Pyrimidine compounds, pulse radiolysis

An almost complete description of both OH radical-mediated and one-electron oxidation reactions of the thymine moiety (3) of DNA and related model compounds is now possible on the basis of detailed studies of the final oxidation products and their radical precursors. Relevant information on the structure and redox properties of transient pyrimidine radicals is available from pulse radiolysis measurements that in most cases have involved the use of the redox titration technique. It may be noted that most of the rate constants implicating the formation and the fate of the latter radicals have been also assessed. This has been completed by the isolation and characterization of the main thymine and thymidine hydroperoxides that arise from the fate of the pyrimidine radicals in aerated aqueous solutions. Information is also available on the formation of thymine hydroperoxides as the result of initial addition of radiation-induced reductive species including H" atom and solvated electron. 

Schuchmann MN, Naumov S, Schuchmann H-P, von Sonntag J, von Sonntag C (2005) 4-Amino-3Ff-pyrimidin-2-one ("isocytosine") is a short-lived non-radical intermediate formed in the pulse radiolysis of cytosine in aqueous solution. Radiat Phys Chem 72 243-250 Schulte-Frohlinde D, Hildenbrand K (1989) Electron spin resonance studies of the reactions of OH and SO4 radicals with DNA, polynucleotides and single base model compounds. In Minisci F (ed) Free radicals in synthesis and biology. Kluwer, Dordrecht, pp 335-359 Schulte-Frohlinde D, Behrens G, Onal A (1986) Lifetime of peroxyl radicals of poly(U), poly(A) and single- and double-stranded DNA and the rate of their reaction with thiols. Int J Radiat Biol 50 103-110... 

In the course of pulse radiolysis studies of purine and pyrimidine bases, Fielden et al. (1970) and Greenstock et al. (1973b) have been able to follow the kinetics of deprotonation of these compounds by OH- produced in the irradiated aqueous solution. The observation is made possible by the difference in ultraviolet absorption between the neutral and basic forms. The rate constants for deprotonation were found to be (1-2) x 101 0 M s-1 and those for the protonation of the anion by H+, 4 x 1010 M I s-1. 

Pulse Radiolysis of DNA and Related Pyrimidine Compounds Reactions of the OH- Free Radical... 

A pulse radiolysis study of the formation, decay, and absorption spectra - of transients produced by reactions of DNA and of some of its constituents with the OH- free radical is presented in this paper. Solutions were saturated with N20 so that the only significant reactive species produced by radiation was the OH- free radical. Rates of formation were determined by direct observation of the growth of transient absorption. Compounds and conditions were selected to permit investigation of (a) the sites of attack by OH- on pyrimidine bases, nucleosides, and DNA under various conditions (b) charge effects on reaction rates (c) comparative rates of addition to pyrimidine bases, and abstraction from... 

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