γ-Radiolysis of aqueous thymine solutions. Determination of relative reaction rates of OH radicals

Abstract

The loss of absorption of the chromophoric group of thymine on irradiation in aqueous solution with γ-rays has been studied under a variety of conditions. The effects of thymine and oxygen concentrations, of pH and of the presence of N₂O have been investigated. In solutions containing oxygen, the loss of absorption is the result of initial OH radical attack on the pyrimidine molecule; radiation-induced electron attachment to thymine does not lead to destruction of the chromophoric group if oxygen is present in the system. Aerated thymine solutions (8 × 10^–5-2 × 10^–4 M) have been used to determine, spectrophotometrically, the relative reactivities of solutes towards OH radicals; because of an unusual pH effect observed in neutral solutions, the competition experiments were carried out below pH 6. The reactivities of a number of organic solutes have been obtained. Similar rate constant ratios were obtained in solutions containing N₂O, indicating that N₂O^– was not an oxidizing species under the conditions of the experiments.