Syntheses, characterizations and biophysical studies of Cu(II) diphenylphosphate complexes: Effect of co-ligands on their biological properties

Abstract

Using the same bridging ligand, diphenyl phosphate (dpp), and different co-ligands, 1,10-phenanthroline (phen)/2,2′-bipyridine (bpy), two structurally similar Cu(II) complexes, [Cu(μ-dpp)(phen)(NO3)]2 (1) and [Cu(μ-dpp)(bpy)(NO3)]2 (2), were synthesized. These complexes were characterized by single crystal X-ray diffraction as well as other physico-chemical methods. Both complexes are dinuclear in nature, but complex 1 is extended into a 3D supramolecular architecture by π–π interactions, whereas complex 2 forms a 2D supramolecular layered structure by π–π and C–H…π interactions. We further explored the DNA binding ability of these complexes by an agarose gel electrophoresis study. Although the coordination structures of these two complexes are very similar, complex 1 was found to be more effective at DNA binding. Complex 1 showed a greater cytotoxic effect on the human hepatocellular carcinoma cell line HepG2 compared to complex 2. Moreover, complex 1 induced more S-phase arrest and apoptosis in HepG2 cells than complex 2, as determined by fluorescence activated cell sorters (FACs). Thus our results indicated that changing the co-ligands in copper complexes may rendered an overall change in the supramolecular structure as well as significant variations in the biological activities.