Novel manganese(II) and oxovanadium(IV) complexes formed from isonitrosoacetophenone and aminoacids such as L-Phenylalanine, L-Tryptophan and L-Histidine have been synthesized. The complexes have also been characterized using elemental analyses, molar conductance, UV-Vis, IR and ESR spectroscopy. The value of molar conductance indicates them to be non-electrolytes. The IR spectra support the binding of the ligands with two N and two O donor sites to the manganese(II) and oxovanadium (IV) ion giving an arrangement of N2O2 donor group.
The ESR data indicate that the covalent character of the metal-ligand bonding in the Mn(II) and VO(IV) complexes increases on going from histidine to phenylalanine and tryptophan.
Electrochemical behavior of the complexes have been investigated by cyclic voltammetry which shows that the chelate structure and electron donating effects of the ligand substituent are among the factors influencing the redox potentials of the complexes.
Density Functional Theory (DFT) calculations were applied to evaluate the cis and trans coordination modes of the two water molecules. The trans form was shown to be energetically more stable than the cis one. HOMO-LUMO energy gap, dipole moments and bond distances have been calculated.
Furthermore, the antioxidant efficiencies of the metal complexes were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavening activity. The antioxidant activity of the complexes indicates their high scavenging activity against the radical DPPH.