Synthesis, Characterization and Potential Applications of Zn(II), Pd(II), Cu(II) and Ni(II) Metal Complexes with O, N and S donor Schiff base ligands

Abstract

In search of achieving less toxic and more potent DNA targeting antimicrobial agents, different types of benzimidazole derivatives, Schiff base ligands, and metal complexes have been prepared. The synthetic products were characterized using FTIR, NMR (1H and 13C), ESI-MS, MALDI-MS, elemental (C, H, N), and singlecrystal X-ray analysis. DNA binding potential of synthons was investigated by UVvisible absorption titrations in conjunction with thermal denaturation studies. It has been demonstrated that several compounds show DNA binding affinities with different magnitudes. The binding strengths are calculated from the absorption data and results are interpreted in the form of intrinsic binding constant (Kb) values which are found to be in the range of 6.4×103 -1.09×106 M‒1. The compounds exhibited intercalation and partial intercalation mode of binding through π-π stacking interactions with DNA. The binding forces were thermodynamically spontaneous owing to negative free energy values (-ΔG°). The binding behavior of the compounds was further explored by thermal denaturation experiments. Binding of compounds with DNA by intercalation mode stabilized its double-helical structure was manifested by the rise in melting temperature of DNA. The binding affinity trend found by absorption study is reproduced here. Thus, the results of two experimental techniques were in excellent agreement. After the confirmation of DNA targeting property, the compounds were screened for in-vitro antibacterial activity. Results indicated that metal complexes showed enhanced activity against several bacteria as compared to the respective ligands. Finally, the cytotoxic properties of the synthesized compounds were explored via brine shrimp cytotoxic assay. Most of the compounds were found non-toxic with LD50 value >200 µg/ml.