NUCLEAR-QUADRUPOLE INTERACTIONS IN COPPER(II) DIETHYLENETRIAMINE-SUBSTITUTED IMIDAZOLE COMPLEXES AND IN COPPER(II) PROTEINS

Electron spin echo envelope modulation spectroscopy was used to study the nuclear quadrupole interactions of the remote 14N of substituted imidazoles coordinated to Cu(II)-diethylenetriamine. Substitution at the carbon adjacent to the remote nitrogen only slightly altered the quadrupole coupling parameters, while alkylation at the remote nitrogen altered them significantly. By applying a modified Townes-Dailey model, we were able to relate the change of quadrupole coupling parameters of the remote nitrogen to the change of electron occupancy in the sp2 hybrid orbital that is external to the imidazole ring and to relate this to N-H or N-C bond polarization. These studies suggest that the variation of quadrupole coupling constants previously observed in Cu(II) proteins may arise from the variations in hydrogen bonding at the remote nitrogen of the coordinated histidine imidazole side chain. © 1990, American Chemical Society. All rights reserved.