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Three mixed ligand copper(II) complexes [Cu(o-vanillin-L-tryptophan Schiff base) (diimine)] (diimine =2,2′-bipyridine (1), 1,10-phenanthroline (2) and 5,6dimethyl-1,10-phenanthroline(3)) were synthesized and characterized using analytical and spectral methods. The molecular structures of 1-3 were optimized using density functional theory (DFT) at B3LYP/LanL2DZ levels in the gas phase. Spectral and DFT studies suggest a distorted square pyramidal geometry around the copper ion. Binding interactions of 1-3 with calf thymus DNA and bovine serum albumin protein were studied using UV-visible and fluorescence spectroscopies, viscometric titrations and cyclic voltammetry and also using molecular docking analysis. Studies of the binding of the complexes with calf thymus DNA reveal intercalation, which is supported by molecular docking simulation. The DNA cleavage nature of 1-3 with pUC19 DNA shows that the complexes can cleave DNA without any external agents, and the efficiency follows the order 1 > 3 > 2. Synchronous and three-dimensional fluorescence spectral studies suggest that the secondary structures of the protein are altered by the complexes. Antioxidant studies reveal that the complexes have significant radical scavenging activity against DPPH. In vitro cytotoxic activity of the complexes was evaluated against breast cancer cells (MCF-7), revealing that complex 2 exhibits higher cytotoxicity than the other complexes. Nuclear chromatin condensation and fragmentation were observed with DAPI staining assay. The mitochondrial membrane potential damage was studied by FITC staining assay. Flow cytometric analysis suggests that all the metal complexes induce cell apoptosis.

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Four mononuclear metal complexes (Cu(II) (1), Ni(II) (2), Zn(II) (3) and V(IV) (4)) were synthesized using the Schiff base ligand 2,2′‐{cyclohexane‐1,2‐diylbis[nitrilo(1E)eth‐1‐yl‐1‐ylidine]}bis[5‐(prop‐2‐yn‐1‐yloxy)phenol] and structurally characterized by various spectral techniques. The catecholase‐mimicking activities of 1–4 were investigated and the results reveal that all the complexes have ability to oxidize 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) to 3,5‐di‐tert‐butylquinone in aerobic conditions. Electrospray ionization mass spectrometry studies were performed for 1–4 in the presence of 3,5‐DTBC to determine the possible complex–substrate intermediates. X‐band electron paramagnetic resonance spectroscopy results indicate that the metal centres are involved in the catecholase activity. Ligand‐centred radical generation was further confirmed by density functional theory calculation. The phosphatase‐like activity of 1–4 was investigated using 4‐nitrophenylphosphate as a model substrate. All the complexes exhibit excellent phosphatase activity in acetonitrile medium. The interactions of 1–4 with calf thymus DNA (CT‐DNA) and bovine serum albumin (BSA) protein were investigated using absorption and fluorescence titration methods. All the complexes strongly interact with CT‐DNA and BSA protein. The complexes exhibit significant hydrolytic cleavage of supercoiled pUC19 DNA. Complexes 1–4 exhibit significant in vitro cytotoxicity against MCF7 (human breast cancer) and MIA‐PA‐CA‐2 (human pancreatic cancer) cell lines. Moreover, the molecular docking technique was employed to determine the binding affinity with DNA and protein molecules.