SUBSTITUTION REACTIONS OF THE MONOFUNCTIONAL GOLD(III) COMPLEX AND SULPHUR-DONOR BIOLOGICALLY IMPORTANT LIGANDS

Abstract

Gold(III) complexes have found application in catalysis, materials science and medical inorganic chemistry. Considering that the right choice of inert ligands in the structure of Au(III) complexes is crucial for their properties and reactivity toward biomolecules, we have studied the substitution reactions between monofunctional Au(III) complex, [Au(Cl-Ph-tpy)Cl]Cl2 (Cl- Ph-tpy = 4′-(4-chlorophenyl)-2,2′:6′, 2″-terpyridine) and sulfur-donor biomolecules, glutathione (GSH) and L-methionine (L-Met), in 25 mM Hepes buffer (pH = 7.2) and 40 mM NaCl. The reactions were followed under the pseudo-first-order conditions as a function of ligand concentration and temperature, using the stopped-flow technique. Calculations were made by Microsoft Excel 2019 and Origin2019b 64Bit. Observed kinetics traces follow a single exponential function, suggesting that the process of the substitution undergoes as one reversible step. Also, L-Met was more reactive than GSH. This order is related to the positive inductive effect of the methyl group, which increases the nucleophilicity of the thioether. According to the values of the activation parameters, the reactions follow an associative model. These results demonstrate the strong connection between the reactivity of Au(III) complexes and the structural and electronic characteristics of the biologically important ligands.