RADIATION-INDUCED REACTIONS OF 2-METHYL-5-NITRO-1H-IMIDAZOLE-1-ETHANOL)NICKEL(II) IN AQUEOUS-SOLUTION - A FLASH-PHOTOLYSIS AND STEADY-STATEGAMMA-RADIOLYSIS STUDY

On gamma radiolysis of the nickel(II) complex of metronidazole (2-meth yl-5-nitro-1H-imidazole-1-ethanol), hydroxyl radicals and the hydrated electron e- (aq) react with the complex leading to the destruction of the nitroimidazole structure. The loss of the complex and the product ion of nitrite have been followed by steady-state experiments, while t he transient kinetics of the hydroxyl reactions have been probed by fl ash photolysis. The OH radicals react with the complex with a rate con stant of almost-equal-to 4.0 x 10(9) dm3 mol-1 s-1, resulting in elimi nation of the nitro group either by adding to the C5 position or throu gh generation of a nickel(III) species. The latter undergoes intramole cular electron transfer from the ring with a rate constant of almost-e qual-to (4.6 +/- 0.4) x 10(3) s-1, while the imidazole radicals formed decay by second-order kinetics with a 2k/epsilon value of (9.1 +/- 1. 3) x 10(5) cm s-1. The hydrated electrons generate the nitroanion radi cals, a fraction of which undergoes denitration while the rest is redu ced by a successive four-electron scheme to a hydroxylamino derivative .