Mechanism of Oxidation of (Meso-5, 7, 7, 12, 14, 14-Hexamethyl-1, 4, 8, 11-Tetraazacyclotetradecane)Nickel(II) by H₂O Free Radicals in Aqueous Solutions. A Pulse Radiolysis Study

The title complex NiL²⁺ is oxidized in aqueous solutions in the pH range 3-7 in the presence of stabilizing anions X, X = HCO₂^-, SO₄^2-, and H₂PO₄^-, by HO₂^· free radicals to Ni^IIILX₂. The dependence of the rate of formation on [NiL²⁺] and X indicates that the H0_2· radical reacts with a [NiL²⁺] complex in the ion pair [NiL²⁺, X], forming the final products. The volumes of activation of the oxidation processes were measured; an analysis of the data indicates that the ion pairs involved are contact ion pairs. The results indicate that in the presence of appropriate transition-metal complexes the superoxide free radical is a potent oxidizing agent and suggest that this might cause some of the aspects of its toxicity.