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Schlagwörter:
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Zusammenfassung:
Nuclear hyperfine and quadnipole coupling parameters for "N of the proximal histidine in low spin ferric heme complexes have been determined by ESEEM.'*3 In contrast, measurements of nuclear quadrupole interaction parameters for pyrrole "N of the porphyrin have presented diffiadties.1 Because of larger values of isotropic ,4N hyperfine interaction constants (am~4-5 MHz) one is unable to reach exact cancellation conditions at frequencies typically available to ESEEM spectrometers (9 GHz). For this reason, pyrrole nitrogens produce very shallow modulations. The current study attempts to overcome this problem using excitation frequencies at ku band (12-18 GHz) to obtain well-resolved spectral lines arising from the nuclear quadrupole transitions. Magnetic field dependence of double quantum transition lines near and away from the exact cancellation conditions allow us to estimate "N hyperfine interaction parameters.
