title: Exploiting the Symmetry of the Resonator Mode to Enhance PELDOR Sensitivity.
abstract: Pulsed electron paramagnetic resonance (EPR) spectroscopy using microwaves at two frequencies can be employed to measure distances between pairs of paramagnets separated by up to 10 nm. The method, combined with site-directed mutagenesis, has become increasingly popular in structural biology for both its selectivity and capability of providing information not accessible through more standard methods such as nuclear magnetic resonance and X-ray crystallography. Despite these advantages, EPR distance measurements suffer from poor sensitivity. One contributing factor is technical: since 65 MHz typically separates the pump and detection frequencies, they cannot both be located at the center of the pseudo-Lorentzian microwave resonance of a single-mode resonator. To maximize the inversion efficiency, the pump pulse is usually placed at the center of the resonance, while the observer frequency is placed in the wing, with consequent reduction in sensitivity. Here, we consider an alternative configuration: by spacing pump and observer frequencies symmetrically with respect to the microwave resonance and by increasing the quality factor, valuable improvement in the signal-to-noise ratio can be obtained.
authors: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH UK ; Institute of Structural and Molecular Biology, University College London, Gower Street, London, WC1E 6BT UK.
authors: Enrico
authors: E
authors: Salvadori
authors: Institute of Structural and Molecular Biology, University College London, Gower Street, London, WC1E 6BT UK.
authors: Mei Wai
authors: MW
authors: Fung
authors: Chemistry Research Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3TA UK.
authors: Markus
authors: M
authors: Hoffmann
authors: Chemistry Research Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3TA UK.
authors: Harry L
authors: HL
authors: Anderson
authors: London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH UK ; Institute of Structural and Molecular Biology, University College London, Gower Street, London, WC1E 6BT UK.
authors: Christopher W M
authors: CW
authors: Kay