Kinetic studies on H~+-eatalysed aquation of chromium(III)-oxalato-asparaginato and chromium(III)-oxalato-histidinato complexes

摘要

Three chromium(III) complexes with aspara-gine (Asn) and histidine (His) of the [Cr(ox)2(Aa)]~(2-) type, where Aa = N,O-Asn, N,O-His or N,N'-His, were obtained and characterized in solution. The complexes with N,O-Aa undergo acid-catalysed aquation to give a free amino acid and cis-[Cr(ox)2(H2O)2]~-, whereas the complex with N,N'-His undergoes parallel reaction paths: (1) isomerization to the N,O-His complex and (2) liberation of an oxalate ligand. Kinetics of the N,0-Aa complexes in HC1O4 media were studied spectrophotometrically under pseudo-first-order conditions. The absorbance changes were attributed to the chelate ring opening at the Cr-N bond. The linear dependence of rate constants on [H~+] was established, and a mechanism for the chelate ring cleavage was postulated. The existence of a metastable intermediate with O-monodentate Aa ligand was proved experimentally. Effect of [Cr(ox)2(Aa)]~(2-) on 3T3 fibroblasts proliferation was studied. The tests revealed low cytotoxicity of the complexes. Complexes with Ala, His and Cys are good candidates for biochromium sources.