Design and synthesis of two macrocyclic dinuclear copper(II) complexes with reversible binding of nitric oxide

Two new macrocyclic dinuclear copper(II) complexes, [Cu2L1(MeOH)2]·(ClO4)2 (1) and [Cu2L2(EtOH)2]·(ClO4)2 (2) have been synthesized and characterized by ES-MS spectra and X-ray crystallography determination. The coordination polyhedron of Cu(II) ions in each complex can be described as approximately square pyramind, where the apical position is occupied by a labile coordinated alcoholic molecule. The reactions of complexes with nitric oxide (NO) cause an immediate color change, and the formation of NO complexes has been further confirmed by UV/Vis spectrophotometry. The binding constants are calculated to be 1.71 × 103 M− 1 and 2.0 × 103 M− 1 in 0.2 M anaerobic phosphate buffer solution (PBS), respectively. The control experiments reveal that the binding of NO to complexes is reversible. Moreover, the interactions of the complexes with calf thymus DNA (CT-DNA) have been measured by UV/Vis, cyclic voltammetry and viscosity study. The moderate binding ability and unobvious DNA cleavage ability account for their low toxicity towards DNA. Overall, the results reveal that these two complexes can be served as potential NO regulators.