Cationic Micelles Of Cetyltrimethylammonium Bromide Research Articles

Micellar effect upon the rate of alkaline hydrolysis of carboxylic and carbonate esters

The alkaline hydrolysis of carboxylate (1-naphthylbutyrate) and carbonate esters (2-(methylsulfonyl)-ethyl-4-nitrophenylcarbonate) in the presence of different surfactants has been studied. The rate of hydrolysis of these esters was determined under pseudo first order condition in which the concentration of NaOH was kept in large excess over the [ester]. The cationic micelles of cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium sulfate ((CTA)2SO4) enhanced the rate of hydrolysis of esters to a maximum value and thereafter, the increasing concentration of surfactant decreased the reaction rate. The anionic micelles of sodium dodecyl sulfate (SDS) inhibited the rate of the hydrolysis. The reaction proceeds through the attack of OH− ions on the carbonyl carbon forming tetrahedral intermediate. The tetrahedral intermediate is unstable and collapses immediately to yield respective acid and alcohol. The micelles influence the stability of tetrahedral intermediate, in turn, altering the rate of hydrolysis. The variation in the rate of hydrolysis by micelles was treated by considering the pseudophase ion-exchange model and Menger–Portnoy model. The added salts viz. NaBr, NaCl, and LiCl inhibited the rate of the reaction in the presence of cationic and anionic micelles. The kinetic parameters i.e. km and Ks were determined from the rate–[surfactant] profile.

Spectroscopic studies of micelle-enhanced ligand exchange of gallium (III)/4-(2-pyridylazo) resorcinol complex by calf thymus DNA

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of gallium (III) with 4-(2-pyridylazo) resorcinol (PAR) under varying conditions has been studied spectrophotometrically. At pH 6.0, CTAB (0.05% w/v) markedly enhanced the absorption intensity of gallium (III)-PAR complex. Furthermore, the introduction of CTAB provided unique selectivity for the ligand exchange of Ga(III)-PAR by calf thymus dsDNA over calf thymus ssDNA. This phenomenon offers a novel spectrophotometric sensing strategy for direct detection of dsDNA.

Spectroscopic probing of the microenvironment of 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one in ionic and nonionic micelles

• Modulation of photophysics in different micellar assembly. • Rotational behavior in confined media. • Dramatic enhancement of the PCM fluorescence in the CTAB micelles upon addition of quencher. • Ion exchange phenomenon operative at the micelle surface. • Development of highly polarity sensitive fluorescence molecular probe. Entrapping of a drug molecule having prospective therapeutic activity in microhetrogeneous environments and modulating important photophysical properties is of immense importance in various potential applications. The photophysical properties of a newly synthesized bioactive 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM) has been studied in micellar solutions of anionic sodium dodecyl sulfate (SDS), cationic cetyl trimethyl ammonium bromide (CTAB) and nonionic p-tert-octylphenoxy polyoxyethanol (TX-100) micelle using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The present effort illustrates the degree of accessibility of the fluorophore toward the heavy ion quencher in the presence of micelles of different surface charge characteristics. Iodide induced quenching leads to a decrease in the fluorescence intensity in case of SDS and TX-100 micelles, where as in CTAB micelles enhancement of fluorescence intensity is observed. Quantitative estimation of the micropolarity at the binding site of the probe has been determined. The imposed motional restriction of the microenvironment around the probe has been established from environment dependent fluorescence parameter, fluorescence anisotropy ( r ) value.

CATALYTIC ACTIVITY OF CETYLTRIMETHYLAMMONIUM BROMIDE (CTAB) IN THE REACTION OF NINHYDRIN AND ZINC GLYCYLTYROSINE COMPLEX

The kinetics of interaction between ninhydrin and zinc-dipeptide (glycyl-tyrosine), [Zn(II)-Gly-Tyr] + complex have been studied in aqueous and in micelles formed by the cationic surface active material, cetyltrimethylammonium bromide (CTAB) at 80 °C and pH 5.0. The reaction follows first- and fractional- order kinetics with respect to [Zn(II)-Gly-Tyr] + and [ninhydrin], respectively, both in the absence and presence of cationic CTAB micelles. The catalytic role of [CTAB] can be related to the extent of incorporation or association of the [Zn(II)-Gly-Tyr] + complex and ninhydrin into the micelles. CTAB micelles decrease the activation enthalpy and make the activation entropy less negative. The micellar catalysis is explained in terms of the pseudo-phase model of the micelles. Binding constants K S for [Zn(II)-Gly-Tyr] + and K N for ninhydrin with micelles are calculated with the help of observed kinetic data.

Kinetics of Cetyltrimethylammonium Bromide Catalysed Oxidation of Cyclopentanone by N-Bromophthalimide in Acidic Medium

Abstract The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulphate (SDS) on the kinetics of oxidation of cyclopentanone by N-bromophthalimide (NBP) was studied iodometrically at 308 K. In addition to the kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties. The kinetic observations indicate fractional order and first order dependence with respect to [cyclopentanone] and [NBP] respectively. Cationic surfactant (CTAB) strongly catalyses the oxidation of Cyclopentanone in aqueous acetic acid medium. Typical kobs and [CTAB] profile were observed i. e. with the progressive increase in [CTAB], the reaction rate increased and at higher concentration of CTAB, constancy in kobs was observed. Anionic surfactant (sodium dodecylsulphate, SDS), mercuric acetate and phthalimide did not influence the reaction rate. The presence of inorganic salts (KCl, KBr) exhibits a severe hike in the reaction rate. The various activation parameters in the presence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed.

Effect of interaction with micelles on the excited-state optical properties of zinc porphyrins and J-aggregates formation

This work reports on the photophysical properties of zinc porphyrins meso-tetrakis methylpyridiniumyl (Zn2+TMPyP) and meso-tetrakis sulfonatophenyl (Zn2+TPPS) in homogeneous aqueous solutions and in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The excited-state dynamic was investigated with the Z-scan technique, UV–Vis absorption, and fluorescence spectroscopy. Photophysical parameters were obtained by analyzing the experimental data with a conventional five-energy-level diagram. The interaction of the charged side porphyrin groups with oppositely charged surfactants can reduce the electrostatic repulsion between porphyrin molecules leading to aggregation, which affected the porphyrin characteristics such as absorption cross-sections, lifetimes and quantum yields. The interaction between anionic ZnTPPS with cationic CTAB micelles induced the formation of porphyrin J-aggregates, while this effect was not observed in the interaction of ZnTMPyP with SDS micelles. This difference is, probably, due to the difference in electrostatic repulsion between the porphyrin molecules. The insights obtained by these results are important for the understanding of the photophysical behavior of porphyrins, regarding potential applications in pharmacokinetics as encapsulation of photosensitizer for drug delivery systems and in its interaction with cellular membrane.

Micellar catalysis of oxidation of glycolic acid by N-bromophthalimide

Catalysis of oxidation of glycolic acid by N-bromophthalimide by micelles of cetyltrimethylammonium bromide (CTAB) at 318 K was investigated. The observed value of critical micelle concentration of CTAB in the presence of other components was lower than those reported in the literature. The oxidation reaction was strongly catalyzed by cationic micelles of CTAB. The reaction rate increased with CTAB concentration until the steady state was achieved. The reaction kinetics corresponded to first, fractional and inverse fiactional orders with respect to changes of concentration of reaction components. Effects of solvent, phthalimide, mercuric acetate, and potassium chloride on the reaction kinetics were also studied. The micelle-catalyzed oxidation reaction was shown to fit Arrhenius equation. The experimental data were rationalized in terms of Menger-Portnoy model considering a distribution of the reactants between the micellar and aqueous phases.

Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Oxalic Acid by N-Bromophthalimide in Acidic Medium

The kinetics of micellar catalyzed oxidation of oxalic acid [OA] by N-bromophthalimide was studied in the presence of perchloric acid at 308 K. The orders of reaction with respect to [Oxalic acid], [oxidant], and [H+] were found to be fractional, first and negative fractional order respectively. Cationic micelles of cetyltrimethylammonium bromide increased the reaction rate. The effect of phthalimide, mercuric acetate and inorganic salts, that is, [Cl−][Br−] has also been done. The rate reaction decreases with increasing dielectric constant of the medium. The results are treated quantitatively in terms of Piszkiewicz and Berezin models. The rate constant (Kobs), cooperatively index (n), binding constant (ks + ko), and corresponding activation parameters (Ea, ΔH#, ΔS#, and ΔG#) were determined. A suitable mechanism consistent with the experimental finding has been proposed.

Micelle catalyzed oxidative degradation of norfloxacin by chloramine-T

Present work reports influence of micellar media (CTAB) upon the oxidative degradation of fluoroquinolone family drug norfloxacin (NOR). The reaction has been studied at constant temperature (308K). The stoichiometry of the reaction was found to be 1:4 and oxidation products were identified by LC–MS technique and other spectral studies. The reaction exhibited first-order-dependence on chloramine-T [CAT] and fractional-order dependence on [NOR]. The rate constant was independent of cationic micelles of cetyltrimethylammonium bromide [CTAB] at lower concentrations followed by a rapid increase in rate constant to a maximum and further gradual decrease in rate constant at higher CTAB was observed. In the presence of CTAB, both the oxidant and substrate are distributed between the aqueous and the micellar pseudo phases and then react to give the product. Compensation between water structure destruction and substrate–micelle interaction plays an important role in the presence of CTAB. The rate constants were obtained and the applicability of Piszkiewicz's, Raghvan–Srinivasan's and pseudo phase models allowed us to obtain the reactivity constants in the aqueous pseudo phase and in the micellar pseudo phase (k2w and k2m) and the binding constants of the reactants to the micellar phase (K1, K2). The effects of inorganic salts i.e. [SO42−], [HSO4−], [Cl−] and [Br−] on reaction rate have also been studied.

Influence of polymer–surfactant aggregates on fluid flow

This paper describes the influence of interactions of poly(ethylene oxide) (PEO) with cationic cetyltrimethylammonium bromide (CTAB) micelles on drag reduction. Since the interactions between PEO and CTAB micelles alone are weak, salicylate ions were used as CTAB counterions. They facilitate formation of polymer–micelle aggregates by screening the electrostatic repulsions between the charged surfactant headgroups. The influence of polymer–surfactant interactions on drag reduction is of biomedical engineering importance. Drag reducing additives introduced to blood produce beneficial effects on blood circulation, representing a novel way to treat cardiovascular disorders. PEO is a blood-compatible polymer. However, it quickly mechanically degrades when subjected to high shear stresses. Thus, there is a need to search for other additives able to reduce drag, which would be more mechanically stable, e.g. polymer–surfactant aggregates. Numerical simulations of the flow were performed using the CFX software. Based on the internal structure of the polymer–surfactant solution, a hypothesis explaining the reason of increase of drag reduction and decrease in dynamic viscosity with increasing shear rate was proposed. It was suggested that the probable reason for the abrupt increase in friction factor, observed when the critical Reynolds number was exceeded, was the disappearance of the difference in the dynamic viscosity.

Catalytic effect of CTAB on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70°C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70×10−3moldm−3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca. 3. Quantitative kinetic analysis of kψ−[CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants KS (268mol−1dm3 for Gly-Tyr) and KN (64mol−1dm3 for ninhydrin).

Quantitative analysis of cationic micelle catalyzed hydrolysis of methyl violet

The kinetics of the decolorization reaction of methyl violet dye (MV) with the hydroxyl ion (nucleophile) was studied in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). The reaction follows pseudo-first order kinetics. The rate constant depends on the surfactant concentration. CTAB micelles catalyze the overall reaction between the dye carbocation and the nucleophile. Quantitative analysis of the micellar data obtained has been done by applying positive cooperativity model of enzyme catalysis. For the dye under study, the value of n (index of cooperativity) has been found to be greater than 1. The catalytic effect has been explained in terms of hydrophobic and electrostatic interactions of various species present in the reaction systems. The addition of a counterion showed inhibitory effect on the reaction.

Photoionization and Time-Dependent Stokes Shift of Coumarin 307 in Soft Matter: Solvation and Radical-Ion Pair Recombination Dynamics

Photoionization, fluorescence time-dependent Stokes shift (TDSS), and rotational dynamics of coumarin 307 (C307) have been investigated in soft matter system such as micelles using time-resolved transient absorption and fluorescence spectroscopy. Photoionization of C307 leads to the formation of coumarin radical cation and hydrated electron, which were characterized by their respective transient absorption. The photoionization yields are significantly higher in anionic sodium dodecyl sulfate (SDS) micelle than in cationic cetyltrimethylammonium bromide (CTAB) and neutral Triton X-100 (TX-100) micelles, indicating the influence of micellar surface charge on the efficient separation of radical cation-hydrated electron pair. The CTAB micelle favors the recombination of radical cation and hydrated electron leading to the formation of triplet state of C307, which causes a decrease in the photoionization yield. C307 exhibits TDSS in all micelles; the time evolution and the magnitude of the TDSS depend on nature of the micelle. In TX-100 micelles, the decay of the TDSS exhibits ultraslow component (165 ns) and is affected by the presence of electron scavengers. The ultraslow component in TX-100 micelle originates from the recombination of radical cation-hydrated electron, which results in the formation of twisted intramolecular charge transfer (TICT) state; such formation of TICT state was not observed in SDS and CTAB micelles. To the best of our knowledge, this is the first report where the radical-ion pair recombination dynamics is probed using TDSS in combination with time-resolved transient absorption studies. The activation energy for the solvent relaxation and radical-ion pair (solvent separated) recombination process was found to be 6.1 and 3.0 kcal mol(-1), respectively. Temperature effect on TDSS in TX-100 micelles confirmed the increase in the water hydration, and size of the micelle influences the relative contribution of the solvation and radical-ion pair recombination dynamics toward the total TDSS. We propose that TDSS observed in neutral micelles and reported in other biomolecules such as proteins by the 7-amino coumarin probe is not only due to the solvation dynamics alone but also due to the radical-ion pair recombination dynamics.

Micelles-Assisted Oxidation of Isoleucine: A Kinetic Study

The title reaction has been studied spectrophotometrically as a function of [], [isoleucine], [H2SO4], and temperature in absence and presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). Under pseudo-first order conditions, the reaction follows first order kinetics with respect [isoleucine]. At lower values of [CTAB] (≤40.0 × 10−4 mol dm−3), the catalytic effect of cationic micelles of CTAB may be due to the incorporation/solubilization of isoleucine and into the interfacial region of Stern- and palisade layer.In contrast, at higher values of [CTAB] (≥40.0 × 10−4 mol dm−3), the inhibitory effect was observed due to the dilution.Thermodynamic parameters were computed by studying the reactions at different temperatures (303–333 K). Plausible mechanisms are suggested.

Effect of Cetyltrimethylammonium Bromide on the Oxidation of Phthalic Acid by in Aqueous Medium

The conventional ultraviolet-visible (UV)-visible spectrophotometric technique was used to monitor the kinetics of the oxidation of phthalic acid by permanganate in absence and presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). Under pseudo-first order conditions ([phthalic acid] ≥ ), the oxidation kinetics follows a complicate reaction path (the reaction rate decreases monotonically with [phthalic acid] which suggest the formation of more than one permanganate- phthalic acid complexes, out of these one of the complex has resistance toward the oxidative cleavage). The micellar catalysis is attributed to the formation of ion-pair between CTAB sub-aggregates and reactants as well as increase in the concentration (solubilization) of both reactants and/or intermediate in the micellar pseudo phase. The changes observed in the direction of the rate constants-[H+] profile correspond to the acid catalyses. The catalytic effect of CTAB may be due to the solubilization and incorporation of both the reactants into the Stern layer of the micelles and results have discussed in terms of pseudo-phase model of the micelles proposed by Menger and Portnoy and modified by Bunton et al. Mechanisms consistent with the observed kinetic data have been proposed. The effects of electrolytes, MnCl2, NaF, NaBr, and NaNO3, have also been studied and discussed. On the bases of observed results, a suitable mechanism has been proposed.

Enhancing fluorescence intensity of Ellagic acid in Borax–HCl–CTAB micelles

Ellagic acid (C 14H 6O 8), a naturally occurring phytochemical, found mainly in berries and some nuts, has anticarcinogenic and antioxidant properties. It is found that fluorescence of Ellagic acid (EA) is greatly enhanced by micelle of cetyltrimethylammonium bromide (CTAB) surfactant. Based on this effect, a sensitive proposed fluorimetric method was applied for the determination of Ellagic acid in aqueous solution. In the Borax–HCl buffer, the fluorescence intensity of Ellagic acid in the presence of CTAB is proportional to the concentration of Ellagic acid in range from 8.0 × 10 −10 to 4.0 × 10 −5 mol L −1; and the detection limits are 3.2 × 10 −10 mol L −1 and 5.9 × 10 −10 mol L −1 excited at 266 nm and 388 nm, respectively. The actual samples of pomegranate rinds are simply manipulated and satisfactorily determined. The interaction mechanism studies argue that the negative EA–Borax complex is formed and solubilized in the cationic surfactant CTAB micelle in this system. The fluorescence intensity of EA enhances because the CTAB micelle provides a hydrophobic microenvironment for EA–Borax complex, which can prevent collision with water molecules and decrease the energy loss of EA–Borax complex.

Micellar and salt kinetic effects upon the reaction [formula omitted

Conventional UV–visible spectrophotometric technique was used to study the kinetics of oxidation of ethylenediaminetetraacetic acid (EDTA) in presence and absence of cationic micelles of cetyltrimethylammonium bromide (CTAB) by MnO4- in alkaline medium. The reaction follows first-order kinetics with respect to each [MnO4-] and [OH-] in both media. The plots of log absorbance versus time clearly indicate that the oxidation process has an induction period followed by autoacceleration (sigmoid behaviour). The extent of the induction period depends on the experimental conditions. The rate constants increase with increasing [CTAB]. The observed catalytic effect has been discussed in terms of the incorporation/association/solublization of MnO4-, reactive species of EDTA and OH- into the Stern layer by using Menger–Portnoy model. The presence of NaCl and NaBr inhibits the reaction rate due to the exclusion of reactant from the Stern layer. On the bases of the observed results, the mechanism has been proposed and discussed.

Effect of cationic micelles of cetyltrimethylammonium bromide on the MnO 4− oxidation of valine

In this paper we report the effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) in the oxidation of valine by permanganate in the absence and presence of sulphuric acid media. The reaction follows fractional- and first-order kinetics with respect to [valine] and [H 2SO 4] in the presence of CTAB whereas [H 2SO 4] has no effect on the reaction rate in the absence of CTAB under our experimental conditions. The observed catalytic effect of CTAB is discussed in terms of penetration of non-polar side chain of valine into the palisade layer of CTAB micelles through hydrophobic interactions. The Menger and Portony model of micelles and the model modified by Bunton's group have been used to explain the catalytic role of CTAB. On the basis of various observations, the most plausible mechanism is proposed and discussed.

Effect of ionic micellar medium on kinetics and mechanism of oxidation of bovine serum albumin: A pulse radiolysis study

Effect of protein–micelle interaction on bovine serum albumin (BSA) oxidation by trichloromethyl peroxyl radical (CCl 3O 2 · ) in anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethyl ammonium bromide (CTAB) micellar media has been studied using nanosecond pulse radiolysis technique. Viscosity measurement and light scattering studies have suggested that SDS and CTAB micelles produce BSA–micelle aggregates of different sizes and polydispersity. Oxidation kinetics and transients have been affected both by anionic SDS and cationic CTAB micelles but in a different manner. Tryptophanyl-CCl 3O 2 · adduct radical to tyrosyl radical transformation in BSA has been observed in anionic SDS micelles but not in cationic CTAB micelles. Similar studies have also been done with tryptophan and tyrosine amino acids, which undergo oxidation in BSA. The study suggests that Coulombic and hydrophobic interactions between micelles and protein affect the structure of the protein to shield its functional amino acids, like tryptophan and tyrosine, to neutral oxidizing radical.

Micellar and Solvent Effects on the Rate of Reaction Between L-Tyrosine and Ninhydrin

Kinetics of the reaction of L-tyrosine and ninhydrin has been studied spectrophotometrically at pH = 5.0 and temperature 80°C in aqueous, aqueous-organic and aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The product formed in all the media remains the same. Also, the reaction is catalyzed in both organic solvent and CTAB micellar media. The results obtained in micellar media are treated quantitatively in terms of pseudo-phase model. The rate constants and binding constants with the micelles have been evaluated.