Radiation chemical reductions using eaq- and CO2- have been carried out in the presence of oxygen with metronidazole, p-nitroacetophenone, misonidazole and three other 2-nitroimidazoles. Low concentrations of oxygen were found to effectively inhibit the reduction of the first two compounds while much higher concentrations of oxygen were required for all of the 2-nitroimidazoles. These results parallel in vitro and in vivo experiments with metronidazole and misonidazole which also indicate that the reduction of the latter is significantly less inhibited by oxygen. Kinetic modelling of the radiochemical system suggests that the explanation for the differences lies in different reactions of the nitro radical anions; it appears that the anion derived from metronidazole undergoes disproportionation while that derived from misonidazole undergoes a unimolecular decay.
