Synthesis, characterization, DNA-binding and cleavage studies of polypyridyl copper(II) complexes

The relative impact of ligand flexibility and redox potential on the activity of Cu superoxide dismutase mimics

Two copper(II) complexes, [Cu(salbn)] and [Cu(py2bn)(OAc)]ClO4, formed with the Schiff-base ligands 1,4-bis(salicylidenamino)butane (H2salbn) and 1,4-bis(pyridin-2-ylmethyleneamino)butane (py2bn), have been prepared and characterized in solid state and in solution, and their ability to catalyse the dismutation of O2˙- has been evaluated in homogeneous medium and immobilized in a mesoporous matrix. The crystal structures show that [Cu(salbn)] possesses a distorted square-planar geometry, while [Cu(py2bn)(OAc)]ClO4 adopts a cis-distorted octahedral geometry. The two complexes experience structural changes in solution, and different spectroscopies were used to examine them. Moreover, their redox potentials are strongly affected by the solvent. In water, the complexes exist as [Cu(salbn)(H2O)] and [Cu(py2bn)(H2O)]2+ with Cu(II)/Cu(I) reduction potential at -361 mV and -229 mV, respectively, well different from redox potentials measured in acetonitrile. Although with a more unfavourable redox potential, [Cu(salbn)(H2O)] reacts with O2˙- faster than [Cu(py2bn)(H2O)]2+, with catalytic rate constants of 3.3 × 107 and 2.9 × 107 M-1 s-1, respectively, at pH = 7.8. Both complexes exhibit higher superoxide dismutase activity than the analogues with a shorter central alkyl chain. The observed catalytic rates essentially correlate with the ligand flexibility, rather than with the redox potential, which is also supported by the slower O2˙- dismutation rate when the complexes are immobilized by encapsulation into the channels of well-ordered mesoporous SBA-15 silica where the pore modifies the complex structures and restraints the ligand rearrangement.

DNA-Binding and Cytotoxicity of Copper(I) Complexes Containing Functionalized Dipyridylphenazine Ligands

A set of copper(I) coordination compounds with general formula [CuBr(PPh₃)(dppz-R)] (dppz-R = dipyrido[3,2-a:2’,3’-c]phenazine (Cu-1), 11-nitrodipyrido[3,2-a:2’,3’-c]phenazine (Cu-2), 11-cyanodipyrido[3,2-a:2’,3’-c]phenazine (Cu-3), dipyrido[3,2-a:2’,3’-c]phenazine-11-phenone (Cu-4), 11,12-dimethyldipyrido[3,2-a:2’,3’-c]phenazine (Cu-5)) have been prepared and characterized by elemental analysis, ¹H-NMR and ³¹P-NMR spectroscopies as well as mass spectrometry. The structure of Cu-1 was confirmed by X-ray crystallography. The effect of incorporating different functional groups on the dppz ligand on the binding into CT-DNA was evaluated by absorption spectroscopy, fluorescence quenching of EtBr-DNA adducts, and viscosity measurements. The functional groups affected the binding modes and hence the strength of binding affinities, as suggested by the changes in the relative viscosity. The differences in the quenching constants (K_sv) obtained from the fluorescence quenching assay highlight the importance of the functional groups in altering the binding sites on the DNA. The molecular docking data support the DNA-binding studies, with the sites and mode of interactions against B-DNA changing with the different functional groups. Evaluation of the anticancer activities of the five copper compounds against two different cancer cell lines (M-14 and MCF-7) indicated the importance of the functional groups on the dppz ligand on the anticancer activities. Among the five copper complexes, the cyano-containing complex (Cu-3) has the best anticancer activities.