Characterization, theoretical investigation, and biological applications of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes of a triazene ligand containing a benzothiazole ring

Abstract Herein, Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes of a previously synthesized triazene ligand, namely, ( E )‐2‐(3‐(4‐nitrophenyl)triaz‐1‐en‐1‐yl)benzo[ d ]thiazole (L), were prepared. The metal:ligand ratio of complexes was determined by molar ratio method, and complexes were synthesized based on the result ratio (1:2 for Co(II), Ni(II), and Zn(II) complexes, and (1:1) for Cu(II) and Mn(II)). The complexes were characterized by infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies, magnetic moment, and/or molar conductance measurements. IR spectra suggested the existence of bidentate binding through the nitrogen atom of the thiazole ring and nitrogen atom of the triazene linkage. Molar conductivities indicated the non‐electrolytic nature of all the complexes. Magnetic moment and EPR of the complexes confirmed their octahedral geometries. Thermal studies were conducted to confirm the structures and analyze the thermal stabilities of the complexes. Activation thermodynamic parameters were determined using the Coats–Redfern and Horowitz–Metzger methods. The calf thymus DNA binding activity was investigated by absorption titration experiments and viscosity measurements, and intrinsic binding constants of complexes range from 4.00 × 10 5 to 5.00 × 10 5 M −1 . Cytotoxic activities were examined against MCF‐7 and HCT‐116 cell lines. Although all the complexes exhibited reasonable cytotoxic effects, their cytotoxic activities were in the following order: Zn(II) > Cu(II) > Mn(II) > Co(II) > Ni(II). Zn(II) complex showed the highest activity with IC 50 values are 2.87 and 1.94 μg ml −1 against MCF‐7 and HCT‐116, respectively. Molecular docking was used to assess the binding affinities of these complexes to colon cancer (3ig7) and breast cancer (1hk7) proteins. Zn(II) complex showed the best docking scores compared with the ligand and other tested complexes. Results of molecular docking well correlated with those of the cytotoxicity experiments.