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H and 13C Hyperfine Coupling Constants of the Tryptophanyl Cation Radical in Aqueous Solution from Microsecond Time-Resolved CIDNP

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journal contribution
posted on 27.09.2007 by Alexey S. Kiryutin, Olga B. Morozova, Lars T. Kuhn, Alexandra V. Yurkovskaya, P. J. Hore
Relative values of the 1H and 13C isotropic hyperfine couplings in the cationic oxidized tryptophan radical TrpH•+ in aqueous solution are determined. The data are obtained from the photo-CIDNP (chemically induced dynamic nuclear polarization) enhancements observed in the microsecond time-resolved NMR spectra of the diamagnetic products of photochemical reactions in which TrpH•+ is a transient intermediate. The method is validated using the tyrosyl neutral radical Tyr, whose 1H and 13C hyperfine couplings have previously been determined by electron paramagnetic resonance spectroscopy. Good agreement is found with hyperfine coupling constants for TrpH•+ calculated using density functional theory methods but only if water molecules are explicitly included in the calculation.