Synthesis, molecular structure, biological properties and molecular docking studies on MnII, CoII and ZnII complexes containing bipyridine–azide ligands

• Manganese(II) (1), Cobalt(II) (2) and Zinc(II) (3) complexes with the bipyridine and azide ligands.
• Metal adopt distorted octahedral for 1, 2 and distorted square pyramidal geometry for 3.
• Complexes (1–3) were able to bind to DNA and protein in the order 2 > 1 > 3.
• Chemical nuclease activity is in the order: 2 > 1 > 3.

Metal complexes of the type Mn(bpy)2(N3)2 (1), Co(bpy)2(N3)2·3H2O (2) and Zn2(bpy)2(N3)4 (3) (Where bpy = 2,2-bipyridine) have been synthesized and characterized by elemental analysis and spectral (FT-IR, UV–vis) studies. The structure of complexes (1–3) have been determined by single crystal X-ray diffraction studies and the configuration of ligand-coordinated metal(II) ion was well described as distorted octahedral coordination geometry for Mn(II), Co(II) and distorted square pyramidal geometry for Zn(II) complexes. DNA binding interaction of these complexes (1–3) were investigated by UV–vis absorption, fluorescence circular dichroism spectral and molecular docking studies. The intrinsic binding constants Kb of complexes 1, 2 and 3 with CT-DNA obtained from UV–vis absorption studies were 8.37 × 104, 2.23 × 105 and 5.52 × 104 M−1 respectively. The results indicated that the three complexes are able to bind to DNA with different binding affinity, in the order 2 > 1 > 3. Complexes (1–3) exhibit a good binding propensity to bovine serum albumin (BSA) proteins having relatively high binding constant values. Gel electrophoresis assay demonstrated the ability of the complexes 1–3 promote the cleavage ability of the pBR322 plasmid DNA in the presence of the reducing agent 3-mercaptopropionic acid (MPA) but with different cleavage mechanisms: the complex 3 cleaves DNA via hydrolytic pathway (T4 DNA ligase assay), while the DNA cleavage by complexes 1 and 2 follows oxidative pathway. The chemical nuclease activity follows the order: 2 > 1 > 3. The effects of various activators were also investigated and the nuclease activity efficacy followed the order MPA > GSH > H2O2 > Asc. The cytotoxicity studies of complexes 1–3 were tested in vitro on breast cancer cell line (MCF-7) and they found to be active.

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