Acid induced decomposition of coenzyme B₁₂ and variants

Abstract

Abstract.The acid-catalyzed heterolytic cleavage of the Co-C bond in coenzyme B,, (1) and adocobinamide hydroxide (2) was studied using the excess-acidity functions of Cox and Yates. The results are compared to the acid-induced decomposition of methyl(5'-deoxyribofuranosyl)cobalamin (3) and (2-ethoxyethy1)cobalamin (4). Evidence is presented to view the bond cleavage in the compounds 1, 2 and 3 as an A , mechanism or as an I , substitution at Co3+, with water as the nucleophile, and in 4 as an A , mechanism. For 1, the temperature dependence (289-320 K) gives A S s = -96 J/(K.mol), in agreement with the I , ( A , ) mechanism. For the A , reactions the volumes of activation [ A V s = -11.4 (I), -8.2 (2) and -11.5 (3) cm3/mol in 2-4M acid at 298K] are consistent with the proposed mechanism, but AVs for the A , mechanism of 4 is exceptionally negative ( -7.2 cm3/mol), probably due to intramolecular coordination in the transition state. A comparison with the much slower acid-induced decomposition of 5'-deoxyadenosine brings out the labilization of the furanosyl oxygen bridge by coordination of the 5'-deoxyadenosyl or 5'-deoxyribofuranosyl group at the P-position to cobalt. For 5'-deoxyadenosine the excess-acidity treatment and the activation volume (AV' = 1.7 cm3/mol in 2 M acid) indicate a clear A , mechanism.

Determination of four forms of vitamin B12 and other B vitamins in seawater by liquid chromatography/tandem mass spectrometry

“…[12,13] The published stable pH range for all analyzed cobalamins is pH 4-7, [29] with lower pHs resulting in lower retention on a C18 SPE and acid-induced heterolysis of Ado-Cbl. [11,30] Me-Cbl and Ado-Cbl are particularly labile, so we focused on decreasing processing time (from 66 to 8 h for the preconcentration step) and eliminating the 2 nd SPE (pH 2) step required in previously published methods. [11] We found poorer recoveries of B 1 (37%) and B 7 (48%) when the pH 6.5 SPE was followed by a pH 2 SPE on a single C18 resin.…”