Radiation-induced hydroxylation of thymine promoted by electron-affinic compounds.
The effect of 20 electron-affinic compounds including nitroimidazoles, nitrofurans, nitrobenzenes, and quinones on the radiation-induced reaction of thymine in aqueous solution was studied under deaerated and N2O-saturated conditions. The radiolysis of thymine in aerated aqueous solution was also performed for comparison. Thymine decomposition was depressed to some extent by the addition of electron-affinic compounds in both deaerated and N2O-saturated solutions, while promoted in aerated solution. The radiolyses with varying concentration of misonidazole indicated that the depression of thymine decomposition can be attributed to a competition between thymine and electron-affinic compounds for the reactions with .OH. Among the radiolysis products, the formation of thymine glycol was remarkably promoted by the addition of electron-affinic compounds. Irrespective of structures of the electron-affinic compounds, the G-value of thymine glycol increased in sigmoidal form with increasing one-electron reduction potential of the electron-affinic compounds and attained the ultimate values of ca. 1.1 and 1.8 in deaerated and N2O-saturated solutions, respectively. The results are in accord with one-electron oxidation of the hydroxythymyl radical, produced by the reaction of thymine with .OH, to the corresponding cation by electron-affinic compounds. The so-formed hydroxythymine cation undergoes solvolytic substitution to give thymine glycol. Based on the ultimate G-values of thymine glycol, the difference in reactivity between hydroxythymine-5-yl and 6-yl radicals toward electron-affinic compounds is discussed.
D000388:Air; D003037:Cobalt Radioisotopes; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D006900:Hydroxylation; D009578:Nitrobenzenes; D009581:Nitrofurans; D009593:Nitroimidazoles; D010084:Oxidation-Reduction; D011809:Quinones; D011838:Radiation-Sensitizing Agents; D012996:Solutions; D013941:Thymine / Q000031:analogs & derivatives / Q000528:radiation effects*; D014867:Water
D003037:Cobalt Radioisotopes; D009578:Nitrobenzenes; D009581:Nitrofurans; D009593:Nitroimidazoles; D011809:Quinones; D011838:Radiation-Sensitizing Agents; D012996:Solutions; D014867:Water; C029389:thymine glycol; D013941:Thymine