Preparation, structure elucidation, free radical scavenging, in-vitro antimicrobial and cytotoxic proficiency of isoniazid incorporated tridentate Co(II), Ni(II), Cu(II) and Zn(II) Schiff base-metal complexes

A series of eight isoniazid-based bivalent mononuclear Schiff base metal complexes containing Co(II), Ni(II), Cu(II) and Zn(II) ions were synthesized and characterized by various spectral analyses. From spectral study, it is confirmed that Schiff base ligands coordinated with metal ions via O, N, N-donor atoms and adopted octahedral geometry. The TGA-DTA technique was used to determine the thermal degradation of synthesized complexes. L1-Cu (C3) and L2-Co (C8) decompose at 300 °C, which revealed that prepared complexes are stable at room temperature. All the synthesized complexes studied for antioxidant, antimicrobial and cytotoxic proficiency were investigated. The antioxidant activity of the free ligand and its metal chelates were evaluated using the standard DPPH method, revealed that the ligand L1 and complexes C3 and C4 show good ability to scavenge DPPH radical compared to standard ascorbic acid. The antibacterial activity index revealed that the synthesized ligand and its metal complexes display good to moderate activity and, particularly, [Ni(L 1 ) 2 ], [Cu(L 1 ) 2 ] and [Zn(L 2 ) 2 ] complexes exhibited the highest inhibitory activity against E. coli . In-vitro cytotoxic and anticancer properties against human cancer cell line MCF-7 revealed that the metal complexes C1 - C4 display IC 50 values 7.26, 70.93, 128.32 and 2.73 μg/mL respectively compared to standard 5-flurouracil (13.38 μg/mL), which implies the metal-complexes exhibits potent inhibitory activity against MCF-7 cancer cell lines. From this study, it was concluded that the coordination of the Co(II) metal ion to ligand (L1) showed potency in inhibiting the growth of cancer cells compared to other metal complexes ( C2 - C4 ).