title: Nonselective excitation of pulsed ELDOR using multi-frequency microwaves.
abstract: 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 S2 state. 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 YD· was 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.
authors: Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furo, Chikusa, Nagoya 464-8602, Japan.
authors: Yuki
authors: Y
authors: Asada
authors: Risa
authors: R
authors: Mutoh
authors: Masahiro
authors: M
authors: Ishiura
authors: Hiroyuki
authors: H
authors: Mino
mesh_terms: D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005609:Free Radicals / Q000032:analysis; D008345:Manganese / Q000737:chemistry; D008566:Membranes / Q000737:chemistry; D008872:Microwaves; D045332:Photosystem II Protein Complex / Q000737:chemistry; D011506:Proteins / Q000737:chemistry; D018724:Spinacia oleracea / Q000737:chemistry
chemical_list: D005609:Free Radicals; D045332:Photosystem II Protein Complex; D011506:Proteins; D008345:Manganese