Synthesis and structures of binuclear copper(II) complexes bridged by N-(5-chloro-2-hydroxyphenyl)-N′-[3-(dimethylamino)propyl]oxalamide ligand: DNA-binding properties and cytotoxic activities

Two new binuclear copper(II) complexes bridged by N-(5-chloro-2-hydroxyphenyl)-N′-[3-(dimethylamino)propyl]oxalamide (H3chdpoxd), and end-capped with 1,10-phenanthroline (phen) or 5-nitro-1,10-phenanthroline (NO2phen), respectively, with formulas of [Cu2(chdpoxd)(H2O)(phen)](NO3)·H2O (1) and [Cu2(chdpoxd)(CH3CH2OH)(NO2phen)](NO3) (2), have been synthesized and characterized by single-crystal X-ray diffraction. In both complexes 1 and 2, the cis-chdpoxd3− ligand bridges two copper(II) ions with the corresponding separations of 5.2003(5) and 5.1664(17) Å, respectively, and the polyhedron of Cu1 is a distorted square-planar, of Cu2 is a square-pyramidal. Through π–π stacking and hydrogen bonding interactions, the two bicopper(II) complexes are assembled to 3D supramolecular structures, which are distinct from each other due to the substituents on terminal ligand. Both the two complexes tested by Sulforhodamine B (SRB) assays exhibit potent anticancer activities against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549. The interactions of the two complexes with herring sperm DNA (HS-DNA) are investigated by using UV absorption and fluorescence spectra and viscometry. The results suggest that the two bicopper(II) complexes interact with HS-DNA in the mode of intercalation, and the DNA-binding abilities are consistent with in vitro antitumor activities following the order 2 > 1. The influence of the substituents on terminal ligands in bicopper(II) complexes on DNA-binding and cytotoxic properties is preliminarily discussed.