Influence of self-assembly on intercalative DNA binding interaction of double-chain surfactant Co(III) complexes containing imidazo[4,5-f][1,10]phenanthroline and dipyrido[3,2-d:2′-3′-f]quinoxaline ligands: experimental and theoretical study

A new class of surfactant Co(III) complexes, cis-[Co(ip)(2)(C12H25NH2)(2)](ClO4)(3) (1) and cis-[Co(dpq)(2)-(C12H25NH2)(2)](ClO4)(3) (2) (ip = imidazo[4,5-f][1,10]phenanthroline, dpq = dipyrido[3,2-d:2'-3'-f]quinoxaline), have been synthesized and characterized by various spectroscopic and physico-chemical techniques. The critical micelle concentration (CMC) values of these complexes in aqueous solution were obtained from conductance measurements. The specific conductivity data (at 303, 308, 313, 318 and 323 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (Delta G(m)(0), Delta H-m(0) and Delta S-m(0)). The trend in DNA-binding affinities and the spectral properties of a series of complexes, cis-[Co(ip)(2)(C12H25NH2)(2)](ClO4)(3) (1) and cis-[Co(dpq)(2)(C12H25NH2)(2)](ClO4)(3) (2), have been experimentally and theoretically investigated. The experimental results indicate that the size and shape of the intercalated ligand and hydrophobicity of the complexes have a marked effect on the binding affinity of the complexes to CT DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K-b is K-b(1) < K-b(2). In addition, the influence of the extended aromatic ring and optical properties of the complexes can be reasonably explained by applying the DFT calculations. The energy gap between HOMO and LUMO indicates that these complexes are prone to interact with CT DNA. Further, molecular docking calculations have also been performed to understand the nature of binding of the complexes and the result confirms that the complexes interact with CT DNA through the alkyl chain. The cytotoxic activity of these complexes on human liver carcinoma cancer cells were determined adopting MTT assay and specific staining techniques, which revealed that the viability of the cells thus treated was significantly decreased and the cells succumbed to apoptosis as seen in the changes in the nuclear morphology and cytoplasmic features.