Synthesis, characterization and biological properties of oxovanadium(IV) complexes

The complexes of oxovanadium(IV) with bidentate heterocyclic azo pyrazolone were synthesized and characterized by elemental analyses, IR, UV-Visible, EPR and magnetic measurements as well as thermal analysis and X-ray diffraction. Reaction of [(VO)-O-IV(acac)(2)] (where acac = acetylacetonate) in methanol with azo pyrazolones (HLn) produced mononuclear vanadium(IV) oxo complexes with general formula [VO(L-n)(2)]H2O. The molar conductance measurements proved that all the complexes are non-electrolytes. IR spectra showed that the ligands (HLn) acts as a monobasic bidentate ligand by coordinating via the nitrogen atom of the pyrazole ring (-HN-N = ) and deprotonated hydroxyl O, thereby forming a square pyramidal chelating ring. Analytical data revealed that all the complexes exhibited 1:2 (metal-ligand) ratio. The thermal data confirm that the complexes have water molecule outside the coordination sphere and the complexes show similar thermogravimetric decomposition fragments which are consistent with the proposed structures. The thermodynamic parameters of VO(II) complexes are calculated using Coats-Redfern and Horowitz-Metzger methods. The optimized bond lengths, bond angles and the calculated quantum chemical parameters for VO(Il) complexes (1-3) were investigated. Their interactions with calf thymus DNA were investigated by absorption spectra and viscosity measurements. The results suggest that these complexes bind to DNA in an intercalative mode (K-b = 4.58-8.96 x 105 M-1). All VO(Il) complexes (1-3) were evaluated against human cancer cell lines, MCF-7 and HepG-2 as compared with the positive controls in the viability assay of colchicine and vinblastine. Complex 2 (IC50 = 30.5 +/- 2.3 and 20.1 +/- 1.9 mu g/ml) exhibit moderate activities against the two cell lines MCF-7 and HepG-2, respectively as compared to the Colchicine (IC50 = 17.7 +/- 0.03 and 10.6 +/- 0.01 mu g/mL). The antimicrobial activities of VO(II) complexes were tested against gram negative bacteria (Escherichia coli), gram positive bacteria (Staphylococcus aureus) and fungal (Candida albicans).