Pulsed electron paramagnetic resonance (EPR) spectroscopy usingmicrowaves at two frequencies can be employed to measure distances between pairsof paramagnets separated by up to 10 nm. The method, combined with site-directedmutagenesis, has become increasingly popular in structural biology for both itsselectivity and capability of providing information not accessible through morestandard 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 anddetection frequencies, they cannot both be located at the center of the pseudo-Lorentzian microwave resonance of a single-mode resonator. To maximize theinversion 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 insensitivity. Here, we consider an alternative configuration: by spacing pump andobserver frequencies symmetrically with respect to the microwave resonance and byincreasing the quality factor, valuable improvement in the signal-to-noise ratio canbe obtained.

Exploiting the Symmetry of the Resonator Mode to Enhance PELDOR Sensitivity

Salvadori E;
2015

Abstract

Pulsed electron paramagnetic resonance (EPR) spectroscopy usingmicrowaves at two frequencies can be employed to measure distances between pairsof paramagnets separated by up to 10 nm. The method, combined with site-directedmutagenesis, has become increasingly popular in structural biology for both itsselectivity and capability of providing information not accessible through morestandard 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 anddetection frequencies, they cannot both be located at the center of the pseudo-Lorentzian microwave resonance of a single-mode resonator. To maximize theinversion 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 insensitivity. Here, we consider an alternative configuration: by spacing pump andobserver frequencies symmetrically with respect to the microwave resonance and byincreasing the quality factor, valuable improvement in the signal-to-noise ratio canbe obtained.
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4
359
368
EPR; distance measurements; dipolar interaction; electron spin
Salvadori E; Fung MW; Hoffmann M; Anderson HL; Kay CWM
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2318/1690198
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