Degradation of Thymine in Aqueous Solution Containing ³HHO. Comparison with ⁶⁰Co Gamma-Radiolysis

Abstract

Thymine aqueous solutions were prepared at a concentration of 5 × 10^-4 M (contained ¹⁴C-thymine and buffered at pH 7.0) and were irradiated with ⁶⁰Co gamma-rays and ³H beta-rays from ³HHO, in the presence of N₂, 0₂, N₂0 or t-BuOH-N₂. Thin-layer chromatography was carried out bidimensionally and autoradiography was performed. Considerable difference in the dose-yield curves was observed between beta-irradiation and gamma-irradiation. Oxygen enhancement ratio, 1.35 and 1.06 at a dose of 1.5 × 10³ Gy, were obtained by gamma-rays and by beta-rays, respectively, for thymine degradation. Oxygen effect on product formation was very low in beta-irradiation. The yield of 5-hydroxy-5-methylbarbituric acid + 5-hydroxy-5-methylhydantoin was much higher in beta-irradiation than in gamma-irradiation under N₂ and N₂O. These results lead to the conclusion that in beta-irradiation there could be a progression of oxidation of materials with some species differed from OH radicals.