Thermochemical studies of vitamin B12. Part II. Thermodynamic data for the interaction of imidazole and methylimidazoles with aquocobalamin (vitamin B12a)

Abstract

Thermodynamic data (ΔG, ΔH, and ΔS) have been obtained for the reaction of imidazole, and 1-methyl-, 2-methyl- and 4(5)-methylimidazole with aquocobalamin in aqueous solution at 25 °C and in an ionic background of 0.1 mol dm^–3[NO₃]^– ions. In addition, protonation equilibria for both the free and vitamin B₁₂-complexed imidazoles have been investigated by a combination of potentiometric and spectrophotometric methods and direct microcalorimetry. The results are discussed.