W-band PELDOR with 1 kW microwave power: Molecular geometry, flexibility and exchange coupling

Gunnar W. Reginsson, Robert I. Hunter, Paul A.S. Cruickshank, David R. Bolton, Snorri Th Sigurdsson, Graham M. Smith*, Olav Schiemann

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


A technique that is increasingly being used to determine the structure and conformational flexibility of biomacromolecules is Pulsed Electron-Electron Double Resonance (PELDOR or DEER), an Electron Paramagnetic Resonance (EPR) based technique. At X-band frequencies (9.5 GHz), PELDOR is capable of precisely measuring distances in the range of 1.5-8 nm between paramagnetic centres but the orientation selectivity is weak. In contrast, working at higher frequencies increases the orientation selection but usually at the expense of decreased microwave power and PELDOR modulation depth. Here it is shown that a home-built high-power pulsed W-band EPR spectrometer (HiPER) with a large instantaneous bandwidth enables one to achieve PELDOR data with a high degree of orientation selectivity and large modulation depths. We demonstrate a measurement methodology that gives a set of PELDOR time traces that yield highly constrained data sets. Simulating the resulting time traces provides a deeper insight into the conformational flexibility and exchange coupling of three bisnitroxide model systems. These measurements provide strong evidence that W-band PELDOR may prove to be an accurate and quantitative tool in assessing the relative orientations of nitroxide spin labels and to correlate those orientations to the underlying biological structure and dynamics.

Original languageEnglish
Pages (from-to)175-182
Number of pages8
JournalJournal of Magnetic Resonance
Publication statusPublished - Mar 2012

Bibliographical note

Funding Information:
This work was supported by the BBSRC (Grant No. BB/H017917/1), the EPSRC (Grant No. F004583/1) and the Icelandic Research Fund (60028021). G.W.R. acknowledges the School of Biology, University of St Andrews for a SORS (Scottish Overseas Research Students) Scholarship and O.S. thanks the Research Councils of the UK for an RCUK fellowship.

Other keywords

  • DEER
  • Exchange coupling
  • Nitroxide spin labels
  • Orientation selective PELDOR


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