Nonselective excitation of pulsed ELDOR using multi-frequency microwaves
Publication year: 2011
Source: Journal of Magnetic Resonance, Available online 17 September 2011
Yuki*Asada, Risa*Mutoh, Masahiro*Ishiura, Hiroyuki*Mino
The use of a polychromatic microwave pulse to expand the pumping bandwidth in pulsed electron-electron double resonance (PELDOR) was investigated. The pumping pulse was applied in resonance with the broad (~100 mT) electron paramagnetic resonance (EPR) signal of the manganese cluster of photosystem II in the S2state. The observation pulses were in resonance with the narrow EPR signal of the tyrosine radical, YD. It was found that in the case of the polychromatic pumping pulse containing five harmonics with the microwave frequencies between 8.5 and 10.5 GHz the PELDOR effect corresponding to the dipole interaction between the Mn cluster and YDwas about 2.9 times larger than that achieved with a monochromatic pulse. In addition to the dipolar modulation, the nuclear modulation effects were observed. The effects could be suppressed by averaging the PELDOR trace over the time interval between the observation microwave pulses. The polychromatic excitation technique described will be useful for improving the PELDOR sensitivity in the measurements of long distances in biological samples, where the pair consists of a radical with a narrow EPR spectrum and slow phase relaxation, and a metal center that has a broad EPR spectrum and a short phase relaxation time.
Graphical abstract
Highlights
? Application of multiple microwave frequencies for pulsed EPR. ? Efficiency of the spin excitation was evaluated by PELDOR. ? Improvement of signal-to-noise ratio of the PELDOR in photosystem II. ? Examination of the PELDOR in site-directed spin-labeled protein.
Source:
Journal of Magnetic Resonance