Cetyltrimethylammonium Hydroxide Research Articles

Sol-gel based optical carbon dioxide sensor employing dual luminophore referencing for application in food packaging technology.

An optical sensor for the measurement of carbon dioxide in Modified Atmosphere Packaging (MAP) applications has been developed. It is based on the fluorescent pH indicator 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilised in a hydrophobic organically modified silica (ormosil) matrix. Cetyltrimethylammonium hydroxide was used as an internal buffer system. Fluorescence is measured in the phase domain by means of the Dual Luminophore Referencing (DLR) sensing scheme which provides many of the advantages of lifetime-based fluorometric sensors and makes it compatible with established optical oxygen sensor technology. The long-term stability of the sensor membranes has been investigated. The sensor displays 13.5 degrees phase shift between 0 and 100% CO2 with a resolution of better than 1% and a limit of detection of 0.08%. Oxygen cross-sensitivity is minimised (0.6% quenching in air) by immobilising the reference luminophore in polymer nano-beads. Cross-sensitivity towards chloride and pH was found to be negligible. Temperature effects were studied, and a linear Arrhenius correlation between ln k and 1/T was found. The sensor is stable over a period of at least seven months and its output is in excellent agreement with a standard reference method for carbon dioxide analysis.

Synthesis and characterization of Ti-MCM-41 and vapor-phase epoxidation of propylene using H 2 and O 2 over Au/Ti-MCM-41

Vapor-phase epoxidation of propylene to propylene oxide (PO) using H 2 and O 2 has been carried out over Au deposited on Ti-MCM-41 and TiO 2–SiO 2 mixed oxides having various Ti/Si molar ratios ranging from 0.25/100 to 6.0/100. The Ti-MCM-41 supports were prepared by using two different structure-directing organic templates: dodecyltrimethylammonium hydroxide (C12TMACl) and cetyltrimethylammonium hydroxide (C16TMACl). TiO 2–SiO 2 mixed oxides were prepared by a sol–gel process. Gold nano-particles were loaded by deposition–precipitation (DP) using various precipitating agents: LiOH, NaOH, KOH, RbOH, and CsOH. Au/Ti-MCM-41 gives increased propylene conversion with an increase in Ti/Si ratio and the PO yield passes through a maximum (conversion=3.2%, PO selectivity=93.5%) at 100°C at a Ti/Si molar ratio of 3/100. However, at higher reaction temperatures of ≥120°C, PO selectivity decreases with an increase in the Ti/Si ratio. At the reaction temperatures of 150 and 200°C, to get better performance, the ideal catalysts should have Ti/Si ratios of 2/100 and 1.5/100, respectively. The critical balance among Ti-content, Au loading and the reaction temperature is important to achieve the higher propylene conversion, PO selectivity above 90% and lower H 2 (and O 2) consumption. Gold supported on TiO 2–SiO 2 mixed oxides showed very poor performance, probably due to higher concentrations of extra framework titanium and lower dispersion of gold particles.

Elucidating the local environment of Ti(IV) active sites in Ti-MCM-48: a comparison between silylated and calcined catalysts

A mesoporous Ti-MCM-48 material was silylated using hexamethyldisilazane (HDMS) and a remarkable increase in the catalytic performances in the cyclohexene epoxidation with tert-butylhydroperoxide obtained. We report on a combined FTIR, diffuse reflectance UV–Vis–NIR, photoluminescence and 29Si MAS NMR study, augmented by TGA and XRD analysis, of the local environment of Ti sites in both calcined and silylated Ti-MCM-48 catalysts. Spectroscopic studies were also performed on the as-synthesised material and showed that both silanols and titanols are formed during the decomposition of the cetyltrimethylammonium hydroxide surfactant used to template the mesoporous structure. Unequivocal evidences that a further silica condensation of the MCM-48 framework structure occurs both during thermal treatments in vacuum and after calcination at 540°C are also reported. Upon silylation, a more hydrophobic surface is obtained where trimethylsilyl groups (Si(CH3)3) are anchored on to the silica surface by reaction of the silylating agent, HDMS, with silanols, and in addition, (SiO)3TiOH sites transformed into (SiO)3TiOSi(CH3)3. It is proposed that the more hydrophobic character of the silylated material prevents the deactivation of the catalyst by decreasing the amount of glycols which may be formed by reaction of the epoxide with water adsorbed on the surface of the Ti-MCM-48, and that poison the titanium catalytic centres.

Simultaneous determination of inorganic anions, organic acids, amino acids and carbohydrates by capillary electrophoresis

A capillary zone electrophoretic method for the simultaneous analysis of inorganic anions, organic acids, amino acids and carbohydrates was developed with indirect UV detection using 2,6-pyridine dicarboxylic acid as the background electrolyte. This is the first paper to report their simultaneous analysis. Highly alkaline conditions were used in order to confer a negative charge not only on inorganic and organic anions but also on amino acids and carbohydrates, and to promote their migration towards the anode. Electroosmotic flow was reversed in the direction of the anode by adding cetyltrimethylammonium hydroxide to the electrolyte. Outstanding separations were obtained and electrophoretic mobilities of 82 compounds including nine inorganic anions, 23 organic acids, 18 amino acids and 32 carbohydrates were determined by the method. Under the optimized conditions 43 compounds were well separated in a single run. The relative standard deviations ( n=5) of the method were better than 0.5% for migration times and between 0.8% and 4.9% for peak areas except for a few compounds. The detection limits for anions and amino acids were in the range from 6 to 12 mg/l and for carbohydrates from 23 to 35 mg/l with 300 mbar·s pressure injection (6 nl) at a signal-to-noise ratio of three. This method could be readily applied to the simultaneous determination of inorganic anions, organic acids, amino acids and carbohydrates in soy sauce, nutrient tonic and pineapple.

Simultaneous determination of inorganic anions, organic acids and metal cations by capillary electrophoresis

A capillary electrophoresis method for the simultaneous analysis of inorganic anions, organic acids and metal cations was developed. 2,6-Pyridinedicarboxylic acid (PDC) was used as the background electrolyte to permit indirect UV detection of anions. The PDC also worked to confer a negative charge on metal cations via PDC-complex formation. In order to detect both anions and metal–PDC complexes simultaneously, the electroosmotic flow was reversed by adding cetyltrimethylammonium hydroxide. In the method detection of anions was carried out with indirect UV detection, whereas metal cations were detected directly. Thirteen anions and three metal cations were completely separated at the operating buffer, pH 5.7. The R.S.D. ( n=6) values of the method were better than 0.2% for migration time and between 1.1% and 3.9% for peak area. Calibration graphs were linear with correlation coefficients better than 0.9992. The minimum detectable levels ranged from 0.2 mg l −1 to 1.9 mg l −1 with 300 mbar pressure injection (6 nl) at a signal-to-noise ratio of 3. This method is simple, rapid and reproducible and could be readily applied to the simultaneous determination of anions and metal cations in a plating bath sample.

Effects of Association Colloids on Elimination from 1,2-Dihalo-1,2-diphenylethanes. The Role of Surfactant Structure

Rates of E2 elimination of D,L-1,2dichloro-1,2-diphenylethane (1) and the analogous dibromide (2) were measured in aqueous cetyltrimethylammonium chloride and hydroxide (CTACI and CTAOH), cetyltripropylammonium hydroxide (CTPAOH), didodecyldimethylammonium chloride and hydroxide (DDDACI and DDDAOH), and N,N-dimethyl-N-(2-hydroxyethyl)-n-hexadecylammonium hydroxide (DOH,OH). Micelles or other association colloids of these surfactants increase rates in solutions that contain OH-, and DOH,-OH is much more effective than the nonfunctional surfactants. Variations of first-order rate constants, k obs , with [surfactant] or [OH-] are fitted by a pseudophase model with water and micelles as distinct reaction media, to give second-order rate constants in the latter. These rate constants are in the sequence DOH,OH > CTPAOH DDDACl > DDDAOH CTAOH > CTACl. Micelles favor reactions of 2 over 1, relative to reactivities in water, due to differences in amphiphilic interactions with the leaving halide ions.

Separation of chemical warfare agent degradation products by the reversal of electroosmotic flow in capillary electrophoresis.

We report the development of analyses for nerve agent degradation products or related species by the reversal of electroosmotic flow in capillary electrophoresis (CE). The developed methods were used in this laboratory for analysis of samples in the second and third official proficiency tests (International Round-Robins) for the Provisional Technical Secretariat/Preparatory Commission for the Organization for the Prohibition of Chemical Weapons, and those results are reported here. Analytes studied include methylphosphonic acid (a dibasic acid), the monoisopropyl ester of ethylphosphonic acid, and the monoalkyl esters of methylphosphonic acid (R = ethyl, isopropyl, isobutyl, pinacolyl (3,3-dimethyl-2-butyl), cyclohexyl, and 2-ethylhexyl). The cationic surfactants used here for the reversal of electroosmotic flow are didodecyldimethylammonium hydroxide and cetyltrimethylammonium hydroxide. CE methods using conductivity or indirect UV detection provide a good separation efficiency and very high sensitivity for the analysis of such compounds. The detection limits for these species were about 75 micrograms/L when using conductivity detection and about 100 micrograms/L when using indirect UV detection. Because pH plays an important role in the CE separation of the alkylphosphonic acids and their monoesters, the influence of pH on these separation systems was investigated. Electrolytes were stable for at least 3 months. Excellent separation efficiency and freedom from interference due to common anions were obtained in the developed methods which typically achieved complete separations in less than 3 min. The method was applied to aqueous leachates of soil, wipes of surfaces, and vegetation sampled from a field site known to have been exposed to nerve agents and subsequently cleaned up. The data from these environmental samples indicated that the method can be expected to be useful for environmental monitoring.

Reactivity in aqueous association colloids. Descriptive utility of the pseudophase model

The ability of aqueous micelles and similar association colloids to control reaction rates is treated in terms of pseudophase models in which micelles and water are regarded as distinct reaction media, with consideration of reactant concentrations and rate constants in the two regions. An alternative model, based on transition state theory, considers the transfer free energy of the activated complex between water and micelles. Both models fit data for reactions in solutions of cetyltrimethylammonium hydroxide, for example. Their values in relating rate effects to reaction mechanism and structures of reactants and surfactants are discussed.

Iron-Modified MCM-48 Mesoporous Molecular Sieves

MCM-48 mesoporous molecular sieves containing iron(III) were obtained using a direct sol−gel route followed by removal of the cetyltrimethylammonium hydroxide template before calcination. UV−visible, ESR, and XANES spectroscopies show that iron mostly occupies tetrahedral sites of the siliceous walls. The formation of oxide nanoclusters in the channels is favored in the presence of the organic template molecules during calcination.

Determination and prediction of transfer ratios for anions in capillary zone electrophoresis with indirect UV detection

Transfer ratios (i.e. the number of moles of the UV-absorbing probe anion displaced by one mole of analyte anion) were determined for the separation of inorganic and organic anions by capillary zone electrophoresis using indirect UV absorbance detection. When the electrolyte was buffered and contained only the probe anion and a single counter-cation, transfer ratios calculated from Kohlrausch theory were found to agree well with values obtained experimentally from accurately determined mobility data. However, these electrolyte systems gave long analysis times and were therefore considered impractical. More useful electrolytes were obtained by the addition of surfactants to suppress or reverse the electroosmotic flow but the co-anion introduced with the surfactant can reduce the value of the measured transfer ratio and hence adversely affect sensitivity. This problem was overcome by the use of a surfactant in the hydroxide from such as cetyltrimethylammonium hydroxide combined with a suitable buffering counter-cation such as protonated 1,3-bis[tris(hydroxymethyl)-methylamino]-propane or tris(hydroxymethyl)aminoethane. Four buffered electrolytes consisting of chromate, benzoate, phthalate, or trimellitate as probes and a suitable surfactant were used to determine transfer ratios. These systems were shown to give transfer ratios that were close to those calculated from Kohlrausch theory, thereby enabling prediction of experimental conditions giving maximum transfer ratios.

Cetyltrimethylammonium hydroperoxide: an efficient reagent for promoting phosphate ester hydrolysis

Cetyltrimethylammonium hydroperoxide solutions are easily prepared by mixing cetyltrimethylammonium hydroxide and hydrogen peroxide and are very efficient in promoting paraoxon (diethyl p-nitrophenyl phosphate) hydrolysis.

Anti-tumour components of the culture filtrates from Tricholoma sp.

The anti-tumour component (Fraction A) found in the culture filtrates of a local mushroom, Tricholoma sp. (strain STC20-T1), was purified using DEAE-cellulose ion exchange chromatography and Sepharose CL-4B gel filtration. Of its two purified sub-fractions, A-1 and A-2, only the latter showed anti-tumor activity. When Fraction A-2 was treated with cetyltrimethylammonium hydroxide and chloroform/butanol (24:1, v/v), it behaved as a proteinbound polysaccharide, with a molecular mass estimated to be 154 kDa by gel filtration. It contained 40% polysaccharide, which consisted of fucose, galactose, glucose, arabinose and mannose, and 30.5% protein, the amino-acid composition of which was determined. Fraction A-2 could inhibit the growth of Sarcoma-180 implanted in mice intraperitoneally and subcutaneously, with no sign of toxicity, at a dose of 20 mg/kg.day for 10 days.

Salt-Gel Synthesis of Porous Transition-Metal Oxides

Hydrothermal reaction of sodium metatungstate with the surfactant template cetyltrimethylammonium (CTA) hydroxide gave the salt (C{sub 19}H{sub 42}N){sub 6}(H{sub 2}W{sub 12}O{sub 40}). Despite the superficial similarity of TEM micrographs and powder X-ray patterns of this material to those of mesoporous silicates, the salt contains unconnected Keggin ions H{sub 2}W{sub 12}O{sub 40}{sup 6-}. These Keggin ions pack in a puckered layer arrangement and create roughly spherical cavities for the surfactant micelle counterions. Attempts to remove the template cations and condense the inorganic portion of the structure invariably lead to dense WO{sub 3-x} phases. Nb{sub x}W{sub 6-x}O{sub 19}{sup (2+x)-} (x = 2, 3, 4) clusters also formed layered salts with CTA cations, which were reacted with tetraethyl orthosilicate (TEOS). The TEOS molecules are absorbed, presumably into the hydrophobic portion of the structure, and can be hydrolyzed to form silica within the salt. Infrared and solid-state NMR double-resonance spectra show that the silica network is anchored to the clusters via covalent Nb-O-Si linkages. Extraction of the silica-modified salts with HCl/ethanol yields materials with both micropores and mesopores and specific surface areas up to 265 m{sup 2}/g. 34 refs., 10 figs., 1 tab.

The Effects of Single- and Twin-Tailed Ionic Surfactants on the Hydroxydehalogenation of Charged Substrates

Reactions of OH- with 4-chloro-3,5-dinitrobenzoic and 2-chloro-3,5-dinitrobenzoic acids have been examined in solutions of cetyltrimethylammonium chloride, bromide and hydroxide, bis ( dodecyl ) dimethylammonium chloride, and bis(tetradecyl) dimethylammonium chloride. Rate effects were analysed quantitatively in terms of the distribution of reactants between water and the colloidal particles. It has been found that twin-tailed ionic surfactants better distinguish between favourable and unfavourable orientations of substrate molecules within micellar aggregates than do single-tailed ionic surfactants.

Dephosphorylation by peroxyanions in micelles and microemulsions

AbstractDephosphorylation of p‐nitrophenyl diphenylphosphate (pNPDPP) by OH− in aqueous cationic micelles of cetyltrimethylammonium hydroxide (CTAOH) is inhibited by tert‐butyl hydroperoxide (t‐BuO2H), which reduces the binding of OH−, and whose anion is a relatively ineffective nucleophile. Reaction is faster in microemulsions of CTACl, n‐octane and OH−, with t‐BuO2H as cosurfactant, than in otherwise similar microemulsions with t‐butyl alcohol as cosurfactant. Dephosphorylation by m‐chloroperoxybenzoate ion is slower in microemulsions of cetyltrimethylammonium mesylate or benzenesulfonate, with n‐octane and tert‐butyl alcohol, than in cationic micelles, but a wide range of concentrations can be examined. The reaction rates qualitatively follow the concentration of peroxy acid relative to surfactant, and inert anions slow the reaction. Dephosphorylation by peroxyphthalate dianion in micelles of CTACl fits a pseudophase kinetic model, except in very dilute surfactant where reaction is faster than predicted.

Quantitative treatment and micellar effects in the reaction of t-butyl perbenzoate and 2-naphthyl benzoate

The basic hydrolysis of t-butyl perbenzoate and 2-naphthyl benzoate has been studied in cationic micelles of cetyltrimethylammonium chloride or hydroxide (CTACl or CTAOH, respectively). The increase in rate constant with surfactant concentration can be analysed in terms of the concentration of (1), (2), and hydroxide ion in the micellar pseudophase; the determined second order rate constants in the micellar pseudophase are smaller than the second order constants in water.

Micellar catalysis of organic reactions. 22. A comparison of the basic hydrolysis of benzodiazepinones in the presence of reactive counterion micelles and vesicles

The basic hydrolysis of diazepam and several N-alkyl nitrazepam derivatives has been studied in the presence of reactive counterion micelles of cetyltrimethylammonium hydroxide (CTAOH) and vesicles of didodecyldimethylammonium hydroxide (DDAOH). In both surfactants, the rate of hydrolysis of all compounds was found to be dependent on the hydroxide concentration at constant surfactant concentration and this was interpreted as evidence for initial amide hydrolysis. The hydrolysis in CTAOH was inhibited by added salts in the order Br− < NO3− < SO42−. At concentrations above 3 mM surfactant, the rate of hydrolysis of each compound was similar in CTAOH and in DDAOH. At lower concentrations of CTAOH, however, the rate of hydrolysis was significantly lower than that in DDAOH. On the basis of this evidence, it was concluded that the cmc of CTAOH was between 2–3 mM, which is in good agreement with the value of 1.8 mM obtained by Zana from conductivity measurements. For diazepam, a mechanistic change is indicated on transfer from water to either micelles or vesicles and since vesicles are considered good models of biological membranes, this suggests that conclusions concerning the bioavailability of diazepam should not be based on studies in water but rather on studies in either micelles or vesicles.

Reaction of N-alkyl-2-bromopyridinium ion in micelles of cetyltrimethylammonium hydroxide

Reaction of N-alkyl-2-bromopyridinium ion in micelles of cetyltrimethylammonium hydroxide

The effects of single- and twin-tailed ionic surfactants upon aromatic nucleophilic substitution

Reactions of OH– with 2,4-dinitro-1-chloro-benzene and -naphthalene have been examined in solutions of didodecyldimethylammonium chloride and hydroxide. Rate effects were analysed quantitatively in terms of distribution of reactants between water and the colloidal particles. Second-order rate constants at the surface of the particles are very similar to those in normal aqueous micelles of cetyltrimethylammonium hydroxide, chloride, and bromide and p-octyloxybenzyltrimethylammonium bromide and are slightly higher than in water. Similar observations were made on the reaction of OH– with 2,4-dinitro-1-fluorobenzene.

Fractional ionization of cetyltrimethylammonium hydroxide micelles determined by dynamic light scattering

Using the method of dynamic light scattering we have measured the diffusion coefficients D of cetyltrimethylammonium hydroxide (CTAOH) micelles as a function of CTAOH and NaOH concentrations at 25°C for 0.01 ≤ [CTAOH] ≤ 0.05 M and 0.02 ≤ [NaOH] ≤ 0.5 M. Substantial enhancements in the diffusivity were observed at low [NaOH] due to the presence of strong intermicellar electrostatic repulsions. We obtained good theoretical fits to the D versus [CTAOH], [NaOH] data over the range 0.01 ≤ [NaOH] ≤ 0.5 M using linear interaction theory (including both thermodynamic and hydrodynamic corrections to D) with a DLVO-type pair interaction potential. From these fits we obtained estimates of the mean micellar hydrodynamic radius, R h ∼ 23.4 Å, and the micellar fractional ionization, α ∼ 0.5.