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Issue 31, 2009
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Structural information from orientationally selective DEER spectroscopy

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Abstract

Double electron–electron resonance (DEER) spectroscopy can determine, from measurement of the dipolar interaction, the distance and orientation between two paramagnetic centres in systems lacking long-range order such as powders or frozen solution samples. In spin systems with considerable anisotropy, the microwave pulses excite only a fraction of the electron paramagnetic resonance (EPR) spectrum and the resulting orientation selection needs to be explicitly taken into account if a meaningful distance and orientation is to be determined. Here, a general method is presented to analyze the dipolar interaction between two paramagnetic spin centres from a series of DEER traces recorded so that different orientations of the spin–spin vector are sampled. Delocalised spin density distributions and spin projection factors (as for example in iron–sulfur clusters), are explicitly included. Application of the analysis to a spin-labelled flavoprotein reductase/reduced iron–sulfur ferredoxin protein complex and a bi-radical with two Cu(II) ions provides distance and orientation information between the radical centres. In the protein complex this enables the proteinprotein binding geometry to be defined. Experimentally, orientationally selective DEER measurements are possible on paramagnetic systems where the resonator bandwidth allows the frequencies of pump and detection pulses to be separated sufficiently to excite enough orientations to define adequately the spin–spin vector.

Graphical abstract: Structural information from orientationally selective DEER spectroscopy

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Publication details

The article was received on 06 Apr 2009, accepted on 15 Jun 2009 and first published on 02 Jul 2009


Article type: Paper
DOI: 10.1039/B907010A
Citation: Phys. Chem. Chem. Phys., 2009,11, 6840-6848
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    Structural information from orientationally selective DEER spectroscopy

    J. E. Lovett, A. M. Bowen, C. R. Timmel, M. W. Jones, J. R. Dilworth, D. Caprotti, S. G. Bell, L. L. Wong and J. Harmer, Phys. Chem. Chem. Phys., 2009, 11, 6840
    DOI: 10.1039/B907010A

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