Micellar effects in the radiation chemistry of pyrimidine bases

Abstract

The yields of the radiolytic products in the reactions of ??OH, e[superscript -][subscript aq] and H?? with thymine and uracil and those in the reactions of e[superscript -][subscript aq] and ??OH/O??[superscript -] with ionized thymine and uracil have been determined quantitatively in Co-60 ??-irradiated aqueous thymine and uracil solutions in the presence of suitable scavengers. These product yields were also determined in the presence of the nonionic polyoxyethylene (15) nonylphenol, cationic hexadecyltrimethylammonium chloride and anionic sodium dodecyl sulfate surfactants at concentrations above and below their CMC's. Good material balances between G(-Pyrimidine) and G(total products) have been obtained in all cases. The products determined in irradiated aqueous thymine solutions were thymine dimer, cis-thymine glycol, trans-thymine glycol, 5-hydroxy dihydrothymine, 6 -hydroxy dihydrothymine, dihydrothymine, 5-hydroperoxy-6 -hydroxy dihydrothymine, 5-hydroxymethyl uracil, formyl pyruvyl urea, acetyl urea, 5-hydroxy-5-methyl barbituric acid, urea and alcohol adducts. The products determined in irradiated aqueous uracil solutions were uracil dimer, cis-uracil glycol, trans-uracil glycol, alloxan, alloxantin, dialuric acid, isobarbituric acid, 5-hydroxy hydantoin, parabanic acid, 5-hydroxy dihydrouracil, 6 -hydroxy dihydrouracil, dihydrouracil, formyl urea, urea and alcohol adducts. Based on the obtained yields of these products and the available literature, mechanisms for the radiolysis of thymine and uracil in aqueous solutions are proposed and discussed. The destruction yield of thymine and uracil and the yields of the corresponding radiolytic products decrease in the presence of micelle forming surfactants mainly at concentrations above the CMC. These micellar effects in the radiation chemistry of thymine and uracil are discussed in terms of competition kinetics between the surfactants and the pyrimidines for the radiolytic species formed in the radiolysis of water and in terms of solubilization of transients and intermediates by the micellar surfactants...