Presence Of Cetyltrimethylammonium Bromide Micelles Research Articles

A Kinetic Investigation of Metal-Dipeptide Complex with Ninhydrin in the Absence and Presence of CTAB Micelles.

This paper presents the results of a kinetic study performed between ninhydrin and a Ni(II) dipeptide complex under various conditions. The rate of formation of the imine adduct was measured spectrophotometrically both in plain aqueous media and in aqueous micellar media in which CTAB (cetyltrimethylammonium bromide) is used as the surfactant. These studies were carried out at pH 5 and over a temperature a range of 50 to 70°C. Studies were also conducted to elucidate the effect of some organic sodium salts on the rate of this reaction. In these studies, it was found that the formation of imine adduct followed a first-order kinetics with respect to [Ni(II)-Gly-Leu]+ in both aqueous and micellar medium. A fractional-order kinetics was observed with respect to ninhydrin, again in both aqueous and micellar media. Increase in the total concentration of CTAB from 0 to 40×10-3 mol dm-3 resulted in approximately two folds increase in the pseudo-first-order rate constant (kψ). The rate constant (kΨ) in micellar medium first increased with increase in CTAB concentration, reached a maximum value, and finally, with further increase in CTAB concentration, a decreasing effect was observed. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. The rate profile in presence of CTAB suggests a cooperative effect in the enhanced formation of the imine adduct as is commonly found in enzyme catalyzed reactions. Addition of organic sodium salts (such as benzoate, salicylate and tosylate) enhanced the rate at lower concentrations but rates start to decrease at higher concentrations. This suggests that tightly binding organic counter-anions were the most effective. Viscosity of the reaction media seems to affect the kinetic behavior in micellar media.

Chiral Plasmonic Nanochains via the Self-Assembly of Gold Nanorods and Helical Glutathione Oligomers Facilitated by Cetyltrimethylammonium Bromide Micelles.

Gold nanorods are excellent anisotropic building blocks for plasmonic chiral nanostructures. The near-infrared plasmonic band of nanorods makes them highly desirable for biomedical applications such as chiral bioimaging and sensing, in which a strong circular dichroism (CD) signal is required. Chiral assemblies of gold nanorods induced by self-associating peptides are especially attractive for this purpose as they exhibit plasmonic-enhanced chiroptical activity. Here, we showed that the presence of cetyltrimethylammonium bromide (CTAB) micelles in a gold nanorod solution promoted the self-association of l-/d-glutathione (GSH) and significantly enhanced the chirality of the resulting plasmonic nanochains. Chiroptical signals for the ensemble in the presence of CTAB micelles were 20 times greater than those obtained below the critical micelle concentration of CTAB. The strong optical activity was attributed to the formation of helical GSH oligomers in the hydrophobic core of the CTAB micelles. The helical GSH oligomers led the nanorods to assemble in a chiral, end-to-end crossed fashion. The CD signal intensities were also proportional to the fraction of nanorods in the nanochains. In addition, finite-difference time-domain simulations agreed well with the experimental extinction and CD spectra. Our work demonstrated a substantial effect from the CTAB micelles on gold nanoparticle assemblies induced by biomolecules and showed the importance of size matching between the inorganic nanobuilding blocks and the chiral molecular templates (i.e., the GSH oligomers in the present case) in order to attain strong chiroptical activities.

Liposomes Can Achieve Enantioselective C-C Bond Formation of an α-Amino Acid Derivative in Aqueous Media.

We first report that a highly enantioselective C–C bond formation reaction was achieved with liposomes in aqueous media. Alkylation of N-(diphenylmethylene)glycine tert-butyl ester (DMGBE) with benzyl bromide was conducted in the presence of cetyltrimethylammonium bromide micelles, resulting in a high conversion of DMGBE but little enantiomeric excess (e.e.) of the product. The same reaction was then carried out in 1,2-dioleoyl-sn-glycero-3-phosphocholine liposome suspensions, where the e.e. values were high (at least 90 % (S)), indicating that the liposome membranes can behave as the promoter of the enantioselective reaction. Changing the type of lipid to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine to form a more ordered bilayer membrane lowered the reaction conversion but still maintained high e.e.% , that is, >90 (S), regardless of lipid chirality. It is indicated that multiple interactions between the DMGBE intermediate and lipid molecules promoted the migration of the intermediate into the interior of the membrane, whose bottom side (Si face) could be free for alkylation. These results suggest that liposomes can promote and regulate the alkylation of amino acid derivatives.

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.

Au+-cetyltrimethylammonium bromide solution: A novel precursor for seed-mediated growth of gold nanoparticles in aqueous solution

The appropriate choice of chemical composition of a metallic precursor, which produces the basic structure units in the growth process of nanocrystals, is a high priority in the synthesis of metal-especially Au-nanoparticles. In the present work, Au seeds (prepared by the reduction of Au3+ solution with NaBH4 in the presence of cetyltrimethylammonium bromide (CTAB)) have been used to initiate the growth of Au nanoparticles from two different Au precursors. When an aqueous Au+ solution prepared in the presence of CTAB micelles was treated with ascorbic acid in the presence of the gold seeds, a high yield (up to 92%) of gold nanoparticles was obtained. By varying the volume of the seed solution with a fixed amount of Au+, we can effectively control the morphological transformation of the resulting Au nanoparticles from cubes to octahedra. When an aqueous Au3+ solution was prepared in the presence of CTAB micelles and treated with ascorbic acid in the presence of the gold seeds, smaller yields of Au nanoparticles were obtained. A preliminary growth mechanism has been proposed based on the changes induced by varying the amount of ascorbic acid and the ratio of the concentration of Au+ to the number of seeds. Open image in new window

Effect of micellar environment on charge transfer dye photophysics

Abstract This paper reports a detailed comparative study of the effect of cationic (cetyltrimethylammonium bromide (CTAB)) and non-ionic (Tweens (TW-20 and TW-80)) micelles on the ICT (intra/intermolecular charge transfer) state of 1, 8-naphthalimide (NAPMD) by using steady state and fluorescence time-resolved spectroscopy. NAPMD forms anion in aqueous solution by intermolecular charge transfer. NAPMD interacts electrostatically with the CTAB and forms complexes with the CTAB positive polar heads. This complexation causes dimerization of anionic NAPMD monomers in the ground state in the presence of CTAB micelle even at lower concentrations. Strong emission quenching inside CTAB is considered due to two factors; complexation of anionic NAPMD with CTAB and presence of bromide ion in CTAB compared to other micelles. The anionic NAPMD interacts with the non-ionic micelles by hydrogen bonding depending on the hydroxyl values of the Tween micelles, thus presenting a new approach towards solubilization of anionic dyes in non-ionic micelles. Comparing the quantum yield, quenching constant, binding constant and free energy values it is evident that anionic NAPMD solubilization is higher in non-ionic micelles than in cationic micelle. Higher adsorption is observed to take place in TW-20 compared to TW-80.

Cu2+-Induced Micellar Charge Selective Fluorescence Response of Acridine Orange: Effect of Micellar Charge, pH, and Mechanism

Photophysical properties of cationic Acridine Orange (AO) have been studied in different micellar environments [anionic SDS (sodium dodecyl sulfate), nonionic TX (TritonX-100), and cationic CTAB (cetyl trimethyl ammonium bromide)] at different pH, in the presence of a metal ion (Cu(2+)). At pH ∼ 8, addition of Cu(2+) results in AO fluorescence quenching in the presence of SDS micelle, enhancement of the same in the presence of TX micelle, and remaining unaltered in the presence of CTAB micelle. At pH ∼ 2, addition of Cu(2+) results in AO fluorescence quenching only in the presence of SDS micelle, and it remains mostly unaffected in the presence of TX and CTAB. Availability of Cu(2+) toward AO and binding of Cu(2+) with AO at the charged micellar interface are responsible for this pH-dependent Cu(2+)-mediated micellar charge selective fluorescence pattern.

Kinetic studies on the reduction of dithiazone by sulphite ions in micellar media

This study reveals the micellar effects on the rate of reduction of dithiazone, an azo compound by sulphite ions in a buffer medium of pH 7. The reduction of dithiazone was studied in absence and presence of micellar forming surfactants, Cetyl Trimethyl Ammonium Bromide (CTAB) and Sodium Dodecyl Sulphate (SDS). A 0.1 M cationic surfactant CTAB catalyses the reaction and increases the rate by five times whereas the same concentration of an anionic micelle SDS has completely inhibited the reduction reaction. The significant rate enhancement of this reaction in presence of CTAB micelles is due to the hydrophobic and electrostatic interactions between the substrate, reductant and micelles. The binding constant between the substrate and CTAB micelles has been found to be 329.3 M -1 .

Synthesis and Characterization of Truncated Triangular Silver Nanoplates

Truncated triangular silver nanoplates have been synthesized in large quantities using a solution phase method in the presence of cetyltrimethylammonium bromide micelles. The obtained particles have an average edge size of 68 nm, thickness of 24 nm, and the degree of truncation of 0.35. They are single crystals, with a (111) lattice plane as the basal plane. The aqueous solution of these particles displays a clear red color due to a strong in-plane dipole plasmon resonance peaked at 552 nm. These particles can self-assemble into chainlike nanostructures through either partial or close stacking of neighborhood nanoplates.

Micellar-catalyzed reactions of a phosphate ester: effect of the dielectric constant of the medium

The hydrolysis of p-nitrophenyl diphenyl phosphate was studied in aqueous solutions containing micelles of cetyltrimethylammonium bromide (CTAB), sodium hydroxide and various concentrations of dimethylsulfoxide (DMSO). Pseudo first-order ( k ψ) and second-order ( k 2) rate constants were determined at 15, 25 and 35°C and activation parameters were also measured. The rate profiles obtained for solutions containing 10–50% DMSO by volume exhibited clear maxima that shifted to higher concentrations of CTAB as a function of DMSO added. For solutions containing 60–80% DMSO by volume there was no maximum in the rate profile and the reaction was inhibited. Solutions containing 90% DMSO by volume exhibited much higher reaction rates and considerably more catalysis. In the absence of surfactant a linear relationship is obtained between log k ψ and the Lorentz function of the dielectric constant of the binary mixtures DMSO–H 2O. When CTAB is added to the reaction medium there are two different situations. Beyond the formation of the hydrate DMSO·2H 2O, which inhibits the CTAB micellization, the results are identical to those obtained in the systems with no surfactant. However, in presence of CTAB micelles, the linear relationship between log k ψ and f( ε) was quite different from that in the other two cases. These results show that a macroscopic property such as the dielectric constant of the medium may be used to describe the effect of DMSO on the hydrolysis rates either in absence of surfactant or when this is dissolved as the monomer, but not in the presence of micellized surfactant.

Effects of salts and mixed CH 3CN–H 2O solvents on alkaline hydrolysis of phenyl benzoate in the presence of ionic micelles

The rate of reaction of phenyl benzoate (PB) with −OH is slower in the micelles of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTABr) than in the aqueous pseudo-phase. The binding constants ( K S) of PB with SDS micelles are almost independent of [NaOH] and [NaBr] at a constant [NaOH]. A non-linear decrease and increase in K S and cmc, respectively, with increase in the contents of CH 3CN in mixed aqueous solvents is obtained under the presence of SDS micelles. The K S values increase non-linearly with increase in [KBr] at a constant [ −OH] in the presence of CTABr micelles.

Kinetics of the hydrolysis of cytotoxic pyronins in micellar systems

As part of an investigation into the biological applications of cationic dyes of the xanthene class, the micellar-enhanced kinetics of pyronin Y (PY) and B (PB) were studied in two types of enriched solution of surfactant. The alkaline hydrolysis which transforms the R + pyronin species into neutral ROH (the so-called fading of red pyronins into colourless xanthydrols) was studied in cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulphate (SDS) micelles. The critical micelle concentration (cmc) at pH7 was measured by the spectral-change technique using rhodamine 123 as the fluorescent probe. In addition, the effective cmcs of the surfactants in strong alkaline solutions (cmc CTAB , cmc SDS ) were determined using the ROH species of PY as the fluorescer. The λ Fluo, max (R + ) values were unaffected by either CTAB or SDS micellization, but the λ Fluo, max values of the ROH forms were blue shifted by CTAB and SDS micellization when compared with the values obtained in neat water solutions of similar pH. Changes in the equilibrium quotient [R + ]/ [ROH] in favour of ROH and R + respectively were observed in the presence of CTAB and SDS micelles (up to 2 pH units) with respect to p K a (S 1 )=p K a (S 0 =11.4 measured for both pyronins in water. The micelles strongly affect the kinetics of the hydrolysis. As determined by fluorometric titration, the pseudo-first-order rate constants k obs (min −1 of R + hydrolysis were substantially enhanced by the positive charges of CTAB micelles but hindered by the negative charges of SDS micelles. The hydrolysis was completely inhibited by SDS micelles when [SDS] &>; cmc SDS , but was speeded up by CTAB micelles when [CTAB]&>;cmc CTAB , as demonstrated by the three-fold higher rate measued in the presence of CTAB micelle when compared with the values obtained in neat water. These results were rationalized in terms of elecrostatic interactions between the R + substrate and the hydroxide ion reactant. The reaction was catalysed by CTAB micelles when the reactants were both concentrated in the interfacial microenvironment (the micellar pseudophase) of the micelles. Conversely, the hydrolysis was inhibited k obs =0) by anionic micelles of SDS which were depleted in OH − . According to Menger's model, the values of the hydrolysis rate constant K m in the micellar phase were obtained by plotting the variation in k obs vs . the micellized surfactant concentration [D m ]. k m (min −1 ) values were three orders of magnitude higher than the pseudo-first-order rate constant k ′2 (min −1 = k 2 [OH − ] measured in water in the same conditions of alkaline pH.

Physico-chemical studies of micelle formation on sepia cartilage collagen solutions in acetate buffer and its interaction with ionic and nonionic micelles. Hydrodynamic and thermodynamic studies.

Sepia cartilage collagen (pepsin-extracted) in acetate buffer (pH = 2.98) forms micelles at a particular concentration below which they do not normally form. The critical micelle concentration (cmc) of the collagen was determined in buffer as well as in SDS, cetyltrimethylammonium bromide (CTAB) and Tween-80 micellar environments at different temperatures. Mutual interaction of collagen micelles with the ionic and nonionic micelles through the formation of the mixed micelle concept has also been found. The cmc of collagen decreased in the presence of SDS and Tween-80 micelles whereas it increased in the presence of CTAB micelles. This clearly suggests that the micelle formation of collagen is facilitated by the presence of SDS and Tween-80 and hindered by CTAB micelles. The various thermodynamic parameters were estimated from viscosity measurements and the transfer of collagen into the micelles of various surfactants and the reverse phenomenon was analyzed. This analysis has also been modelled conceptually as a different phase and the results have supported the above phenomenon. Our thermodynamic results are also able to predict the exact denaturation temperature as well as the structural order of water in the collagen in various environments. The hydrated volumes, Vh, of collagen in the above environments and intrinsic viscosity were also calculated. The low intrinsic viscosity, [eta], of collagen in an SDS environment compared to buffer and other surfactant environments suggested more workable systems in cosmetic and dermatological skin care preparations. The one and two-hydrogen-bonded models of this collagen in various environments have been analyzed. The calculated thermodynamic parameters varied with the concentration of collagen. The change of thermodynamic parameters from coil-coil to random-coil conformation upon denaturation of collagen were calculated from the amount of proline and hydroxyproline residues and compared with viscometric results. Thermodynamic results suggest that the stability of the collagen in the additive environments is in the following order: SDS greater than Tween-80 greater than buffer greater than CTAB.

Stereoselective micellar catalysis. Part 3. Co-operative effects of N-decanoyl-L-histidine for the hydrolysis of enantiomeric substrates

The catalytic activities of N-decanoyl-L-histidine (Ia) and its methyl ester (Ib) toward the hydrolyses of enantiomeric substrates (II) have been investigated in the presence of cetyltrimethylammonium bromide micelles. The comparison of catalytic effects (both the rate constants and stereoselectivities) of (Ia) and (Ib) strongly suggests that carboxylate ion of (Ia) intramolecularly enhances the reactivity of the imidazole group. The presence of co-operative effects is also supported by the pH–rate profile and by the thermodynamic parameters of the reaction.

Co-operative effects in the catalytic action of N-decanoyl-L-histidine in micelles

A comparison of catalytic effects in the hydrolysis of the enantiomeric esters (2) by N-decanoyl-L-histidine (1a) and its methyl ester (1b) in the presence of cetyltrimethylammonium bromide micelle strongly suggests that the carboxylate ion of (1a) enhances the reactivity of the imidazole group through intramolecular hydrogen-bonding.