Synthesis, crystal structure, antibacterial activities, and DNA-binding studies of a new μ-oxamido-bridged binuclear copper(II) complex

A new mu-oxamido-bridged dicopper(II) complex, Cu-2(heap)(NO3)(2) (1), where heap is the dianion of N,N'-bis(N-hydroxyethylaminopropyl) oxamide, has been synthesized and characterized by elemental analysis, molar conductivity, IR and electronic spectral studies, and X-ray single-crystal diffraction. The complex consists of a neutral centro-symmetric binuclear copper(II) unit with an inversion center at the midpoint of the Cl-Cl-i bond. The copper(II) has square-pyramidal coordination geometry and the bridging heap adopts a bis-tetradentate conformation. The binuclear units are linked into a 3-D framework by N-H center dot center dot center dot O, O-H center dot center dot center dot O, and C-H center dot center dot center dot O hydrogen bonds. Due to weak coordination between copper(II) and nitrate, the neutral dicopper(II) units are present as binuclear cations and nitrate anions in solution. Antibacterial assays indicate that the complex shows better activity than the ligand. Interactions of the complex with herring sperm DNA (HS-DNA) have been investigated by using cyclic voltammetry, UV absorption titrations, ethidium bromide fluorescence displacement experiments, and viscometry measurements. The results suggest that the binuclear copper(II) complex interacts with HS-DNA by electrostatic interaction with intrinsic binding constant of 3.33 x 10(4) M-1.