Subramanian Sakthinathan

Nucleic acid binding study of surfactant copper(II) complex containing dipyrido[3,2-a:2′-3′-c]phenazine ligand as an intercalator: in vitro antitumor activity of complex in human liver carcinoma (HepG2) cancer cells

A new surfactant copper(II) complex, [Cu(dppz)2DA](ClO4)2, where dppz = dipyrido[3,2-a:2′-3′-c]phenazine and DA-dodecylamine, has been synthesized and characterized by physico-chemical and spectroscopic methods. The critical micelle concentration (CMC) value of this surfactant copper(II) complex in aqueous solution was determined from conductance measurements. Specific conductivity data at different temperatures was obtained for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG0m, ΔH0m and ΔS0m). The binding interaction of this complex with nucleic acids (calf thymus DNA and yeast t-RNA) was investigated using electronic absorption, fluorescence spectroscopy, viscometry, cyclic voltammetry (CV) and thermal denaturation studies. In the presence of the nucleic acids, the UV-Vis spectrum of our complex exhibited a redshift of the absorption band at 268 nm along with significant hypochromicity, indicating intercalation of our complex with the nucleic acids. The intrinsic binding constant values are Kb = 1.1 × 106 M−1 for DNA and 1.6 × 106 M−1 for RNA. The viscosity measurements confirmed that the complex–nucleic acid interaction occurs through intercalation. A competitive binding study with ethidium bromide (EB) showed that the complex exhibits the ability to displace the nucleic acid-bound EB, indicating that the complex binds to nucleic acids in strong competition with EB for the intercalative binding site. CV results also confirmed this mode of binding. Some significant thermodynamic parameters of the binding of the titled complex to DNA were also determined. The antimicrobial and antifungal screening tests of this complex have shown good results. The copper(II) complex exhibited pronounced activity against a human liver carcinoma (HepG2) cancer cell line.

Thermodynamics and kinetic investigation of electron transfer reactions of surfactant cobalt( iii ) complexes containing diimine ligands with iron( ii ) in the presence of liposome vesicles and amphiphilic salt media

The kinetics of reductions of surfactant cobalt(III) complexes, cis-[Co(L)2(C12H25NH2)2](ClO4)3 (L = imidazo[4,5-f][1,10]phenanthroline, dipyrido[3,2-d:2′,3′-f]quinoxaline and dipyrido[3,2-a:2′,4′-c](6,7,8,9-tetrahydro)phenazine, C12H25NH2 = dodecylamine) by iron(II) in liposome vesicles (DPPC) and amphiphilic salt ((BMIM)Br) were studied at different temperatures by UV-Vis absorption spectroscopy method under pseudo first order conditions using an excess of the reductant. The reactions were found to be second order and the electron transfer is postulated as outer-sphere. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. It is concluded that below the phase transition temperature, there is an accumulation of surfactant cobalt(III) complexes at the interior of the vesicle membrane through hydrophobic effects, and above the phase transition temperature the surfactant cobalt(III) complexes are released from the interior to the exterior surface of the vesicle. The effects of amphiphilicity of the long aliphatic double chains of these surfactant complex ions into ionic liquids on these reactions have also been studied. The second order rate constant for the electron transfer reactions were found to increase with increasing concentrations of amphiphilic salts. The results have been interpreted in terms of the hydrophobic effect.

A comparative study on the electron transfer reaction (ETR) of surfactant cobalt(III) complexes of aliphatic/aromatic ligands in micro heterogeneous media: a thermodynamic approach

The kinetics of the electron transfer reaction (ETR) between the surfactant cobalt(III) complex ions, cis-[Co(ip)2(C12H25NH2)2](ClO4)3, cis-[Co(dpq)2(C12H25NH2)2](ClO4)3 and cis-[Co(dpqc)2(C12H25NH2)2](ClO4)3 (ip = imidazo[4,5-f][1,10]phenanthroline, dpq = dipyrido[3,2-d:2′-3′-f]quinoxaline, dpqc = dipyrido[3,2-a:2′,4′-c](6,7,8,9-tetrahydro)phenazine, C12H25NH2 = dodecylamine) and Fe2+ ions in micelles as well as β-cyclodextrin (β-CD) were studied at different temperatures by a spectrophotometric method under pseudo first order conditions with an excess of reductant. The results from surfactant complexes containing aromatic ligands, which have a higher ETR than that of aliphatic ligands due to the results obtained, have been explained based on the hydrophobic effect. Experimentally the reactions were found to be second order and the electron transfer is postulated as outer sphere. The rate constant increases with increase in the concentration of micelles but the inclusion of the long aliphatic chain of the surfactant cobalt(III) complexes into β-cyclodextrin decreases the rate of the reaction. Thermodynamic parameters were also evaluated.

Effect of hydrophobicity on intercalative binding of some surfactant copper(II) complexes with tRNA

The binding interaction between tRNA and surfactant copper(II) complexes with imidazo[4,5-f][1, 10]phenanthroline, 6,7,8,9-tetrahydrodipyrido[3,2-a:2′,4′-c]phenazine, and benzo[1]dipyrido[3,2-a′:2′,3′-c]phenazine ligands has been studied using various physicochemical techniques. In the presence of tRNA, UV–Vis spectrum of surfactant complexes showed red shift of the absorption band along with significant hypochromicity indicating intercalation of surfactant complexes with tRNA. Competitive binding study with ethidium bromide shows that complexes exhibit the ability to displace the tRNA-bound EB indicating that these complexes bind to tRNA in strong competition with EB for the intercalative binding site. Observed changes in the circular dichroic spectra of tRNA in the presence of surfactant complexes support the strong binding of complexes with tRNA. CV and viscosity results also affirm this mode of binding. The results reveal that the extent of tRNA binding of the benzo[1]dipyrido[3,2-a′:2′,3′-c]phenazine complex was greater than that of the other complexes. Binding to tRNA appears to be mainly intercalative in nature.Graphical abstract