Pulse radiolysis experiments have been carried out to investigate the reaction of O2 with the radicals produced by ·OH attack on nucleic acid derivatives and single-stranded polynucleotides. The ·OH adducts of the pyrimidine polynucleotides poly C and poly U react with O2 giving rise to species whose absorption spectra are similar to the peroxy adducts of the monomers CMP and UMP. There may be two forms of polynucleotide radicals, reacting with O2 at different rates. The situation for purine polynucleotides is complex. Radicals on single-stranded DNA react with O2 on the same time scale as the reaction of O2 with ·OH adducts on pyrimidine polynucleotides. Typical values of the rate constant for this reaction are <tex-math>$\sim 4\times 10^{8}\ M^{-1}\ {\rm sec}^{-1}$</tex-math>, a value which agrees approximately with an estimated collision frequency of O2 with the polynucleotide radicals.

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