Distance measurements in biological systems by EPR The foundation for understanding function and dynamics of biological systems is knowledge of their structure. Many experimental methodologies are used for determination of structure, each with special utility. Volumes in this series on Biological Magnetic Resonance emphasize the methods that involve magnetic resonance. This volume seeks to provide a critical evaluation of EPR methods for determining the distances between two unpaired electrons. The editors invited the authors to make this a very practical book, with specific numerical examples of how experimental data is worked up to produce a distance estimate, and realistic assessments of uncertainties and of the range of applicability, along with examples of the power of the technique to answer biological problems. The first chapter is an overview, by two of the editors, of EPR methods to determine distances, with a focus on the range of applicability. The next chapter, also by the Batons, reviews what is known about electron spin relaxation times that are needed in estimating distances between spins or in selecting appropriate temperatures for particular experiments. Albert Beth and Eric Hustedt describe the information about spin-spin interaction that one can obtain by simulating CW EPR line shapes of nitroxyl radicals. The information in fluid solution CW EPR spectra of dual-spin labeled proteins is illustrated by Hassane Mchaourab and Eduardo Perozo.

Dr. Lawrence J. Berliner is currently Professor and Chair of the Department of Chemistry and Biochemistry at the University of Denver after retiring from Ohio State University, where he spent a 32-year career in the area of biological magnetic resonance (EPR and NMR). He is the Series Editor for Biological Magnetic Resonance, which he launched in 1979.

Preface. Part I: Introduction. 1. Distance Measurements by CW and Pulsed EPR; S.S. Eaton, G.R. Eaton. 2. Relaxation Times of Organic Radicals and Transition Metal Ions; S.S. Eaton, G.R. Eaton. Part II: CW Measurements. 3. Structural Information from CW-EPR Spectra of Dipolar Coupled Nitroxide Spin Labels; E.J. Hustedt, A.H. Beth. 4. Determination of Protein Folds and Conformational Dynamics using Spin-Labeling EPR Spectroscopy; H.S. Mchaourab, E. Perozo. 5. EPR Spectroscopic Ruler: the Deconvolution Method and its Applications; Wenzhong Xiao, Yeon-Kyun Shin. 6. TOAC: The Rigid Nitroxide Side Chain; J.C. McNulty, G.L. Millhauser. 7. Depth of Immersion of Paramagnetic Centers in Biological Systems; G.I. Likhtenshtein. Part III: Pulsed EPR Measurements of Electron-Electron Interactions. 8. Determination of Distances Based on T1 and Tm Effects; S.S. Eaton, G.R. Eaton. 9. Double-Quantum ESR and Distance Measurements; P.P. Borbat, J.H. Freed. 10. 2+1'' Pulse Sequence as Applied for Distance and Spatial Distribution Measurements of Paramagnetic Centers; A. Raitsimring. 11. Double Electron-Electron Resonance; G. Jeschke, et al. Part IV: Applications to Photosynthesis. 12. Electron Paramagnetic Resonance Distance Measurements in Photosynthetic Reaction Centers; K.V. Lakshmi, G.W. Brudvig. 13. Photo-Induced Radical Pairs Investigated using Out-of-Phase Electron Spin Echo; S.A. Dzuba, A.J. Hoff.