Radicals produced by the reactions of SO4- with uridine and its derivatives. Studies by pulse radiolysis and gamma-radiolysis.

Using a pulse radiolysis technique, the sulphate radical, SO4-, has been demonstrated to react with uridine, 3'-UMP and 5'-UMP to produce intermediates of a new type, decaying according to a first-order rate law with k = 2.1, 4.1, 3.0 x 10(5) s-1 respectively at pH 7. The rate for uridine increases slightly with increasing pH. With deoxyuridine and 2', 3'-isopropylidene uridine, on the other hand, OH adduct radicals with longer lives (second-order decay) were found in accordance with the known fact that similar radicals are produced from N(1)-methylated uracils with SO4-. On gamma-irradiation of similar solutions containing the substrates that produce such short-lived species, chain reactions and high yields of unaltered uracil were found. Some optical properties are detailed and a probable structure of the short-lived species is discussed in relation to the substituent effect at the 2' position of the sugar part and to its strong reducing ability revealed by the rapid reaction with TNM.