Radiation-induced Oxidation of Cytosine and Uracil in Aqueous Solution of Copper (II)

Abstract

BOTH the hydrated electron, e⁻_aq, and the hydroxyl radical, OH, which are formed as the principal intermediates in water radiolysis, react rapidly with the pyrimidine bases through preferential addition to the 5, 6 double bond to give the hydropyrimidyl radical, BH, and the hydroxypyrimidyl radical, BOH, respectively^1–4. The yields for base destruction (molecules/100 eV) in oxygen-free solutions under γ-rays are, however, consistently low, G(−B) ⩽ 1 (refs. 5 and 6), when compared with primary yields of the radical species derived from water, Ge⁻_aq = 2.85, G_OH = 2.4 (ref. 7); recent work indicates that secondary reactions of BH and BOH lead to regeneration of the parent compound⁴. In oxygen-saturated solutions, e⁻_aq, is scavenged by oxygen to form O⁻₂(HO₂), the regeneration reaction is quenched, and the yield for base destruction increases to G(−B)∼2 through reactions involving the peroxy radical, B(OH)⨀₂. Many organic products are formed, however, from the intermediate, B(OH)⨀₂, and the overall product stoichiometries have yet to be fully elucidated⁸.