The reaction between methylcobalamin and cyanide revisited.

Abstract

The reaction between the vitamin B12 coenzyme methylcobalamin and cyanide has been re-investigated by UV-Vis and 1H NMR spectroscopies under the same conditions. On the basis of the results and recent results of other studies on the reaction between other alkylcobalamins and cyanide, the changes in the 1H NMR chemical shifts and linewidths in the aromatic region observed upon addition of cyanide to methylcobalamin can be attributed to the rapid formation of (β-CH3)(α-CN)Cbl-, rather than the formation of MeCbl·CN- as proposed earlier (Inorg. Chem. 36 (1997) 4891). There is excellent agreement between the equilibrium constant for formation of (β-CH3)(α-CN)Cbl- determined by the two methods (0.35±0.03 M-1 and 0.31±0.01 M-1 from the UV-Vis and 1H NMR spectroscopic data, respectively (D2O, pD 12.1, 25.0°C)). Show more