Cationic Micelles Of Cetyltrimethylammonium Bromide Research Articles

Solubilization of pyrene by mixed polymer-cationic/nonionic surfactant systems: Effect of polymer concentration

Polymers can be used to alter the ability of surfactant micelles to solubilize PAHs depending upon polymer–surfactant interactions. The focus of this study is to investigate the solubilization ability of the mixtures of anionic polymer sodium carboxymethyl cellulose (NaCMC) with nonionic polyoxyethylene [10] cetyl ether (Brij 56) and cationic cetyltrimethylammonium bromide (CTAB) surfactant micelles towards pyrene (PAH). Solubilization efficiency of these mixed systems and their comparison with individual systems has been quantified in terms of the molar solubilization ratio, micelle - water partition coefficient and free energy of solubilization. While the addition of anionic polymer NaCMC accelerates the solubilization capacity of cationic CTAB micelles, that of nonionic Brij56 micelles was retarded. Moreover, enhancement in the solubilization capacity of the above said mixed systems is observed as the polymer concentration changes from below overlap (i.e.; 0.5 %) to overlap (i.e.; %).

The Catalytic Influence of Polymers and Surfactants on the Rate Constants of Reaction of Maltose with Cerium (IV) in Acidic Aqueous Medium

Kinetics of the reaction of maltose with cerium ammonium sulfate were analyzed spectrophotometrically by observing the decrease of the absorbance of cerium (IV) at 385 nm in the presence and absence of polyethylene glycols (600, 1500, and 4000) and polyvinylpyrrolidone (PVP), in addition to anionic micelles of sodium dodecyl sulfate (SDS), cationic micelles of cetyltrimethylammonium bromide (CTAB) and non-ionic micelles of Tween 20 surfactants. Generally, there is little literature about using the polymers (PEGs and PVP) as catalysts in the oxidation-reduction reactions. Therefore, the major target of this work was to investigate the influence of the nature of polymers and surfactants on the oxidation rates of maltose by cerium (IV) in acidic aqueous media, as well as employing the Piszkiewicz model to explain the catalytic effect. The kinetic runs were derived by adaptation of the pseudo first-order reaction conditions with respect to the cerium (IV). The reaction was found to be first-order with respect to the oxidant and fractional-order to maltose and H2SO4. The reaction rates were enhanced in the presence of polymer and micellar catalysis. Indeed, the surfactants were found to work perfectly close to their critical micelle concentrations (CMC). Electrostatic interaction and H-bonding appear to play an influential role in binding maltose molecules to polymer/surfactant micelles, while oxidant ions remain at the periphery of the Stern layer within the micelle.

Effect of Cetyltrimethylammonium Bromide and Sodium Dodecyl Sulphate on Oxidation of Indigo Carmine with Potassium Peroxy Diphosphate: A Kinetic and Mechanistic Study

The oxidative kinetic study of Indigo carmine (IC) with potassium peroxydiphosphate (PDP) in absence and presence of cationic cetyl-trimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) micelles was studied in an aqueous sulphuric acid medium by maintaining the ionic strength at 3.0 mol dm-3 using sodium sulphate. The pseudo-zero-order constant was determined from the linear plots of absorbance versus time under the conditions [IC] < [PDP]. The reaction obeys zero-order kinetics with respect to varying [IC], first order kinetics with respect to varying [H+] and [PDP] in the absence and in presence of micelles. The reaction rate was accelerated with varying [CTAB] and [SDS] and reached a limiting value. The [surfactant] rate profile has limited nature since the reaction is unimolecular on the micelle surface. The binding constant of peroxy diphosphate was also determined with CTAB and SDS micelles by applying Berezin equation for the kinetic pattern.

Templated Mesoporous Silica Outer Shell for Controlled Silver Release of a Magnetically Recoverable and Reusable Nanocomposite for Water Disinfection.

In this work, we encapsulated Fe3O4@SiO2@Ag (MS-Ag), a bifunctional magnetic silver core-shell structure, with an outer mesoporous silica (mS) shell to form an Fe3O4@SiO2@Ag@mSiO2 (MS-Ag-mS) nanocomposite using a cationic CTAB (cetyltrimethylammonium bromide) micelle templating strategy. The mS shell acts as protection to slow down the oxidation and detachment of the AgNPs and incorporates channels to control the release of antimicrobial Ag+ ions. Results of TEM, STEM, HRSEM, EDS, BET, and FTIR showed the successful formation of the mS shells on MS-Ag aggregates 50-400 nm in size with highly uniform pores ∼4 nm in diameter that were separated by silica walls ∼2 nm thick. Additionally, the mS shell thickness was tuned to demonstrate controlled Ag+ release; an increase in shell thickness resulted in an increased path length required for Ag+ ions to travel out of the shell, reducing MS-Ag-mS' ability to inhibit E. coli growth as illustrated by the inhibition zone results. Through a shaking test, the MS-Ag-mS nanocomposite was shown to eradicate 99.99+% of a suspension of E. coli at 1 × 106 CFU/mL with a silver release of less than 0.1 ppb, well under the EPA recommendation of 0.1 ppm. This high biocidal efficiency with minimal silver leach is ascribed to the nanocomposite's mS shell surface characteristics, including having hydroxyl groups and possessing a high degree of structural periodicity at the nanoscale or "smoothness" that encourages association with bacteria and retains high Ag+ concentration on its surface and in its close proximity. Furthermore, the nanocomposite demonstrated consistent antimicrobial performance and silver release levels over multiple repeated uses (after being recovered magnetically because of the oxidation-resistant silica-coated magnetic Fe3O4 core). It also proved effective at killing all microbes from Long Island Sound surface water. The described MS-Ag-mS nanocomposite is highly synergistic, easy to prepare, and readily recoverable and reusable and offers structural tunability affecting the bioavailability of Ag+, making it excellent for water disinfection that will find wide applications.

CTAB-modified carboxymethyl cellulose/bagasse cryogels for the efficient removal of bisphenol A, methylene blue and Cr(VI) ions: Batch and column adsorption studies

The simultaneous removal of organic and inorganic pollutants from water requires multifunctional adsorbents. Cryogels of carboxymethyl cellulose (CMC) and sugarcane bagasse (BG) were modified with cetyltrimethylammonium bromide (CTAB) micelles for the adsorption of methylene blue (MB), Cr(VI) ions and bisphenol A (BPA) separately, in binary or ternary aqueous mixtures. Batch adsorption studies of MB and Cr(VI) and BPA on the CMCBG-CTAB adsorbents indicated removal capacities of 100%, 70% and 95%, respectively. MB adsorbed as multilayers on the CMCBG walls by electrostatic interaction, whereas Cr(VI) and BPA adsorbed on the cationic CTAB micelles surface and hydrophobic core of CTAB micelles, respectively. The breakthrough curves obtained for pure adsorbates and their mixtures showed that the adsorption of Cr(VI) ions increased (i) ~ 3.5 times in binary mixture with BPA or in the ternary mixture, in comparison to pure Cr(VI) solution, and (ii) 1.4 times in binary mixture with MB molecules, due to synergistic effects. In the presence of Cr(VI) ions in binary or ternary mixtures, the adsorption of MB was dramatically reduced due to screening effects. The adsorption of BPA was not significantly affected by the presence of MB or Cr(VI). The adsorbents were recycled five times without significant efficiency loss.

Micelle-Type Sensor for Saccharide Recognition by Using Boronic Acid Fluorescence Amphiphilic Probe and Surfactants

ABSTRACT Controlling molecular assembly by analytes is attractive for analytical techniques. Herein, we designed and synthesized amphiphilic boronic acid fluorescent probes (B-Nap-C8) possessing naphthaleneboronic acid as a saccharide recognition site and alkyl chain as a hydrophobic moiety. We evaluated their saccharide recognition function in relation to the fluorescent or absorption intensity changes of the assembled B-Nap-C8. Also, we evaluated the saccharide recognition function of B-Nap-C8 by the effect of co-surfactants. B-Nap-C8 forms micelles and recognizes fructose at pH 10. In the presence of surfactants, B-Nap-C8 with the cetyltrimethylammonium bromide (CTAB) micelle can recognize fructose at neutral pH. On the other hand, B-Nap-C8 with the sodium dodecyl sulfate (SDS) micelle recognizes fructose at pH > 10. This is caused by the decrease of the apparent pK a of B-Nap-C8 on the surface of the cationic CTAB micelle. The micelle formation of B-Nap-C8 with CTAB was confirmed by TEM observation, and the critical micelle concentration of B-Nap-C8 with CTAB was determined to be 1.79 mM from the CTAB titration measurements. From the saccharide titration experiments, B-Nap-C8 with CTAB micelles selectively recognizes fructose at neutral pH. The selectivity for saccharides was not observed in the saccharide titration of B-Nap-C8 with SDS. Thus, the co-surfactant systems with B-Nap-C8 were found to control the selectivity for saccharide recognition in water.

Citrus sinensis peel waste assisted synthesis of AgNPs: effect of surfactant on the nucleation and morphology

Silver nanoparticles (AgNPs) were synthesized by using Citrus sinensis peel waste extract. Optical images and UV-visible spectroscopy reveals the appearance of yellow to brown-red color and surface plasmon resonance (SPR) band at 400–480 nm, respectively, due to the formation of AgNPs. The stable perfect transparent silver sols were formed in presence of cetyltrimethylammonium bromide (CTAB). The brownish precipitates appeared with sodium dodecyl sulphate (SDS) after 3 h. The nucleation, position of SPR band and intensity depends on the head group nature of cationic and anionic micelles of SDS and CTAB. The as-prepared AgNPs were characterized using conventional techniques such as Fourier-transform infra-red, energy dispersed X-ray detector, scanning electron microscope, transmission electron microscope, and X-ray diffractometer. Zeta potential of CTAB-AgNPs was calculated and found to be stable for ca. 1 week. Molar concentration (3.3 × 10−4 mol/L) and aggregation number (607,339.917) of DPE-AgNPs were calculated. Ascorbic acid, citric acid and total reducing sugars were estimated in dry and fresh peel extract. Gram positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria shows excellent antibacterial activities toward DPE-AgNPs.

Potentiometric studies of complex equlibria of CaII, MgII and ZnII with 5-sulphosalicylic acid in cationic micelles of CTAB

Formation of metal ligand complex species of 5-sulphosalicylic acid with CaII, MgII and ZnII metal ions have been studied potentiometrically in various composition (0.0, 0.5, 1.0. 1.5, 2.0, and 2.5% w/v) of cetyltrimethylammonium bromide (CTAB). The study has been carried out at 303 K temperature and maintaining 0.16 mol dm−3 ionic strength using NaCl. The dynamic species belongs to 5-sulphosalicylic acid are LH2- and LH2-. The best fit of complex speciation has been preferred on basis of statistical parameters like skewness, χ2, Kurtosis and crystallographic R-factor. ML2H, ML2H2 and ML3H3 type complex were formed by the complexation of 5-sulphosalicylic acid with the metal ions. The change in stability of complex species with composition of the surfactant has been illustrated on the basis electrostatic grounds. Distribution of chemical species with respect to pH and various compositions medium and probable complex equilibria are also studied.

Interaction of Tyrosine Analogues with Quaternary Ammonium Head Groups at the Micelle/Water Interface and Contrasting Effect of Molecular Folding on the Hydrophobic Outcome and End-Cap Geometry.

The surface property of the cationic micelles of cetyltrimethylammonium bromide (CTAB) in an aqueous medium is highly modified in the presence of tyrosineoctyl ester (TYOE) and tyrosinedodecyl ester (TYDE), the models for aromatic amino acid side chains of transmembrane proteins. While the synergistic interaction between the quaternary ammonium head group of CTAB and the π-electron cloud of aromatic amino acid ester is influenced by the relative orientation and the unusual molecular geometry of the latter, this eventually triggers a morphology transition of the spherical micelle to cylindrical/wormlike micelles and imparts a strong viscoelasticity in the medium. Physical characteristics of the elongated micelles have been investigated by high resolution transmission electron microscopy (HRTEM) and the small angle neutron scattering (SANS) technique; the complex fluidic nature of the system is investigated by a dynamic rheological measurement. The intermolecular interactions have been recognized via 1H NMR and 2D nuclear Overhauser effect spectroscopy (NOESY), and the unambiguous geometry of the end-caps of the rods has been ascertained for the first time. While the interplay between lipids and transmembrane proteins is thought to be crucial in controlling the membrane shape of the cells during many vital events such as cellular fission, fusion, and virus entry, the observed tuning of the micellar surface curvature via the cation-π interaction involving tyrosine analogues is thought provoking and opens up an avenue for new physical chemistry research on a vital biological phenomena.

Conductometric and fluorescence probe analysis on molecular interactions between cationic surfactants in aqueous medium of glycyl dipeptide: Concentration and temperature effect

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) on interactions of glycyl dipeptide in aqueous medium have been studied in varying concentrations (0.001, 0.005 and 0.010mol·kg–1) at different temperatures (293.15K to 293.15K). The conductivity method has been employed to determine critical micelle concentration, CMC i.e. point of aggregation and the results have been discussed in terms of glycylglycine–CTAB/DTAB hydrophobic and electrostatic interactions in aqueous medium. The obtained CMC values reveal the fact that the micellization tendency of the surfactant increases in the presence of glycyl dipeptide. The CMC’s of CTAB and DTAB have been found to decrease from 0.87 to 0.66mmol·kg–1 and 14.2–13.7mmol·kg–1 respectively as the [Glycyl dipeptide] increased from 0.001 to 0.010mol·kg–1. The temperature dependence of the CMC values has been established in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions around the hydrophobic part of surfactants. Furthermore, the standard thermodynamic parameters of micellization have been evaluated and interpreted which enable to grasp fully the ion–ion/ion–hydrophilic interactions existing in the present ternary (surfactant–dipeptide–water) system. In addition, the pyrene fluorescence technique has been used to study the change of micropolarity produced by the interactions of surfactants with glycyl dipeptide and the aggregation behaviour (CMC determination) of surfactants.

Zinc(II) Ion Sensing in Aqueous Micellar Solution Using Modified Bipyridine-Based "Turn-On" Fluorescent Probes and its Application in Bioimaging.

The bipyridine-based constructs 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) and [6-(3H-pyrrolo[2,3-c]quinolin-4-yl)pyridin-2-yl]methanol (PPQ-OH) and their assemblies with surfactants are evaluated as turn-on fluorescent sensors for Zn2+ ions in aqueous solution. This study strives to overcome the problem of low water solubility of the hydrophobic PPQ and PPQ-OH by using micelles. Whereas the ligands show selective sensing behavior for Zn2+ over important biological cations including Na+ , K+ , Ca2+ , Mg2+ in anionic sodium dodecyl sulfate and non-ionic Tween 80 micelles, no Zn2+ sensing is observed in cationic cetyltrimethylammonium bromide micelles. Unlike in DMF, Cd2+ interference is observed in aqueous conditions, which can be avoided either by performing the study at pH≥9 or by carrying out a time-resolved fluorescence study. Analysis of the Job plot data, the fluorescence lifetimes, and experiments on varying micellar shape and pH, confirms that the coordination volume of the resulting octahedral metal complex and formation of a five-membered chelate ring are critical factors for Cd2+ interference. The described sensing systems are capable of detecting Zn2+ ions at the micromolar level. Additionally, it is shown that PPQ and PPQ-OH can be used to detect Zn2+ in HeLa cells under physiological conditions in bioimaging studies.

Micelle Catalyzed Oxidative Degradation of Paracetamol by Water Soluble Colloidal MnO2 in Acidic Medium

AbstractThe catalytic effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the MnO2-paracetamol (PCM) redox reaction has been examined spectrophotometrically in acidic medium at 298 K. The reaction demonstrates that the stoichiometric ratio of MnO2 and PCM is 1 : 1. The reaction exhibited first order kinetics with respect to [MnO2] and [PCM] but a negative fractional order was observed with respect to [H2SO4]. Various effects such as ionic strength, dielectric constant, [Mn(II)], [salts] and temperature have been studied. The catalytic effect of CTAB has been treated quantitatively by the well known Menger Portnoy and Piszkiewicz model. The values of binding constant (Ks), rate constant in the micellar phase (km), cooperativity index (n) and dissociation constant (KD) have also been calculated. From the several observations, a reaction mechanism has been proposed and the rate law has been derived. Applying the Arrhenius equation, various thermodynamic activation parameters have also been evaluated.

Effect of Surfactants on Hydrolysis of Mono-N-ethyl-o-toluidine Phosphate

AbstractHydrolysis of phosphate ester (Mono-N-ethyl-o-toluidine phosphate) in the presence of different surfactants has been studied at 303 K. The rate of reaction has been found to be first-order and fractional order kinetics with respect to [substrate] and [HCl] respectively. The cationic micelles of cetyltrimethylammonium bromide (CTAB), anionic micelles of sodium dodecyl sulfate (SDS) and nonionic micelles of Brij-35 enhanced the rate of reaction to a maximum value and thereafter, the increase in concentration of surfactant decreased the reaction rate. The rate of reaction increased with increase of dielectric constant of the medium. The variation in the rate of hydrolysis by micelles was treated by considering the Menger-Portnoy, Piszkiewicz's and Berezin kinetic models. The various thermodynamic parameters have also been evaluated. The added salts viz KCl, KNO3, K2SO4 enhanced the rate of reaction in the presence of cationic, anionic and non-ionic micelles. The kinetic parameters i. e. micellar phase (kΨ) and binding constant (KS) were determined from the rate (surfactant) profile.

Solubilization of octane in cationic surfactant–anionic polymer complexes: Effect of ionic strength

Polymers may alter the ability of oppositely charged surfactant micelles to solubilize hydrophobic molecules depending on surfactant–polymer interactions. This study was conducted to investigate the effect of ionic strength on the solubilization thermodynamics of an octane oil-in-water emulsion in mixtures of an anionic polymer (carboxymethyl cellulose) and cationic cetyltrimethylammonium bromide (CTAB) surfactant micelles using isothermal titration calorimetry (ITC). Results indicated that the CTAB binding capacity of carboxymethyl cellulose increased with increasing NaCl concentrations up to 100mM, and the thermodynamic behavior of octane solubilization in CTAB micelles, either in the absence or presence of polymer, was found to have a strong dependence on ionic strength. The increasing ionic strength caused the solubilization in CTAB micelles to be less endothermic or even exothermic, but increased the solubilization capacity. Based on the phase separation model, the solubilization was suggested to be driven by enthalpy. It is indicated that increasing ionic strength gave rise to a larger Gibbs energy decrease but a smaller unfavorable entropy increase for octane solubilization in cationic surfactant micelles.

Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media

The applicability of cellulose acetate membranes (CAMs) as a solid matrix for the luminescence determination of pyrene in aqueous micellar solutions is shown. The effect of the concentrations of various surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic polyoxyethylene (10) mono-4-isooctyl phenyl ether (TX-100), on the fluorescence of pyrene in aqueous micellar solutions before and after sorption preconcentration and in an adsorbed state on a CAM has been studied. It has been found that the fluorescence intensity of pyrene on the solid-phase matrix increases as a result of pyrene solubilization in surfactant hemimiceles formed on the sorbent surface. The highest degree of pyrene extraction on CAMs has been achieved in the presence of cationic CTAB micelles. The CAM has a negative surface potential (−31.5 ± 2.5 mV), which affects the hydrocarbon recovery. The degree of extractlion and the polarity index of a microenvironment of pyrene molecules in solutions decrease in the order CTAB → SDS → TX-100.

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.

Solubilization of octane in cationic surfactant–anionic polymer complexes: Effect of polymer concentration and temperature

Polymers may alter the ability of oppositely charged surfactant micelles to solubilize hydrophobic molecules depending on surfactant–polymer interactions. This study was conducted to investigate the effects of polymer concentration and temperature on the solubilization thermodynamics of an octane oil-in-water emulsion in mixtures of an anionic polymer (carboxymethyl cellulose) and cationic cetyltrimethylammonium bromide (CTAB) surfactant micelles using isothermal titration calorimetry (ITC). Results showed that the CTAB binding capacity of carboxymethyl cellulose increased with increasing temperature from 301 to 323K, and correspondingly the thermodynamic behavior of octane solubilization in CTAB micelles, either in the absence or presence of polymer, was found to depend on temperature. The addition of carboxymethyl cellulose caused the solubilization in CTAB micelles to be less endothermic, and increased the solubilization capacity. Based on the phase separation model, the solubilization was suggested to be mainly driven by enthalpy gains. Results suggest that increasing concentrations of the anionic polymer gave rise to a larger Gibbs energy decrease and a larger unfavorable entropy increase for octane solubilization in cationic surfactant micelles.

Micellar Effects upon the Alkaline Hydrolysis of Acetaminophen Prodrugs: Carboxylic and Carbonic Acid Esters

The rates of alkaline hydrolysis for four carboxylate esters (4-acetaminophenyl acetate, 4-acetaminophenyl butyrate, 4-acetaminophenyl heptanoate and 4-acetaminophenyl benzoate) and three carbonate ester (4-acetaminophenyl methylcarbonate, 4-acetaminophenyl ethylcarbonates and 4-acetaminophenyl propylcarbonates) prodrugs of acetaminophen derivatives were determined in aqueous and micellar media. The cationic micelles of cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium sulfate [(CTA)2SO4] catalyzed the rate of the reaction. The anionic sodium dodecyl sulphate (SDS) and non-ionic Brij-35 surfactants inhibited the rate of the reaction. Added salt did not influence the rate of the reaction in the aqueous medium but decreased the values of observed rate constant in the micellar media. The rate enhancement in cationic micelles was treated by applying the pseudophase ion exchange model while the inhibition effect on the rate of hydrolysis was described using the Poisson–Boltzman pseudophase model. The binding constant (K s ) for the acetaminophen derivatives increased with increasing hydrocarbon chain length while the values of micellar rate constant (k m ) decreased with the increase in chain length. The increase in values of K s and decrease in k m are ascribed to the hydrophobic interaction between the acetaminophen derivative and surfactant molecule and molecular orientation of the substrate in the micelles.

Interaction of the antibiotic norfloxacin with ionic micelles: pH-dependent binding.

The interaction of the antimicrobial drug norfloxacin (NFX) with anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) micelles was studied using the intrinsic spectroscopic properties of NFX to obtain association constants and molecular modifications. Nonionic Tween(®) 20 micelles were also investigated, but the spectroscopic properties of NFX did not detect interactions with these micelles, and quenching by iodide suggested a weak association constant around 47M(-1). For SDS and CTAB, UV-Vis absorption spectroscopy, steady-state and time-resolved fluorometry were monitored as a function of surfactant concentration ranging from the premicellar to micellar region. It was found that cationic (pH 4.0) and zwitterionic NFX (pH 7.4) associate with SDS micelles, with binding constants equal to 5.4×10(3) and 1.7×10(3) M(-1), respectively. Premicellar interaction slightly decreases the critical micelle concentration of SDS. Association of anionic NFX (pH 10.6) is very weak. The fluorescence spectrum and lifetime showed that SDS-associated NFX is cationic and that the heterocycle penetrates the interfacial environment of decreased polarity. Cationic CTAB micelles do not bind cationic NFX, and the association constant with zwitterionic NFX is two orders of magnitude lower than that of SDS micelles. From a pharmacological point of view, it is important that at neutral pH, NFX presented a two orders of magnitude higher affinity for anionic than for cationic sites, and did not interact significantly with nonionic or zwitterionic micelle interfaces.

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.