title: W-band frequency-swept EPR.
abstract: This paper describes a novel experiment on nitroxide radical spin labels using a multiarm EPR W-band bridge with a loop-gap resonator (LGR). We demonstrate EPR spectroscopy of spin labels by linear sweep of the microwave frequency across the spectrum. The high bandwidth of the LGR, about 1 GHz between 3 dB points of the microwave resonance, makes this new experiment possible. A frequency-tunable yttrium iron garnet (YIG) oscillator provides sweep rates as high as 1.8x10(5) GHz/s, which corresponds to 6.3 kT/s in magnetic field-sweep units over a 44 MHz range. Two experimental domains were identified. In the first, linear frequency sweep rates were relatively slow, and pure absorption and pure dispersion spectra were obtained. This appears to be a practical mode of operation at the present level of technological development. The main advantage is the elimination of sinusoidal magnetic field modulation. In the second mode, the frequency is swept rapidly across a portion of the spectrum, and then the frequency sweep is stopped for a readout period; FID signals from a swept line oscillate at a frequency that is the difference between the spectral position of the line in frequency units and the readout position. If there is more than one line, oscillations are superimposed. The sweep rates using the YIG oscillator were too slow, and the portion of the spectrum too narrow to achieve the full EPR equivalent of Fourier transform (FT) NMR. The paper discusses technical advances required to reach this goal. The hypothesis that trapezoidal frequency sweep is an enabling technology for FT EPR is supported by this study.
authors.affiliation: National Biomedical EPR Center, Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA. jshyde@mcw.edu
authors.forename: James S
authors.initials: JS
authors.lastname: Hyde
authors.forename: Robert A
authors.initials: RA
authors.lastname: Strangeway
authors.forename: Theodore G
authors.initials: TG
authors.lastname: Camenisch
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Ratke
authors.forename: Wojciech
authors.initials: W
authors.lastname: Froncisz
mesh_terms: D000465:Algorithms; D003497:Cyclic N-Oxides / Q000737:chemistry; D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D005583:Fourier Analysis; D007202:Indicators and Reagents; D008872:Microwaves; D009589:Nitrogen Oxides / Q000737:chemistry; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl / Q000737:chemistry
chemical_list: D003497:Cyclic N-Oxides; D007202:Indicators and Reagents; D009589:Nitrogen Oxides; D013113:Spin Labels; D014216:Triacetoneamine-N-Oxyl; C047253:3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-1-yloxyl
references.citation: J Magn Reson. 2004 Sep;170(1):127-35
references.pmid: 15324766
references.citation: J Magn Reson. 2007 Apr;185(2):259-63
references.pmid: 17267251
references.citation: Rev Sci Instrum. 2007 Mar;78(3):034701
references.pmid: 17411204
references.citation: J Magn Reson. 2008 Aug;193(2):297-304
references.pmid: 18547848