A comparative study of complex formation in the reactions of gold(III) with Gly-Gly, Gly-l-Ala and Gly-l-His dipeptides

Abstract

Proton NMR spectroscopy was applied to study the reactions of the dipeptides glycyl-glycine (Gly-Gly) and glycyl-l-alanine (Gly-l-Ala) with hydrogen tetrachloridoaurate(III) (H[AuCl4]). All reactions were performed at pH 2.0 and 3.0 and at 40 °C. The final products in these reactions were [Au(Gly-Gly-κ3NG1,N G2,OG2)Cl] and [Au(Gly-l-Ala- κ3NG,NA,OA)Cl] complexes. Tridentate coordination of the corresponding dipeptides and square-planar geometry of these Au(III) complexes was confirmed by NMR (1H and 13C) spectroscopy. This study showed that at pH < 3.0 the Au(III) ion was able to deprotonate the amide nitrogen atom. However this displacement reaction was very slow and the total concentration of the corresponding Au(III)-peptide complex formed after 5 days was less than 60% for the Gly-l-Ala or 70% for the Gly-Gly dipeptide. The kinetic data of the reactions between the Gly-Gly and Gly-l-Ala dipeptides and [AuCl4]- were compared with those for the histidine-containing Gly-l-His dipeptide. The differences in the reactivity of these three dipeptides with the Au(III) ion are discussed. © 2010 Elsevier Inc.