Binary Complex Formation of Transition Metal Ions with Amoxicillin Trihydrate: Potentiometric Studies

The present work deals with the potentiometric determination of stability constants of binary complexes of transition metal ions with amoxicillin trihydrate in aqueous medium. The complexation behaviour of biologically important transition metal ions such as Cu(II), Ni(II), Co(II), Zn(II), Cd(II) and Fe(II) with amoxicillin trihydrate has been studied by the potentiometric titration technique at constant ionic strength and temperature using an ELICO Model L-120 pH Meter. The proton-ligand and metal-ligand stability constants were obtained from the potentiometric titration data in order to have a better insight into the coordination tendencies of the ligand towards different metal ions. The complexation of Cd(II) with amoxicillin trihydrate was stable but the complexation process seemed to be a little slow as compared, which was reflected by the longer buffering region in the titration curve. The relative stability of the metal–amoxicillin complexes may be approximately represented in the order: Fe(II) ≈ Ni(II) > Cu(II) > Co(II) ≈ Zn(II) > Cd(II), as reveals from the potentiometric behavior and the extent of curve deviation. The order of stability observed has been interpreted in terms of ionic radius, electronic configuration and ligand field stabilization effects. The study provides valuable insight into the coordination chemistry, metal binding behavior and solution equilibria of the transition metal complexes with amoxicillin trihydrate.