On the reaction of Co(II) cobalamin with hydrogen peroxide

Co(II) cobalamin (Co(IICbl) is easily oxidized to Co(III) by a variety of oxidizing agents; with hydrogen peroxide, this reaction entails oxygenation of the corrin ring to species known as stable yellow corrinoids (SYC), as described by Makarov and co-workers. Reported here is a stopped-flow UV–Vis analysis of the initial steps of the Co(II)Cbl with hydrogen peroxide, prior to formation of SYC. The earliest recorded spectra in this reaction, 2 ms after mixing, consist of a mixture of Co(II) and Co(III)-aqua cobalamin. Direct formation of SYC is observed from this stage, with no evidence of inner-sphere interaction between Co(II) and the oxidant, hydrogen peroxide. Outer-sphere monoelectronic oxidation of Co(II) by H2O2 with concerted formation of a hydroxyl radical is therefore proposed as the source of subsequent SYC formation.