Metal ion interactions with penicillins: Part VI-Equilibrium study on the mixed-ligand complex formation of cobalt/H), nickel(II), copper(II) and zinc(II) with 6-aminopenicillanic acid as the primary ligand and bipyridine, glycinate and imidazole as secondary ligands

Abstract

Equilibrium study on the complex formation of M²⁺ions (where M = Co, Ni, Cu and Zn) with 6-aminopenicillanic acid (apaH^±) in the presence of typical ligands, viz., bipyridine, glycinate and imidazole (B) in aqueous solution at 37ᵒC and ionic strength <i>I</i> = 0.1 <i>M</i> NaNO₃ has indicated the formation of mixed-ligand complexes of the types M(apa)(B), M(apa)(B)(OH) and M(apa)(B)(OH)₂ in addition to the binary M(B) and M(apa) complexes. The orders of stability constants, viz. Cu²⁺ > Ni²⁺ > Co²⁺ > Zn²⁺ with regard to the metal ions and bipyridine > glycinate > imidazole with regard to secondary ligands have been correlated with the electronic structures of M²⁺ ions, modes of bonding of the ligands and the nature of the metal-ligand bonds.