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This present work deals with the synthesizes of nine novel thiosemicarbazone copper(II) complexes {[Cu(L) 2 ]Cl C3, [Cu(L)(bpy)]Cl C4-C6, [Cu(L) (phen)]Cl C7-C9 (where, L = H(L1)-H(L3), H(L1) = (E)-N-methyl-2-(1-phenyl-2-((5-(pyridin-3-yl)-4H-1,2,4-triazol-3-yl)thio)ethylidene)hydrazinecarbothioamide, H(L2) = (E)-N-ethyl-2-(1-phenyl-2-((5-(pyridin-3-yl)-4H-1,2,4-triazol-3-yl)thio)ethylidene) hydrazinecarbothioamide, H(L3) = (E)-N-phenyl-2-(1-phenyl-2-((5-(pyridin-3-yl)-4H-1,2,4-triazol-3-yl)thio)ethylidene) hydrazinecarbothioamide, bpy = 2,2′-bipyridyl and phen = 1,10-phenanthroline) with improved pharmacological results. The synthesized complexes were characterized by various spectral-analytical techniques. The structure of the copper(II) complexes C1-C9 was proposed by EPR spectroscopy. It confirmed the square planar coordination around Cu(II) complexes. The antibacterial screening of the complexes revealed that complexes C7 and C8 demonstrated significant activity against Gram-positive (B. thuringiensis) and Gram-negative (E. coli) bacteria. The concentration-dependent DNA cleavage activity of supercoiled (SC) pUC18 DNA exhibited complete DNA degradation effect on complex C6 at a minimum concentration of 40 μM. In vitro cytotoxic results showed that the mixed ligand copper(II) complexes C4, C5 and C7 exhibited higher effects on human cervical cancer cell lines, HeLa, when compared to cisplatin. Hence, the results obtained from each biological screening indicated the superior biological efficacy of the mixed ligand copper(II) complexes bearing diimine moieties. It could be considered as a promising alternative to an existing anticancer drug.

Objective: In modern years, the biggest dare is to develop new chemotherapeutic agents with high efficiency as well as low toxicity. Hence, to defeat this challenge, extensive endeavors were taken on thiosemicarbazone based metal complexes. Methods: A sequence of nine thiosemicarbazone based diimine copper(II) complexes derived from three sulfur-containing ligands N-methyl-2- ((1-methyl-1H-pyrrol-2-yl)methylene)hydrazinecarbothioamide H(L1), N-ethyl-2-((1-methyl-1H-pyrrol-2-yl)methylene)hydrazinecarbothioamide H(L2), and N-benzyl-2-((1-methyl-1H-pyrrol-2-yl)methylene)hydrazinecarbothioamide H(L3). The molecular structures and coordination possibilities of thiosemicarbazone ligands toward the central metal ions have been validated by analytical and spectral techniques such as molar conductance, elemental analysis, ultraviolet–Vis, Fourier-transform infrared, and electron paramagnetic resonance spectroscopy confirms that the thiosemicarbazones ligands are coordinated to copper through NS’ donor and NN’ donor of diimine. The antimicrobial activity and DNA cleavage effectiveness of thiosemicarbazone derivatives and copper(II) complexes were assessed by disc diffusion and agarose gel electrophoresis methods. Results: All the spectral studies authenticated that the square planar geometry of the thiosemicarbazone copper(II) complexes 1–9. From the results of antibacterial activity against selected Gram-positive (Bacillus thuringiensis) and Gram-negative (Escherichia coli) bacterial strains, complex 8 exhibited noteworthy activity. Interestingly, copper(II) complexes bearing 1,10-phenanthroline (phen) moiety displayed outstanding results together with N(4)-substituted thiosemicarbazone derivatives and causes complete DNA degradation of SC (supercoiled) pUC18 DNA. Conclusion: A variety of substitutions at the thioamide nitrogen atoms have shown potential biological activity. Henceforth, N(4)-substituted thiosemicarbazone based copper(II) complexes virtually reach the effectiveness of conventional chemotherapeutic drugs.