Designed Synthesis of Amino-Azo-Quinoline and Their Nickel(II) Complexes: Molecular Structure, Electrochemistry and an Insight Into Their In Vitro Anti-Cancer Activities.

Amino-quinolines are potential candidates that may provide some insight into the current chemotherapeutic research due to their demonstrated anti-cancer activity. This led us to synthesize and explore a new amino-azo-quinoline ligand HL 1 and its square planar nickel(II) complexes [Ni(HL) (OAc)], 2 and [Ni(HL)Cl], 3 and the structures were determined by Single Crystal X-Ray Diffraction. Theoretical investigation of redox orbitals of the complexes discloses that the reduction process is due to ligand reduction whereas both metal and ligand are contributing towards oxidation. The anti-cancer properties of the ligand and one of the nickel(II) complexes have been assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay, cell migration along with the generation of reactive oxygen species using human epithelial cancer cell line cells. The ligand 1 and complex 3 have been found to show effective anti-cancer activity and for the latter, it is more promising. This may be ascribed to the rigid and robust nature of square planar complex 3, which supports stronger binding with DNA than that of free ligands, possibly due to the flexible nature of the latter. This result has also been validated by molecular docking using nine conformers of the ligand and complex 3 via interaction with B-DNA (PDB ID: 1BNA) where the binding affinity with the complex has been found to be stronger.