Synthesis, structure elucidation, antioxidant, antimicrobial, anti-inflammatory and molecular docking studies of transition metal(II) complexes derived from heterocyclic Schiff base ligands

In the search of significant biological agents for the pathogenic causing deformities, four bidentate heterocyclic Schiff base ligands and their sixteen Co(II), Ni(II), Cu(II) and Zn(II) metal complexes were derived by the condensation of 3,4-dihydro-2H-1,5-benzodioxepin-7-amine with salicylaldehyde derivatives/2-hydroxy-1-naphthaldehyde. Further, the synthesized compounds were characterized by numerous analytical techniques such as NMR, FT-IR, UV–Vis, SEM, EDAX, mass spectrometry, ESR, powder XRD, TGA, magnetic susceptibility, elemental analysis, magnetic susceptibility and molar conductance measurement for structural elucidation. The antioxidant ability of the compounds was examined by DPPH and ABTS assays while the antimicrobial (against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Rhizopus oryzae and Candida albicans microbial strains) and anti-inflammatory activities of the synthesized compounds were evaluated by serial dilution and egg albumin assays, respectively. The results of pharmacological activities showed that the ligand HL4 (4) and Cu(II) complexes have significant antioxidant activity while the ligand HL2 (2) and Zn(II) complexes have excellent antimicrobial and anti-inflammatory activities because of their dependency on electron donating and electron withdrawing groups, respectively. Further, the cytotoxic study was carried out for the most potent antimicrobial and anti-inflammatory HL2 (2), HL3 (3) ligands and their (9–16) metal complexes on Vero cell lines using calorimetric assay which revealed that the complex (12) is lesser cytotoxic than the other tested compounds. After that, the less cytotoxic and more potential antimicrobial Zn(II) complex (12) and its ligand HL2 (2) were assessed by molecular docking study to know the interaction modes and binding affinity of these compounds with the active sites of Staphylococcus aureus S1: DHFR, Escherichia coli DNA gyrase B and Candida albicans sterol-14-alpha-demethylase enzymes.