ENDOR and EPR studies of highly isotopically 13C-enriched ubiquinone radicals

Abstract

ENDOR and EPR measurements of anionic, neutral and diprotonated radical cations of ¹³C-1-labelled ubiquinone 0 in solution are presented. The ¹³C-carbonyl hyperfine coupling constant in protic solvents is roughly half of that in aprotic solvents. Preferred conformers of diprotonated ubiquinone and neutral radicals exist as a result of intramolecular H-bonding interactions. The variation of spin densities on the ubiquinone ring carbon atoms correlates with the calculated out-of-plane twist angles of the methoxy groups.