DOCSLIB.ORG

Nuclear Magnetic Resonance Spectroscopy of Porphyrins and Metalloporphyrins Hugo Scheer and Joseph J

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Nuclear Magnetic Resonance Spectroscopy of Porphyrins and Metalloporphyrins Hugo Scheer and Joseph J PORPHYRINS AND METALLOPORPHYRINS A new edition based on the original volume by J. E. Falk Edited by KEVIN M. SMITH University of Liverpool ELSEVIER SCIENTIFIC PUBLISHING COMPANY AMSTERDAM - OXFORD - NEW YORK ELSEVIER SCIENTIFIC PUBLISHING COMPANY 335 Jan van Galenstraat P.O. Box 211, Amsterdam, The Netherlands AMERICAN ELSEVIER PUBLISHING COMPANY, INC. 52 Vanderbilt Avenue New York, New York 10017 Universe- - : Bibliothek - München ì Staatsbibliothenek Münch en Library of Congress (.'alalo^in^ in I 'ublkation Data Main entry under title: Porphyrins and metalloporphyrins. Ausgeschieden •Us den Beständen Includes bibliographical references and index. der BSß München 1. Porphyrins and porphyrin compounds. I. Falk, J. E. Porphyrins and metalloporphyrins. II. Smith, Kevin M. QD401.P7 1975 547'.593 75-20551 ISBN 0-444-41375-8 ISBN 0-444-41375-8 Copyright © 1975 by Elsevier Scientific Publishing Company, Amsterdam All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopy• ing, recording, or otherwise, without the prior written permission of the publisher, Elsevier Scientific Publishing Company, Jan van Galenstraat 335, Amsterdam Printed in The Netherlands PREFACE In 1964, J.E. Falk was able to give one man's view of the porphyrin and metalloporphyrin field at possibly the last time that such a major task was possible. Since then the area has mushroomed outwards and blossomed in a quite remarkable manner, and this may in no small way be due to the stimu• lus provided by the appearance of Porphyrins and Metalloporphyrins. Around the time of his death, Falk was addressing himself to the task of updating and revizing his highly successful book, ,and realizing the magnitude of the undertaking, had begun to gather about him varioiïs colleagues who might be willing to contribute to a multi-authored Secoq|| Edition. Alas, all of this came to nothing, but the demand for a new andexpanded edition of Falk remained. The present book represents an attempt by some of the leading authori• ties in the field to fill the gap left by the progress of porphyrin chemistry past the account written by Falk. It differs considerably from the original, mainly in size, but also in the organization of the chapters into eight sec• tions. A detailed description of the content of each section would be out of place 1ère, but it is worth commenting that sections dealing with synthetic and biological aspects have been added, as well as chapters dealing in depth with many spectroscopic methods which were only in their infancy in 1964. In the whole book Falk's 'systematic and rational exposition which would have been quite impossible some years ago' has been carried to the bounda• ries of present research. An attempt has been made to retain the idea of a 'Laboratory Handbook' which was the underlying concept in Falk. Though the book has grown dra• matically in siz&, a substantial section dealing with laboratory methods has been included.' Many of the procedures have not been noticeably im• proved since 1964, and in these cases there are few changes from the account written by Falk; however, in other respects, the Laboratory Methods Section has been expanded and revized. The manuscript deadline for the present book was 1st January 1975, and with the exception of a few chapters which arrived in late March 1975, literature published after December 1974 has not been considered. However, as always when accounts are written by active research workers in the field, the chapters contain abundant references to unpublished work, or work in press, as well as personal communications from other researchers. In order to preserve the timeliness of the contributions in this book, it was necessary to VI PREFACE proceed to publication without two manuscripts which were estimated, by the authors, to be one month or more from completion on 1st June 1975. It is a pleasure to record my thanks to Professor G.W. Kenner, F.R.S., for his advice and encouragement during the past two years. In contributed volumes of this type with about twenty chapters, crises arise at fairly regular intervals; I would like to thank Professor Dr J.W. Buchler (Aachen) and Dr J.-H. Fuhrhop (Stöckheim über Braunschweig) for unhesitating assistance during these difficult times, and for providing the encouragement to go ahead in the formative days of this project. Liverpool, June 1975 Kevin M. Smith CONTENTS Preface V SECTION A: GENERAL AND SYNTHETIC ASPECTS Chapter 1 General features of the structure and chemistry of porphyrin compounds Kevin M. Smith 1.1 Structures and nomenclature 3 1.1.1 Nomenclature 5 1.1.2 Related structures 6 1.1.2.1 Reduced porphyrin macrocycles 6 1.1.2.2 Oxidized porphyrin macrocycles 8 1.1.2.3 Porphyrin analogs 8 1.1.3 Isomerism in porphyrins 9 1.2 General chemistry 9 1.2.1 Aromaticity of the macrocycle 9 1.2.2 Tautomerism in the macrocycle 10 1.2.3 Ionization of porphyrins 11 1.2.3.1 Nitrogen atoms 11 1.2.3.2 Carboxylic acid side-chains 14 1.2.3.3 Acid (HCl) numbers 15 1.2.3.4 Complexation with metal ions 15 1.2.4 Stability of porphyrin compounds 15 1.2.4.1 General features 15 1.2.4.2 Instability to light 16 1.2.4.3 Other examples of instability 16 1.3 Occurrence of porphyrin compounds 16 1.3.1 Metal complexes 16 1.3.2 Metal-free porphyrins 18 1.4 Chromophores of porphyrin systems 19 1.4.1 Porphyrins 20 1.4.1.1 In neutral solvents 20 1.4.1.1.1 Etio type spectra 20 1.4.1.1.2 Rhodo type spectra 21 1.4.1.1.3 Oxorhodo type spectra 23 1.4.1.1.4 Phyllo type spectra 23 1.4.1.1.5 Spectra of porphyrins containing isocyclic rings 23 1.4.1.2 In acidic solvents 24 1.4.1.3 In alkaline solvents 24 Vili CONTENTS 1.4.2 Chlorins 25 1.4.3 Metalloporphyrins 25 1.4.4 Phlorins and oxophlorins 25 References 2 7 Chapter 2 Synthesis and preparation of porphyrin compounds Kevin M. Smith 2.1 Scope 29 2.2 Syntheses of dipyrrolic intermediates 30 2.2.1 Pyrromethenes 30 2.2.2 Pyrrome thanes 31 2.2.3 Pyrroketones 31 2.3 Syntheses of porphyrins 32 2.3.1 By polymerization of monopyrroles 32 2.3.2 From dipyrrolic intermediates 33 2.3.2.1 From pyrromethenes 33 2.3.2.2 From pyrromethanes 35 2.3.2.3 From pyrroketones 36 2.3.3 From open-chain tetrapyrrolic intermediates 36 2.3.3.1 From bilanes and oxobilanes 37 2.3.3.1.1 Using bilane intermediates 37 2.3.3.1.2 Using a-oxobilane intermediates 38 2.3.3.1.3 Using ò-oxobilane intermediates 40 2.3.3.2 From bilenes 41 2.3.3.2.1 Using l',8'-dimethyl-6-bilenes 41 2.3.3.2.2 Using 6-bilene-l',8'-diesters 42 2.3.3.2.3 Using other 6-bilenes 43 2.3.3.3 From a,c-biladienes 44 2.3.3.3.1 Using l',8'-dimethyl-a,c-biladienes 44 2.3.3.3.2 Using l'-bromo-8'-methyl-a,c-biladienes 46 2.3.3.3.3 Using other a,c-biladienes 46 2.3.4 General conclusions 47 2.4 Preparation of porphyrins by degradation of natural pigments 48 2.4.1 From hemoglobin 48 2.4.1.1 Protohemin 48 2.4.1.2 Hematoporphyrin-IX 49 2.4.1.3 Protoporphyrin-IX 49 2.4.1.4 Mesoporphyriri-IX 50 2.4.1.5 Deuteroporphyrin-IX and its derivatives 50 2.4.1.6 Coproporphyrin-III 51 2.4.1.7 Other porphyrins of biological significance 51 2.4.2 From the plant chlorophylls 52 References 55 SECTION B: BIOLOGICAL ASPECTS Chapter 3 Biosynthesis of porphyrins, chlorins, and corrins A.R. Battersby and E. McDonald 3.1 Introduction 61 3.2 The biosynthesis of porphobilinogen 62 CONTENTS IX 3.2.1 Historical background and fundamental studies 62 3.2.2 ALA synthetase 66 3.2.2.1 Mechanistic studies 66 3.2.2.1.1 Cofactor requirement 66 3.2.2.1.2 Binding and activation of glycine 68 3.2.2.1.3 Binding of succinyl coenzyme A and the acyla- tion step 70 3.2.2.1.4 The decarboxylation step 70 3.2.2.2 Inhibition of ALA synthetase in vivo 72 3.2.3 ALA dehydratase 7 2 3.2.3.1 Binding of ALA 73 3.3 Conversion of porphobilinogen into uroporphyrinogen-III 74 3.3.1 Porphyrinogens as biosynthetic intermediates 74 3.3.2 Outline of the problem 75 3.3.3 Porphobilinogen deaminase 77 3.3.4 Uroporphyrinogen-III cosynthetase 78 3.3.5 Enzymic formation of uroporphyrinogen-I 78 3.3.5.1 Stoichiometry 78 3.3.5.2 Intermediates 79 3.3.5.3 Possible mechanistic scheme 82 3.3.6 Enzymic formation of uroporphyrinogen-III 83 3.3.7 Analysis of hypotheses regarding formation of the type-Ill isomer 85 3.3.8 Basic studies with carbon-13 n.m.r. and integrity of the type-Ill macrocycle 87 13 3.3.9 Nature of the rearrangement process from experiments with C2-PBG 89 3.3.10 Enzymic studies with pyrromethanes 92 3.3.10.1 The AP • PA pyrromethane 92 3.3.10.2 The PA • PA pyrromethane 93 3.3.10.3 The AP • AP pyrromethane 93 3.3.10.4 The PA • AP pyrromethane 94 3.3.10.5 Conclusions 95 3.3.11 Enzymic studies with a tripyrrole and a bilane 96 3.3.12 Conclusions 96 3.4 Side-chain modifications and aromatization to protoporphyrin-IX 96 3.4.1 Decarboxylation of uroporphyrinogen-III 96 3.4.1.1 The partially decarboxylated intermediates 97 3.4.2 Oxidative decarboxylation of coproporphyrinogen-III 99 3.4.2.1 Enzymic studies 100 3.4.2.2 Mechanistic studies 101 3.4.2.3 Intermediates 102 3.4.3 Aromatization of protoporphyrinogen-IX 104 3.4.3.1 Intermediates 105 3.5 The iron, magnesium, and cobalt branches 106 3.5.1 The iron branch 106 3.5.1.1 Formation of protoheme 106 3.5.1.2 The hemoproteins 106 3.5.2 The magnesium branch 107 3.5.2.1 Chelation of magnesium 109 3.5.2.2 Esterification of magnesium protoporphyrin-IX 109 3.5.2.3 Reduction of the vinyl group at position-4 109 3.5.2.4 Oxidative formation of the carbocyclic ring 110 3.5.2.5 Reduction of ring D 111 3.5.2.6 Formation of chlorophyll-a 111 X
Load more

Recommended publications
  • Ring Currents Modulate Optoelectronic Properties of Aromatic Chromophores at 25 T
    Ring currents modulate optoelectronic properties of aromatic chromophores at 25 T Bryan Kudischa, Margherita Maiuria,b, Luca Morettia,b, Maria B. Oviedoa,c,d,e, Leon Wangf, Daniel G. Oblinskya, Robert K. Prud’hommef, Bryan M. Wongc, Stephen A. McGillg, and Gregory D. Scholesa,1 aDepartment of Chemistry, Princeton University, Princeton, NJ 08540; bDipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy; cDepartment of Chemical & Environmental Engineering, University of California, Riverside, CA 92521; dDepartment of Materials Science & Engineering, University of California, Riverside, CA 92521; eInstituto de Investigaciones Fisicoquímicas de Cordoba, Consejo Nacional de Investigaciones Científicas y Técnicas, Departamento de Química Teorica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, X5000HUA Córdoba, Argentina; fDepartment of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08540; and gNational High Magnetic Field Laboratory, Tallahassee, FL 32310 Edited by Catherine J. Murphy, University of Illinois at Urbana–Champaign, Urbana, IL, and approved April 1, 2020 (received for review October 16, 2019) The properties of organic molecules can be influenced by magnetic This perspective in many ways is inspired by some of the sa- fields, and these magnetic field effects are diverse. They range lient features that govern the magneto-optical responses in from inducing nuclear Zeeman splitting for structural determina- magnetic circular dichroism (MCD) spectroscopy. While best tion in NMR spectroscopy to polaron Zeeman splitting organic known for its ability to interrogate the degeneracy of electronic spintronics and organic magnetoresistance. A pervasive magnetic states, many electronic transitions will display a weak MCD due field effect on an aromatic molecule is the aromatic ring current, to the magnetic field-induced mixing of electronic states that which can be thought of as an induction of a circular current of gives rise to the B-terms, even in diamagnetic systems (19).
    [Show full text]
  • Cycloosmathioborane Compounds: Other Manifestations of the Hückel
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Repositorio Universidad de Zaragoza Communication Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX pubs.acs.org/IC Cycloosmathioborane Compounds: Other Manifestations of the Hückel Aromaticity † ‡ † † Miguel A. Esteruelas,*, Israel Fernandez,́ Cristina García-Yebra, Jaime Martín, † and Enrique Oñate † Departamento de Química Inorganica,́ Instituto de Síntesis Química y Catalisiś Homogenea,́ Centro de Innovacioń en Química Avanzada (ORFEO−CINQA), Universidad de Zaragoza, CSIC, 50009 Zaragoza, Spain ‡ Departamento de Química Organicá I, Facultad de Ciencias Químicas, ORFEO−CINQA, Universidad Complutense de Madrid, 28040 Madrid, Spain *S Supporting Information have reported EP2 triangles (E = Ge, Sn, Pb), which are ABSTRACT: The discovery of cycloosmathioborane stabilized within the coordination sphere of a sterically protected compounds is reported. These species, which are prepared diniobium unit,13 whereas Guha’s group has computationally by the simultaneous dehydrogenation of a trihydride predicted that the substitution of a B atom in the triangle fi 2− ff hydrogensul de osmium(IV) complex and a BH3NHR2 [B3H3] by a group 15 element should a ord neutral aromatic − − − 14 amine borane, bear an Os S B three-membered ring, H2B2XH rings (X = N, P). Herein, we take one step forward in being a manifestation of the 4n +2Hückel aromaticity in this fascinating field by reporting the preparation and full which n = 0 and where the two π electrons of the ring are characterization of the first aromatic triangles having three provided by the S atom. different vertexes, namely, two main-group elements, S and B, and a transition metal with its associated ligands.
    [Show full text]
  • FULL PAPER Hückel's Rule of Aromaticity Categorizes
    FULL PAPER Hückel’s Rule of Aromaticity Categorizes Aromatic closo Boron Hydride Clusters Jordi Poater,[a,b] Miquel Solà,*[c] Clara Viñas,[d] and Francesc Teixidor*[d] Abstract: A direct connection is established between tridimensional P, N, or other incorporating transition or lanthanide metal aromatic closo boron hydride clusters and planar aromatic fragments. Consequently, the icosahedron or bicapped square antiprism are very relevant geometrical features in BHs and, by [n]annulenes for medium and large size boron clusters. In particular, extension, to other areas in which clusters are significant, e.g. our results prove the existence of a link between the two-dimensional Zintl phases. Hückel rule followed by aromatic [n]-annulenes and Wade-Mingos’ 2- In the last few years, we have given evidence that the concept rule of three-dimensional aromaticity applied to the aromatic [BnHn] of aromaticity, in terms of planar or tridimensional aromaticity, was closo boron hydride clusters. Our results show that closo boron not too distant, and that most probably -aromaticity and 3D hydride clusters can be categorized into different series according to aromaticity were based on the same grounds.[4] This is why we the n value of the Hückel (4n+2) rule. The distinct categories studied named them as the two sides of the same coin.[4b] To reach such in this work correspond to values of n = 1, 2, and 3. Each category conclusion we compared the conventional (4n+2) planar organic increases in geometrical difficulty but, more importantly, it is possible cyclic compounds with closo BHs. The aromaticity properties of to associate each category with the number of pentagonal layers in planar organic cyclic compounds had been demonstrated by their stability, hydrogenation experimental studies, substitution but not the structure perpendicular to the main axis.
    [Show full text]
  • NICS – Nucleus Independent Chemical Shift Renana Gershoni-Poranne and Amnon Stanger
    Preprint of Chapter 4 in the book “Aromaticity: Modern Computational Methods and Applications” Ed. Israel Fernandez, Pub. Elsevier, May 2021 NICS – Nucleus Independent Chemical Shift Renana Gershoni-Poranne and Amnon Stanger “With great power comes great responsibility.” – the Peter Parker principle, Spider-Man, Stan Lee The Nucleus Independent Chemical Shift (NICS) method1 was introduced by Paul v. R. Schleyer in 1996 as a computational tool for the evaluation of aromaticity, exemplified for monocyclic systems. Since then, the easy-to-use NICS technique has become the computational method of choice for identification and quantification of aromaticity.2–4 However, the user-friendliness of NICS is a double-edged sword. On the one hand, it has made the study of aromaticity significantly more accessible to non-expert users and has contributed to a wealth of knowledge and insight into aromatic systems. On the other hand, it can mislead users into thinking that the interpretation of NICS results is as simple as running the calculation itself. In this chapter, we provide a critical review of all things NICS. We describe the various versions of NICS methods that are available, including their differences and inherent limitations. We discuss common mistakes in using and interpreting NICS results and list “dos” and “don’ts” for more accurate chemical insight, depending on the information that is sought. Historical and Physical Background of NICS The NICS method is one of several that fall under the magnetic criteria of aromaticity,3 meaning, it uses the response of an aromatic system to an external magnetic field to identify and quantify aromatic character.
    [Show full text]
  • 1 1H Chemical Shifts in NMR, Part 18 1. Ring Currents and Π-Electron
    1 1H chemical shifts in NMR, part 18 1. Ring currents and π-electron effects in hetero-aromatics. Raymond J. Abraham* and Matthew Reid *Chemistry Department, The University of Liverpool, P.O.Box 147, Liverpool L69 3BX Abstract. The 1H chemical shifts of a number of heteroaromatics and related compounds were obtained by the assignment of the NMR spectra in CDCl3 solution or from the literature. These included furan, pyrrole, thiophene, oxazole, imidazole and thiazole, various methyl and 4,5-dihydro derivatives, the benzo derivatives benzofuran, indole and benzothiophene plus the related compounds vinylmethylether, phenol, anisole, aniline, vinylmethylsulfide and thiophenol. The six membered heteroaromatics pyridine, pyrimidine, pyrazine, pyridazine, quinoline and iso-quinoline and a number of their methyl derivatives were also investigated. The 1H chemical shifts in these molecules were analysed in terms of the ring currents and π electron effects together with a model (CHARGE7h) for the calculation of the two-bond and three-bond electronic effects. This model gives the first comprehensive calculation of the proton chemical shifts in these compounds. For the data set considered (215 proton chemical shifts) ranging from δ = 1.9 to 9.4ppm the rms error of observed vs. calculated shifts was 0.096ppm. The model also allows the interpretation of the chemical shifts in terms of the separate interactions calculated in the programme. This showed the large effects of the ring currents and π electron densities on the 1H chemical shifts. Methyl substitution has a large effect on the chemical shifts which is due to increased π electron densities in the methyl compounds.
    [Show full text]
  • Nuclear Magnetic Resonance Spectroscopy. Ring-Current Effects on Carbon-13 Chemical Shifts (Dihydropyrenes/Bridged Annulenes) RICHARD DU VERNET and V
    Proc. Nat. Acad. Sci. USA Vol. 71, No. 8, pp. 2961-2964, August 1974 Nuclear Magnetic Resonance Spectroscopy. Ring-Current Effects on Carbon-13 Chemical Shifts (dihydropyrenes/bridged annulenes) RICHARD DU VERNET AND V. BOEKELHEIDE Department of Chemistry, University of Oregon, Eugene, Oregon 97403 Contributed by V. Boekelheide, April 22, 1974 ABSTRACT A comparison of the '-C nuclear magnetic hybridization, and charge. Although in these studies compari- resonance chemical shifts of some 15,16-dialkyl-15,16- son was made to reference models, the models available were dihydropyrenes with the corresponding 15,16-dialkyl- 2,7,15,16-tetrahydropyrenes provides a measure of the not ideal. For example, comparison of 5 with either 6 or 7 as effect of ring current on carbon-13 chemical shifts in reference models involves changes in geometry. One particular which other effects may be expected to be negligibly effect of change in the peripheral geometry is to alter the 7r- small. The general conclusion is that the absolute magni- orbital interaction of the C-1 and C-6 carbons (12-14) and the tude of the ring-current effect is the same for carbon-13 as should be for protons when they occupy the same position in space chemical shift of the bridging methano carbon sensi- relative to the aromatic 7r-electron cloud. tive to these changes (15, 16). Early in the investigation of nuclear magnetic resonance the (CH2)1 concept of a ring current was introduced to explain the ob- served chemical shifts of protons in the vicinity of aromatic rings (1). In the case of protons this ring current effect is 4 5 6 7 usually large compared to the other factors affecting the value of the chemical shift, and this is dramatically evident for the In their study on 1 ,6-methano [10]annulene Jones, Mlasu- simple and bridged annulenes (2-4).
    [Show full text]
  • Ring Current Effects: Factors Affecting the NMR
    Ring Current Effects: Factors Affecting the NMR Chemical Shift of Molecules Adsorbed on Porous Carbons Alexander C. Forse,a John M. Griffin,a Volker Presser,b Yury Gogotsi,c Clare P. Grey*a,d aDepartment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK bINM – Leibniz Institute for New Materials & Saarland University, Campus D2 2, 66123 Saarbrücken, Germany cDepartment of Materials Science and Engineering and A.J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, PA 19104, USA dDepartment of Chemistry, Stony Brook University, Stony Brook, New York, NY 11794-3400, USA *Corresponding author. Email: [email protected] Nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to study the adsorption of molecules in porous carbons, a process which underpins applications ranging from electrochemical energy storage to water purification. Here we present density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2 hybridized carbon fragments to explore the structural factors that may affect the resonance frequencies observed for adsorbed species. The domain size of the delocalized electron system affects the calculated NICSs, with larger domains giving rise to larger chemical shieldings. In slit-pores, overlap of the ring current effects from the pore walls is shown to increase the chemical shielding. Finally, curvature in the carbon sheets is shown to 1 have a significant effect on the NICS. The trends observed are consistent with existing NMR results as well as new spectra presented for an electrolyte adsorbed on carbide-derived carbons prepared at different temperatures. TOC Graphic Keywords Nuclear Magnetic Resonance Activated Carbon Supercapacitor DFT Calculations Introduction Porous carbons are used in a wide range of applications including the storage of charge in supercapacitors, gas storage, deionization of water, and purification of gases.1–4 In each case the excellent adsorptive properties of the carbon are exploited to store molecules or ions.
    [Show full text]
  • Investigation of the Stability of Oxadiasole and Their Analogs Using Quantum Mechanics Computation
    Computational Chemistry, 2016, 4, 11-16 Published Online January 2016 in SciRes. http://www.scirp.org/journal/cc http://dx.doi.org/10.4236/cc.2016.41002 Investigation of the Stability of Oxadiasole and Their Analogs Using Quantum Mechanics Computation Masoud Karimi Department of Chemistry, Faculty of Science, Islamic Azad University, Arak Branch, Arak, Iran Received 20 November 2015; accepted 10 January 2016; published 13 January 2016 Copyright © 2016 by author and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract This study aimed at investigating factors affecting the stability as well as structural properties of different Oxadiasole and Thiadiasole isomers based on theoretical level B3LYP/6-311+G**, Nuc- lear Magnetic Resonance (NMR), and Nucleus-independent Chemical Shift (NICS). Qualitative rela- tionships between relative stabilities of 1,2,3-Oxadiazole, 1,2,4-Oxadiazole, 1,2,5-Oxadiazole and 1,3,4-Oxadiazole were obtained. Aromatic stabilization energy (ASE), aromatic ring current (NICS), HUMO-LUMO gaps, electro-negativity (X), hardness (η), softness (S), electro-philicity (ω) and struc- tural parameters were also calculated in the same theoretical level. The results show that 1,3,4- Oxadiazole is more stable than 1,2,3-Oxadiazole, 1,2,4-Oxadiazole and 1,2,5-Oxadiazole. Unlike the trends observed in Oxadiazoles, 1,2,5-Thiadiazole isomer is more stable than other corresponding Isomers. Keywords Oxadiazole, DFT, Ab Initio, NMR 1. Introduction Most components consisted of five-member heterocyclic rings have special chemical properties and are used for multipurpose biological activities [1].
    [Show full text]
  • Using Chemical Shift Perturbation to Characterise Ligand Binding ⇑ Mike P
    Progress in Nuclear Magnetic Resonance Spectroscopy 73 (2013) 1–16 Contents lists available at SciVerse ScienceDirect Progress in Nuclear Magnetic Resonance Spectroscopy journal homepage: www.elsevier.com/locate/pnmrs Using chemical shift perturbation to characterise ligand binding ⇑ Mike P. Williamson Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK Edited by David Neuhaus and Gareth Morris article info abstract Article history: Chemical shift perturbation (CSP, chemical shift mapping or complexation-induced changes in chemical Received 22 January 2013 shift, CIS) follows changes in the chemical shifts of a protein when a ligand is added, and uses these to Accepted 18 February 2013 determine the location of the binding site, the affinity of the ligand, and/or possibly the structure of Available online 21 March 2013 the complex. A key factor in determining the appearance of spectra during a titration is the exchange rate between free and bound, or more specifically the off-rate koff. When koff is greater than the chemical shift difference between free and bound, which typically equates to an affinity Kd weaker than about 3 lM, Keywords: then exchange is fast on the chemical shift timescale. Under these circumstances, the observed shift is Chemical shift the population-weighted average of free and bound, which allows Kd to be determined from measure- Protein ment of peak positions, provided the measurements are made appropriately. 1H shifts are influenced Exchange rate to a large extent by through-space interactions, whereas 13C and 13Cb shifts are influenced more by Dissociation constant a 15 13 0 Docking through-bond effects.
    [Show full text]
  • Analysis of Chemical Bonding Using Ab Initio Valence Bond Theory
    Analysis Of Chemical Bonding Using Ab Initio Valence Bond Theory Analyse van chemische bindingen met ab initio valentiebindingstheorie (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus prof. dr. G. J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op woensdag 18 januari 2017 des middags te 4.15 uur door Jeroen Johan Engelberts geboren op 7 december 1972 te Rotterdam Promotor: Prof. dr. L. W. Jenneskens Copromotor: Dr. R. W. A. Havenith Voor Eveline "Never give up and good luck will find you." - Falcor, The Neverending Story, 1984. Paranimfen: Sylvia Kuijpers Heleen Nagy–van den Boom Cover design: Roel Savert Printed by Ipskamp Printing Analysis Of Chemical Bonding Using Ab Initio Valence Bond Theory Jeroen Johan Engelberts PhD Thesis Utrecht University, November 30, 2016 ISBN: 978-90-393-6685-1 Contents 1 Introduction 1 1.1 From Alchemy to Chemistry2 1.2 Quantum Mechanics in Chemistry3 1.2.1 Hartree Products and Slater Determinants4 1.2.2 The Hartree-Fock (HF) Method5 1.2.3 The Configuration Interaction (CI) Method7 1.2.4 The Multi Configuration Self Consistent Field (MCSCF) Method9 1.2.5 The Coupled Cluster (CC) Method9 1.2.6 Density Functional Theory (DFT) 10 1.3 The Valence Bond Method 11 1.3.1 Classical Valence Bond 12 1.3.2 Generalized Valence Bond (GVB) 16 1.3.3 Valence Bond Configuration Interaction (VBCI) 17 1.3.4 Valence Bond Self Consistent Field (VBSCF) 19 1.3.5 Spin-Coupled
    [Show full text]
  • Magnetic Criteria of Aromaticity
    Chemical Society Reviews Magnetic Criteria of Aromaticity Journal: Chemical Society Reviews Manuscript ID: CS-TRV-02-2015-000114.R2 Article Type: Review Article Date Submitted by the Author: 10-May-2015 Complete List of Authors: Stanger, Amnon; Technion, Chemistry Gershno-Poranne, Renana; Technion, Chemistry Page 1 of 34 Chemical Society Reviews Magnetic Criteria of Aromaticity Renana Gershoni-Poranne [a] and Amnon Stanger* [a] Addresses [a] R. Gershoni-Poranne, Prof. A. Stanger Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion – Israel Institute of Technology, Haifa 32000, Israel. E-mail: [email protected] Dedication Dedicated to Prof. Yitzhak Apeloig on the occasion of his 70 th birthday. Introduction Preface: Benzene was discovered in 1825 by Faraday. The determination and understanding of its structure presented a great challenge to scientists: the compound was highly unsaturated, yet did not show any of the typical reactions of unsaturated compounds, e.g., addition of bromine. The first suggestion that the molecule is cyclic is traditionally attributed to Kekulé in his 1865 1 and 1866 2 papers, although some argue that this idea was presented earlier by Josef Loschmidt. 3 In any event, accumulating experimental evidences, mainly experiments that were conducted by Ladenburg and Wroblewsky, indicated that the proposed structure was unsatisfactory, as it did not account for there being only three disubstituted isomers of benzene instead of the expected four. It was only in 1872 that Kekulé suggested oscillating structures, in which synchronous 1,2-shifts of the three double bonds occur very rapidly. 4 It took about six decades until Erich Hückel 5-9 and Linus Pauling 10 introduced their quantum mechanical based MO and VB explanations, respectively, which introduced the concept of delocalization (of bonds and electrons).
    [Show full text]
  • QM Chemical Shift Calculations to Infer on the Long-Range Aromatic Ring Current-Induced Field Contributions
    Journal of Materials Science and Engineering A 5 (5-6) (2015) 181-196 doi: 10.17265/2161-6213/2015.5-6.001 D DAVID PUBLISHING QM Chemical Shift Calculations to Infer on the Long-Range Aromatic Ring Current-Induced Field Contributions Sankarampadi Aravamudhan Department of Chemistry, North Eastern Hill University, Shillong 793022, India Abstract: The quantum chemical PMR (Proton magnetic resonance) chemical shift calculation, inherently, has the information on the induced field values not only within the molecular system, but also in the neighborhood of the molecule, to the extent, which is significant. Within the molecule the locations of the protons are specified by the way of the complete description of coordinate of all the atoms in the molecule. If the information about the induced fields in the neighborhood is to be known, then it is necessary to place protons at appropriate locations in the neighborhood irrespective of whether the proton is part of the molecule and or bonded to any other atom of the molecule. Such a stand-alone proton in the neighborhood is specified by the coordinates with reference to the molecular axes system, which would sense this induced field and in the result would be reported as proton chemical shift. Such induced field contributions are usually calculated using a classical dipole model for reasons that the protons are not part of the molecule and is at extraneous locations when the molecular magnetic susceptibilities can be used conveniently for calculating induced fields and thus chemical shifts. Such a QM (Quantum mechanical) calculation of chemical shifts and comparison with values from classical equations is being reported.
    [Show full text]