Abstract
Although now recognized to be an important reactive nitrogen species in biological systems that modifies the structures of proteins, DNA and lipids, there are few studies on the reactivity of NO2, including the reactions between NO2 and transition metal complexes. We report kinetic studies on the reactions of NO2 with two forms of vitamin B12 — cob(II)alamin and nitrocobalamin. UV–visible spectroscopy and HPLC analysis of the product solution show that NO2 cleanly oxidizes the metal center of cob(II)alamin to form nitrocobalamin, with a second-order rate constant of (3.5±0.3)×108M−1s−1 (pH7.0 and 9.0, room temperature, I=0.20M). The stoichiometry of the reaction is 1:1. No reaction is detected by UV–visible spectroscopy and HPLC analysis of the product solution when nitrocobalamin is exposed to up to 2.0molequiv. NO2.
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