Electron Spin Interactions in Chemistry and Biology: Fundamentals, Methods, Reactions Mechanisms, Magnetic Phenomena, Structure Investigation

355 Pages·2016·10.177 MB·English

by  Gertz Likhtenshtein (auth.)

Biological and Medical Physics, Biomedical Engineering
Gertz Likhtenshtein
Electron Spin
Interactions in
Chemistry and
Biology
Fundamentals, Methods, Reactions
Mechanisms, Magnetic Phenomena,
Structure Investigation
Electron Spin Interactions in Chemistry
and Biology
BIOLOGICAL AND MEDICAL PHYSICS,
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More information about this series at http://www.springer.com/series/3740
Gertz Likhtenshtein
Electron Spin Interactions
in Chemistry and Biology
Fundamentals, Methods, Reactions
Mechanisms, Magnetic Phenomena,
Structure Investigation
123
Gertz Likhtenshtein
Department ofChemistry
Ben-Gurion University of the Negev
Beersheba
Israel
and
Institute of Problems of Chemical Physics
Russian Academy of Science
Chernogolovka
Russia
ISSN 1618-7210 ISSN 2197-5647 (electronic)
Biological andMedical Physics, Biomedical Engineering
ISBN978-3-319-33926-9 ISBN978-3-319-33927-6 (eBook)
DOI 10.1007/978-3-319-33927-6
LibraryofCongressControlNumber:2016942036
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Preface
Pivotal role of electron spin interactions in Nature cannot be overestimated. In
manyprocessesfromenergytransductioninbiologytospecificityofbiorecognition
these spin interactions appear as defining contributors. Another role involves
determiningthepropertiesofmolecularandfunctionalmaterials’systemsthatdrive
today’stechnology byfinding uses inelectronic,spintronic, andmagneticdevices.
Electron spin effects are manifesting in the fundamental quantum phenomenon
of spin exchange. This interaction enables a number of important elementary
processesincludingelectrontransfer,tripletenergytransfer,andinterspincrossing.
One should consider interactions of both electronic and nuclear spins including
electron–electron, electron–nuclear dipolar, and electron–nuclear contact interac-
tions among the others. Such interactions could be precisely studied by electron
magneticresonance,nuclearmagneticresonance,andrelatedhyphenatedresonance
techniques providing researchers with unique spectroscopic tools to investigate
detailed molecular structure and dynamics of both small and large chemical and
biological molecules.
For rather long time the scientists were stuck with paradigm that chemical and
biochemical reactions are only ruled by interactions that energetically prevail over
the thermal motion. However, contrary to such a strong thermodynamic argument,
the last decades of intense research resulted in conclusive evidence of many
essential chemical and biological processes being governed by very weak inter-
actionsoriginatingfromelectronicspinsystemsinstead.Advancingtheknowledge
of molecular mechanisms responsible for photosynthesis in plants and model
compounds, radical reactions and influence of magnetic field on these and other
processes, as well as rational design of advanced molecular magnets, spintronic
devices,catalysts,etc.,wouldnotbepossiblewithoutunderstandingthespineffects
in these systems.
This book represents a collective perspective from physical chemist with long
and broad expertise in spin phenomena and related fields. The main intention was
nottoprovidethereaderwithanexhaustivesurveyofeachtopicofvastliterature,
butrathertodiscussthekeytheoreticalandexperimentalbackgroundandfocuson
v
vi Preface
recentdevelopments.Thus,chemistsandbiologistswouldfindthefundamentalsof
spinphenomena,instrumentationanddatainterpretation,andareviewofthemajor
milestones.Thisgainedknowledgeisexpectedtopromotesomecriticalthinkingto
solvenewemergingproblemintheirfields.Physicistsandexperts,forexample,in
magnetic resonance and photoluminescence methods and instrumentation may
know already about the above-mentioned technical and quantum mechanical
aspects,butwouldbenefitfromoverviewofcurrentproblemsandachievementsin
variousareasofchemistryandmolecularbiology,includingrapidlyevolvingfields
of natural and artificial photosynthesis, photochemistry, material science, etc.
The Chap. 1 of the monograph provides a brief outline offundamental theories
of spin exchange and electron transfer. Non-radiative spin exchange processes
involving excited triplet state is the subject of Chap. 2. Electron spin dipolar and
electron-nuclear spin contact interactions are described in Chap. 3 as the basis for
investigation of molecular structures. A general survey offundamentals and recent
results on spin-selective processes of electron and nuclear spins is presentedin the
Chap. 4. Three subsequent Chaps. 5–7 are dedicated to experimental methods of
investigation of electron spin interactions based on measurements by continuous
wave and pulse EPRand byother physicalmethods.Thesespectroscopic methods
form an experimental basis for investigation of electron spin effects in chosen
chemicalandphysicalprocesses(Chap.8),effectsofmagneticandelectromagnetic
fields on chemical and biological processes (Chap. 9), establishing structure and
spin state of organic and metalloorganic compounds (Chap. 10), and electron
transfer in biological systems focusing on the light energy conversion (Chap. 11).
Chapter 12 is a brief review of the fundamentals and main results obtained by the
methods of spin and triplet (phosphorescence) labels. Chapter 11, Preface and
Conclusion have been written in collaboration with professor Alex I. Smirnov
This monograph is intended for scientists working in basic areas related to spin
interactions such as spin chemistry and biology, electron transfer, light energy
conversion, photochemistry, radical reactions and magneto-chemistry and
magneto-biology. The book will be also useful for engineers designing advance
magneticmaterials,opticalandspintronicdevices,andphotocatalysts.Thistextasa
whole or as separate chapters can also be employed as subsidiary manuals for
instructors and graduate and undergraduate students of university physics, bio-
physics, chemistry, and chemistry engineering departments.
Beersheba, Israel Gertz Likhtenshtein
Contents
1 Basic Conceptions: Spin Exchange and Electron Transfer . . . . . . . 1
1.1 Basic Conceptions and Definitions. . . . . . . . . . . . . . . . . . . . . 1
1.2 First Elements of Quantum Mechanics . . . . . . . . . . . . . . . . . . 4
1.3 Spin Exchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Direct Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.2 Superexchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.3 Dynamic Spin Exchange in Solution. . . . . . . . . . . . . . 10
1.3.4 Dynamic Spin Exchange in Flexible Biradicals
in Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Electron Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 Prerequisite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 Electron Transfer Theories . . . . . . . . . . . . . . . . . . . . 14
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2 Spin Exchange Processes Involving Exited Triplet States. . . . . . . . 27
2.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Dexter Triplet-Triplet Energy Transfer . . . . . . . . . . . . . . . . . . 28
2.3 Triplet-Triplet Annihilation . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.4 Dexter Singlet-Singlet Energy Transfer. . . . . . . . . . . . . . . . . . 34
2.5 Intersystem Crossing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.5.1 Direct Intersystem Crossing. . . . . . . . . . . . . . . . . . . . 38
2.5.2 Induced Intersystem Crossing . . . . . . . . . . . . . . . . . . 43
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3 Spin Electron Dipolar and Contact Interactions . . . . . . . . . . . . . . 51
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.2 Spin Relaxation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.3 Electron Spin-Spin Dipole-Dipole Interaction. . . . . . . . . . . . . . 55
3.3.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.3.2 Interaction Between Slow Relaxing Dipoles . . . . . . . . 55
3.3.3 Interaction Between a Slow Relaxing Dipole
and Fast Relaxing Dipole . . . . . . . . . . . . . . . . . . . . . 59
vii
viii Contents
3.4 Electron Spin Nuclear Spin Interaction. . . . . . . . . . . . . . . . . . 61
3.4.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.4.2 Nuclear Magnetic Resonance of Paramagnetic
Molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.4.3 Nuclear Relaxation Rates Enhancement
by Electron Spin . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.4.4 Contrast Enhancement of Water Protons
in Magnetic Resonance Imaging . . . . . . . . . . . . . . . . 67
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4 Spin-Selective Processes of Electron and Nuclear Spins . . . . . . . . . 73
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.2 Chemically Induced Spin Correlated Dynamic Electron
Polarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2.1 Triplet Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2.2 Spin-Correlated Coupled Radical-Pair Mechanism . . . . 75
4.2.3 Radical-Pair Mechanism . . . . . . . . . . . . . . . . . . . . . . 77
4.2.4 Radical-Triplet Dynamic Electron Polarization
Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.2.5 Triplet Pair Mechanism of Chemically Induced
Dynamic Electron Polarization. . . . . . . . . . . . . . . . . . 80
4.3 Dynamic Nuclear Polarization . . . . . . . . . . . . . . . . . . . . . . . . 81
4.3.1 Chemical-Induced Dynamic Nuclear Polarization. . . . . 85
4.4 Chiral-Induced Spin Selectivity. Spin Filter. . . . . . . . . . . . . . . 89
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5 Experimental Methods of Investigation of Electron Spin
Interactions Based on ESR Phenomena: Continuous
Wave EPR Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 Spin Electron Relaxation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.2.1 Determination of Spin-Spin Relaxation Rates
from the Form of the ESR Spectrum . . . . . . . . . . . . . 95
5.2.2 Determination of Spin-Lattice Relaxation Rates
from ESR Spectral Saturated Curves. . . . . . . . . . . . . . 95
5.3 Exchange Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
5.4 Multiquantum ESR Spectroscopy. . . . . . . . . . . . . . . . . . . . . . 99
5.5 Electron Spin Electron Spin Electron Dipolar Interaction. . . . . . 100
5.6 Hyperfine Interaction in ESR Spectra. . . . . . . . . . . . . . . . . . . 100
5.6.1 Hyperfine Interaction Parameters in CW-ESR
Spectra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.6.2 Electron Spin Nuclear Spin Interaction and
Dynamical Phenomena . . . . . . . . . . . . . . . . . . . . . . . 103
Contents ix
5.7 CW Double Resonance Techniques . . . . . . . . . . . . . . . . . . . . 106
5.7.1 Electron Nuclear Double Resonance. . . . . . . . . . . . . . 106
5.7.2 Continuous Wave Electron–Electron Double
Resonance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5.8 Methods Based on the Effect of an Applied External
Magnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.8.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.8.2 Optically Detected ESR . . . . . . . . . . . . . . . . . . . . . . 111
5.8.3 Reaction Yield Detected Magnetic Resonance . . . . . . . 112
5.8.4 Magnetically Field Effects on Reaction Yield . . . . . . . 113
5.8.5 Time-Resolved Magnetic Field Effect. . . . . . . . . . . . . 115
5.8.6 Singlet–Triplet Oscillations . . . . . . . . . . . . . . . . . . . . 116
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
6 Experimental Methods for the Investigation of Electron
Spin Interactions Based on ESR Phenomena. Pulse EPR
Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.2 Electron Spin Echo Methods. . . . . . . . . . . . . . . . . . . . . . . . . 126
6.2.1 Two and Three Pulse Methods. . . . . . . . . . . . . . . . . . 126
6.2.2 Spin Echo Detected ESR . . . . . . . . . . . . . . . . . . . . . 127
6.3 Electron Spin Resonance Methods Based on Pulse ELDOR . . . 128
6.3.1 Three-Pulse ELDOR. . . . . . . . . . . . . . . . . . . . . . . . . 128
6.3.2 Four-Pulse PELDOR . . . . . . . . . . . . . . . . . . . . . . . . 132
6.3.3 5 Pulse ELDOR (DEER 5) . . . . . . . . . . . . . . . . . . . . 133
6.4 Two-Dimentional Fourier Transfer ESR . . . . . . . . . . . . . . . . . 136
6.4.1 COSY (Correlation Spectroscopy), SECSY
(Spin–Echo Correlation Spectroscopy) . . . . . . . . . . . . 136
6.5 Two-Dimensional Electron-Electron Double Resonance
(2D-ELDOR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
6.6 Double-Quantum Coherence ESR . . . . . . . . . . . . . . . . . . . . . 139
6.7 Electron Spin Echo Envelope Modulation. . . . . . . . . . . . . . . . 143
6.8 Pulse ENDOR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.9 Pulse Saturation and Inversion Recovery. . . . . . . . . . . . . . . . . 149
6.10 ESR Spectra Hole Burning . . . . . . . . . . . . . . . . . . . . . . . . . . 151
6.11 ESR Nutation Spectroscopy. . . . . . . . . . . . . . . . . . . . . . . . . . 152
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
7 Miscellaneous Methods of Investigation of Electron Spin
Interactions Based on Optical and Other Techniques. . . . . . . . . . . 159
7.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
7.2 Optical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
7.2.1 Intramolecular Excited Triplet States Decay
Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
7.2.2 Intermolecular Singlet and Triplet Excited States
Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162