The Radiation Chemistry of Thymine in Aqueous Solution

Summary

The electron and OH adducts of thymine formed on irradiation of thymine in aqueous solutions containing O₂ react rapidly with the dissolved O₂ : k(TOH + O₂) = 1·5 × 10⁹ M⁻¹ sec⁻¹ and k(T⁻ + O₂) = 8 × 10⁹ M⁻¹ sec⁻¹. In both reactions O₂ adds to the thymine radical, producing T(OH)O₂ and TO₂⁻. It is shown that TO₂⁻ is ultimately converted into H₂O₂ and thymine, when the OH radicals are scavenged by a second organic solute. In the absence of O₂ and in the presence of formate or isopropanol evidence is presented that the thymine negative ion (or its protonated form) disproportionates, producing thymine and dihydrothymine. In low dose-rate, steady-state radiolysis, CO₂⁻ radicals destroy the chromophore of thymine in competition with a radical-radical combination reaction of CO₂⁻. With the high dose-rates used in pulse-radiolysis only these radical—radical reactions can occur.