Synthesis, Characterization, and Biological Activity of Oxidovanadium(IV) Hydroxamate Complexes Supported by Density Functional Theory

Abstract

The oxidovanadium(IV) complex [VO(HL)2]\n(1) (where, HL = 4-nitrocinnamohydroxamate; 4-NO2C6H4CH=CHCONHOH)\nhas been synthesized by the condensation reaction of VOSO4∙5H2O\nand potassium 4-nitrocinnamohydroxamate in methanol-water medium. The complex\nis characterized by elemental analysis, molar conductivity, magnetic susceptibility\nmeasurement, FTIR, UV-Vis, Electron Paramagnetic Resonance (EPR) spectral\ntechniques and mass spectrometry. The bidentate linkage of hydroxamate ligand\ninvolving O,O-coordination through hydroxamic and carbonyl oxygen atoms has\nbeen deduced. The magnetic susceptibility, EPR and mass spectra (ESI-MS) indicate\nthat the complex exists as monomer and a distorted square pyramidal geometry\naround vanadium is proposed. The electrochemical study of 1 has shown it is to be electrochemically active exhibiting VOV/VOIV\nquasi-reversible redox couple. The thermal study of the complex yielded VO2\nas sole decomposition product. The coordination compounds 2 and 3 have been isolated from the reaction of complex 1 with 2-cyanopyridine (2-CNPy) and 4-aminobenzonitrile\n(4-CNAn) respectively and characterized by physicochemical and IR spectral\nstudy. The biological activity of 1-3 has been studied against various\npathogenic bacteria E. coli, S. aureus, S. typhi, S. paratyphi, S.\nepidermidis, K. pneumonia and fungi\nC. albicans, B. fulva, and F. oxysporum by minimum\ninhibitory concentration (MIC) method. The complexes exhibit enhanced antimicrobial\nactivity relative to both the free ligand and vanadyl sulphate. The cytotoxicity\nof 1-3 has been studied on mammalian transformed cell line Hep2c, a\nderivative of human cervix carcinoma HeLa cells by MTT assay. 2 and 3 exhibit higher cytotoxic activity than 1 and reveal a marked effect of the coordination of nitrogen bases.\nDensity functional theory studies have been carried out to determine the\nrelative free energy of formation and stable molecular structures of 1-3.\nTime dependent density functional theory (TD-DFT) based calculation have been performed\nto find out the frontier molecular orbitals and to corroborate with the experimentally\nobserved UV-Vis spectrum of 1. Other\nparameters like HOMO, and LUMO energies, density of state (DOS), and global\nreactivity descriptors clearly support higher biological activity of 2 and 3 than 1.