Investigation of 133Inm-indium oxinate as a possible lung-scanning agent

Radiolysis of nucleosides in aqueous solutions: base liberation by the base attack mechanism

On the radiolysis of uridine and some other nucleosides in aqueous solution, a pH-dependent liberation of uracil or the corresponding base was found. e-aq and HO-.2 gave no freed bases, although many oxidizing radicals, including OH, Cl-.2, Br-.2, (CNS)-.2 and SO-.4, did cause the release of unaltered bases, depending on the pH of the solutions. The base yields were generally high at pH greater than or equal to 11, with the exception of SO-.4, which gave a rather high yield of uracil (from uridine) even in the pH region of less than or equal to 11. The pattern of the base formation against pH varied with the reacting radical, but was the same for the different nucleosides. With regard to the OH radical system, bases are considered to be formed after H-abstraction of the sugar moiety at low pH. The other oxidizing radicals, however, may cause base release by attack at the base. It is possible that O-, present at high pH as the dissociated form of OH, may act partly as an oxidizing radical. A plausible mechanism of 31'-radical formation is discussed.

E.S.R. of spin-trapped radicals in aqueous solutions of pyrimidine nucleosides and nucleotides. Reactions of the hydroxyl radical

Free radicals produced by the reactions of OH radicals with ribose phosphates, pyrimidine nucleosides and nucleotides in aqueous solutions have been investigated by e.s.r. and spin-trapping techniques. OH radicals were generated by U.V. -photolysis of hydrogen peroxide and short-lived free radicals of the samples were spin-trapped by t-nitrosobutane and identified by e.s.r. spectroscopy. For ribose-5'-phosphate and 2' -deoxyribose-5' -phosphate, e.s.r. spectra observed consisted mainly of singles due to -C(5')H2 radicals which were initiated by H-abstraction from the sugar at the C-4' position and formed by the radical transfer to the C-5' position. It has also been shown that OH radicals abstract a hydrogen atom from the sugar at C-1' and C-5' positions. For cytidine, deoxycytidine, 5'-CMP, 3' -CMP and 5' -dCMP, four radicals have been observed and for uridine, deoxyuridine, 5' -UMP, 3' -UMP and 5' -dUMP, the existence of at least three radical species have been established. In contrast to the case of ribose phosphates, no signals due to -C(5')H2 radicals were detected for pyrimidine nucleosides and nucleotides. The results are discussed in relation to a recent mechanism which described OH-induced strand breaks of DNA.