A series of N-substituted isatin thiosemicarbazone ligands (L1–L5) and their nickel(II) complexes [Ni(L)₂] (1–5) were synthesized and characterized by elemental analyses and UV-Visible, FT-IR, ¹H & ¹³C NMR, and mass spectroscopic techniques. The molecular structure of the ligands (L1 and L2) and complex 1 was confirmed by single crystal X-ray crystallography. The single crystal X-ray structure of 1 showed distorted octahedral geometry. The interaction of calf thymus (CT) DNA and bovine serum albumin (BSA) with the nickel(II) complexes was explored using absorption and emission spectral methods. A DNA cleavage study showed that the complexes cleaved DNA without any external agents. The alterations in the secondary structure of the protein by the nickel(II) complexes (1–5) were confirmed by synchronous and three dimensional fluorescence spectroscopic studies. The interaction of the complexes with DNA/protein also has been supported by molecular docking studies. An in vitro cytotoxicity study of the complexes found significant activity against human breast (MCF7) and lung (A549) cancer cell lines, with the best results for complexes 4 and 2 respectively, where the IC50 value is less than 0.1 μM concentration.

Five copper(II) complexes containing N,N′,N′′-trisubstituted guanidine ligands were synthesized and characterized by elemental analyses and UV-Visible, FT-IR, EPR and mass spectroscopic techniques. The synthesized copper(II) complexes (1–5) bear the general formula [Cu{C₆H₅CONC(NR)NHCH₂C₆H₅}₂] where R = phenyl (1), 4-methylphenyl (2), 4-ethoxyphenyl (3), 2-methoxyphenyl (4) or 1-naphthyl (5). The four coordinated square planar geometry of the complexes was confirmed by the single crystal X-ray diffraction study. The interaction of the Cu(II) complexes with calf thymus DNA (CT DNA) was explored using absorption and fluorescence spectroscopic methods. The results revealed that the complexes have an affinity constant for DNA in the order of 10⁴ M⁻¹ and the mode of interaction is non-covalent intercalation. The DNA cleavage study showed that the complexes cleaved DNA without any external agent. The interaction of Cu(II) complexes with bovine serum albumin (BSA) was also studied using absorption and fluorescence techniques. The cytotoxic activity of the Cu(II) complexes was probed in vitro against human breast (MCF7) and lung (A549) cancer cell lines. The complexes were also tested against mouse embryonic fibroblast (NIH 3T3) cell lines. Complexes 1 and 3 have good cytotoxic activity which is comparable with the cyclophosphamide drug. The complexes were less cytotoxic towards normal cell lines showing that they affect only cancer cell lines. Superoxide radical scavenging property of the complexes was assessed using the NBT assay. Copper(II) complexes showed appreciable superoxide radical scavenging activity with IC₅₀ values ranging from 1.53 to 5.62 μM. A further molecular docking technique was employed to understand the binding of the complexes toward the molecular target DNA and human DNA topoisomerase I.