Formation and hydrolysis of pyridoxal-5′-phosphate hydrazones and Schiff bases: Prediction of equilibrium and rate constants

Abstract

Hydrazones and Schiff bases synthesized using aldehyde species of the B6 vitamin family (pyridoxal and pyridoxal 5′-phosphate) are of great interest due to their biological activities and chemical properties. Their probable applications include metal chelation in living organisms, cation and anion sensing, catalysis, etc. Their stability in water at different pH values should be studied because the aqueous solution is the most relevant medium for using hydrazones. The present paper reports on the efforts to predict the equilibrium and rate constants of the formation and hydrolysis reactions of hydrazones/Schiff bases derived from pyridoxal 5′-phosphate. A simple additive model is proposed that takes into account the presence or absence of the amine or hydrazide group and five- or six-membered aromatic cycles. New experimental data on the stability and kinetics of formation/hydrolysis of two hydrazones and two Schiff bases at different pH in aqueous medium were obtained to test the proposed model.