ENDOR AND EPR STUDIES OF HIGHLY ISOTOPICALLY C-13-ENRICHED UBIQUINONERADICALS .2.

ENDOR and EPR spectroscopy of ubiquinone double dagger (UQ)-0 and UQ-1 0 radicals, singly C-13-labelled at the 1,6,5,5' and 4(UQ-0) or the co rresponding 1,2,3,3' and 4(UQ-10) positions has been carried out in pr otic and aprotic solutions. The C-13-hyperfine coupling constant for t he various C-13-positions in the semiquinone, neutral and cation radic als are presented. The semi-empirical MO schemes AM1, PM3 and INDO hav e been used for calculating, in addition to the spin-density distribut ion, the geometry of isolated radicals and hydrogen-bonded radical-sol vent complexes, and the results are compared.