Redox reactions of hydrogen adducts of thymine: Comparisons with the reactions of hydroxyl adducts

Hydrogen atoms form two kinds of adducts with thymine (oxidizing and reducing). Redox reactions of these two kinds, popularly known as 5-hydrogenated-6-thyminyl (reducing) and 6-hydrogenated-5-thyminyl (oxidizing), were investigated where ferric ions (oxidizing) and ferrous ions (reducing) were used as the corresponding redox partners. A steady-state gamma radiolytic system was chosen where hydroxyl radicals were scavenged using t-butyl alcohol in acidic (pH 1.8) solution. It is inferred that the redox potential of oxidizing hydrogenated thyminyl radicals lies between 0.77 and 1.4 V vs. NHE. The reducing hydrogenated thyminyl radical has a redox value less than 0.8 V because it efficiently undergoes electron transfer reaction with Fe(III). A probable range of redox values for hydroxyl adduct of thymine is included for comparison.