Calculation of spin densities of radicals of pyrimidine-type bases by density functional theory. Influence of solvent and comparison with EPR results

Spin densities and hyperfine coupling (hfc) constants of thymine, 1-methylt hymine, uracil, 1-methyluracil, 6-methyluracil, 1,3-dimethyluracil, cytosin e and 1-methylcytosine radicals were calculated through the use of density functional theory (DFT) considering the influence of the surrounding solven t molecules by their dielectric properties by applying the Onsager model. T he results are compared with experimental hfc constants obtained with Fouri er-transform (FT) EPR experiments. The radicals were generated in aqueous s olution using the triplet sensitized electron transfer from the pyrimidine- type bases to photoexcited spin-polarized anthraquinone-2,6-disulfonate. It is found that the geometry and the spin density distribution of the radica l cations and their deprotonated successor radicals are influenced by a sur rounding dielectric solvent. The hfc constants calculated for an aqueous me dium are in good agreement with the experimental FT EPR results.