Multifrequency Electron Paramagnetic Resonance E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 623

Veröffentlichungsjahr: 2014

Beschreibung

This handbook is aimed to deliver an up-to-date account of some of the recently developed experimental and theoretical methods in EPR, as well as a complete up-to-date listing of the experimentally determined values of multifrequency transition-ion spin Hamiltonian parameters by Sushil Misra, reported in the past 20 years, extending such a listing published by him in the Handbook on Electron Spin Resonance, volume 2. This extensive data tabulation makes up roughly 60% of the book`s content. It is complemented by the first full compilation of hyperfine splittings and g-factors for aminoxyl (nitroxide) radicals since 197 by Larry Berliner, a world expert on spin labeling, helping to identify and interpret substances and processes by means of EPR techniques. The book also includes coverage of the recently developed experimental technique of rapid-scan EPR by Sandra Eaton and Gareth Eaton, and a thorough review of computational modeling in EPR by Stefan Stoll, author of Easy Spin.

Leseprobe

Table of Contents

Cover

Related Titles

Title Page

Copyright

Chapter 1: Preface

List of Contributors

Chapter 1: Introduction

Chapter 2: Rapid-Scan Electron Paramagnetic Resonance

2.1 Introduction

2.2 Post-Acquisition Treatment of Rapid-Scan Signals

2.3 Simulation of Rapid-Scan Spectra

2.4 Scan Coils

2.5 Design of Scan Driver

2.6 Use of ENDOR-Type Coils and RF Amplifiers for Very Fast Scans

2.7 Resonator Design

2.8 Background Signals

2.9 Bridge Design

2.10 Selection of Acquisition Parameters

2.11 Multifrequency Rapid Scan

2.12 Examples of Applications

2.13 Extension of the Rapid-Scan Technology to Scans That Are Not Fast Relative to Relaxation Times

2.14 Summary

Acknowledgments

References

Chapter 3: Computational Modeling and Least-Squares Fittingof EPR Spectra

3.1 Introduction

3.2 Software

3.3 General Principles

3.4 Static cw EPR Spectra

3.5 Dynamic cw EPR Spectra

3.6 Pulse EPR Spectra

3.7 Pulse and cw ENDOR Spectra

3.8 Pulse DEER Spectra

3.9 Least-Squares Fitting

3.10 Various Topics

3.11 Outlook

References

Chapter 4: Multifrequency Transition Ion Data Tabulation

4.1 Introduction

4.2 Listing of Spin-Hamiltonian Parameters

References

Chapter 5: Compilation of Hyperfine Splittings and g-Factors for Aminoxyl (Nitroxide) Radicals

5.1 Introduction

5.2 Tabulations

5.3 Concluding Remarks

References

Index

End User License Agreement

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Guide

Cover

Table of Contents

Chapter 1: Introduction

List of Illustrations

Figure 2.1

Figure 2.6

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.7

Figure 2.8

Figure 2.10

Figure 2.9

Figure 2.11

Figure 2.12

Figure 2.13

Figure 2.14

Figure 2.15

Figure 2.16

Figure 2.17

Figure 2.18

Figure 2.19

Figure 2.20

Figure 2.21

Figure 2.22

Figure 2.23

Figure 2.24

Figure 2.25

Figure 2.26

Figure 2.27

Figure 2.28

Figure 2.29

Figure 2.30

Figure 2.31

Figure 2.32

Figure 2.33

Figure 2.34

Figure 4.1

List of Tables

Table 2.1

Table 2.2

Table 2.3

Table 2.4

Table 2.5

Related Titles

Misra, S.K. (ed.)

Multifrequency Electron Paramagnetic Resonance

Theory and Applications

2011

Print ISBN: 978-3-527-40779-8

ISBN: 978-3-527-63353-1

Adobe PDF ISBN: 978-3-527-63354-8

ePub ISBN: 978-3-527-63355-5

eMobi ISBN: 978-3-527-64049-2

Handbook of Multifrequency Electron Paramagnetic Resonance

Data and Techniques

Edited by

Sushil K. Misra

The Editor

Sushil K. Misra

Concordia University

Department of Physics

1455 de Maisonneuve Boulevard

West

Montreal

Quebec H3G 1M8

Canada

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Print ISBN: 978-3-527-41222-8

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Preface

Research into electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR) and electron magnetic resonance (EMR), has been constantly expanding since the first article on this topic by Zavoisky in 1945. The field of EPR imaging, previously considered unachievable, is now well developed, complementing MRI (magnetic resonance imaging), a development of NMR (nuclear magnetic resonance), based on the resonance of protons possessing a nuclear magnetic moment. Moreover, EPR finds extensive applications in biology, medicine, chemistry, physics, and geology. It is, therefore, important to provide the scientific community with information on the latest developments in the field of EPR.

This volume is in continuation of the efforts put forward by my colleagues C. P. Poole, Jr. and H. A. Farach, who edited ESR Handbooks (ESRHB), Volume 1 (AIP Press, New York, 1994) and Volume 2 (Springer, AIP Press, New York, 1999), and by myself, editing the book “Multifrequency Electron Paramagnetic Resonance: Theory and Applications” (MFEPRTA; Wily-VCH, Weinheim, Germany, 2011). ESRHB Volume 1 dealt with the general aspects of the literature, with chapters on computer techniques, relaxation, and electron-nuclear double resonance (ENDOR), whereas Volume 2 contained chapters on sensitivity, resonators, lineshapes, electron-spin-echo envelope modulation (ESEEM), transition metal (TM) ion series, spin-Hamiltonian (SH) types and symmetries, evaluation of SH parameters from EPR data, EPR imaging, high-field EPR, and a thorough tabulation of TM ion data on SH parameters till 1993. Since the publication of these handbooks the technique of multifrequency EPR has been used extensively in EPR research. As for MFEPRTA book, it covered extensively the latest developments in theory and applications of multifrequency EPR. The present volume is aimed to provide chapters on the latest state-of-the-art information on EPR. It covers the technique of rapid-scan EPR and a thorough coverage of the literature on compilation of multifrequency EPR spectra and evaluation of SH parameters, as well as an exhaustive tabulation of TM ion SH parameters covering the period of 20 years (1993–2012, inclusive). In addition, a small chapter is devoted to a tabulation of hyperfine splittings and g-factors of some typical aminoxyl (nitroxide) ions published over the years. It is hoped that this volume will serve a useful and timely purpose to EPR researchers at large.

I am grateful to Professor C. P. Poole, Jr., University of South Carolina, for his constant mentoring throughout my efforts to put together this volume. Thanks are also due to Danielle Dennie and Katharine Hall, reference librarians at Concordia University, for their searches through the various databases to find the relevant articles.

Finally, I dedicate this book to my parents Mr. Rajendra Misra and (late) Mrs. Prakash Wati Misra, my daughters Manjula and Shivali, and my son Paraish.

List of Contributors

Lawrence J. Berliner

Department of Chemistry and Biochemistry

E Iliff Ave

University of Denver

Denver

CO 80208

USA

Stefan Diehl

Justus Liebig University Griessen

2nd Physics Institute

Heinrich-Buff-Ring 16

Griessen, Germany

Gareth R. Eaton

Department of Chemistry and Biochemistry

University of Denver

Denver

CO 80208

USA

Sandra S. Eaton

Department of Chemistry and Biochemistry

University of Denver

Denver

CO 80208

USA

Sushil K. Misra

Concordia University

Department of Physics

de Maisonneuve Boulevard West

Montreal

Quebec H3G 1M8

Canada

Deborah G. Mitchell

Department of Chemistry and Biochemistry

University of Denver

Denver

CO 80208

USA

Sean Moncrieff

Concordia University

Physics Department

de Maisonneuve Boulebard West

Montreal

Quebec H3G 1M8

Canada

Richard W. Quine

Daniel Felix Ritchie School of Engineering and Computer Science

University of Denver

Denver

CO 80208

USA

George A. Rinard

Daniel Felix Ritchie School of Engineering and Computer Science

University of Denver

Denver

CO 80208

USA

Stefan Stoll

University of Washington

Department of Chemistry

Seattle

WA 98195

USA

Mark Tseitlin

Department of Chemistry and Biochemistry

University of Denver

Denver

CO 80208

USA

Chapter 1Introduction

Sushil K. Misra

This volume consists of five chapters including the introduction, covering the various aspects of the technique of EPR (electron paramagnetic resonance, also known as ESR – electron spin resonance and EMR – electron magnetic resonance), in a timely manner. The most notable feature in this context is the multifrequency aspect of the contents, which is now the practice in EPR research. The various chapters are briefly described here.

Recording of EPR spectra using the recently developed techniques in rapid scan

. In this chapter (Chapter 2), the background, theory, instrumentation, and methodology of rapid-scan EPR, including the hardware and software required to implement rapid scans and analysis of the data, are described. Among other advantages, the ability of rapid scans to acquire data quickly permits higher temporal resolution for kinetics than can be achieved with CW (continuous wave) spectroscopy. In rapid-scan EPR, the magnetic field is scanned through resonance in a time that is short relative to electron spin-relaxation times. Direct detection of the EPR response yields the absorption and dispersion signals, instead of the derivatives that are recorded in the usual CW experiment. The rapid-scan signal provides the full amplitude of EPR absorption, and not just a small approximately linear segment as is recorded in field-modulated EPR. In a rapid scan, if the time on resonance is short relative to relaxation times, there is a scan-rate dependence response that can be deconvolved to yield the undistorted absorption signal. If the time on resonance is long enough that the signal is independent of scan rate, the deconvolution procedure does not change the spectrum; therefore, the data analysis method is general for any rate of passage through resonance. The signal-to-noise ratios obtained by rapid scan are higher by factors of as much as 20 to >250 than those obtained by CW EPR for samples ranging from spin-trapped superoxide and nitroxide radicals in fluid solution to paramagnetic centers in materials.

Simulation of EPR spectra and evaluation of spin-Hamiltonian parameters (SHP)

as developed over the years. After summarizing the key aspects of available simulation software packages, the basic aspects of EPR simulations are discussed in Chapter 3. Thereafter, methods for simulation of static and dynamic CW EPR, pulse EPR, ENDOR (electron nuclear double resonance), and DEER (double electron electron resonance) spectra are described. Subsequently, a section is dedicated to least-squares fitting. After a short section covering topics such as spin quantization and data formats, some of the challenges that still lie ahead are summarized in the conclusion. This chapter provides an expert overview of computational modeling and least-squares fitting of EPR spectra. A well-written summary of the theory and methods involved in EPR spectral simulation, covering a wide range of regimes (solids, liquids, slow motion, chemical exchange), experiments (cw and pulse EPR, ENDOR), and methods (Liouville space, Hilbert space, matrix diagonalization, perturbation theory) is provided. The discussion of least-squares fitting includes many aspects that are often only discussed in isolation. Apart from the author's very general and widely used software package EasySpin, many other existing programs are mentioned. The chapter concludes with an extensive list of over 500 references that encompasses not only the seminal high-impact papers from the last half century but also many less known contributions.

Chapter 4 is devoted to an exhaustive

tabulation of Spin-Hamiltonian parameters (SHPs) of transition metal ions

, as published in the last 20 years (1993–2012, inclusive). It supplements a similar data listing published in the

ESR Handbook

, Volume 2, edited by C. P. Poole, Jr. and H. A. Farach (Springer, AIP Press, New York, 1999), which covers the period from 1960s to 1992. Since then, in contrast, the technique of multifrequency EPR has been used extensively in EPR research. This information is useful for various purposes, which includes verification of new EPR results, planning of experiments, and finding what parameters have been reported in the literature, without having to do an extensive database search that may quite frequently involve journals that are not readily available.

Finally, Chapter 5 contains a tabulation of

hyperfine splitting and g-factors of some typical aminoxyl (nitroxide) radicals

. Since the first

Spin Labeling: Theory and Applications

volume in 1976, edited by L. Berliner, no compilation has been published on this topic. With the use of organic radicals such as spin labels, calibration agents, and so on, a complete reference listing of their physical parameters is useful. In particular, the aminoxyl (nitroxide) radicals are stable organic compounds that have found a plethora of uses in chemistry, biology, and physics. The compiled data, while not thorough, cover a range of these radical types at several frequencies, solvent environments, and hosts. In some selected cases, where the data were readily available, parameters in several host environments, solvents, and other states have been included, since polarity affects both the hyperfine and g-values.

Chapter 2Rapid-Scan Electron Paramagnetic Resonance

Sandra S. Eaton, Richard W. Quine, Mark Tseitlin, Deborah G. Mitchell, George A. Rinard, and Gareth R. Eaton

2.1 Introduction

The focus of this chapter is on the emerging and very powerful implementation of electron paramagnetic resonance (EPR) that is designated as rapid scan. Historically, most EPR instrumentation and methodology have been in one of two regimes: continuous wave (CW) [1, 2], or pulsed (saturation recovery, spin echo, and Fourier Transform) [3–6]. In a CW experiment the microwave power is constant, the magnetic field is scanned to achieve resonance, and the EPR signal is recorded by phase-sensitive detection at the frequency that is used for magnetic field modulation. Microwave powers and scan rates are selected such that spectra are independent of relaxation times. In pulse experiments, the microwave power is on only during excitation, signals are detected after the pulse(s), and differences in relaxation times are exploited to optimize information content. The rapid-scan regime is an intermediate case. As in CW experiments the microwave power is constant, but the magnetic field (or microwave frequency) is scanned through resonance in a time that is short relative to relaxation times, and phase-sensitive detection at a magnetic field modulation frequency is not used. Instead, the absorption and dispersion signals are recorded by direct detection with a double balanced mixer. Rapid scans and data analysis as discussed in the following paragraphs permit spectral acquisition with lineshapes that are not modulation broadened and have substantially improved signal-to-noise ratio (S/N) relative to CW spectroscopy. These experiments can be performed without the use of the high powers that are required for pulse experiments. In pulse experiments, data acquisition requires samples for which the decay time for a free induction decay (FID), T2*, is long relative to the instrument dead time. This is not a limitation for rapid scans. The combination of rapid scan with improvements in digital electronics provides opportunities to revolutionize the way that much EPR will be done in the future.

Historical development, analysis of data to recover the equivalent slow-scan spectrum, and hardware modifications of conventional spectrometers to implement rapid scans are discussed in this chapter. The technology and methodology to acquire, deconvolve, and interpret the transient responses are emphasized. In terms of instrumentation, the difference between CW and rapid scan is in the scan coils and drivers, optimized resonators, and detector bandwidth. The Hyde laboratory has developed segmental acquisition of spectra, scanning a few gauss at a time [7], while the Denver laboratory engineered faster and larger magnetic field sweeps to encompass spectra of most organic radicals [8, 9] to improve S/N [10, 11], to enhance EPR imaging [12], and to measure relaxation times [13, 14]. Section 2.12 of this chapter provides examples of the dramatic improvements in S/N that have been obtained by rapid scans of samples ranging from spin-trapped radicals to paramagnetic centers in materials. Most of the results surveyed are from the Denver laboratory.

2.1.1 Historical Background and Literature Survey

Rapid-scan EPR builds on prior work in NMR (nuclear magnetic resonance). Bloembergen et al. [15] observed a transient effect (“wiggles”) after the magnetic field passed through resonance [16]. In 1974, it was shown that these transient effects could be deconvolved to obtain useful NMR spectra (“correlation NMR spectroscopy” or “rapid-scan Fourier transform NMR spectroscopy” (FT-NMR)) [16–19]. Rapid-scan NMR achieved almost as high an S/N as pulsed FT-NMR, with the additional advantage that rapid-scan NMR could measure a portion of a spectrum, and hence avoid a strong solvent peak. Rapid-scan NMR was soon eclipsed by FT-NMR owing to the wide range of pulse sequences that became available. However, its use continued in a routine commercial NMR spectrometer.