A new series of dinuclear Cu(I) complexes with hexaazamacrocyclic Schiff base ligand containing pyridyl pendant arms has been synthesized and characterized. The solid-state structures of [Cu(2)(I)(bsp3py)](CF(3)SO(3))(2) (1(CF(3)SO(3))(2)), [Cu(2)(I)(bsm3py)](SbF(6))(2) (2(SbF(6))(2)), and [Cu(2)(I)(bsp2py)](CF(3)SO(3))(2) (3(CF(3)SO(3))(2)) have been established by single-crystal X-ray diffraction analysis. The geometries of the copper centers in all three cases are almost identical showing a distorted tetrahedral coordination, very close to a trigonal pyramidal arrangement. Interactions of complexes with calf thymus DNA have been investigated by circular dichroism spectroscopy (CD) which suggests that the interaction for each complex is a nonintercalative mode with regard to DNA. The electrophoretic mobility study and the atomic force microscopy (AFM) in the presence of H(2)O(2) reveal a cleavage of pBR322 supercoiled DNA that depends on the nature of the Cu(I) complex used. The most efficient reactivity is observed for complexes 1(CF(3)SO(3))(2) and 2(CF(3)SO(3))(2) whereas complex 3(CF(3)SO(3))(2) displays a lesser reactivity. The different DNA-cleavage activity of complexes 1-3 is due the different electronic factors and complex topology induced by the natures of the different ligands. This work constitutes an example of how small modifications introduced in the macrocyclic backbone of the metal complexes lead to dramatic changes in the nuclease activity.