Dinuclear phenoxo-bridged "end-off" complexes containing a piperazine that shows chemical nuclease and cytotoxic activities

Three dinuclear cobalt(II), nickel(II), and copper(II) complexes (1-3) of a phenol-based 'end-off' compartmental ligand, 2,6-bis[1-(N-ethyl) piperazineiminomethyl]-4-methylphenol (HL), have been synthesized and characterized by spectral analysis. The molecular structure of one of these complexes, 2,6-bis[1-(N-ethyl) piperazineiminomethyl]-4-methylphenolato-diaqua-mu-hydroxo-mu-nitrato-dicobalt(II) nitrate, [Co-2(H2L)(mu-OH)(mu-NO3)(H2O)(2)](NO3)(3)] (1), was determined by single crystal X-ray crystallography. The complex exhibits a distorted octahedral geometry around cobalt with a Co-Co distance of 2.9882(8) angstrom. Electrochemical studies of 1-3 reveal that the redox processes are due to ligand reactions. The EPR spectrum of 3 showed a broad signal at g = 2.11 indicating magnetic interaction between the two copper ions. The mu(eff) values for 1 and 3 are 4.94 and 1.93 BM, respectively, which indicate a spin-spin interaction between the metal ions. Complex 3 caused a cleavage of circular plasmid pBR322 DNA into nicked circular and linear forms in the presence of a co-reactant. Human epidermoid carcinoma cells, A431, were employed for in vitro cytotoxicity studies of the synthesized complexes. The IC50 value of 3 is lower than that of the other two complexes. The copper complex (3) exhibited better chemical nuclease and cytotoxic activity than the other two complexes.