A pulse radiolytic study of the interaction of nitroxyls with free-radical adducts of purines: consequences for radiosensitization.

Using the technique of pulse radiolysis, it has been demonstrated that the radicals, produced on interaction of the hydroxyl radical with purine nucleotides/nucleosides, interact with the nitroxyls, TMPN and NPPN. It has been possible to discern the various interactions in terms of the known redox properties of the various OH-radical adducts of the purines based upon spectral and kinetic data. It has been confirmed that the properties of the radical produced on interaction of Br2-. with dGMP, based upon its subsequent interactions with nitroxyls, are quantitatively the same as those for the .OH-radical adduct of dGMP with oxidizing properties. The implications of these findings are presented in terms of the potential competition between nitroxyls and cellular radiation modifiers for the various DNA radicals with different redox potentials, and thereby assess the potential importance of the reactivity of the oxidizing-purine radicals towards nitroxyls in radiobiological studies.