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Journal of pharmaceutical and biomedical analysis

Effect of nicotinamide on the photolysis of cyanocobalamin in aqueous solution.


PMID 12609676

Abstract

The photolysis of cyanocobalamin by visible light in the presence of nicotinamide at pH 1.0-7.0 has been studied. The second-order rate constants for the bimolecular interaction of these vitamins have been determined which vary from 9.50 x 10(-3) (pH 1.0) to 1.25 x 10(-3) M(-1) min(-1) (pH 7.0). The rate-pH profile indicates a gradual slow decrease in rate in the pH range 1-3 followed by a relatively fast decrease in the pH range 3-7. The protonated form of cyanocobalamin appears to be more susceptible to photolysis than the non-ionised form. Cyanocobalamin photolysis leads to the formation of hydroxocobalamin at pH 1.0-7.0.