DNA/BSA binding, DNA cleavage and electrochemical properties of new multidentate copper(II) complexes

A new series of multidentate copper(II) complexes [Cu(L1-5)](ClO4) (1-5) were synthesized [where L1-5 represents [N-(salicylaldimine)-N'-[(2-formyl-4-bromo-6-(4-methylpiperazine-1-yl)methyl)phenol] diamines; diamines viz., L-1-1,2-diamino ethane, L-2-1,3-diamino propane, L-3-1,2-diamino benzene, L-4-2-aminobenzylamine and L-5-1,8-diamino naphthalene] and characterized by elemental analysis and spectroscopic methods. The single crystal X-ray diffraction analysis shows that the multidentate copper(II) complex (1), in which the copper atom exhibits a distorted square planar geometry, coordinates with two phenolic oxygen atoms and two ethylenediamine nitrogen atoms. The assembly of molecular constituents exhibits an interesting supramolecular architecture through the C-H center dot center dot center dot O interactions forming two dimensional supramolecular sheets, and extending infinitely along the (1 0 0) plane. The channels thus formed are large enough to hold the guest (solvent) molecules. Cyclic voltammograms of these copper(II) complexes exhibit one quasi reversible reduction wave in the cathodic region. The DNA/BSA binding, DNA cleavage, antimicrobial activity and MTT assay of these complexes were also investigated. The binding propensities of the complexes toward calf thymus DNA (CT DNA) were also investigated by UV and fluorescent spectroscopy, viscosity measurements and circular dichroism spectral studies. The binding constant (K-b) values are in the range of 0.84 x 10(4)-3.0 x 10(4) M-1, and the apparent binding constants (K-app) in the range from 1.9 x 10(6) M-1 to 4.2 x 10(6) M-1, as measured by UV and fluorescent methods. The cleavage activities are in the following order (5) > (4) > (3) > (1). The mechanistic investigation suggests that singlet oxygen plays a vital role in the cleavage process. All the copper(II) complexes (1-5) exhibit significant interaction with bovine serum albumin (BSA), and the results show that the binding mechanism is a static quenching process.