Reactions of aquacobalamin and cob(II)alamin with chlorite and chlorine dioxide

Reactions of aquacobalamin (H₂O-Cbl(III)) and its one-electron reduced form (cob(II)alamin, Cbl(II)) with chlorite (ClO₂^-) and chlorine dioxide (ClO ₂^• ) were studied by conventional and stopped-flow UV-Vis spectroscopies and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ClO₂^- does not react with H₂O-Cbl(III), but oxidizes Cbl(II) to H₂O-Cbl(III) as a major product and corrin-modified species as minor products. The proposed mechanism of chlorite reduction involves formation of OCl^- that modifies the corrin ring during the course of reaction with Cbl(II). H₂O-Cbl(III) undergoes relatively slow destruction by ClO ₂^• via transient formation of oxygenated species, whereas reaction between Cbl(II) and ClO ₂^• proceeds extremely rapidly and leads to the oxidation of the Co(II)-center.