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Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines.

ABSTRACT: Multiharmonic electron paramagnetic resonance spectroscopy was demonstrated for two samples with both narrow and broad lines: (i) ?,?-Bisdiphenylene-?-phenylallyl (BDPA) with ?Bpp of 0.85 G plus ultramarine blue with ?Bpp of 17 G, and (ii) a nitroxide radical immobilized in sucrose octaacetate. Modulation amplitudes up to 17 G at 41 kHz were generated with a rapid scan coil driver and Litz wire coils that provide uniform magnetic field sweeps over samples with heights of 5mm. Data were acquired with a 2-D experiment in the Xepr software through the transient signal path of a Bruker E500T and digitized in quadrature with a Bruker SpecJet II. Signals at the modulation frequency and its harmonics were calculated by digital phase-sensitive detection. The number of harmonics with signal intensity greater than noise increases as the ratio of the modulation amplitude to the narrowest peak increases. Spectra reconstructed by the multiharmonic method from data obtained with modulation amplitudes up to five times the peak-to-peak linewidths of the narrowest features have linewidths that are broadened by up to only about 10% relative to linewidths in spectra obtained at low modulation amplitudes. The signal-to-noise improves with increasing modulation amplitude up to the point where the modulation amplitude is slightly larger than the linewidth of the narrowest features. If this high a modulation amplitude had been used in conventional methodology the linewidth of the narrowest features would have been severely broadened. The multiharmonic reconstruction methodology means that the selection of the modulation amplitude that can be used without spectral distortion is no longer tightly tied to the linewidth of the narrowest line.

SUBMITTER: Yu Z

PROVIDER: S-EPMC4420703 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines.

Yu Zhelin Z Tseytlin Mark M Eaton Sandra S SS Eaton Gareth R GR

Journal of magnetic resonance (San Diego, Calif. : 1997) 20150323

Multiharmonic electron paramagnetic resonance spectroscopy was demonstrated for two samples with both narrow and broad lines: (i) α,γ-Bisdiphenylene-β-phenylallyl (BDPA) with ΔBpp of 0.85 G plus ultramarine blue with ΔBpp of 17 G, and (ii) a nitroxide radical immobilized in sucrose octaacetate. Modulation amplitudes up to 17 G at 41 kHz were generated with a rapid scan coil driver and Litz wire coils that provide uniform magnetic field sweeps over samples with heights of 5mm. Data were acquired ...[more]

PMID: 25863892

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Project description:The fleeting ferric peroxo and hydroperoxo intermediates of dioxygen activation by hemoproteins can be readily trapped and characterized during cryoradiolytic reduction of ferrous hemoprotein-O2 complexes at 77 K. Previous cryoannealing studies suggested that the relaxation of cryogenerated hydroperoxoferric intermediates of myoglobin (Mb), hemoglobin, and horseradish peroxidase (HRP), either trapped directly at 77 K or generated by cryoannealing of a trapped peroxo-ferric state, proceeds through dissociation of bound H2O2 and formation of the ferric heme without formation of the ferryl porphyrin π-cation radical intermediate, compound I (Cpd I). Herein we have reinvestigated the mechanism of decays of the cryogenerated hydroperoxyferric intermediates of α- and β-chains of human hemoglobin, HRP, and chloroperoxidase (CPO). The latter two proteins are well-known to form spectroscopically detectable quasistable Cpds I. Peroxoferric intermediates are trapped during 77 K cryoreduction of oxy Mb, α-chains, and β-chains of human hemoglobin and CPO. They convert into hydroperoxoferric intermediates during annealing at temperatures above 160 K. The hydroperoxoferric intermediate of HRP is trapped directly at 77 K. All studied hydroperoxoferric intermediates decay with measurable rates at temperatures above 170 K with appreciable solvent kinetic isotope effects. The hydroperoxoferric intermediate of β-chains converts to the S = 3/2 Cpd I, which in turn decays to an electron paramagnetic resonance (EPR)-silent product at temperature above 220 K. For all the other hemoproteins studied, cryoannealing of the hydroperoxo intermediate directly yields an EPR-silent majority product. In each case, a second follow-up 77 K γ-irradiation of the annealed samples yields low-spin EPR signals characteristic of cryoreduced ferrylheme (compound II, Cpd II). This indicates that in general the hydroperoxoferric intermediates relax to Cpd I during cryoanealing at low temperatures, but when this state is not captured by reaction with a bound substrate, it is reduced to Cpd II by redox-active products of radiolysis.

Dataset Information

Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines.

Publications

Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines.

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