Design, synthesis, and characterization of M(II)-Schiff base complexes containing 3,5-di-tert-butyl salicylaldehyde: DNA binding/cleavage, DPPH radical scavenging activity, cytotoxic activity, and catalytic activity investigation

Abstract

Two mononuclear Cu(II) and Zn(II) based complexes were synthesized via microwave-assisted method utilizing Schiff base ligand based on 3,5-di-tertbutylsalicylaldehyde. The compounds were characterized using elemental and spectroscopic analysis methods. The ligand posed as an ON-donor ligand, confirmed by spectrum analysis in the complexes. A geometry optimization analysis was also performed using density functional theory to obtain the geometry, stability, and electronic properties of the synthesized compounds. CuL1 has a distorted square planar geometry, whereas ZnL1 has a distorted tetrahedral geometry. Fluorescence and absorbance spectroscopy were utilized to explore the interaction properties of calf thymus-deoxyribonucleic acid (CT-DNA) with the complexes. The CuL1 and ZnL1 are highly sensitive to DNA binding, with binding constant (Kb) in the range of 105 M−1, representing substantial interaction with CT-DNA, combining intercalation and electrostatic interactions. The Stern-Volmer constant (Ksv) obtained from the fluorescence spectroscopy method varied from 3.31 x 104 to 8.42 x 104 M−1, indicating moderate DNA binding. Circular dichroism spectroscopy confirmed the presence of intercalative binding among the DNA and the complexes. The in-vitro DNA cleavage activity revealed that complexes could efficiently break the supercoiled plasmid DNA without using any external agents. The complex CuL1 induced significant cytotoxicity for Dalton’s lymphoma cancer cell lines, having IC50 values of 18.96 ± 0.021 μM. The antioxidant activity of the compounds was also studied, confirming CuL1 to be the most active antioxidant with IC50 = 399.27 µM. A molecular docking simulation was also conducted to comprehend the compounds' interaction mechanism with CT-DNA (1BNA) and cancer cells (BCL-family proteins). Furthermore, the catalytic activity of the zinc metal complex was assessed for multi-component reactions involving substituted benzaldehydes, malononitrile, and resorcinol.