Radiolysis of cytosine in dilute neutral aqueous solution

Cytosine, 0.1 to 10 mM, has been radiolyzed at constant dose rates in 0.02 M phosphate buffer, pH 7. If the pH is then adjusted to 3, the absorption of the radiolysis products at 275 nm becomes negligible, and the radiochemical decomposition yield G(--cyt) can be calculated from the decrease in absorbance. In oxygen-saturated solutions it is described by the expression (D* = dose in krad): G(--cyt) = 3.3 -- 0.024D* (to at least 40 percent decomposition). The radiolysis products react with the radicals derived from the solvent about one fifth as fast as cytosine does. The radiolysis products have appreciable absorbance at less than 260 nm and pH 3, and at 266 nm and pH 7 or ll. The spectral characteristics of the predominant products resemble those of known dihydrocytosine derivatives. In solutions containing greater than 1 mM cytosine and initially saturated with air, the oxygen is soon depleted; in absence of oxygen, different radiolysis products having a higher absorbance are formed