ENDOR and EPR studies of highly isotopically 13C-enriched ubiquinone radicals. Part 2

ENDOR and EPR spectroscopy of ubiquinone (UQ)-0 and UQ-10 radicals, singly 13C-labelled at the 1,6,5,5′ and 4(UQ-0)or the corresponding 1,2,3,3′ and 4(UQ-10) positions has been carried out in protic and aprotic solutions. The 13C-hyperfine coupling constant for the various 13C-positions in the semiquinone, neutral and cation radicals are presented.The semi-empirical MO schemes AM1, PM3 and INDO have been used for calculating, in addition to the spin-density distribution, the geometry of isolated radicals and hydrogen-bonded radical–solvent complexes, and the results are compared.