Radiation-induced reactions of (2-methyl-5-nitro-1H-imidazole-1-ethanol)nickel(II) in aqueous solution: a flash-photolysis and steady-state gamma-radiolysis study
On gamma radiolysis of the nickel(II) complex of metronidazole (2-methyl-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 production of nitrite have been followed by steady-state experiments, while the transient kinetics of the hydroxyl reactions have been probed by flash photolysis. The OH radicals react with the complex with a rate constant of ≈ 4.0 × 109 dm3 mol–1 s–1, resulting in elimination of the nitro group either by adding to the C5 position or through generation of a nickel(III) species. The latter undergoes intramolecular electron transfer from the ring with a rate constant of ≈(4.6 ± 0.4)× 103 s–1, while the imidazole radicals formed decay by second-order kinetics with a 2k/Îµ value of (9.1 ± 1.3)× 105 cm s–1. The hydrated electrons generate the nitroanion radicals, a fraction of which undergoes denitration while the rest is reduced by a successive four-electron scheme to a hydroxylamino derivative.