Synthesis, characterization, electrochemical and biological activities of mixed ligand copper(II) complexes with dimethylglyoxime and amino acids

Six new copper (II) complexes with dimethylglyoxime and the amino acids tryptophan, glutamate, proline, arginine and valine were prepared and characterized using elemental analysis, molar conductance, melting points, UV-Vis and IR spectroscopy. The compounds prepared are solids, insoluble in water, ethanol and methanol, but soluble in dimethylsulfoxide (DMSO) and dimethylformamide (DMF). The IR study shows that dimethylglyoxime as primary ligand is coordinated to the metal ion in a bidentate manner with NN donor sites of the oxime function. The secondary ligand is coordinated by the carboxylate oxygen and the N atom of the amino acid, with the exception of glutamate, which is coordinated through the N atom of the amine function. Spectroscopic studies show that all the synthesized copper (II) complexes have an octahedral geometry. The electrochemical behavior of these compounds was determined by cyclic voltammetry, which indicated an irreversible oxidation corresponding to Cu(I) → Cu(II). The antimicrobial activity of ligands and their complexes were studied by the agar diffusion technique using DMSO as solvent on different species of pathogenic bacteria (Escherichia coli and Bacillus cereus) and fungi (Candida albicans and Aspergillus niger). It has been found that some of the complexes are antimicrobially active and show higher activity than the free ligand. Metal chelation affects significantly the antimicrobial behavior of the ligands. In addition, these compounds were screened for their in vitro antioxidant properties using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging. The results obtained show that the antioxidant activity is moderate for complexes with tryptophan and glutamate, but the complex with arginine shows a good antioxidant activity in comparison with ascorbic acid as positive control.