Cetyltrimethylammonium Halide Research Articles

A study of the underpotential deposition of copper on cetyltrimethylammonium halides covering gold nanoparticle thin films

This study presents a novel method for the synthesis of self-assembled cationic surfactants covering gold nanoparticle thin films and determines the underpotential deposition behavior of copper on such films. Based upon the solid–liquid interface penetration of copper ions through a self-assembled molecular layer, the variations in oxidation–reduction potential and the amount of copper ion desorption are determined, using cyclic voltammetry and linear sweep voltammetry analysis. The influence of various capping agents, cetyltrimethylammonium fluoride (CTAF), cetyltrimethylammonium chloride (CTAC), and cetyltrimethylammonium bromide (CTAB), on gold substrates is also determined. The blocking capabilities of surfactants that hinder ion penetration from the solution to the Au surface, through bilayers, are in the order: CTAB ≥ CTAC > CTAF.

Determination of selected cetyltrimethylammonium halide parameters by molecular modeling. Study of their adsorption on montmorillonite

There are new chemical substances that increase the strength of washing products such as surfactants. However, these products are not biodegradable and can all be found in surface water, groundwater. Cationic surfactants are one of the pollutants of greatest danger to man is his environment. Therefore, we have determined some parameters of three cationic surfactants by molecular modeling, using the CHEM 3D bio. We, therefore, optimized geometries and minimized the energy of cetyltrimethylammonium chloride (CTAC), the cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium iodide (CTAI) by molecular mechanics. we calculated the size of these molecules and their molecular partition coefficients and their ovalities using molecular dynamics. The results showed that the three pollutants are adsorbed on Mt (natural), Mt (Mg) and Mt (Ca) and are not adsorbed on Mt (Na). Mt (K) can adsorb only CTAC. The values of the partition coefficient of the three surfactants are equal to unity. The cationic surfactants studied are highly hydrophilic and spend very little through a membrane. Al so, these values showed that these surfactants are much more soluble in water than in octanol. Both surfactants, CTAB and CTAI have the highest ovality values. They can therefore more easily approach a spheric or cylindric form. CTAC has the lowest ovality, it presents more difficulty to approach a spherical or cylindrical shape.

Temporal evolution of composition and crystal structure of cobalt hexacyanoferrate nano-polymers synthesized in reversed micelles

Nanometer-size metal coordination polymers are fascinating to explore, since their unique properties are controlled by a large ratio of surface atoms, which is an entirely different effect from that in a bulk crystal. In this report, we have demonstrated the reaction time-induced structural conversion of nanometer-sized metal coordination nano-polymers (MCNPs). The MCNP selected here was a Prussian blue analogue, cobalt hexacyanoferrate (Fe-CN-Co) with ca. 3 nm. When Fe-CN-Co MCNPs were synthesized in reverse micelles of cationic surfactants, cetyltrimethylammonium halides [CTAX, X = B (bromide), C (chloride)], their color dramatically changed from red to green with increasing the reaction time. We investigated the mechanism of this characteristic color change using XRD, FT-IR, UV–vis spectra, CHN elemental analyses, ICP, and TGA, which indicated that the coordination geometry of Co II ions was changed from a 6-coordinate octahedral (Oh) to a 4-coordinate tetrahedral (Td) with clear crystal distortion. The magnetic behavior of the prepared Fe-CN-Co MCNPs was also reaction-time dependent, as illustrated by SQUID and 57Fe Mössbauer spectra.

Study of Singlet Oxygen Equilibrium in Dioctadecyldimethylammonium Chloride Vesicles Employing 2-(n-(N,N,N-trimethylamine)-n-alkyl)- 5-alkylfuryl Halides†

Steady state photolysis and time resolved near infrared luminescence detection were employed to study the reaction kinetics of singlet oxygen with three different lipid-soluble probes incorporated in large unilamellar dioctadecyldimethylammonium chloride (DODAC) vesicles. The probes: 2-(4-(N,N,N-trimethylamine)-butyl)-5-dodecylfuryl bromide (DFTA), 2-(12-(N,N,N-trimethylamine)-dodecyl)-5-hexylfuryl bromide (HFDA) and 2-(1-(N,N,N-trimethylamine)-methyl)-5-methylfuryl iodide (MFMA) are useful in studying both singlet oxygen dynamics and its equilibrium in microcompartmentalized systems because they are actinometers in lipidic microphases. These probes contain a reactive furan ring, which will be located at different depths in the bilayer of DODAC vesicles. In the limit of the approximations, the result indicates an inhomogeneous equilibrium distribution of singlet oxygen across the bilayer. The calculated mean partitioning constant of singlet oxygen equals 2.8 and 8.3 at 20 degrees C and 40 degrees C, respectively, in the order of the previously reported constants for other microorganized systems such as sodium dodecylsulfate and cetyltrimethylammonium halide micelles and water/oil microemulsions.

Concentration of Urea in Interfacial Regions of Aqueous Cationic, Anionic, and Zwitterionic Micelles Determined by Chemical Trapping

A molecular level description of the effect of urea on the stability of proteins or supramolecular aggregates such as micelles requires information about its interfacial concentration. Estimating interfacial urea concentrations has proved refractory because urea's association with interfaces is difficult to observe spectrometrically. Here we used a chemical trapping method based on product yields from spontaneous dediazoniation of micelle-bound 2,6-dimethyl-4-hexadecylbenzenediazonium ion to estimate the interfacial concentration of urea in micelles of cationic cetyltrimethylammonium halide (CTAX, X = Cl, Br), anionic sodium dodecyl sulfate, SDS, and sodium dodecyl sulfonate, SDSu, and zwitterionic N-hexadecyl-N,N-dimethylammonium propanesulfonate, HPS, surfactants. Up to 6−8 M added urea, the interfacial urea concentration is about 70% (HPS), 80% (CTABr), and 90% (CTACl, SDS, and SDSu) of its stoichiometric concentration in solution, that is, not much less than its concentration in bulk solution. These r...

Optimization of micellar catalysis of nucleophilic substitution reactions in buffered solutions of cetyltrimethylammonium halide surfactants, part 2: buffers in the pH range 7–8

Optimization of micellar catalysis of nucleophilic substitution reactions in buffered solutions of cetyltrimethylammonium halide surfactants, part 2: buffers in the pH range 7–8

Optimization of micellar catalysis of nucleophilic substitution reactions in buffered solutions of cetyltrimethylammonium halide surfactants, part 2: buffers in the pH range 7–8

AbstractBinding of the phosphate, tris‐(hydroxymethyl)‐methylamine, aminomethylpropanediol, and glycinemethylester buffers by cetyltrimethylammonium chloride (CTACl) in aqueous solutions has been probed by investigating: (1) the dependence of the buffer pH (starting pH 7.9) on [CTACl], and (2) the micellar effect on the kinetics of dephosphorylation of p‐nitrophenyldiphenylphosphate (PNDPP) by the anion of isonitrosoacetylacetone (INAA) in CTACl solutions in the presence of the same buffers. The pH–[CTACl] profiles showed a marked dependence on the buffer employed and the coion, Y−, of its acidic component, $\hbox{RNH}_{3}^{+}\hbox{Y}^{-}$. The sizeable pH decrease observed with phosphate buffer (0.43 pH units for [Buffer] = 10−2 M at [CTACl] = 2 × 10−2 M) indicates that both buffer components, namely $\hbox{H}_{2}\hbox{PO}_{4}^{-}$ and $\hbox{HPO}_{4}^{2-}$, exchange with the surfactant counterion, Cl−. This ion exchange occurs at the expense of the nucleophile (anion of INAA)–Cl− counterpart. Indeed, the micellar acceleration of the phosphate‐buffered reaction is the smallest, kmax/kw = 410 (kmax and kw are the maximum pseudo first‐order rate constants in buffered micellar solutions and bulk water, respectively). Although CTACl micelles do not seem to incorporate the neutral component of amino buffers, the pH–[CTACl] profiles were found to depend on the nature in Y− (F−, Cl− or AcO−). The micellar accelerations (kmax/kw ≈ 600), however, were not strongly altered by a change in the buffer coion, except where Y− = F−. In the interfacial region, the partially desolvated fluoride ion behaves as a nucleophile, competing with INAA anion for the dephosphorylation of PNDPP. The rate–[surfactant] profiles were interpreted in terms of the pseudophase ion‐exchange model, as applied to a reaction scheme involving competitive exchanges of the oximate and Y− for the surfactant counterion. The second‐order rate constant of the micelle‐mediated reaction, smaller (ca one‐third) than that in bulk aqueous solution, is discussed in terms of the properties (ionic strength and microscopic polarity) of interfacial water. Copyright © 2001 John Wiley & Sons, Ltd.

Interfacial compositions of cationic and mixed non-ionic micelles by chemical trapping: a new method for characterizing the properties of amphiphilic aggregates

A specially synthesized arenediazonium ion bound to amphiphilic aggregates decomposes spontaneously via rate determining loss of N 2 to give a highly reactive, unselective, aryl cation intermediate. This intermediate is trapped competitively by weakly basic nucleophiles in the interfacial region of aggregates such as micelles and other association colloids. Product yields, analyzed by HPLC with UV detection, are used to estimate, simultaneously, the interfacial concentrations of a number of different nucleophiles, including water, that are commonly found at the surfaces of biomembranes and in many commercial products. Two applications of the method are discussed. First, we show that the interfacial concentrations of X − ( X=Br, Cl) increase steadily with increasing cetyltrimethylammonium halide (CTA X) and tetramethylammonium halide (TMA X) concentrations and that the interfacial concentrations of these counterions increase continuously with their aqueous phase concentrations at a constant degree of micelle ionization. Interfacial Br − and Cl − concentrations also show marked increases at their respective sphere-to-rod transitions. This steady increase in interfacial counterion concentration with increasing aqueous counterion concentration contradicts a basic assumption of the pseudophase ion exchange (PIE) model of chemical reactivity in aggregates, i.e. that the total concentrations of ions at aggregate interfaces is constant and independent of the amphiphile and salt concentrations. The consequences for the PIE model are discussed. Second, the chemical trapping reaction is used to estimate: (a) distributions of terminal OH groups of non-ionic amphiphiles in mixed non-ionic micelles composed of amphiphiles with different lengths of oligoethylene oxide chains and (b) hydration numbers of the inner layers of interfacial region next to the hydrocarbon core in these mixed micelles. Terminal OH groups distributions are well fitted by a radial one-dimensional random walk model. The average hydration number for the inner layers at 40°C is about 3, in agreement with estimates from NMR water (D 2O) self-diffusion measurements and with the hydration number of 3 for aqueous solutions of polyethylene oxide. The results suggest that the hydration states of the ethylene oxide (EO) units near the micellar core are near their minimum value. Recent and potential applications of the chemical trapping method are briefly discussed.

New Method for Estimating the Degree of Ionization and Counterion Selectivity of Cetyltrimethylammonium Halide Micelles: Chemical Trapping of Free Counterions by a Water Soluble Arenediazonium Ion

Products from spontaneous reaction of a short-chain, water soluble arenediazonium salt, 2,4,6-trimethylbenzenediazonium tetrafluoroborate (1-ArN2BF4), in aqueous micellar solutions of cetyltrimethylammonium halides ((CTA)X (X = Cl, Br)) are used to estimate the degree of ionization, α, and the ion exchange constant, KBr/Cl. The arenediazonium ion (1-ArN2+) reacts by rate-determining loss of N2 to give an aryl cation that traps available nucleophiles, i.e. H2O, Cl-, and Br-, to give stable phenol (1-ArOH) and halobenzene products (1-ArCl and 1-ArBr), respectively. Product yields are determined by HPLC from calibration curves obtained from independently prepared standards. Reproducible yields are obtained at very low halide ion concentrations, on the order of millimolar, well within the range needed to detect the “free counterions” in the aqueous intermicellar pseudophase. The basic assumption of the method is that 1-ArN2+ remains in the aqueous pseudophase at all (CTA)X and NaX concentrations. Trends in th...

Arenediazonium salts: new probes of the interfacial compositions of association colloids. 1. Basic approach, methods, and illustrative applications

Product yields from the reactions of two different arenediazonium salts, z-ArN2+ BF4.>-, bound to cetyltri' methylammonium halide ((CTA)X; X=Cl Br) micelles, and 10 aqueous three-ccmponent (CTA)X microemulsions containing an alcohol (R'OH), either 1· butanol (BuOH) or 1-hexanol (HexOH), are snapshots of the relative quantities of halide ion, water, and alcohol nucleophiles at the aggregates' interfaces. Yields of aryl ether, aryl halide, and phenol products measured simultaneously by HPLC arc consistent with high concentrations of these nucleophiles in the immediate vicinity of the aggregates' interfaces. The Interfacial concentration of each nucleophiles is estimated from the yield of its respective product over wide ranges of (CTA)X and R'OH concentrations by assuming that the selectivities of the long-chain (hexadecyl), water-insoluble, aggregate- bound arenediazonium ions, 16- ArN2+, toward anionic or neutral nucleophiles compared to water are the same as the selectivities of the short-chain (methyl), water-soluble analogues, l- ArN2+ toward the same nucleophiles in aqueous solutions. The suitability of dediazoniation reactions as interfacial probes and the basic assumptions used in our approach arc described. The observed rate constants for dediazoniation of the arenediazonium salts are almost completely independent of the salt. (CTA)X. and R'OH concentrations, consistent with rate-determining loss of N2 to give an aryl cation which reacts at diffusion-controlled rates with available nucleophiles. Salt-induced spectral shifts indicate formation of ion pairs in tbe ground state, and all our data are consistent with a heterolytic dediazoniation mechanism in which product distributions ere determined by the equilibrium distribution of the ensemble of ground-state arenediazonium cation-anion and arenediazonium cation-molecule intimate pairs. Comparisons with previous results and potential applications are briefly discussed. The companion paper shows that ether product yields can also be used to estimate R'OH binding constants over a wide range of alcohol and surfactant concentrations.

Cationic surfactant/bile salt interaction studied by fluorescence quenching

Fluorescence quenching measurements were performed on aqueous solutions of the cationic surfactant cetyltrimethylammonium halide (CTAX) and two bile salts, sodium cholate (NaC) and sodium deoxycholate (NaDC), to study the state of aggregation in the mixtures. Pyrene was used as a photoluminiscence probe in the study, and dimethylbenzophenone (DMBP) as the quencher. Analysis of time-resolved decay data with and without quencher using a simple kinetic model gave information of the different aggregation characteristics in the above two cases. Mixed micelles of CTAX/NaC were small and spherical at all compositions, while those of CTAX/NaDC tended to grow from spherical micelles to larger rod-like mixed aggregates at equimolar and close-to-equimolar concentrations. In the latter case more complex kinetics ensues and the fluorescence decays were treated using a generatized model for diffusion-controlled quenching along one dimension for infinitely long rod-like micelles. The mutual diffusion coefficient for the probe-quencherpair was determined.

Fluorescence quenching studies of the aggregation behavior of the mixed micelles of bile salts and cetyltrimethylammonium halides

Fluorescence quenching studies of the aggregation behavior of the mixed micelles of bile salts and cetyltrimethylammonium halides

Acid hydrolyses of hydrophobic dioxolanes in cationic micelles: a quantitative treatment based on the Poisson-Boltzmann equation

Acid hydrolyses of hydrophobic dioxolanes, 1a and 1b, are inhibited by cationic micelles of myristyl- and cetyltrimethylammonium halides, MTAX and CTAX, respectively (X = Cl, Br), but at surfactant concentrations sufficient to bind all the substrate, first-order rate constants, K{psi} at constant (HX), increase with increasing (surfactant) and on addition of NaX. In the absence of added NaX k{psi} increases linearly with (MTAX) and (CTAC), but at constant (surfactant) there are breaks in plots of k{psi} against (NaX). These results can be explained quantitatively in terms of a pseudophase model in which hydrogen ion concentrations at micellar surfaces are calculated by solution of the Poisson-Boltzmann equation.

Fluorescence of anthracene in frozen aqueous micellar solutions

Excitation spectra of anthracene were recorded in the temperature range 80 – 270 K in various frozen aqueous solutions containing the surfactants cetyltrimethylammonium halide CTAX (X ≡ F, Cl, Br, I) or alkali dodecylsulphate MDS (M ≡ Na, Cs). Fluorescence quantum yields (relative values) were obtained by integrating the area under the excitation spectra. A new, hitherto unobserved, emission was detected at temperatures above 250 K and was assigned to the formation of an anthracene—halide anion exciplex. It was most pronounced in the presence of fluoride and chloride anions. The existence of exciplexes under the given conditions is taken as evidence for the diffusion of species at temperatures well below the macroscopic melting point.

A new method for estimating counter-ion selectivity of a cationic association colloid: Trapping of interfacial chloride and bromide counter-ions by reaction with micellar bound aryldiazonium salts

Yields of aryl halides and phenolic products from dediazoniation of a hydrophobic aryldiazonium salt bound to cetyltrimethylammonium halide, CTAX, micelles in 0.1 to 0.2 M HX with added NaX(XCl − and Br −) are used to estimate, simultaneously, the quantity of halide counter-ions and water at the micelle surface. The interfacial counter-ion concentration increases, both in solutions of CTABr with added NaBr and CTACl with added NaCl with a proportionate decrease in interfacial water. The selectivity of CTAX micelles toward Br − and Cl − in solutions containing mixtures of the two ions is obtained directly, unlike all previous methods which require an estimate of the fraction of bound counter-ions. Counter-ion exchange constants, K Br Cl, estimated from aryl bromide/aryl chloride yield ratios at high NaX, are consistent with published values. Our results show, for the first time, that K Br Cl is insensitive to ionic strength up to 3.0 M NaX when [Br −]/[Cl −]=1.0, but has modest dependence on the mole fraction of Br − at constant total NaX. K Br Cl is also independent of surfactant concentration, after correcting for the fraction of bound counter-ions. In principle, product ratios from reaction of hydrophobic aryldiazonium salts can be used to estimate the relative concentrations of all nucleophiles at the surfaces of association colloids, provided stable aryl substituted products are formed via rate determining loss of N 2.