γ-Radiolysis of 1,3-Dimethyluracil in N2O-Saturated Aqueous Solutions

Abstract

The γ-radiolysis of N2O-saturated aqueous solutions generates OH radicals and a small amount of H atoms. In 1,3-dimethyluracil solutions (10-3 M) these radicals add mainly to the 5-position of the C(5) -C(6) double bond of the solute. The resulting products have been identified by GC-MS after trimethylsilylation. The major products (G values in brackets) are dimers of the C(5) OH-adduct radicals (3.4), 5,6-dihydro-5,6-dihydroxy-1,3-dimethyl- uracil (0.85), 5,6-dihydro-5-hydroxy-1,3-dimethyluracil (0.75), dimer of the C(5)-OH- adduct with the C(5)-H-adduct radical (0.2) and 5,6-dihydro-6-hydroxy-1,3-dimethyl- uracil (0.2). G( 1,3-dimethyluracil consumption) has been found to be 5.7. The major reaction in this system is the dimerisation of the primary radicals. To a small extent the primary radicals also disproportionate by electron transfer to give the glycol 5,6-dihydro-5,6-dihydroxy-1,3-dimethyluracil as one of the products. Radiolytically formed H2O2 which could oxidise the C(5)-OH-adduct radical does not contribute to the formation of the glycol because the H2O2 yield is not reduced with respect to its expected “molecular yield” (G = 0.75). In contrast to the uracil system where it has been reported that drastic changes in radiolytic yields occur on going from neutral to alkaline irradiation conditions no such changes have been observed with 1,3-dimethyluracil. However, an acid-catalysed rearrangement from the C(5)-OH-adduct to the C(6)-OH-adduct radical is observed in the present system