Effects of solvent and ionic medium on the kinetics of axial ligand substitution in vitamin B 12. Part VI. Partial molar volumes of some cobalamin derivates

Abstract

Apparent molar volumes φ v, were measured at 25 °C in 0.1 molal NaClO 4 for aquocobalamin chloride, methylcobalamin, 5′-deoxyadenosylcobalamin and aquanitrocobaloxime. For the organocobalamins the pH dependence of φ v was studied, and for aquocobalamin and aquanitrocobaloxime the dependence on solvent composition was studied. The base-off forms of the organocobalamins have the same volumes as the base-on forms. The apparent molar volume of aquocobalamin chloride is almost independent of solvent composition in dioxane-water mixtures, but increases dramatically in acetonitrile-water mixtures.