DOCSLIB.ORG

Coherent Spin Dynamics of Radical Pairs in Weak Magnetic Fields

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Coherent Spin Dynamics of Radical Pairs in Weak Magnetic Fields Coherent Spin Dynamics of Radical Pairs in Weak Magnetic Fields by Hannah J. Hogben A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Trinity Term 2011 University of Oxford Department of Chemistry Physical and Theoretical Chemistry Laboratory Oriel College Abstract Coherent Spin Dynamics of Radical Pairs in Weak Magnetic Fields Hannah J. Hogben Department of Chemistry Physical and Theoretical Chemistry Laboratory and Oriel College Abstract of a thesis submitted for the degree of Doctor of Philosophy Trinity Term 2011 The outcome of chemical reactions proceeding via radical pair (RP) intermediates can be in- fluenced by the magnitude and direction of applied magnetic fields, even for interaction strengths far smaller than the thermal energy. Sensitivity to Earth-strength magnetic fields has been sug- gested as a biophysical mechanism of animal magnetoreception and this thesis is concerned with simulations of the effects of such weak magnetic fields on RP reaction yields. State-space restriction techniques previously used in the simulation of NMR spectra are here applied to RPs. Methods for improving the efficiency of Liouville-space spin dynamics calculations are presented along with a procedure to form operators directly into a reduced state-space. These are implemented in the spin dynamics software Spinach. Entanglement is shown to be a crucial ingredient for the observation of a low field effect on RP reaction yields in some cases. It is also observed that many chemically plausible initial states possess an inherent directionality which may be a useful source of anisotropy in RP reactions. The nature of the radical species involved in magnetoreception is investigated theoretically. It has been shown that European Robins are disorientated by weak radio-frequency (RF) fields at the frequency corresponding to the Zeeman splitting of a free electron. The potential role of superoxide and dioxygen is investigated and the anisotropic reaction yield in the presence of a RF-field, without a static field, is calculated. Magnetic field effect data for Escherichia coli photolyase and Arabidopsis thaliana cryptochrome 1, both expected to be magnetically sensitive, are satisfactorily modelled only when singlet-triplet dephasing is included. With a view to increasing the reaction yield anisotropy of a RP magnetoreceptor, a brief study of the amplification of the magnetic field experienced by a RP from nearby magnetite particles is presented. Finally in a digression from RPs, Spinach is used to determine the states expected to be immune from relaxation and therefore long-lived in NMR experiments on multi-spin systems. i Acknowledgments I must begin by thanking Prof. Peter Hore for allowing me to come and join his group for my DPhil, especially considering my previous organic tendencies, and for suggesting such interesting projects over the last three years. I am deeply grateful for all of his help when I was stuck and for always allowing me time to get to grips with each new idea at my own pace. I could not have asked for a kinder and more patient supervisor. Secondly I must thank Dr Ilya Kuprov for introducing me to state space restriction tech- niques and subsequently letting me loose with Spinach. I appreciate his help, suggestions and encouragement throughout the last three years. I am grateful to Dr. Chris Rodgers for not only giving me his γ-COMPUTE codes but also for teaching me how to use them and then for letting me modify them. I thank Prof. Blundell for helping me to understand the dynamics of magnetite nanoparticles. On a technical note thanks are due to Dr Pete Biggs for keeping my linux machine running. He has tirelessly fixed software and hardware problems for this, often rather inept, linux user. I am extremely grateful to the other members of the Hore group. The part II's of the last three years, Ian, Mikey and Dave, have been great fun to work with. Alice Bowen was delightful to have in the office, and was a source of lots of useful information about cryptochromes. Special thanks to Jason \Top Cat" Lau for helpful discussions about theory and computation, as well as being excellent company at tea time. Finally, I would like to thank Dr Till Biskup for teaching me more than a theoretical chemist really ought to know about cryptochromes and photolyases, for help with the technical aspects of writing in LATEXand for putting up with my thesis-related rants. Thanks also go to members of the Timmel group for keeping me in touch with the real world. Drs Kiminori Maeda, Kevin Henbest and Alex Robinson were invaluable for discussions about the data fitting in Chapter Five, and for showing me the experimental set-up. Kelly-Anne Ferguson kindly showed me her rotary-RYDMR experiments and has always patiently answered my questions about her experiments. ii Thanks are also due to Prof. Harry Anderson, Prof. Stephen Faulkner and Dr Brid Cronin for letting me teach physical chemistry at Keble over the last three years, I have thoroughly enjoyed it. They have provided interesting conversation and encouragement over the course of many SCR lunches. I must acknowledge my home for the past seven years, Oriel. I am very grateful to the college for awarding me a graduate scholarship for the last two years and for in general providing an extremely supportive academic and social environment. I must thank my undergraduate tutors, Prof. David Hodgson and Dr. Hugh Cartwright, both of whom are excellent teachers and have been sources of support and guidance, as well as being founts of knowledge, over the years. I would like to thank the (mostly) chemists whose company over soup at lunch time never failed to amuse me and from whom I have learnt many things about experimental magnetic field effects, electron paramagnetic resonance, neutron scattering and rocks. My house-mate and fellow part-II back in the day, Nicola Davis, I thank for lots of cups of tea. I am grateful to my marvelous friends from Oriel: Pete, Georgie, Liz, Stu, James, Katie, Mark, Tessa, Sarah and Nick who despite growing up and joining the real world still have time for their student chum and without whose friendship I would not have made it through seven years in Oxford. I would like to thank the members of Headcorn Baptist Church for their support and prayers, especially over the last few months. My final acknowledgment must be to my parents. Thanks for the unwavering love and support! I really do love you both hugely. \The heavens display the glory of God, and the firmament shows His handiwork" Psalm 19v1 iii Contents 1 Introduction 1 1.1 Spin . .1 1.1.1 Properties of Spin . .2 1.1.2 Single-Spin Operators . .3 1.1.3 Irreducible Spherical Tensors . .4 1.1.4 Multi-spin Operators . .5 1.2 Spin Chemistry . .6 1.2.1 Radical Pair Mechanism . .7 1.2.2 Evidence for the Radical Pair Mechanism from Magnetic Resonance . 10 1.2.3 Experimentally Observed Magnetic Fields Effects . 11 1.2.4 Biological Significance . 13 1.3 Theoretical Description . 14 1.3.1 Equation of Motion . 15 1.3.2 Calculating the Singlet Yield . 16 1.3.3 The Hamiltonian . 19 1.3.4 Liouville Space Simulations . 24 1.3.5 Reaction Kinetics . 26 1.3.6 Relaxation . 27 1.4 Summary . 31 2 State Space Restriction 33 2.1 Introduction . 33 2.1.1 Basis States . 35 2.1.2 Separating the Radicals . 37 2.1.3 MS Block Diagonalisation . 40 iv 2.2 Initial Aims . 41 2.2.1 Clusterisation . 41 2.2.2 Zero-Track Elimination . 43 2.2.3 Anisotropic Calculations . 45 2.3 Summary One . 46 2.4 Unpopulated States . 46 2.4.1 Conservation Laws . 48 2.5 Separating the Singlet State . 50 2.5.1 Path Tracing . 53 2.6 Summary Two . 53 2.7 Formation of Operators Directly into the Reduced Basis . 54 2.7.1 Implementation . 57 2.8 Symmetrisation . 58 2.8.1 Symmetry Adapted Linear Combinations . 58 2.8.2 Clebsch-Gordon Symmetrisation . 60 2.9 Relaxation . 61 2.9.1 Redfield Theory . 62 2.9.2 Generating the Full Relaxation Superoperators . 64 2.9.3 Relaxation Superoperators Directly in the Reduced State-Space . 68 2.10 Reaction Kinetics . 70 2.10.1 State-Space Restriction of Kinetic Superoperators . 70 2.11 Summary Three . 71 2.12 Spinach ......................................... 73 2.13 Some Examples . 74 2.14 Conclusion . 78 3 Entanglement, Triplet States and the Radical Pair Mechanism 79 3.1 Introduction . 79 3.2 Some Definitions . 80 3.2.1 Quantifying Entanglement . 83 3.2.2 Singlet State . 86 3.3 Entanglement and the RPM . 87 3.3.1 Isotropic Low-Field Effect . 88 v 3.3.2 Isotropic Low-Field Effect { The Directional Triplet . 94 3.3.3 Anisotropic Reaction Yields . 96 3.3.4 Entanglement Conclusion . 96 3.4 The Directional Triplet . 98 3.4.1 Intersystem Crossing . 98 3.4.2 Chemical Compass . 100 3.5 Conclusion . 103 4 The Effects of Radio-Frequency Fields on the Avian Magnetocompass 105 4.1 Introduction to Animal Navigation . 105 4.1.1 Proposed Biophysical Mechanisms of Magnetoreception . 106 4.1.2 Avian Magnetoreception . 108 4.2 Disruption of the RPM by RF-Fields . 113 4.2.1 Calculation of Time-Dependent Field Effects Using γ-COMPUTE . 114 4.2.2 Oxygen/Superoxide as Possible Counter Radicals . 117 4.2.3 Other Possible Candidates . 130 4.2.4 Summary . 132 4.3 Orientation Using RF-Fields Only . 133 4.4 Conclusions . 135 5 Modelling Experimentally Observed Magnetic Field Effects in Arabidopsis thaliana Cryptochrome 1 and Escherichia coli Photolyase 137 5.1 Introduction .
Load more

Recommended publications
  • Advances in Photosynthesis and Respiration
    Biophysical Techniques in Photosynthesis Volume II Advances in Photosynthesis and Respiration VOLUME 26 Series Editor: GOVINDJEE University of Illinois, Urbana, Illinois, U.S.A. Consulting Editors: Julian EATON-RYE, Dunedin, New Zealand Christine H. FOYER, Newcastle upon Tyne, U.K. David B. KNAFF, Lubbock, Texas, U.S.A. Anthony L. MOORE, Brighton, U.K. Sabeeha MERCHANT, Los Angeles, California, U.S.A. Krishna NIYOGI, Berkeley, California, U.S.A. William PARSON, Seatle, Washington, U.S.A. Agepati RAGHAVENDRA, Hyderabad, India Gernot RENGER, Berlin, Germany The scope of our series, beginning with volume 11, reflects the concept that photosynthesis and respiration are intertwined with respect to both the protein complexes involved and to the entire bioenergetic machinery of all life. Advances in Photosynthesis and Respiration is a book series that provides a comprehensive and state-of-the-art account of research in photo- synthesis and respiration. Photosynthesis is the process by which higher plants, algae, and certain species of bacteria transform and store solar energy in the form of energy-rich organic molecules. These compounds are in turn used as the energy source for all growth and reproduction in these and almost all other organisms. As such, virtually all life on the planet ultimately depends on photosynthetic energy conversion. Respiration, which occurs in mitochondrial and bacterial membranes, utilizes energy present in organic molecules to fuel a wide range of metabolic reactions critical for cell growth and development. In addition, many photosynthetic organisms engage in energetically wasteful photorespiration that begins in the chloroplast with an oxygenation reaction catalyzed by the same enzyme responsible for capturing carbon dioxide in photosynthesis.
    [Show full text]
  • Simulation and Theory of Classical Spin Hopping on a Lattice
    magnetochemistry Article Simulation and Theory of Classical Spin Hopping on a Lattice Richard Gerst , Rodrigo Becerra Silva and Nicholas J. Harmon * Department of Physics, University of Evansville, Evansville, IN 47722, USA; [email protected] (R.G.); [email protected] (R.B.S.) * Correspondence: [email protected] Abstract: The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the presence of varying degrees of energy disorder when the carrier spin is treated classically and random spin rotations are suffered during the hopping process (to mimic spin–orbit coupling effects) instead of during the wait time period (which would be more appropriate for hyperfine coupling). The problem was studied under a variety of different assumptions regarding the hopping rates and the random local fields. In some cases, analytic solutions for the spin relaxation rate were obtained. In all the models, we found that exponentially distributed energy disorder led to a drastic reduction in spin polarization losses that fell nonexponentially. Keywords: spintronics; organic semiconductors; hopping transport; spin transport 1. Introduction Citation: Gerst, R.; Becerra Silva, R.; Spin relaxation of carriers has garnered much interest in the past few decades due to Harmon, N.J. Simulation and Theory the prospect of spin electronic or spintronic devices that use spin functionality in addition to of Classical Spin Hopping on a charge functionality. However, most work has been concentrated on band transport [1–5].
    [Show full text]
  • Structure and Bonding Electron Configurations in the Periodic Table
    Structure and Bonding The study of organic chemistry must at some point extend to the molecular level, for the physical and chemical properties of a substance are ultimately explained in terms of the structure and bonding of molecules. This module introduces some basic facts and principles that are needed for a discussion of organic molecules. Electronic Configurations Electron Configurations in the Periodic Table 1A 2A 3A 4A 5A 6A 7A 8A 1 2 H He 1 2 1s 1s 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 2 2 2 2 2 2 2 2 1s 1s 1s 1s 1s 1s 1s 1s 2s1 2s2 2s22p1 2s22p2 2s22p3 2s22p4 2s22p5 2s22p6 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar [Ne] [Ne] [Ne] [Ne] [Ne] [Ne] [Ne] [Ne] 3s1 3s2 3s23p1 3s23p2 3s23p3 3s23p4 3s23p5 3s23p6 Four elements, hydrogen, carbon, oxygen and nitrogen, are the major components of most organic compounds. Consequently, our understanding of organic chemistry must have, as a foundation, an appreciation of the electronic structure and properties of these elements. The truncated periodic table shown above provides the orbital electronic structure for the first eighteen elements (hydrogen through argon). According to the Aufbau principle, the electrons of an atom occupy quantum levels or orbitals starting from the lowest energy level, and proceeding to the highest, with each orbital holding a maximum of two paired electrons (opposite spins). Electron shell #1 has the lowest energy and its s-orbital is the first to be filled.
    [Show full text]
  • VSEPR Theory
    VSEPR Theory The valence-shell electron-pair repulsion (VSEPR) model is often used in chemistry to predict the three dimensional arrangement, or the geometry, of molecules. This model predicts the shape of a molecule by taking into account the repulsion between electron pairs. This handout will discuss how to use the VSEPR model to predict electron and molecular geometry. Here are some definitions for terms that will be used throughout this handout: Electron Domain – The region in which electrons are most likely to be found (bonding and nonbonding). A lone pair, single, double, or triple bond represents one region of an electron domain. H2O has four domains: 2 single bonds and 2 nonbonding lone pairs. Electron Domain may also be referred to as the steric number. Nonbonding Pairs Bonding Pairs Electron domain geometry - The arrangement of electron domains surrounding the central atom of a molecule or ion. Molecular geometry - The arrangement of the atoms in a molecule (The nonbonding domains are not included in the description). Bond angles (BA) - The angle between two adjacent bonds in the same atom. The bond angles are affected by all electron domains, but they only describe the angle between bonding electrons. Lewis structure - A 2-dimensional drawing that shows the bonding of a molecule’s atoms as well as lone pairs of electrons that may exist in the molecule. Provided by VSEPR Theory The Academic Center for Excellence 1 April 2019 Octet Rule – Atoms will gain, lose, or share electrons to have a full outer shell consisting of 8 electrons. When drawing Lewis structures or molecules, each atom should have an octet.
    [Show full text]
  • 8.3 Bonding Theories >
    8.3 Bonding Theories > Chapter 8 Covalent Bonding 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8.3 Bonding Theories > Molecular Orbitals Molecular Orbitals How are atomic and molecular orbitals related? 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8.3 Bonding Theories > Molecular Orbitals • The model you have been using for covalent bonding assumes the orbitals are those of the individual atoms. • There is a quantum mechanical model of bonding, however, that describes the electrons in molecules using orbitals that exist only for groupings of atoms. 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8.3 Bonding Theories > Molecular Orbitals • When two atoms combine, this model assumes that their atomic orbitals overlap to produce molecular orbitals, or orbitals that apply to the entire molecule. 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8.3 Bonding Theories > Molecular Orbitals Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole. • A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital. 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8.3 Bonding Theories > Molecular Orbitals Sigma Bonds When two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting two atomic nuclei, a sigma bond is formed. • Its symbol is the Greek letter sigma (σ).
    [Show full text]
  • Chemical Bonding & Chemical Structure
    Chemistry 201 – 2009 Chapter 1, Page 1 Chapter 1 – Chemical Bonding & Chemical Structure ings from inside your textbook because I normally ex- Getting Started pect you to read the entire chapter. 4. Finally, there will often be a Supplement that con- If you’ve downloaded this guide, it means you’re getting tains comments on material that I have found espe- serious about studying. So do you already have an idea cially tricky. Material that I expect you to memorize about how you’re going to study? will also be placed here. Maybe you thought you would read all of chapter 1 and then try the homework? That sounds good. Or maybe you Checklist thought you’d read a little bit, then do some problems from the book, and just keep switching back and forth? That When you have finished studying Chapter 1, you should be sounds really good. Or … maybe you thought you would able to:1 go through the chapter and make a list of all of the impor- tant technical terms in bold? That might be good too. 1. State the number of valence electrons on the following atoms: H, Li, Na, K, Mg, B, Al, C, Si, N, P, O, S, F, So what point am I trying to make here? Simply this – you Cl, Br, I should do whatever you think will work. Try something. Do something. Anything you do will help. 2. Draw and interpret Lewis structures Are some things better to do than others? Of course! But a. Use bond lengths to predict bond orders, and vice figuring out which study methods work well and which versa ones don’t will take time.
    [Show full text]
  • Electron Configurations, Orbital Notation and Quantum Numbers
    5 Electron Configurations, Orbital Notation and Quantum Numbers Electron Configurations, Orbital Notation and Quantum Numbers Understanding Electron Arrangement and Oxidation States Chemical properties depend on the number and arrangement of electrons in an atom. Usually, only the valence or outermost electrons are involved in chemical reactions. The electron cloud is compartmentalized. We model this compartmentalization through the use of electron configurations and orbital notations. The compartmentalization is as follows, energy levels have sublevels which have orbitals within them. We can use an apartment building as an analogy. The atom is the building, the floors of the apartment building are the energy levels, the apartments on a given floor are the orbitals and electrons reside inside the orbitals. There are two governing rules to consider when assigning electron configurations and orbital notations. Along with these rules, you must remember electrons are lazy and they hate each other, they will fill the lowest energy states first AND electrons repel each other since like charges repel. Rule 1: The Pauli Exclusion Principle In 1925, Wolfgang Pauli stated: No two electrons in an atom can have the same set of four quantum numbers. This means no atomic orbital can contain more than TWO electrons and the electrons must be of opposite spin if they are to form a pair within an orbital. Rule 2: Hunds Rule The most stable arrangement of electrons is one with the maximum number of unpaired electrons. It minimizes electron-electron repulsions and stabilizes the atom. Here is an analogy. In large families with several children, it is a luxury for each child to have their own room.
    [Show full text]
  • Atomic Structure and Bonding
    IM2665 Chemistry of Nanomaterials Atomic Structure and Bonding Assoc. Prof. Muhammet Toprak Division of Functional Materials KTH Royal Institute of Technology Background • Electromagnetic waves • Materials wave motion, • Quantified energy and – Louis de Broglie (1892-1987) photons • Uncertainity principle – Max Planck (1858-1947) – Werner Heisenberg (1901-1976) – Albert Einstein (1879-1955) • Schrödinger equation • Bohr’s atom model – Erwin Schrödinger (1887-1961) – Niels Bohr (1885-1962) IM2657 Nanostr. Mater. & Self Assembly 2 Electromagnetic Spectrum Visible light is only a small part of the Electromagnetic Spectrum IM2657 Nanostr. Mater. & Self Assembly 3 Electromagnetic Waves • Wavemotion is defined by • Calculations – ν = Frequency ( Hz) – c = ν × λ – λ = wavelength (m) – c = 3,00 × 108 m/s (speed of light) IM2657 Nanostr. Mater. & Self Assembly 4 Quantified Energy and Photons • E = h × ν; where h = 6,63 × 10-34 J s (Planck’s constant) • Photoelectric Effect (1905) IM2657 Nanostr. Mater. & Self Assembly 5 Thomson´s Pudding Model For a helium atom, the model proposes a large spherical cloud with two units of positive charge. Th e two electrons lie on a line through the center of the cloud. The loss of one electron produces the He+1 ion, with the remaining electron at the center of the cloud. The loss of a second electron prod uces He+2 , in which there is just a cloud of positive charge. IM2657 Nanostr. Mater. & Self Assembly 6 Rutherford’s Experiment The notion that atoms consist of very small nuclei containing protons and neutrons surrounded by a much larger cloud of electrons was IM2657 Nanostr. Mater. & Self Assembly 7 developed from an α particle scattering experiment.
    [Show full text]
  • VSEPR Molecular Geometry Tutorial
    Constructing Molecular Shapes A Tutorial on Writing the Shape of Molecules Dr. Fred Omega Garces Chemistry 100 Miramar College 1 Determining Molecular Shape 10.7.00 10:09 PM VSEPR- Valence Shell Electron-Pair Repulsion Theory Main premise of model- Valence electron pair repel each other in molecule with shapes the molecule Molecule assumes Geometry that minimizes electrostatic repulsion: Occurs when electron pair are far apart as possible. Driving force is the Pauli exclusion principle : 2 electrons with same spin can't occupy the same space. Electronic Geometry is the geometry around the central atom in which electron-electron repulsion is minimize. AEn (system) Molecular Geometry is geometry around central atom when electron pairs are replace by bonding atoms and the nonbonding electrons are ignored. ABmEn (system) 2 Determining Molecular Shape 10.7.00 10:09 PM VSEPR- Procedural Steps 1) Determine the Lewis Structure. a) Valence electrons for each atom in the structure. b) Determine the atomic sequence, the number of bonds, remaining electrons c) Write Lewis structure with each atom obeying the octet rule Example: HNO3 ( See Lewis Structure Tutorial) O N O O H 3 Determining Molecular Shape 10.7.00 10:09 PM VSEPR- Procedural Steps 2) Determine electronic geometry (AEn system) from Lewis structure. a) Count the electron domain (region) around the central atom. b) Arrange electron domain to minimize electron-electron repulsion. Occurs when electron pair are far apart as possible. c) 2-domainglinear, 3-domaingtrigonal, 4-domaingtetrahedral O N O Example: HNO3 O Central Atoms, N and O H O N O O N: Three electron domain AE3 Trigonal H O N O O: Four electron domain O AE4 Tetrahedral H 4 Determining Molecular Shape 10.7.00 10:09 PM VSEPR- Procedural Steps 3) Determine molecule geometry (ABmEn) from electronic geometry.
    [Show full text]
  • Amine-Based Zinc(II), Copper(II), and Oxidovanadium(IV) Complexes: SOD Scavenging, DNA Binding, and Anticancer Activities
    Int. J. Electrochem. Sci., 7 (2012) 7526 - 7546 International Journal of ELECTROCHEMICAL SCIENCE www.electrochemsci.org Synthesis, Characterization, and Electrochemical Properties of Bis(2-benzimidazolylmethyl-6-sulfonate)amine-based zinc(II), copper(II), and oxidovanadium(IV) Complexes: SOD Scavenging, DNA binding, and Anticancer Activities Mohamed M. Ibrahim1,2, Gaber A. M. Mersal1,3, Samir A. El-Shazly4,5, Abdel-Motaleb M. Ramadan2 1 Department of Chemistry, Faculty of Science, Taif University, Taif, Saudi Arabia 2 Departmentof Chemistry, Faculty of Science, Kafr El-Sheikh University, Egypt 3 Department of Chemistry, Faculty of Science, South Valley University, Qena, Egypt 4 Departmentof Biochemistry, Faculty of Veterinary Medicine, Kafr El-Sheikh University, Egypt 5 Department of Biotechnology, Faculty of Science, Taif University, Taif, Saudi Arabia *E-mail: [email protected] Received: 8 June 2012 / Accepted: 9 July 2012 / Published: 1 August 2012 The synthesis of a tridentate ligand, bis(2-benzimidazolylmethyl-6-sulfonate)amine H2SBz is described together with its zinc(II), copper(II), and oxidovanadium(IV) complexes [SBz-M(H2O)2] (M = Zn2+ 1, Cu2+ 2, and VO2+ 3). The ligand and its metal complexes 1-3 were characterized based on elemental analysis, conductivity measurements, spectral, and magnetic studies. The magnetic and spectroscopic data indicate a square pyramidal geometry is proposed for all complexes. The redox properties of the ligand and its complexes 1-3 were extensively investigated by using cyclic voltammetry. Complexes 1 and 2 exhibited quasi-reversible single electron transfer process. Whereas in complex 3, only one electron oxidation peak was observed at + 0.72 V, which is due to the oxidation of VIV to VV.
    [Show full text]
  • Dirac Material Graphene
    Dirac Material Graphene Elena Sheka Russian Peoples’ Friendship University of Russia Moscow, 117198 Russia [email protected] Abstract. The paper presents author’s view on spin-rooted properties of graphene supported by numerous experimental and calculation evidences. Correlation of odd pz electrons of the honeycomb lattice meets a strict demand “different orbitals for different spins”, which leads to spin polarization of electronic states, on the one hand, and generation of an impressive pool of local spins distributed over the lattice, on the other. These features characterize graphene as a peculiar semimetal with Dirac cone spectrum at particular points of Brillouin zone. However, spin-orbit coupling (SOC), though small but available, supplemented by dynamic SOC caused by electron correlation, transforms graphene-semimetal into graphene-topological insulator (TI). The consequent topological non-triviality and local spins are proposed to discuss such peculiar properties of graphene as high temperature ferromagnetism and outstanding chemical behavior. The connection of these new findings with difficulties met at attempting to convert graphene-TI into semiconductor one is discussed. Key words: graphene, Dirac fermions, quasi-relativistic description, hexagonal honeycomb structure, local spins, open-shell molecules, spin-orbital coupling, quantum spin Hall insulator, high temperature ferromagnetism, chemical activity. 1. Introduction Presented in the current paper concerns three main issues laying the foundation of spin features of graphene: (1) a significant correlation of pz odd electrons, exhibited in terms of spin peculiarities of the unrestricted Hartree-Fock (UHF) solutions, (2) spin-orbital coupling (SOC) and (3) the crucial role of the C=C bond length distribution over the body in exhibiting the spin- based features.
    [Show full text]
  • Loudon Ch. 3 Review: Acids/Bases/Curved Arrows Jacquie Richardson, CU Boulder – Last Updated 9/16/2020
    Loudon Ch. 3 Review: Acids/Bases/Curved Arrows Jacquie Richardson, CU Boulder – Last updated 9/16/2020 There are two different definitions of acids and bases that show up in this chapter: 1. Lewis acids (a.k.a. electrophiles, E or E +) accept an electron pair; Lewis bases (a.ka. nucleophiles, Nu or Nu -) donate an electron pair 2. Brønsted-Lowry acids (a.k.a. acids ) donate a proton (H + ion); Brønsted-Lowry bases (a.k.a. bases ) accept a proton Brønsted-Lowry acids/bases are a subset of Lewis acids/bases. If something is a Brønsted- Lowry base it must also be a Lewis base but the reverse is not true. When an organic chemist says “acid” or “base”, what we normally mean is Brønsted-Lowry acid or base. We use the terms nucleophile for Lewis bases (things that love nuclei), and electrophile for Lewis acids (things that love electrons). Confusingly, chemists will often use “nucleophile” to mean “only- nucleophile-but-not-a-base”. Officially, though, bases are a subset of nucleophiles, and acids are a subset of electrophiles. We’re going to look some more at the differences between them, but first, here are some tools to help explain what’s going on during a reaction: curved arrows, and frontier molecular orbitals. Curved Arrows Show Electron Movement We can show the flow of electrons to a Lewis acid by using curved arrows. These are used to show the movement of electrons only , not anything else! Two electrons moving as a pair (like in a reaction between a Lewis acid and base) are shown as a full-headed arrow.
    [Show full text]