The reactions of [Au(dien)Cl]2+ with L-histidine-containing dipeptides. Dependence of complex formation on the dipeptide structure

Abstract

Reactions between the monofunctional [Au(dien)Cl]2+ complex with L-histidine-containing dipeptides, L-histidyl-glycine (L-His-Gly), and glycyl-L-histidine (Gly-L-His) were studied by 1H NMR spectroscopy. All reactions were performed in aqueous solution at 3.50 pD 5.50 at ambient temperature. In reaction of [Au(dien)Cl]2+ with L-His-Gly, only 1 with N3-monodentate coordinated dipeptide was formed. The reaction was completed within 3 min and the complex was very stable during several days with no release of dien from Au(III). However, in the reaction of [Au(dien)Cl]2+ with Gly-L-His, depending on the pD, different Au(III)-dipeptide complexes were observed. When this reaction was carried out at 3.50 pD 4.50, only 4 with tridentate coordination of the dipeptide via the amino, deprotonated amide, and N3 imidazole nitrogen were observed after 4 days. However, during this time, at 4.50 < pD 5.50, two Au(III)-dipeptide products, 5 which represents an imidazole-bridged species along with the already described 4, were observed. The formation of these complexes proceeds through intermediates, 2 and 3 with N3-monodentate and NP,N3-bidentate coordinated dipeptide, respectively, and with complete loss of dien.