DNA binding, cleavage, and cytotoxicity of binuclear phenolate nickel(II) complexes

Three binuclear phenolate complexes, [Ni2(L1)2(OAc)](BPh4)·DMF (1), [Ni2(L2)2(OAc)](BPh4) (2), and [Ni2(L3)2(OAc)](OH)·3H2O (3), where L1 = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-methyl-phenol, L2 = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-methoxy-phenol, and L3 = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-tert-butyl-phenol), have been synthesized. Single-crystal diffraction reveals that all the metal atoms are in a distorted octahedral geometry. The interactions of the complexes with calf thymus DNA (CT-DNA) have been investigated by UV–vis absorption, fluorescence emission, and circular dichroism spectroscopy and viscosity measurements. Furthermore, DNA cleavage mechanism shows that the complexes may be capable to promote DNA cleavage through oxidative DNA damage pathway, which is indicative of the involvement of hydroxyl radical, singlet oxygen, or singlet oxygen-like entity in the cleavage process. Cytotoxicity studies on the Hela and MCF-7 cancer cell lines show that complexes 1–3 exhibit excellent activity toward the tested tumor cell lines with respect to the standard drug carboplatin, revealing that they have the potential to act as effective metal-based anticancer drugs.