Redox active and inactive binuclear cobalt(II) and zinc(II) complexes with N6O/N3O coordinating ligands: synthesis, biological activities and cytotoxicity

Four complexes, namely [Zn2L1(OAc)(2)](PF6) (1); [Zn2L1(OAc)(2)](BPh4) (2); [(Co2LCl2)-Cl-1](PF6) (3); and [Zn2L2(PhCOO)(2)Cl] (4) (L-1=2,6-bis(((2-(dimethylamino)ethyl)(pyridine-2-ylmethyl)amino)methyl)-4-methoxyphenol; L-2=2-(((2-(dimethylamino)ethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methoxyphenol), have been synthesized. Single-crystal diffraction reveals that the metal atoms in the four complexes are in different coordination environments. The interactions of the complexes with calf thymus DNA (CT-DNA) have been investigated using UV absorption, fluorescence and circular dichroism spectroscopies and viscosity measurements, and the modes of CT-DNA binding for the complexes have been proposed. Further experiments show that the Zn(II)/H2O2 system displays significant oxidative cleavage of supercoiled DNA attributed to the peroxide ion coordinated to the Zn(II) ions enhancing their nucleophilicity. This is a rare phenomenon. DNA cleavage mechanism shows that the complexes examined here may be capable of promoting DNA cleavage through an oxidative DNA damage pathway, which is indicative of the involvement of singlet oxygen in the cleavage process. In vitro cytotoxicity of complexes against three human tumor cell lines (HeLa, MCF-7 and HepG2) demonstrates that these complexes have the potential to act as effective metal-based anticancer drugs. Copyright (c) 2016 John Wiley & Sons, Ltd.