Antioxidant, Biological Activity, and Analytical Study of Vanadium(IV) Complexes With (N, N), (O, O) and Monodentate Nitrogen Ligands

Three vanadium(IV) complexes have been prepared, and a range of techniques, including Fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis), mass spectroscopy, elemental microanalysis, magnetic sensitivity, electrical conductivity, and DET calculation were used to investigate the prepared complexes. The mentioned complexes have the following chemical formulas: [VO(DABA)(HNQ)], [VO(DABA)(HNQ)(AMP)], and [VO(DABA)(HNQ)(Atri)], where 3,4-diaminobenzoic acid (DABA), 2-hydroxy-1,4-naphthoquinone (HNQ), 6-amino-2-methylpyridin (AMP), and 3-amino-1,2,4-triazole (Atri). The FTIR spectra demonstrated how the nitrogen and oxygen atoms in the ligands coordinate with the vanadium(IV). The mass spectroscopy gave an acceptable fragmentation for the prepared complexes and the UV-Vis spectral data confirm the electronic transitions in the complexes with the charge transfer bands. Two methods Job's continuous method and the mole-ratio method have been used to confirm the mole ratios of the vanadium(IV) ion and the ligands coordinated in the complexes. The optimum pH of the complexation has been determined using a spectrophotometric approach at an ideal pH 6 and the effect of time on the stability of the complexes has been carried out. The validity, sensitivity, accuracy, and precision of the method were evaluated and the results indicate that it is suitable for application in future studies to determine the vanadium in the solutions. The main role of the other type of ligand (monodentate) is to adduct the vanadium(IV) ion from the sixth position to produce six-coordinate complexes with octahedral geometry. Based on spectroscopic and DFT results, the complexes [VO(DABA)(HNQ)(AMP)] and [VO(DABA)(HNQ)(Atri)] exhibit octahedral geometry, while the complex [VO(DABA)(HNQ)] displays a square pyramidal structure. The biological activity of the (DABA) ligand and the complexes were examined against the bacteria Staphylococcus aureus (50 ppm), Escherichia coli (12.5 ppm), Acinetobacter baumannii (12.5 ppm), and Bacillus licheniformis (12.5 ppm), according to experimental results. The vanadium(IV) complexes' antioxidant activity was assessed through the use of a DPPH free radical-scavenging test and compared with the Gallic acid as reference compound. The complexes' antioxidant activity is ranked as follows: gallic acid > [VO(DABA)(HNQ)] > [VO(DABA)(HNQ)(Atri)] > [VO(DABA)(HNQ)(AMP)] in 60 min, where the complexes demonstrated the highest level of antioxidant activity as determined by calculating the value of IC₅₀, as shown [VO(DABA)(HNQ)] > [VO(DABA)(HNQ)(Atri)] > [VO(DABA)(HNQ)(AMP)].