Hydrolytic and redox transformations of chromium(III) bis-oxalato complexes with glutaminic acid and glutamine: a kinetic, UV–Vis and EPR, study

Emilia Kiersikowska,Ewa Kita,Przemysław Kita,Grzegorz Wrzeszcz

doi:10.1007/s11243-016-0039-2

Abstract

The title complexes have been synthesized, chromatographically isolated and characterized by their ligands to metal ratio determinations and spectroscopic analyses. The kinetics of the first aquation stage, i.e., the amino acid chelate ring opening via the Cr–N bond cleavage, has been studied spectrophotometrically in acidic and alkaline media. Hydrogen peroxide oxidizes the complexes in alkaline media to CrO 4 2− anion and a relatively stable Cr(V) complex. Consecutive biphasic kinetics through two first-order steps were observed for the base hydrolysis and the oxidation process, whereas the acid-catalyzed aquation obeys a simple first-order pattern. Based on the kinetic and spectroscopic data, mechanisms of the coordinated amino acid liberation and chromium(III) oxidation are discussed.

Highlights

For the last two decades, numerous dietary supplements for humans containing so-called biochromium have been offered
We studied chemical and biological activity of several chromium(III) complexes with amino acids, e.g., [19–21]
Glutamine (Gln), the ligand chosen in this work, is the most abundant free amino acid in the human body, 60 % of all free amino acids, and is involved in many metabolic processes

Summary

Introduction

For the last two decades, numerous dietary supplements for humans containing so-called biochromium have been offered. Based on the kinetic and spectroscopic data, mechanisms of the coordinated amino acid liberation and chromium(III) oxidation are discussed. The present work deals with kinetics and mechanism of ligand substitution and redox transformations of chromium(III) bis-oxalato-glutaminic acid/glutamine complexes.

Results

Conclusion