A comparison of copper(I) and silver(I) complexes of glycine, diglycine and triglycine

Abstract

Density functional calculations at B3LYP/DZVP were used to obtain structural information, relative free energies of different isomers and binding energies for the following reaction in the gas phase: M⁺ + (glycyl)_nglycine → M–(glycyl)_nglycine⁺, where M = Ag or Cu and n = 0–2. For the complexes with Cu⁺, optimizations were also performed at B3LYP/6–31++G(d,p) and single-point calculations at MP2(fc)/6–311++G(2df,2p)//B3LYP/DZVP. The calculated binding energies for the Cu⁺ complexes are all higher than those of the structurally similar Ag⁺ ions. These calculated binding energy differences become larger as the size of the ligand increases. For all the Cu⁺ complexes examined, the coordination number of the copper ion does not exceed two, whereas for the silver complexes tri- and tetracoordinate Ag⁺ structures are calculated to be at low energy minima. Significant structural and relative free energy differences occur between the lowest energy ‘zwitterionic ’ forms of the M–(glycyl)_nglycine⁺ complexes.