Introduction of the antibacterial drugs Norfloxacin and Ciprofloxacin into a polyoxometalate structure: Synthesis, characterization, and antibacterial activity

Abstract In this study, two new antibacterial complexes based on the quinolone antibacterial drugs Norfloxacin (NF) and Ciprofloxacin (CF) and the polyoxometalates (POMs) were synthesized, that is, [CoII(C16H18FN3O3)2]2H4[SiW12O40]·6H2O (1) and [Co II (C17H18FN3O3)2]2H4[SiW12O40]·2H2O (2). Then the complexes were comprehensively characterized by elemental analysis, infrared (IR) spectroscopy, and X-ray single-crystal diffraction. Single-crystal structural analysis revealed that complexes 1 and 2 were made up of SiW12 clusters, binuclear cobalt clusters, and water molecules. Moreover, it was observed that the SiW12 clusters in complexes 1 and 2 formed inorganic chains through covalent bonds and three-dimensional (3D) supramolecular structures through noncovalent N⋯O interactions. In this work, we also assessed the antibacterial activities of complexes 1 and 2 using Escherichia coli, Staphylococcus aureus, and Bacillus subtilis strains. In general, it was found that the antibacterial activities of complexes 1 and 2 were slightly higher than those of free NF and CF at the same mass concentrations. Furthermore, we evaluated the capacity of complexes 1 and 2 to bind to calf thymus DNA (CT-DNA) using spectroscopic titrations in the UV range. These studies showed that complexes 1 and 2 bound to CT-DNA with binding constants (Kb) of 4.1 × 104 and 1.6 × 104 M L−1, respectively, which were somewhat lower than those of pure NF and CF (8.2 × 104 and 4.9 × 104 M L−1), respectively. These results indicated that the introduction of different drug molecules into the POM system can affect their antibacterial activities.