Studies on DNA Binding of a Double-chain Surfactant Cobalt(III) Complex Containing 2,2′-Bipyridine Ligand

The critical micelle concentration (CMC) value of the double chain surfactant-cobalt(III) complex, cis-[Co(bpy)(2)(DA)(2)](ClO4)(3) (bpy = 2,2'-bipyridine, DA = dodecyl amine) in aqueous beta-cyclodextrin medium was obtained from conductance measurements at 303, 308 and 313 K. The CMC value was found to be higher in beta-cyclodextrin medium compared to that in aqueous medium containing no beta-cyclodextrin. These results indicate that the surfactant complex has been incorporated into the cavity of beta-cyclodextrin through its two aliphatic chains thereby reduce the capacity of our complex to form micelles. This strong interaction between beta-cyclodextrin and our complex has been confirmed by the changes occurred in the UV-Visible absorption spectrum of the complex in beta-cyclodextrin. The surfactant complex has been found to bind strongly to CT DNA with apparent binding constants at below and above CMC are 1.69 x 10(5), 2.1 x 10(6) M-1 respectively. Binding of this surfactant-cobalt(III) complex with CT DNA was through intercalative mode via the long aliphatic chains present in the ligands. The binding was investigated by various techniques, UV-Visible absorption, fluorescence spectroscopy, circular dichroism, and viscosity measurements. This binding of the surfactant cobalt(III) complex with CT DNA has been reduced in presence of beta-cyclodextrin medium due to the combined effect of incorporation of the aliphatic chains into the cavity of beta-cyclodextrin and trapping of a base from within the DNA by beta-cyclodextrin. The cytotoxic activity of the surfactant cobalt(111) complex was tested in vitro on human tumor cell lines (HepG2 liver carcinoma) using different cell death indicator stains and MTT assay and found to be active. The experiments suggest that the complex suffered loss of viability and death mostly through apoptosis.