Theoretical identification of a radical produced by radiolysis of uracil

Ab initio calculations were performed to determine the identity of a radical produced in the radiolysis of aqueous solutions of uracil. The radical in question can be produced in basic solution by .OH attack at the C6 position of uracil or in neutral solution by a mechanism involving ionization by SO4- and subsequent deprotonation. Proposed structures include a ring-opened radical 3 and a ring-closed radical 4. Calculations were made on various conformations of 3 as well as on 4 and two isomers of 4. Comparison with the experimental isotropic hyperfine coupling constants, as well as energetic considerations, clearly point to 4 as being the radical actually observed