Biology Commons Recommended Citation Gruner, Morgan, "The Reaction of Platinum Triamine Complex with Different DNA and Protein Complexes" (2014). Honors College Capstone Experience/Thesis Projects. Paper 465. https://digitalcommons.wku.edu/stu_hon_theses/465 This Thesis is brought to you for free and open access by TopSCHOLAR®. It has been accepted for inclusion in Honors College Capstone Experience/Thesis Projects by an authorized administrator of TopSCHOLAR®. For more information, please contact [email protected]. THE REACTION OF A PLATINUM TRIAMINE COMPLEX WITH DIFFERENT DNA AND PROTEIN COMPLEXES A Capstone Experience/Thesis Project Presented in Partial Fulfillment of the Requirements for the Degree of Bachelors of Science with Honors College Graduate Distinction at Western Kentucky University By Morgan Fay Gruner ***** Western Kentucky University 2014 CE/T Committee: Approved by Dr. Kevin Williams Dr. Chad Snyder ____ Advisor Dr. Michael Smith Department of Chemistry Copyright by Morgan Fay Gruner 2014 ABSTRACT The platinum compound ( ) Cl [Chloro[N,N- diethyldiethylenetriamine] Platinum(II) Chloride] was synthesized and reacted with N-acetylmethionine (N-AcMet) and guanosine 5’-monophosphate (5’-GMP). Previous experiments show that N-AcMet reacts kinetically faster with the central platinum atom and that 5’-GMP bonds slower yet stronger. When ( ) Cl was reacted with N-AcMet the N-AcMet displaced the chloride ion as expected.
    [Show full text]
  • INTRODUCTION Understanding the Mechanisms of Enzymes Has Been the Focus of Numerous Research Areas in the Past Few Years. in Or
    INTRODUCTION Understanding the mechanisms of enzymes has been the focus of numerous research areas in the past few years. In order to study these enzymes, complexes have been synthesized and studied to model the active sites of enzymes. Such complexes have provided valuable information that has increased our knowledge of enzyme mechanism. In biological systems, the chemical makeup of many enzymes involves the use of 1st and 2nd row transition metal ions. Such metal ions include Zn, Fe, Co, Cu, Mn and Mo. It has been shown that metal ions play an important role in enzyme activation. Understanding the exact chemistry behind how metal ions activate enzymes is still an area of ongoing research. Zinc has proven to be an extremely crucial 1st row transition metal. Zinc has a role as a nutrient in biological systems. With the significance that zinc has in biological systems, it becomes important to study the behavior of zinc in a biological environment. One of the most interesting areas of recent research is the crucial role zinc plays in activating metalloenzymes.1 Metalloenzymes are enzymes that utilize a metal ion located at the active site to catalyze biological processes. Examples of metalloenzymes that use zinc in order to function are carbonic anhydrase, an enzyme that interconverts CO2 and bicarbonate, and alcohol dehydrogenase, an NAD+/NADH dependent enzyme that catalyzes reversible oxidation of alcohols to aldehydes or ketones. Both of these enzymes require a zinc metal ion complexed at the active site in order to function. Despite known involvement of zinc in enzyme activity, many of the mechanisms governing coordination chemistry of zinc with metalloenzymes still remain unclear.
    [Show full text]
  • The Coordination Chemistry of Solvated Metal Ions in DMPU
    The Coordination Chemistry of Solvated Metal Ions in DMPU A Study of a Space-Demanding Solvent Daniel Lundberg Faculty of Natural Resources and Agricultural Sciences Department of Chemistry Uppsala Doctoral thesis Swedish University of Agricultural Sciences Uppsala 2006 Acta Universitatis Agriculturae Sueciae 2006: 23 ISSN 1652-6880 ISBN 91-576-7072-2 © 2006 Daniel Lundberg, Uppsala Tryck: SLU Service/Repro, Uppsala 2006 Abstract Lundberg, D., 2006, The Coordination Chemistry of Solvated Metal Ions in DMPU – A Study of a Space-Demanding Solvent. Doctor’s dissertation. ISSN 1652-6880, ISBN 91-576-7072-2 This thesis summarizes and discusses the results of several individual studies on the solvation of metal ions in the solvent N,N’-dimethylpropyleneurea, DMPU, including the iron(II), iron(III), zinc(II), cadmium(II), and lanthanoid(III) ions. These studies have shown that the solvation process in DMPU is sometimes very different to those in corresponding aqueous systems. This is due to the the space-demanding properties the DMPU molecule has when coordinating to metal ions, with its two methyl groups close to the coordinating oxygen atom. The methyl groups effectively hinder/hamper the metal ion from reaching the coordination numbers present in hydrate and solvate complexes with solvent molecules with much lower spatial demands. The investigations were performed with different X-ray techniques, including extended X-ray absorption fine structure (EXAFS), large angle X-ray scattering (LAXS), and single crystal X-ray diffraction (XRD) and included both studies in solution (EXAFS and LAXS) and solid state (EXAFS and XRD). A coordination number reduction, compared to the corresponding hydrates, was found in all of the studied systems, except cadmium(II).
    [Show full text]
  • MODULE No. 19, Ambident Nucleophile and Regioselectivity 1. Ht
    Weblinks : 1. http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch06/ch6-0-1.html 2. www.chem.ucla.edu/harding/IGOC/A/ambident_nucleophile.html 3. www.adichemistry.com/inorganic/.../hsab/hard-soft-acid-base-theory.htm 4. www.nature.com/nrmicro/journal/v11/n6/fig.../nrmicro3028_F1.html 5. www.masterorganicchemistry.com/.../addition-reactions-regioselectivity/ CHEMISTRY PAPER No. 5: Organic chemistry-2 (Reaction Mechanism-1) MODULE No. 19, Ambident nucleophile and regioselectivity Suggested readings Atkins, P. W. & Paula, J. de Atkin’s Physical Chemistry 9th Ed., Oxford University Press (2012). Jerry March, Advanced Organic Chemistry, Fourth Edition. P. S. Kalsi, Organic Reactions And Their Mechanisms CHEMISTRY PAPER No. 5: Organic chemistry-2 (Reaction Mechanism-1) MODULE No. 19, Ambident nucleophile and regioselectivity Named Organic Reactions By Thomas Laue, Andreas Plagens William Brown, Christopher Foote, Brent Iverson, Eric Anslyn, Organic Chemistry, Enhanced Edition Glossary A CHEMISTRY PAPER No. 5: Organic chemistry-2 (Reaction Mechanism-1) MODULE No. 19, Ambident nucleophile and regioselectivity Ambident nucleophile: An ambident nucleophile is an anionic nucleophile whose negative charge is delocalized by resonance over two unlike atoms or over two like but non-equivalent atoms. Aprotic Solvent: Polar aprotic solvents are solvents that will dissolve many salts, but lack an acidic hydrogen. These solvents generally have intermediate dielectric constants and polarity. Although discouraging use of the term "polar aprotic", IUPAC describes such solvents as having both high dielectric constants and high dipole moments, an example being acetonitrile. Other solvents meeting IUPAC's criteria include DMF, HMPA, and DMSO D Dields –Alder reaction: The Diels–Alder reaction is an organic chemical reaction (specifically, a [4+2] cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system.
    [Show full text]
  • Coordination Chemistry Transition Metal Complexes
    Coordination Chemistry Transition Metal Complexes Direct Application of Lewis AB and Hard/Soft AB “Theories” A TEP (Thermal Ellipsoid Plot) of a single molecule of tungsten hexacarbonyl, W(CO)6 Thermal ellipsoids indicate extent of thermal motion. The tighter, rounder the atom, the better the structure. This one looks great. Overview of Transition Metal Complexes 1.The coordinate covalent or dative bond applies 2.Lewis bases are called LIGANDS—all serve as σ-donors some are π-donors as well, and some are π-acceptors 3. Specific coordination number and geometries depend on metal and number of d-electrons 4. HSAB theory useful a) Hard bases stabilize high oxidation states b) Soft bases stabilize low oxidation states Properties of Transition Metal Complexes 1. Highly colored (absorb light in visible, transmit light which eye detects) 2. Metals may exhibit multiple oxidation states 3. Metals may exhibit paramagnetism dependent on metal oxidation state and on ligand field. 4. Reactivity includes: A) Ligand exchange processes: i) Associative (SN2; expanded coordination no.) ii) Dissociative (SN1; slow step is ligand loss) B) Redox Processes i) inner sphere atom transfer; ii) outer sphere electron processes) iii) Oxidative Addition and Reductive Elimination Classification of Ligands (ALL are Lewis Bases) Ligands, continued Oxidation States Available to Essential Bulk and Trace Metals Metal Available Oxidation States Na 1 K 1 Mg 2 Ca 2 V 2 (3) (4) (5) Cr 2 (3) (4) (5) (6) Mn 2 3 4 (5) (6) (7) Fe 1 2 3 4 (5) Co 1 2 3 Ni 1 2 3 Cu 1 2 Zn 2 Mo 2 The parentheses indicate oxidation levels not normally found in biological molecules.
    [Show full text]