ENDOR AND EPR STUDIES OF HIGHLY ISOTOPICALLY C-13-ENRICHED UBIQUINONERADICALS

ENDOR and EPR measurements of anionic, neutral and diprotonated radica l cations of C-13-1-labelled ubiquinone 0 dagger in solution are prese nted. The C-13-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 int ramolecular H-bonding interactions. The variation of spin densities on the ubiquinone ring carbon atoms correlates with the calculated out-o f-plane twist angles of the methoxy groups.