Kinetics and mechanism of copper II catalyzed oxidative deamination of basic amino acids by peroxomonosulphate

Abstract

In biological systems, enzymes catalyse the oxidative deamination of and#945;-amino acids to and#945;-keto acids. Extensive research has been carried out to mimic this reaction in vitro, using metal complexes and salts as catalyst. This research is an attempt to construct a model oxidative deamination system of basic amino acids using peroxomonosulphate (PMS) and copper(II) ions, mimicking the reactions catalyzed by enzymes in biological systems. PMS with its high oxidation potential and propensity to react through oxygen transfer is an important, environmentally benign oxidant and hence was chosen for this study. In the study, it was observed that the oxidation of basic amino acids (ornithine, histidine and arginine), by PMS in acetic acid-sodium acetate buffer both in the presence and absence of copper(II) catalyst at 308 K. The pseudo first order rate constants were calculated from the plot of log [PMS]t vs time for the oxidation studies both in the presence and absence of copper(II) catalyst. The effect of all the reactants on kobs was studied. The products obtained in the oxidation of amino acids by PMS both in the presence and absence of copper(II) catalyst were characterized by HPLC, FT-IR and 1H NMR studies and were identified as 4-aminobutanal in the case of ornithine, and#945;-imidazolyl acetaldehyde in the case of histidine and citrulline in the case of arginine. Cyclic voltammetric and UV visible absorption studies confirmed the formation of (copper(II) amino acid PMS) complex. Detailed reaction mechanism of the oxidation of amino acids by PMS in the presence and absence of copper(II) ions was elucidated from UV-visible spectral analysis. Kinetic parameters for the oxidation reaction both in the presence and absence of copper(II) catalyst were calculated. Among the three systems studied, oxidation of arginine by PMS alone was mimicking the biological system. newline newline newline