Radiolysis of Cytosine, 5-Methyl Cytosine and 2'-Deoxycytidine in Deoxygenated Aqueous Solution A Pulse Spectroscopic and Pulse Conductometric Study of the OH Adduct*

Cytosine, G-Values, pK-Values, Absorption Spectra, Pulse Radiolysis Using the pulse radiolysis technique the OH adducts of cytosine, 5-methyl cytosine and 2'-deoxycytidine were investigated in alkaline N20 saturated aqueous solutions. Absorption spectra were recorded and their change with time was correlated with the change in conductivity. An OH induced reaction (1.4 • 108 1 • mol-1 • s -1) was observed with OH adducts of cytosine and 5-methyl cytosine leading to radicals (pK = 10.3), the G-values of which were 3.2 and 1.6 respectively (conductivity measurements). These intermediates were assigned to the C-5 OH radical adducts. After completion of the free radical reactions (2k = 6 • 108 1 • mol-1 • s -1) the resulting product mixture showed pK-values of 8.3 (cytosine, G = 0.6), 10.5 (5-methyl cytosine, G = 0.8), 10.7 (cytosine, G=1 .5 ; 2'-deoxycytidine, G=1.5) and 12.4 (cytosine, no G-value, determinable with optical detection). Ammonia, which is a product measured after y-radiolysis of all the three compounds investigated (G(NHs) = 0.6 ± 0.1), is not released within 15 ms after the pulse.