Structural diversity in aroylthiourea copper complexes – formation and biological evaluation of [Cu(i)(μ-S)SCl]2, cis-Cu(ii)S2O2, trans-Cu(ii)S2O2 and Cu(i)S3 cores

Abstract

Copper complexes of types [Cu(HL1-{μ-S})(HL1-S)Cl]₂ (1), cis-[Cu(L1-O,S)₂] (2), [Cu(L2-S)₃]Cl (3) and trans-[Cu(L2-O,S)₂] (4) were synthesized and characterized by analytical, spectroscopic (UV-vis, FT-IR, and NMR/EPR) and single crystal X-ray diffraction techniques. In order to understand the structure, bonding, and band gap of complex 1, DFT calculations were performed. The computed results revealed that the absorption was associated with ¹MLCT transitions while the emission had ³MLCT character. The calculated geometrical parameters agreed well with the experimental values. The binding affinity and binding mode of these copper complexes toward calf thymus (CT) DNA were determined by using UV-vis spectroscopic titrations and the fluorescent indicator displacement (FID) method. These studies showed that the complexes bind in the order of 1 > 2 > 3 > 4 to CT DNA. The protein binding ability has been monitored by the quenching of tryptophan emission in the presence of the complexes using bovine serum albumin (BSA) as a model protein. These copper complexes displayed high cytotoxicity against two cancer cell lines (A549 and MCF7).