Synthesis, characterization, biological evaluation, and molecular docking approach of nickel (II) complexes containing O, N-donor chelation pattern of sulfonamide-based Schiff bases

A series of Schiff bases (L-1-L-4) that possess in their structure bioactive sulfonamide group and their nickel (II) complexes have been synthesized. Microanalytical analyses, various spectroscopic methods such as Fourier transform infrared spectroscopy (FT-IR), H-1 nuclear magnetic resonance (NMR), C-13 NMR, UV-Vis, and MS, are used to explore the nature of bonding and to elucidate the chemical structures. The analytical and magnetic values suggest a range of stoichiometries 1:1, 1:2, and 2:1 (M:L) for the synthesized complexes of almost square planar geometry. The spectral comparative interpretation reveals that L-1 and L-2 coordinate to the central Ni (II) in tetradentate ONON donor sequence, whereas L-3 and L-4 in bidentate ON pattern through deprotonated phenolic-O and the azomethine-N. Density functional theory (DFT) and MOE-docking approaches are used to evaluate the molecular parameters and the binding propensity of the synthesized ligands and their complexes with 3s7s protein and to signify their inhibition strength. Besides, the anticancer, antimicrobial and antifungal activities have been screened against number of tumor cells and human pathogen strains. These in vitro studies reveal that Schiff base L-4 and its complex, [Ni(L-4-H)(OAc)(H2O)], have superior activities reflecting the importance of inserting bioactive pendant substituents such as thiazole ring and 3-fluorophenylazo to the pharmacophoric sulfonamide moiety. Moreover, some of the synthesized Ni (II) complexes display promising therapeutic effects as novel non-platinum antitumor agents after further preclinical investigations.