Effect of coordination sphere of the copper center and Cu-•Cu distance on catechol oxidase and nuclease activities of the copper complexes

To explore the effect of Cu-•Cu distance in the structure of copper complexes on their catechol oxidase and nuclease activity, six copper complexes with a similar coordination sphere but different Cu-•Cu distances were synthesized and characterized with elemental analysis, single-crystal X-ray diffraction, molar conductivity measurements, IR and UV-visible spectroscopy. Complex 1 is a binuclear copper complex and complex 4 is a polynuclear complex with a Z-chain structure, as evidenced by their crystal structures. Complementary characterizations showed that complexes 2 and 3 have a similar binuclear structure to the complex 1; and complexes 5 and 6 are analogous to complex 4. The catechol oxidase activity of complexes 1, 2, 3 is quite akin to that of 4, 5, 6, suggesting that the catechol oxidase activity of the complexes was determined by the coordination environment of the copper center, when Cu-•Cu distance is large. In contrast, DNA cleavage activity of the complexes 1, 2 and 3 are much higher than that of 4, 5 and 6, indicating that the planar ligand structure in the complexes 4, 5 and 6 is more critical than the copper coordination sphere and the Cu-•Cu distance for their nuclease activity.