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The flavin cofactor of Escherichia coli DNA photolyase in its neutral radical form, FADH • , was investigated by high-frequency/high-field continuous-wave electron paramagnetic resonance at 360 GHz. The data presented are the first flavin radical spectra where the full rhombic symmetry of the g-tensor is resolved. A fit of the spectrum yields accurate principal values of g, which show only a small anisotropy: g X ) 2.004 31(5), g Y ) 2.003 60(5) and g Z ) 2.002 17(7). The hyperfine splitting observed in the g Y region could be assigned to a hyperfine tensor component of the H(5) proton in the 7,8-dimethyl isoalloxazine moiety of FADH • . From a comparison of this effective hyperfine coupling with the principal value obtained from pulsed (Davies) electron-nuclear double resonance, the orientation of the g-tensor principal axes with respect to the H(5) hyperfine principal axes could be derived. Remaining ambiguities in the sign of the angle between the principal axes of g and the molecular axes are discussed by taking into account results from g-tensor calculations using density functional theory and semiempirical AM1 based methods.

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We present a model and web-based tool for rapid and efficient prediction and rationalization of chemical membrane degradation in PEMFCs including protection mechanisms.

Articles you may be interested inMassively parallel implementations of coupled-cluster methods for electron spin resonance spectra. I. Isotropic hyperfine coupling tensors in large radicals Density functional calculations of molecular g -tensors in the zero-order regular approximation for relativistic effectsThe results of calculations of doublet state G tensors of organic radicals often show unsatisfactory agreement with the respective experimental data. This led us to reconsider the results of the Rayleigh-Schrödinger perturbation theory approach found in the literature. We came to the conclusion that neither the expressions given for restricted nor for unrestricted Hartree-Fock functions are fully correct. In this paper new expressions for the G tensor to be used with restricted Hartree-Fock functions will be introduced and results of calculations employing these new formulas in conjunction with molecular states from semiempirical Hartree-Fock-type calculations are discussed.

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The interpretation of EPR and ENDOR measurements on an organic free radical which appears to be a universal concomitant of senescence in plants is discussed. On the basis of EPR spectra obtained at 95 GHz it is speculated that the radical is derived from a quinone.