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

Abstract

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, ¹H & ¹³C 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 10⁴ 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 × 10⁵ 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.