An ENDOR and ESR Study of Semi-Quinones Related to Vitamins K and E

摘要

The electron nuclear double resonance (ENDOR) spectra of ethanolic solutions of several semiquinones of biological interest have been observed, and splitting constants as well as percent enhancement measurements have been made. The ENDOR results, which are especially useful in obtaining unequivocal analyses of the more complex ESR spectra, also showed greatly increased resolution by resolving small splitting constant differences unobservable in the ESR. These results were used to evaluate accurate spin densities. It was found that the introduction of a long side chain in the vitamin semiquinones in place of a methyl group has very little effect on the spin density distribution including that at the ring carbon to which the side chain is attached. Alternating linewidth effects were observed in the ESR of the semiquionones derived from vit. K(1) and co-enzyme Q-10 (ubisemiquinone, USQ) with associated linewidth effects in the ENDOR. (Modified author abstract)