Karuppiah Nagaraj

Binding of a double-chain surfactant-cobalt(III) complex to CT DNA: effect of β-cyclodextrin in the medium.

The interaction of cis-[Co(phen)2(HA)2](ClO4)3, a cationic surfactant complex (phen=1,10-phenanthroline, HA=hexadecylamine), with calf thymus DNA has been studied by UV-vis absorption, fluorescence spectroscopy, cyclic voltammetry, circular dichroism, and viscosity measurements. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that the surfactant-cobalt(III) complex binds to calf thymus DNA (CT DNA) by intercalation through the aliphatic chain present in the complex into the base pairs of DNA. The presence of phenanthroline ligand with larger π-frame work may also enhance intercalation. Besides the effect of binding of surfactant cobalt(III) complex to DNA in presence of β-cyclodextrin has also studied. In presence of β-cyclodextrin the binding occurs through surface and (or) groove binding. The complex was investigated as one of the potential selective anticancer prodrugs. The complex was tested also in vitro on human monolayer tumor cell lines: HepG2 (human hepatocellular liver carcinoma).

Synthesis, CMC Determination, and Outer Sphere Electron Transfer Reaction of the Surfactant–Complex Ion, cis-[Co(en)2(4CNP)(DA)]3+ with [Fe(CN)6]4– in Micelles, β-cyclodextrin, and Liposome (Dipalmidoylphosphotidylcholine) Vesicles

The surfactant cobalt(iii) complex, cis-[Co(en)2(4CNP)(DA)](ClO4)3, en = ethylenediamine, 4CNP = 4-cyanopyridine, DA = dodecylamine, was synthesized and characterized by physico-chemical and spectroscopic methods. The critical micelle concentration value of this complex was obtained from the conductivity measurements at different temperatures to evaluate, ΔGm0, ΔHm0, and ΔSm0. The kinetics of outer sphere electron transfer reaction of this complex with Fe(CN)64– ion in micelles, β-cyclodextrin as well as in liposome vesicles media were studied. The rate constant increases with increase in the concentration of micelles but decreases in presence of β-cyclodextrin, which is a good structure breaker of micelles. In liposome vesicles media the rate constant is different at below and above phase transition temperature. The results have been explained based on the hydrophobic effect, the presence of pyridine ligand containing 4-cyano substituent and the reactants with opposite charge.

Synthesis, CMC determination, nucleic acid binding and cytotoxicity of a surfactant–cobalt(III) complex: effect of ionic liquid additive

The surfactant–cobalt(III) complex, cis-[Co(trien)(4CNP)(DA)](ClO4)3 (trien = triethylenetetramine, 4CNP = 4-cyanopyridine and DA = dodecylamine) was synthesized and characterized by various spectroscopic and physicochemical techniques. The critical micelle concentration (CMC) value of this surfactant–cobalt(III) complex in aqueous solution was obtained from conductance measurements. The conductivity data (at 303, 308, 313, 318 and 323 K) were used for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG0m, ΔH0m and ΔS0m). Absorption, fluorescence, cyclic voltammetry, circular dichroism and viscosity experiments have been carried out to study the interaction of the surfactant–cobalt(III) complex with DNA and RNA. The results suggest that the complex can bind to nucleic acids by intercalation via the long aliphatic chain of the complex into the base pairs of DNA/RNA. In the presence of an ionic liquid additive, the binding strength of the surfactant–cobalt(III) complex to the nucleic acids increased. The complex was tested in vitro on HepG2 (human hepatocellular liver carcinoma) tumor cell lines and found to be active.

Synthesis, CMC determination, and intercalative binding interaction with nucleic acid of a surfactant–copper(II) complex with modified phenanthroline ligand (dpq)

A surfactant–copper(II) complex, [Cu(dpq)2DA](ClO4)2 (dpq = dipyrido[3,2-d:2′-3′-f]quinoxaline; DA-dodecylamine), was synthesized and characterized on the basis of elemental analyses, UV–vis, IR, and EPR spectra. The critical micelle concentration (CMC) value of this surfactant–copper(II) complex in aqueous solution was found out from conductance measurements. Specific conductivity data at different temperature served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (, , and ). In addition, the complex has been examined by its ability to bind to nucleic acids (DNA and RNA) in tris-HCl buffer by UV–vis absorption, emission spectroscopy techniques, and viscosity measurements. The complex has been found to bind strongly to nucleic acids with apparent binding constants at DNA and RNA is 4.3 × 105, 9.0 × 105 M−1, respectively. UV–vis studies of the interaction of the complex with DNA/RNA have revealed that the complex can bind to both DNA and RNA by the intercalative binding mode via ligand dpq into the base pairs of DNA and RNA which has been verified by viscosity measurements. The presence of long aliphatic chain in the surfactant complex increases this hydrophobic interaction. The binding constants have been calculated. The cytotoxic activity of this complex on human liver carcinoma cancer cells was determined by adopting 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyl tetrazolium bromide assay and specific staining techniques. The antimicrobial and antifungal screening tests of this complex have shown good results.

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

Abstract 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 β-cyclodextrin medium was obtained from conductance measurements at 303, 308 and 313 K. The CMC value was found to be higher in β-cyclodextrin medium compared to that in aqueous medium containing no β-cyclodextrin. These results indicate that the surfactant complex has been incorporated into the cavity of β-cyclodextrin through its two aliphatic chains thereby reduce the capacity of our complex to form micelles. This strong interaction between β-cyclodextrin and our complex has been confirmed by the changes occurred in the UV-Visible absorption spectrum of the complex in β-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 × 105, 2.1 × 106 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 β-cyclodextrin medium due to the combined effect of incorporation of the aliphatic chains into the cavity of β-cyclodextrin and trapping of a base from within the DNA by β-cyclodextrin. The cytotoxic activity of the surfactant cobalt(III) 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.

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.

Electron Transfer Reaction of Ion Pairs: 1. Surfactant Cobalt(III) Complexes by Fe(CN)64− in Microheterogeneous Media

Abstract The kinetic study of reduction of single chain surfactant octahedral cobalt(III) complexes, cis-[Co(en)2(4AMP)(DA)](ClO4)3 and cis-[Co(trien)(4CNP)(DA)](ClO4)3 (where en = ethylenediamine; trien = triethylenetetramine; 4AMP = 4-aminopyridine; 4CNP = 4-cyanopyridine; DA = dodecylamine) with [Fe(CN)6]4– has been carried out by spectrophotometric method under pseudo first order conditions using an excess of a reductant in different media namely, micelles, β-cyclodextrim (β-CD), liposome vesicles (DPPC) and ionic liquids ((BMIM)Br) at different temperatures in order to have deep insight into the molecular behavior during the electron transfer reaction. The analysis of kinetic results strongly suggests that the reduction reaction between the surfactant complex and [Fe(CN)6]4– occurs via a second order outer sphere electron transfer mechanism. The remarkable increase in the rate of electron transfer from the oxidant to reductant is observed in ionic liquid medium as compared to the rest of all other media studied in the present investigation. This can be ascribed due to the fact that the formation of aggregated and constrained geometry of the surfactant cobalt(III) complexes (oxidants) in ionic liquid medium renders the rate of one electron transfer from the oxidants to the reductant, [Fe(CN)6]4– to be higher. Furthermore, the rate constant value increases with increase in the concentration of micelles, however in the presence of β-cyclodextrin medium the rate of electron transfer substantially decreases due to the inclusion of long aliphatic chain of the surfactant cobalt(III) complexes into β-cyclodextrin. In liposome media, second order rate constant for this electron transfer reaction from both the oxidants was found to decrease with increase in the concentration of the liposome below the phase transfer temperature of DPPC. However, above the phase transition temperature the reaction was found to increase with increase in the concentration of the DPPC. The main driving force for this phenomenon is considered to be the intervesicular hydrophobic interaction between the surfactant complexes and vesicular surface. The activation parameters (ΔS‡ and ΔH‡) of this outer sphere electron transfer reaction have been calculated by varying temperatures and the analysis of the data corroborates the kinetics of the reaction.

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.

Kinetics and mechanism of electron transfer reaction of single and double chain surfactant cobalt(III) complex by Fe2+ ions in liposome (dipalmitoylphosphotidylcholine) vesicles: effects of phase transition

In this study, we report the kinetics of reduction reactions of single and double chain surfactant cobalt(III) complexes of octahedral geometry, cis-[Co(en)2(4AMP)(DA)](ClO4)3 and cis-[Co(dmp)2(C12H25NH2)2](ClO4)3 (en = ethylenediamine, dmp = 1,3-diaminopropane, 4AMP = 4-aminopropane, C12H25NH2 = dodecylamine) by Fe2+ ion in dipalmitoylphosphotidylcholine (DPPC) vesicles at different temperatures under pseudo first-order conditions. The kinetics of these reactions is followed by spectrophotometry method. The reactions are found to be second order and the electron transfer is postulated as outer sphere. The remarkable findings in the present investigation are that, below the phase transition temperature of DPPC, the rate decreases with an increase in the concentration of DPPC, while above the phase transition temperature the rate increases with an increase in the concentration of DPPC. The main driving force for this phenomenon is considered to be the intervesicular hydrophobic interaction between vesicles surface and hydrophobic part of the surfactant complexes. Besides, comparing the values of rate constants of these outer-sphere electron transfer reactions in the absence and in the presence of DPPC, the rate constant values in the presence of DPPC are always found to be greater than in the absence of DPPC. This is ascribed to the double hydrophobic fatty acid chain in the DPPC that gives the molecule an overall tubular shape due to the intervesicular hydrophobic interaction between vesicles surface and hydrophobic part of the surfactant complexes more suitable for vesicle aggregation which facilitates lower activation energy, and consequently higher rate is observed in the presence of DPPC. The activation parameters (ΔS# and ΔH#) of the reactions at different temperatures have been calculated which corroborate the kinetics of the reaction.