The dipeptide alanylphenylalanine (H-Ala-Phe-OH) – protonation and coordination ability with Au(III)

The dipeptide alanylphenylalanine (H-Ala-Phe-OH), its hydrochloride (HCl × H-Ala-Phe-OH) and Au(III)-complex have been characterized structurally. Quantum chemical DFT and ab initio calculations, solid-state linear-dichroic infrared (IR-LD) spectroscopy and 1H and 13C NMR data were employed. The results are confirmed by a single crystal X-ray diffraction analysis of HCl × H-Ala-Phe-OH. The coordination with Au(III) is supported by data from MS, TGV, DSC methods and by elemental analysis. The H-Ala-Phe-OH coordinates in a bidentate manner via an O-atom of the COO−-group and N-amide nitrogen, after a previous deprotonation of the NH-group has taken place. Two Cl− ions are attached to the metal center as terminal ligands, yielding a completely planar geometry for the AuNOCl2 chromophor in the mononuclear [Au((H-Ala-Phe-OH)H−1)Cl2] complex.