Polyoxometalate cobalt-gatifloxacin complex with DNA binding and antibacterial activity

An unusual inorganic-organic antibacterial complex based on polyoxometalates (POMs) and the cobalt-gatifloxacin (GT), [Co-II(C19FH22N3O4)(3)][C19FH23N3O4][HSiW12O40]center dot 23H(2)O (1), has been synthesized. Single-crystal structural analysis shows that 1 represents for the first time an unusual tripodal coordination style with three GT molecules coordinating to cobalt(II) by six carboxylate and hydroxyl oxygens. The biological activity of 1 has been evaluated by investigating its binding ability to calf thymus DNA (CT-DNA). UV spectrum study of 1 has shown that it can bind to CT-DNA by intercalation. The DNA-binding constant K-b was 9.6 x 10(4) M L-1, higher than that of pure GT, 3.8 x 10(4) M L-1. Furthermore, the antibacterial activities of 1 were tested against Staphylococcus aureus and Escherichia coli, respectively, and have shown slightly lower antibacterial activity than that of free GT at the same mass concentration. If the GT component in the complexes was controlled at the same molar concentration, 1 generates the biggest antibacterial area during the Kirby-Bauer disc diffusion detection. This result indicates that the integration of heteropolyanions and GT exhibits synergistic effects on the antibacterial activity, which paves a new way to design low-cost antibacterial compound by the introduction of POMs.