Reaction of Cob(I)alamin with nitrous oxide and Cob(III)alamin

Abstract

Cob(I)alamin (vitamin B_12s) has been generated by pulse radiolysis of N₂O-saturated solutions of cob(II)alamin (vitamin B_12r) containing sodium formate. It reacts with N₂O with rate constants in the range 200–1200 dm³ mol^–1 s^–1, depending on pH and buffer concentration. The final product is cob(II)alamin, formed in 100 % yield. The initial product is thought to be cob(III)alamin (vitamin B_12a or B_12h) but this does not build up to significant concentrations. Cob(III)alamin (vitamin B_12a or B_12h) reacts with cob(I)alamin with a rate constant of 3.2 × 10⁷ dm³ mol^–1 s^–1 independent of pH in the range 5.8–11.0. Cyanocobalamin (vitamin B₁₂) does not react with cob(I)alamin.