Au(III) interaction with methionine- and histidine-containing peptides

Mononuclear Au(III) complexes of the peptides H-His-Met-OH (D) and H-Gly-Gly-Met-OH (T) and their N-protected forms Ac-His-Met-OH (Ac-D) and Ac-Gly-Gly-Met-OH (Ac-T) were structurally characterized by means of IR, MS and NMR. In the complexes with dipeptides [AuLCl2]Cl (L=D or Ac-D), Au(III) is coordinated through S and imidazole N atoms from methionine and histidine fragments of the ligands forming macrochelate rings at mol ratio An: L= 1 : 1. Additionally, Au(III) is coordinated by two terminal chloride ions in a square-planar arrangement. In complexes with the tripeptides [AuL'Cl] (L'=T or Ac-T), however, the metal ion is coordinated in a tridentate fashion, through S and two N atoms, also at mol ratio M : L= I : 1. The fourth position of Au(III) is occupied by a Cl- ligand.