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The Radiolysis of Uracil in Oxygenated Aqueous Solutions. A Study by Product Analysis and Pulse Radiolysis
Schuchmann, Man Nien,Sonntag, Clemens von
, p. 1525 - 1532 (2007/10/02)
Hydroxyl radicals are generated by the radiolysis of N2O-O2 (4:1 v/v)-saturated aqueous solutions of uracil.They add to the 5,6-double bond of the substrate .These radicals are converted by oxygen into the corresponding peroxyl radicals (I) and (II), respectively.Peroxyl radical (I) undergoes a base-induced O2(1-.) elimination (kobs 8x1E3 s-1 at pH 10.5).As an intermediate 5-hydroxy-isopyrimidine is formed which rearranges into isobarbituric acid and adds water forming 5,6-dihydro-5,6-dihydroxyuracil.Competing with this base-induced reaction of radical (I) there is a bimolecular decay of radicals (I) and (II).These processes become predominant at low pH.For this reason a strong pH dependence of G (products) is observed.The major products are (G values at pH 3 and 10 in parentheses) 5,6-dihydroxy-5,6-dihydrouracil (1.1; 2.4), isobarbituric acid (0; 1.2), N-formyl-5-hydroxyhydantoin (1.6; 0.2), 5-hydroxybarbituric acid (0.9; 0.2). 5-Hydroxybarbituric acid is formed in its keto form.Its deprotonation (k 4.4 s-1) has been followed by pulse conductometry.Details of the reaction mechanism, e.g. the involvement of oxyl radicals in the bimolecular decay of (I) and (II), are discussed.
