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Amidst the very many metallodrugs for the treatment of cancer regularly reported, the development of the next generation of compounds with an aim of overcoming the shortcomings by enhancing biological activity and cytotoxicity but exhibiting low toxicity is essential. Herein we report such octahedral metal(II) complexes (1-12) containing triazole-derived Schiff base as the scaffold. The complexes were synthesized and characterized by means of elemental analysis and various spectroscopic techniques. The complexes were subjected to various investigations that involved their interaction with calf thymus DNA and supercoiled pBR322 DNA.In vitro antimicrobial studies were also conducted in addition to the use of spectrophotometric, spectrofluorometric, cyclic voltammetric and hydrodynamic techniques. Although all complexes showed activity, complex 9 revealed excellent DNA proclivity, DNA cleaving tendencies and antimicrobial efficacy. All copper (II) complexes were evaluated for their antiproliferative activity against a panel of human cancer cell lines (HeLa, Hep-2, MCF-7 and NHDF). Complexes 1-12 showed activity against all the cell lines with low toxicity towards normal cell line, and the activity of complex 9 towards Hep-2 was prominent. The effect of the ligand system on the complexes is also discussed along with the importance of tuning the ligand system.

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A heterocyclic compound, 2‐(aminomethyl)benzimidazole dihydrohydrochloride, was treated with nitrobenzaldehyde to form a Schiff base that was made to react with divalent metals. A co‐ligand, either 1,10‐phenanthroline or 2,2′‐bipyridine, was added to this mixture to obtain metal chelators of type [ML(co‐L)2]Cl2. They were in 1:1:2 stoichiometry ratio, which was characterized by various spectroscopic techniques that suggested an octahedral geometry around the central metal ions. These complexes were investigated for their binding affinities with calf thymus (CT) DNA, using various techniques, such as UV–Vis, viscosity, cyclic voltammetry (CV), etc. The binding interaction studies revealed intercalation as the possible binding mode of the complexes with the CT DNA. In addition, these complexes were screened for their antimicrobial potential and DNA denaturing tendencies using gel electrophoretic assay. The antimicrobial screening investigation showed that the complexes behaved as better antimicrobial agents than the ligand, especially, complex 5 shows exceptional activity even in the electrophoretic assay along with the antimicrobial efficacy. Moreover, complex 5 was able to denature the plasmid DNA better than the other compounds. All the compounds were screened for cytotoxic efficacy, and the IC50 values suggest that the compounds possess cytotoxic activity to some extent that is almost the same as the activity of cisplatin.

The NMR spectrum is exploiting to determine the identity of prepared ligand and its diamagnetic metal complexes. Ligand and Zn(II) complex were recorded in DMSO-d 6 , using tetramethylsilane (TMS) as internal standard. The 1 H NMR spectrum of ligand shows a singlet peak at 9.71 ppm (1H, CH=N), multiplet in the range 6.60-7.90 ppm for the aromatic ring protons and a multiplet peak at 2.80-3.40 ppm for (12H, N-CH 3 ) protons. The proton 1 H NMR spectrum of Zn complex shows (Fig. S2.) a singlet peak at 9.67 ppm (1H, CH=N), multiplet in peaks at 6.60-7.90 ppm for the aromatic ring protons and a multiplet peak at 2.80-3.40 ppm for (6H, N-CH 3 ) protons. From the above observation, it is inferred that the azomethine group (CH=N) is involved in metal co-ordination. Powder XRDX-ray powder diffraction has been obtained for further confirmation, regarding the structure of the metal complexes. They are complicated to isolate single crystal suitable for a single crystal X-ray crystallography; it might be due to powder or polycrystalline nature of the complexes. However, the structural information on the majority of inorganic metal complexes is not suitable, because the materials have been polycrystalline or powder in nature. Generally it is hard to develop good quality single crystals of these inorganic complexes. In this metal complex, powder X-ray diffraction studies may be useful. The X-ray diffraction of metal complex is given in Fig. S3. which exhibits reflecting peaks of 2θ scattering angles at 13.