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Structural Information from Spin-Labels and Intrinsic Paramagnetic Centres in the Biosciences

Volume 152 of the series Structure and Bonding pp 283-327

Date:

Orientation-Selective DEER Using Rigid Spin Labels, Cofactors, Metals, and Clusters

  • Alice M. BowenAffiliated withDepartment of Chemistry, Centre for Advanced Electron Spin Resonance, University of Oxford
  • , Claudia E. TaitAffiliated withDepartment of Chemistry, Centre for Advanced Electron Spin Resonance, University of Oxford
  • , Christiane R. TimmelAffiliated withDepartment of Chemistry, Centre for Advanced Electron Spin Resonance, University of Oxford Email author 
  • , Jeffrey R. HarmerAffiliated withDepartment of Chemistry, Centre for Advanced Electron Spin Resonance, University of OxfordCentre for Advanced Imaging, University of Queensland Email author 

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Abstract

The dipolar interaction between two paramagnetic centres depends upon their spin–spin distance and relative orientation. Generally most experiments are carried out under conditions where the DEER signal only reports on the spin–spin distances and, for this type of data, sophisticated analysis methods for obtaining distance distributions have been developed. Recently there have been an increasing number of studies on systems where the DEER signals depend upon both distance and spin pair orientation. These investigations have relied on the use of rigid spin labels (those with a well-defined spatial position) and/or spectrometers operating at Q-band frequencies and above capable of performing DEER experiments with high resolution and sensitivity. In this article we discuss in detail orientation-selective DEER experiments for which the modulation depth and the dipolar frequencies depend on the relative orientation of the two paramagnetic centres and the distance. Analysis of the data in the presence of distance and orientation distributions is discussed, and representative examples from the literature are given for systems containing spin labels, organic cofactors, metals, and metal clusters.

Keywords

Distance measurement DEER EPR ESR Metal Metal cluster Orientation selection PELDOR Spin label Structural information