DNA/protein binding and cytotoxicity studies of copper(II) complexes containing N, N′,N"-trisubstituted guanidine ligands

A series of N, N', N"-trisubstituted guanidine ligands (L1-L5) and their copper(II) complexes (1- 5) [Cu(II) {C4H3SCONC( NHR)NC6H5} 2] [ where R p-tolyl ( 1), phenyl ( 2) benzyl ( 3), butyl ( 4) and cyclohexyl ( 5)] were synthesized and characterized by elemental analyses and UV-visible, FT-IR, H-1 & C-13 NMR/EPR and mass spectroscopic techniques. The molecular structure of L1-L5, 3, and 5 was confirmed by single crystal X-ray crystallography. The single crystal X-ray structure of the complexes reveals the square planar geometry. The interaction of calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) with the copper( II) complexes was investigated using UV-visible and fluorescence spectrophotometric methods. Spectral evidence shows the intercalative mode of DNA binding (in the order of 10(4) M (1)) with the complexes. The Stern-Volmer quenching constant (K-q) values were found from competitive binding studies and found to be in the range of 1.07-1.30 x 10(5) M-1 for the complexes. Spectral evidence also shows good binding properties of the complexes with the protein. Complexes 3 and 4 showed significant cytotoxicity against human breast (MCF7) and lung cancer (A549) cell lines.