Complexes of Th(IV), Zr(IV) and V(IV) with Norfloxacin: Synthesis, Spectroscopic, Thermal, Kinetic Measurements and Antimicrobial Evaluation

M(IV) complexes of thorium, zirconium, and vanadium with norfloxacin were synthesized and characterized with physical and spectroscopic techniques, including elemental analysis (C,H,N), IR, electronic, 1H NMR spectral methods, as well as thermogravimetric (TG) and differential thermogravimetric (DTG) analyses. Based on these studies, the proposed structure of the obtained complexes are [Th(NFX)2Cl4], [Zr(NFX)2Cl2]Cl2 and [VO(NFX)2]SO4 (where, NFX: norfloxacin). In all complexes, norfloxacin acts as a bidentate deprotonated ligand bound to the metal through the pyridone and one carboxylate oxygen atoms, forming eight, six, five atoms ring with Th (IV), Zr(IV) and V(IV) metal ions, respectively. The kinetic thermodynamic parameters, such as, activation energy, E*, enthalpy, DH*, entropy, DS*, and Gibbs free energy, DG*, have been calculated from the TG and DTG curves, using Coats-Redfern and Horowitz-Metzger methods. Norfloxacin as well as their metal complexes were also evaluated for their antibacterial activity against several bacterial species, such as Bacillus subtilis, Pseudomonas aeruginosa (P. aeruginosa), and Escherichia coli (E. coli) and antifungal screening was studied against three species: Aspergills flavus, Fusarium solani, and Penicillium verrcosum (P. verrcosum). The results show significant increase in antibacterial and antifungal activity of metal complexes as compared to the NFX itself.