Synthesis, structure, and in vitro biological studies of benzothiazole based Schiff base ligand and its binary and ternary Co(III) and Ni(II) complexes

Abstract

Schiff base and its complexes are a renowned class of compounds that are frequently used for clinical investigation to develop less toxic, more potent, and multidrug resistance reversing agents for anticancer activity and other pharmacological actions. Herein, we describe the synthesis of ternary and binary imine base metal complexes derived from benzothiazole heterocyclic core. The Schiff base ligand was prepared by the condensation reaction between of 2,5-dichlorosalicylaldehyde and 2-(2-aminophenyl) benzothiazole. The Schiff base, 2-((E)-(2-(benzo[d]thiazol-2-yl)phenylimino)methyl)-3,5-dichlorophenol, thus obtained was utilized for the preparation of Co(III) and Ni(II) complexes. In addition, 1,10 phenanthroline was used as a co-ligand in the formation of mixed ligand complexes with Co(III) and Ni(II) metal ions. The physico-chemical characterization of the above prepared ligand and coordination complexes was performed using methods viz., elemental analysis, electronic absorption, mass and NMR spectral studies and thermal analysis. Furthermore, the crystalline nature of the compounds was studied using powder-XRD patterns, which revealed that the mixed ligand complexes have a more amorphous nature with slight semicrystalline portions. All the synthesized coordination complexes agree with the expected octahedral geometry. The biological potency of the ligand and its complexes were evaluated for their antioxidant properties using DPPH assay, antibacterial studies against two gram-positive (Staphylococcus aureus, and Bacillus subtilis), and two gram-negative bacterial strains (Escherichia coli, andPseudomonas aeruginosa). The complexes were also investigated for their DNA binding efficacy, DNA incision properties, and in vitro cytotoxicity using the MTT assay. The current study indicates that the mixed complexes exhibit increased pharmacological behaviour compared to their ternary complexes and organic counterparts.