Kinetic studies on H+- and OH−-catalysed aquation of bis-aspartatochromium(III)

Abstract

A potential synthetic biochromium source, bis-aspartatochromium(III) ion (where Asp is a tridentate N,O,O′-ligand, bonded via amine nitrogen and carboxylate oxygen atoms) has been obtained and characterized in aqueous solution. Kinetics of partial dechelation of the complex catalysed by H+ and OH− ions has been studied spectrophotometrically within 0.1–1.0 M HClO4 and 0.1–1.0 M NaOH ranges under first-order conditions. A linear dependence of the k obs,H on [H+] and independence of the k obs,OH on [OH−] were established. The derived rate expression and identification of components of the reaction mixture provide evidence for a reaction mechanism, where the key role in the overall process is the formation of an intermediate species with bidentate N,O-bonded Asp via both spontaneous and H+(OH−)-catalysed reaction paths. The intermediate is meta-stable and at pH 5–7 restores the substrate.