DNA binding, nuclease activity and cytotoxicity studies of Cu(ii) complexes of tridentate ligands

Abstract

Cu(II) complexes of three tridentate ligands, L₁, L₂ and L₃,[ L₁, N-((1H-imidazole-2-yl)methyl)-2-(pyridine-2-yl)ethanamine; L₂, N-((1-methyl-1H-imidazole-2-yl)methyl)-2-(pyridine-2-yl)ethanamine; L₃, 2-(pyridine-2-yl)-N-((pyridine-2-yl)methyl)ethanamine] respectively, were synthesized and characterized. The single crystal X-ray structure of complex 1 reveals the pseudo octahedral coordination geometry around the copper center. Absorption and fluorescence experimental evidence show good DNA binding propensity (in the order of 10⁵ M⁻¹) of the complexes. Thermal denaturation and circular dichroism (CD) analyses reveal minor structural changes of calf thymus (CT) DNA in presence of complexes and groove and/or surface binding of the complexes to CT-DNA. Kinetic DNA cleavage assay shows pseudo-first-order kinetic reaction between the complex and supercoiled (SC) DNA. In addition, mechanistic SC DNA cleavage results show higher DNA cleavage activity in presence of reducing agent, due to the presence of hydroxyl radicals. In vitro cytotoxicity assay of the complexes demonstrate that the complexes have low toxicity for different cancer cell lines and IC₅₀ values were between 37 and 156 μM.