Electrochemical and Spectrophotometric Study of the Reactions of L-Leucine with Pyridoxal and Pyridoxal Phosphate

Abstract

The reactions of L-leucine (Leu) with pyridoxal (PL) and pyridoxal-5'-phosphate (PLP) were studied over pH 6 - 13.5. Formation of the Schiff bases was indicated by UV-VIS absorption bands and reduction waves on a mercury electrode. A comparative electrochemical and spectrophotometric study on the reaction mixtures as a function of pH and the amino acid-to-aldehyde concentration ratio was carried out. Apparent formation constant, KpH and acid-base constants for the Schiff bases were obtained. Reduction mechanisms of the imines are proposed in different pH zones. The formation constant, KSo, of an unprotonated Schiff base from unprotonated species of aldehyde and amino acid was determined by voltammetry. The results are compared to those obtained in analog Schiff bases in order to improve the quantitative description of the enzymatic models.