Complexation of amoxicillin by transition metals: Physico-chemical and antibacterial activity evaluation

Some bacteria have developed resistance to antibiotics that were once commonly used to treat them. Moreover, this resistance has become more and more massive and worrying. During this work, we succeeded in synthesizing "metal-antibiotic" complexes, combining as a ligand for the metals of Cu (II), Zn (II) and Fe (III). These complexes AMX - M (M = Cu, Fe and Zn) were characterized by UV-Vis spectrophotometry, IR spectroscopy, and electrochemical methods. Job's method of continuous variation suggested 1:1 metals to ligand stoichiometry for all amoxicillin complexes. The binding constant/association constant (K) of the AMX with Zn(II), Cu(II), and Fe(III) were found to be 4.46 × 10⁴, 7.17 × 10² and 7.65 × 10² L mol^-1, respectively. The IR spectra shows that the ligands coordinated to the metal ions through amino, imino, carboxylate, β-lactamic and carbonyl groups. The electrochemical results proved that amoxicillin oxidation process can be delayed by transition metal complexation. After, the complex synthesis, the antibacterial activity of ligand and its metal complexes were evaluated against Escherichia. coli bacteria by antibiogram method. The results show that the metal-amoxicillin complexes have better antibacterial activity against Escherichia coli (E. coli) than the free ligand (amoxicillin) due to the AMX protection against oxidation after complexation.