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

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 acidcatalyzed 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.

Oxidation in vitro of chromium(III) dietary supplements mer-[Cr(pic)3] and trans(S,S)-[Cr(Cys)2]− by hydrogen peroxide

“…2b) as observed in other systems [29]. The chromium(V) complex produced spectroscopically is identical to that observed in our previous studies [18,30,31] -. In most cases the reaction rate was determined from absorption data in the UV region (CrO 4 2-generation).…”

“…On the other hand, it has been suggested that chromium(IV) and chromium(V) play the major role in a recently proposed redox mechanism for the antidiabetic activity of chromium pharmaceuticals [14][15][16][17]. Studies on chromium(III) behaviour in vitro are quite rare; furthermore, its oxidation was carried out either at pH values outside the biological range [18] or using non-biological oxidants such as PbO 2 [19]. Partial H 2 O 2 oxidation of chromium(III) in peptide adducts of its dietary supplements in blood serum [20] and partial intracellular chromium(III) oxidation of its nutritional supplement metabolites have been observed [6].…”