New cyclic tetranuclear copper(II) complexes containing quadrilateral cores: Synthesis, structure, spectroscopy and their interactions with DNA in aqueous solution

Three new water-soluble cyclic tetranuclear copper(II) complexes, Tetrakis{3-[(2-pyridylmethyl)-amino]-propionato}(tetrachloro)tetracopper(II)methanolhydrate (1·CH3OH·H2O), Tetrakis{3-[(2-pyridylmethyl)-amino]-propionato}(tetrathiocyanato)tetracopper(II) (2) and Tetrakis{3-[(2-pyridylmethyl)-amino]-propionato}(tetraazido)tetracopper(II) (3) have been prepared by exploiting the chelating ability and bridging potential of a carboxyamine functionalized tridentate ligand, HL (HL = 3-[(2-Pyridylmethyl)-amino]-propionic acid) and fully characterized. Single crystal X-ray structure analysis of one of these complexes reveals that the metallic cores of the complexes consist of four distorted square pyramidal copper(II) ions arranged at the corners of a quadrilateral displaying a μ2:η1:η1syn-anti bidentate bridging mode of the carboxylates with each bridging between two copper(II) ions. A combined approach of UV-Vis and fluorescence titration techniques, and viscosity measurements establish the binding properties of the complexes with CT-DNA in aqueous solution at pH∼7.5.230