Photoreduction of thymine glycol sensitized by aromatic amines in aqueous solution

Abstract

Photolyses (λ_ex > 280 nm or λ_ex 300 nm) of thymine glycol (TG)(1 mM) in the absence and presence of aromatic amines (1 mM) have been performed in aqueous solution at pH 7.0. The photoconversion of TG was quite inefficient without aromatic amines, but was remarkably promoted by the addition of the amines. The main products in the amine-sensitized photolysis were thymine (T) and 6-hydroxy-5,6-dihydrothymine (6HODHT). With the exception of NNN′N′-tetramethyl-p-phenyl-enediamine (TMPD), the amine-sensitized reaction of TG was quenched by a triplet quencher, biacetyl. The yield of T increased on decreasing the half-wave oxidation potential (E_1/2^Ox) of the aromatic amines. The yield of 6HODHT in the photolysis with aniline increased on increasing the concentration of sodium formate added as a hydrogen-atom donor. The effects of E_1/2^Ox and sodium formate on the product yields were consistent with an intermediacy of 6-hydroxythymin-5-yl radicals (6HOT˙) produced by reductive dehydroxylation of TG.