Dipolar Spectroscopy – Single-Resonance Methods

2017 - Volume 6 eMagRes
Volume 6, Issue 4
Peter P. Borbat

Peter P. Borbat

Cornell University, Ithaca, NY, USA

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Jack H. Freed

Jack H. Freed

Cornell University, Ithaca, NY, USA

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First published: 04 December 2017
Citations: 24

Abstract

A range of powerful techniques based on pulse EPR spectroscopies is used extensively for measuring electron spin dipolar couplings between native or introduced paramagnetic reporters, from which accurate distances, and in certain cases molecular orientations, can be determined to aid in solving biomolecular structures. Notably, several versatile pulse EPR methods of high sensitivity were developed over the past two decades. The two main groups of pulse methods are represented by single- and double-resonance techniques, which together constitute pulse dipolar EPR spectroscopy (PDS). We describe the first group by outlining the basic principles and illustrate key techniques with several examples from the literature, as well as some newly produced for purposes of this chapter. Specifically, we describe double-quantum coherence (DQC) methods for robust selection of the dipolar coupling by filtering out undesired spin coherence pathways via phase cycling, and we also discuss single-resonance methods such as four- and five-pulse single-quantum coherence (SQC) methods, all of which benefit from maximizing the spectral coverage. The common features and conceptual differences between single- and double-resonance methods are discussed. In addition, the extensions of modern DQC and SQC methods to two-dimensional correlation spectroscopy for eliciting orientational information are included. Other types of ‘single-frequency’ PDS methods, not all of which are based on principles behind fully coherent single-resonance methods, are also discussed to show the diversity of PDS methods.

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