Radical Oxidation Mechanisms in Cellular Radiosensitisation: Electron Transfer in the Pulse Radiolysis of Aqueous Nucleotide Solutions

Pulse radiolysis has been used to study one-electron transfer reactions in aqueous solutions containing various nucleic acid derivatives and, also, in solutions containing some highly electron-affinic compounds which can function as cellular radiosensitisers. These include 2 methyl naphthaquinone and paranitroacetophenone (PNAP). Radicals derived from nucleic acid derivatives transfer electrons to the sensitisers at rates which approach diffusion-limited values. The electron affinity of the substituted pyrimidine, orotic acid (OA) is intermediate between those of the common nucleic acid derivatives and those of the radiosensitisers. This, together with the intense absorption spectrum of its electron adduct, makes it a useful marker for these studies. The relevance of these model studies in aqueous solution to mechanisms of radiosensitisation, are discussed.