Kinetics, DFT Study and Antibacterial Activity of Zinc(II) and Copper(II) Terpyridine Complexes

Abstract

The kinetics of ligand substitution reactions between zinc(II) and copper(II) terpyridine complexes and biologically relevant nucleophiles were investigated at pH 7.38 as a function of nucleophile concentration. Substitution reactions include two steps of consecutive displacement of the chlorido ligands. The order of reactivity of the investigated nucleophiles for the first reaction step is: glutathione (GSH) > > DL-aspartic acid (DL-Asp) > guanosine-5’-monophosphate (5’-GMP) > inosine-5’-monophosphate (5’-IMP) > L-methionine (L-Met) (for [CuCl2(terpy)]), while for [ZnCl2(terpy)] order is: DL-Asp > GSH  > 5’-GMP > 5’-IMP > > L-Met.  Chelate formation and pre-equilibrium were obtained for the substitution process between [ZnCl2(terpy)] complex and glutathione. Activation parameters support an associative mechanism A or Ia for the both reaction steps. The best antibacterial effect was exhibited against Sarcina lutea, and stronger antibacterial activity of [CuCl2(terpy)] complex than [ZnCl2(terpy)] was observed. In order to verify the structural geometries of investigated complexes in crystal and solute forms, their structures were optimized by DFT method. Based on energetic stability of complexes, it can be concluded that both of complexes make hydrates very easy, but the bond between water molecule and metal ion is pretty week.