Cetyltrimethyl Ammonium Research Articles

Effect of Additives on LiMo3Se3 Nanowire Film Chemical Sensors

Here we investigate the effect of lithium iodide and cetyltrimethylammonium (CTA) bromide additives on the ability of LiMo(3)Se(3) nanowire film sensors to bind and detect organic solvents electrically. Both additives decrease the electrical conductivity of the films. Lithium iodide increases the response of the films to both polar and nonpolar analytes. CTA increases the response of the films to nonpolar analytes but reduces the response to polar analytes. Quartz crystal microbalance measurements show that the modified electrical sensitivities of the films are due to altered analyte adsorption abilities of the films. These results show that the Li(+) ions are involved in analyte binding in native LiMo(3)Se(3) films and that a programming of LiMo(3)Se(3) nanowire film sensors is possible by replacing lithium cations with other receptors.

Synthesis of Thermally Stable Zirconia-Based Mesoporous Materials via a Facile Post-treatment

A novel method of preparing thermally stable zirconia-based mesoporous materials was developed. The zirconia-based mesoporous materials of 2D-hexagonal structure were prepared using zirconium sulfate as the zirconium precursor and cetyltrimethylammonium (CTMA) as the pore-directing agent with the aid of salt in the synthesis solution to reduce the sulfate content in the final product and significantly improve the crystallographic ordering. Post-treatment of the mesoporous material with NaCl solution and lowering the ramping rate to less than 0.2 degrees C/min during the calcination process, however, were the key steps to hinder the growth of the dense zirconia phase and to retain the ordered mesostructure up to 600 degrees C. It was found that a portion of the surfactant (8.9-17.4 wt %) and sulfate ions (0.5-1.2 wt %) were removed during the post-treatment, which prevented the remaining sulfate groups from being reduced by the hydrogen-rich surfactant during the calcination process as confirmed by sulfur K-edge X-ray absorption near edge structure (XANES) and infrared spectroscopy. The maintenance of sulfur in the sulfate state seemed to be important in stabilizing the mesoporous structure of zirconia materials. The mesoporous zirconia materials after extraction with NaCl solution three times and calcination at 550-600 degrees C had the composition ZrO(2-x)(SO4)x with x = 0.10-0.27. The material possesses high surface area (approximately 200 m2/g), large pore volume (approximately 0.10 cm3/g), and wormlike mesopores. In comparison with the mesoporous zirconia materials stabilized by chemical treatment, the present route was simpler and more environmentally friendly and resulted in mesoporous zirconia materials of better thermal stability.

Delamination of surfactant intercalated smectites in alcohols: Effect of chain length of the solvent

Cetyl trimethylammonium and stearyl trimethylammonium ion-intercalated montmorillonite delaminates in alcohols. While delamination is observed in all alcohols, the amount of delaminated particles and the stability of the resultant colloidal dispersion increases with the chain length of the alcohol. The organoclay could be easily reassembled from the colloidal dispersions either by evaporation or by the addition of a polar solvent.

Calorimetric effects in rapidly frozen micellar solutions below the macroscopic melting point

Small samples of aqueous solutions of three cetyltrimethylammonium (CTA) salts and of sodium dodecyl sulfate (SDS) were rapidly frozen by plunging into liquid Nitrogen. The frozen samples were heated and recooled in a differential scanning calorimeter between −50 and −5°C, i.e., below the macroscopic melting point. Upon first heating an exothermic process was observed in CTA salts (but not in SDS) at between −20 and −30°C. The process was assigned to crystallization of micellar microdomains that had not taken place upon rapid freezing. The mobility for crystallization in the frozen environment was possible because of local melting point depression. In the presence of sufficient sodium chloride the local melting was proven by according endo- and exothermic DSC peaks upon heating and recooling, respectively.

Synthesis and characterization of zeogrid molecular sieves

Clear solution was prepared by hydrolyzing tetraethylorthosilicate (TEOS) in tetrapropylammonium (TPA) hydroxide and heated at 120 °C for various times in order to generate half-nanoslabs, nanoslabs, tablets, intermediates and colloidal Silicalite-1 crystals. These building units were precipitated by addition of cetyltrimethylammonium (CTMA) bromide. After evacuation of TPA and CTMA from the precipitates through calcination, microporous materials having substantial micropore volumes of 0.5–0.7 ml/g designated as Zeogrids were obtained. The micropores comprise ultra-micropores inside the zeolitic building units, and super-micropores between these building units. The ultra-micropores of Zeogrids render molecular sieving properties to these materials, which can be fine-tuned by adapting the size of the zeolitic building units. To cite this article: S.P.B. Kremer et al., C. R. Chimie 8 (2005).

Spectrophotometric Determination of Titanium(IV) by Extraction of its Thiocyanate Complex with Cationic Surfactants

A spectrophotometric method for the determination of titanium(IV) is described. It is based on the extraction of titanium(IV) as an ion‐associated complex, formed between the titanium(IV)–thiocyanate anion and the cetyltrimethylammonium (CTMA), cetylpyridinium (CP), or tetradecyldimethylbenzylammonium (TDMA) cation in chloroform or dichloromethane. Optimum conditions for the extraction and spectrophotometric determination of titanium(IV) by all extractants were determined. The effect of chloride ions on the extraction was also examined. In their presence the systems studied were most sensitive. The apparent molar absorptivities of the complex, at 420 nm, and limit of detection, in the presence of chloride ions, were (6–7) × 104 L mol−1 cm−1 and 20–35 ng Ti(IV) mL−1, respectively, depending upon the reagent used. Titanium determination was feasible in the presence of many foreign ions. The ratios of titanium(IV) and CTMA, CP or TDMA determined by Job's method were 1:2. The validity of the method was tested on bauxite and aluminum alloy samples. The values determined were in good agreement with the certified values.

Preparation of highly porous silica nanocomposites from clay mineral: a new approach using pillaring method combined with selective leaching

A silica xerogel was synthesized from a clay mineral by a new approach using a pillaring method combined with a selective leaching method. Preparation was conducted by applying an HCl/ethanol treatment after intercalation and condensation of tetraethoxysilane (TEOS) and/or methyltriethoxysilane (MTS) into cetyltrimethylammonium (CTA) ion-exchanged vermiculite. The products are porous nanocomposites consisting of TEOS and/or MTS-derived polysiloxane and hydrated silica, resulting from the selective leaching process of the inorganic constituents and the extraction of CTA ions from CTA-exchanged vermiculite after the intercalation of TEOS and/or MTS. The morphology remains similar to the originated vermiculite owing to the topotactic dissolution process. The products have high porosity with 1205–715 m 2 g −1 of BET surface area when prepared with up to 2 mol dm −3 HCl concentration. The pore size distributions of the products show a wide distribution from 1 nm to 4 nm in diameter due to the presence of micropores and mesopores. The HCl concentration dependence of the surface area suggests that the main porosity arises from the porous polysiloxane which is formed by the pillaring process. Water adsorption isotherms reveal that the products have a hydrophilic surface originating from silanol groups on the polysiloxane and the hydrated silica. However, the incorporation of MTS in the pillaring process results in successful surface modification of the products. This novel approach is advantageous for the synthesis of highly porous xerogels with different kinds of surface properties.

Alkali-containing mesoporous (alumino) silicate materials with very high metal loading

Mesoporous aluminosilicates with Si/Al ratios ranging from approximately 1 to ∞ (for a pure-silica compound) have been synthesized in the presence of sodium and cetyl trimethyl ammonium (CTMA +) cations. All materials are thermally stable and retain their highly ordered hexagonal structure upon removal of surfactant molecules at 800 K. Original procedures have been explored to exchange selectively surfactant and/or sodium cations from as-made materials. Treatments in water exchange exclusively sodium ions, without extracting surfactant molecules, whilst treatments in ethanol remove preferentially organic molecules. Combining these two procedures allowed us to exchange completely CTMA + and Na + cations and to prepare highly ordered Li +, K +, Cs + and Ca 2+-modified materials with very high alkali metal concentrations. The stability of the exchanged mesoporous compounds depends on the aluminum content and on the nature of the alkali cation. All materials are particularly stable upon exchange with Li + and Ca 2+ cations. By contrast, the stability of solids exchanged with Cs + or K + cations decreases with decreasing the aluminum content. In the particular case of pure silica MCM-41, the hexagonal structure is retained upon exchange of surfactant molecules with Li + and Ca 2+ cations but is severely damaged with other cations. The procedures reported here are not only efficient to introduce a large amount of cations in mesoporous materials, but they can also be used to remove completely surfactant molecules from MCM-41 under mild conditions.

Electroluminescence as a probe for elucidating electrical conductivity in a deoxyribonucleic acid-cetyltrimethylammonium lipid complex layer

We fabricated an organic light-emitting diode (OLED) using a DNA (deoxyribonucleic acid)-CTMA (cetyltrimethylammonium) lipid complex as an active charge transport layer to elucidate the semiconducting characteristics of the DNA-CTMA complex. From these OLED characteristics, we conclude that a DNA-CTMA layer preferentially transports holes rather than electrons. Furthermore, in using sandwiched device structures with the DNA-CTMA layer, we conclude that the DNA-CTMA layer basically possesses both hole and electron transport abilities and preferentially transports holes due to a shallow lowest unoccupied molecular orbital (LUMO) level that prohibits an efficient electron injection from an adjacent carrier transport layer.

Chromatographic analysis and sequencing approach of heparin oligosaccharides using cetyltrimethylammonium dynamically coated stationary phases

C 18 and C 8 bonded stationary phases dynamically coated with cetyltrimethylammonium (CTA) and strong anion exchange (SAX) were developed to obtain separations of oligosaccharide mixtures resulting from chemical or enzymatic depolymerization of heparin. With this method, the retention of sulfated oligosaccharides is directly adjustable depending on the amount of CTA adsorbed into the column. Oligosaccharides containing up to 20 sulfates were separated with a resolving power superior to that of conventional SAX analysis. The stability of the column coating enables hundreds of injections. Using ammonium methane sulfonate aqueous solutions as ultraviolet transparent mobile phases, it was possible to set up double detection, including selective detection of acetylated oligosaccharides. Analytical gel permeation chromatography was directly coupled to CTA-SAX, obtaining a two-dimensional profile of analyzed oligosaccharidic mixtures. A sequencing method of heparin oligosaccharides using partial depolymerization by heparinases according to their size and sulfation pattern and digest analysis by CTA-SAX was developed. A direct application of this method to the analysis of oligosaccharide mixtures obtained by complete digestion of heparins by heparinases I, II, and III was done. It allowed a reliable quantification of heparin building blocks. We also focused our attention on di- and tetrasaccharidic species containing the 3-O-sulfated glucosamines taken as markers of the active sites for antithrombin III. The method was also applied to more complex mixtures resulting from porcine heparin partially depolymerized with heparinase I. The specificity of the reaction was studied up to decasaccharidic fractions.

Acceleration of nucleophilic attack on an organophosphorothioate neurotoxin, fenitrothion, by reactive counterion cationic micelles. Regioselectivity as a probe of substrate orientation within the micelle.

31P NMR and UV-vis spectrometric evidence has revealed an unexpected regioselectivity in the reaction of fenitrothion, 1, an organophosphorus pesticide, with the cetyltrimethylammonium (CTA) surfactants CTAOH and CTAMINA, that incorporate the reactive counterions OH- and MINA- (the anti-pyruvaldehyde 1-oximate anion). While both micellar solutions accelerate decomposition of 1 compared to aqueous OH- alone, CTAMINA produced the largest rate enhancement (ca. 10(5)) at a pH (8.39) appropriate for environmental applications. In the absence of surfactant, reaction proceeds solely via the SN2(P) pathway. In the presence of surfactant but below the critical micelle concentration (cmc), a competitive SN2(C) pathway was observed in addition to SN2(P). Above the cmc, however, the CTAOH reaction again proceeded solely via the SN2(P) pathway while both pathways were operative with CTAMINA. The changes in reactivity and mechanistic pathway are discussed in terms of premicellar and micellar influences on rates and regioselectivity. A proposal that would account for the observed regioselectivity in the micellar system is that the aromatic ring and aliphatic side-chains of 1 are oriented toward the micellar interior, while the P=S moiety faces the aqueous pseudophase.

Strictinin as an efficient antioxidant in lipid peroxidation

The antioxidant effect of strictinin (SOH), which was extracted from green tea leaves, against the peroxidation of linoleic acid in sodium dodecyl sulfate (SDS) and cetyl trimethylammonium (CTAB) micelles, against the peroxidation of low-density lipoprotein (LDL) and against oxidative hemolysis of human red blood cells (RBCs), has been studied. The peroxidation of linoleic acid and LDL, and oxidative hemolysis of RBCs were initiated thermally by a water-soluble azo initiator 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH), and the reaction kinetics in micelles and LDL were monitored by uptake of oxygen. The synergistic antioxidant effect of SOH with α-tocopherol (Vitamin E) was also studied by following the decay kinetics of α-tocopherol. Kinetic analysis of the antioxidation process demonstrates that SOH, used either alone or in combination with α-tocopherol, is an effective antioxidant against lipid peroxidation, but its effects significantly depend on the reaction medium.

Solubilization of Phenol in an Intercalated Surfactant Bilayer

Solubilization of phenol molecules in an intercalated surfactant bilayer, formed within the galleries of an inorganic layered solid, {CdPS_3}, is reported. The bilayer, formed by grafting of cetyl trimethylammonium (CTA) ions to the internal surface of {CdPS_3}, functionlizes the surface, converting it from a hydrophilic to a hydrophobic surface. The CTA ions being devoid of functional groups, the interaction between the guest phenol molecules and the methylene chains of the bilayer are dispersive in nature. It is shown that there are two phases of the phenol-solubilized intercalated bilayer, distinguishable by their interlayer lattice spacing and corresponding to solubilized phenol to intercalated CTA ion concentration ratios less than 0.5 and greater. The presence of the guest phenol, which is rotationally mobile, induces conformational disorder in the methylene chains of the intercalated bilayer. The nature and extent of conformational disorder have been studied using infrared and Raman vibrational spectroscopy and {^{13}C CP-MAS NMR} spectroscopy. Conformational disorder in the two phases of the phenol-solubilized bilayer is different, and the observed differences in the interlayer lattice spacings have been related to differences in the nature of conformational disorder.

Pyrocatechol Violet in New Optical Methods for Determining Molybdenum(VI)

The complexation of molybdenum(VI) with Pyrocatechol Violet (PCV) in the absence or presence of a cationic surfactant, cetyltrimethylammonium (CTMA), was studied. Conditions for the preconcentration of molybdenum(VI) as its PCV complex on adsorbents of different nature were found. Concentration factors were at least 67 at a liquid phase volume of 20 mL and for an adsorbent sample of 0.3 g. Chromaticity characteristics of complexes were determined in the solution and on the adsorbent. It was shown that the PCV complex of molybdenum(VI) in the presence of CTMA can be used in the analysis of low-molybdenum samples. A test scale for the semiquantitative determination of molybdenum was obtained.

Differential pulse polarographic determination of uranium(VI) in complex materials after adsorption of its trifluoroethylxanthate cetyltrimethylammonium ion-associated complex on naphthalene adsorbent.

Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the pH range 4.2 - 7.0. Without cetyltrimethylammonium as the counter ion, the adsorption is hardly 70%. The metal has been desorbed with HCI and determined with a differential pulse polarograph. Uranium can alternatively be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1 - 5 ml/min and determined similarly. A well-defined peak has been obtained in this medium at -0.20 V versus a saturated calomel electrode. Cyclic voltammetry, differential pulse polarography and D.C. polarography studies indicate that uranium has been reduced irreversibly under these conditions. The detection limit is 0.30 microg/ml at the minimum instrumental settings (signal-to-noise ratio of 2) (with a preconcentration factor of 10, the detection limit would be 30 ng/ml for uranium when the volume in the cell is 15 ml). However if the volume in the cell is 5 ml, it would have been 10 ng/ml with a preconcentration factor of 30. Linearity is maintained in a concentration range of 0.5 - 19.0 microg/ml (2.1 - 79.83 x 10(-9) M) with a correlation factor of 0.9994 and a relative standard deviation of +/-1.1% (in this case 7.5 microg may be concentrated from 150 ml of the aqueous sample where its concentration is as low as 50 ng/ml). Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials, like alloys, coal fly ash, biological, synthetic, and waste-water samples.

Surfactant-assisted UV-photolysis of nitroarenes

Photochemical transformations ( λ=254 nm) of 2,4-dinitrotoluene (2,4-DNT) in aqueous solutions containing the cationic surfactant cetyltrimethylammonium (CTA) and the anionic nucleophile borohydride (BH 4 −) were investigated. The overall decay rate was enhanced at CTA concentrations above the critical micelle concentration (cmc) when stoichiometric excess BH 4 − was present in solution. A kinetic model that separates the overall reaction rate into micellar and aqueous pseudo-phase components indicates transformation in micelles is 17 times faster that in the homogeneous water phase under those conditions investigated. Intermediate products were identified by comparing the HPLC retention times and ultraviolet-visible absorption spectra of product peaks to those of analytical standards. 2-Methyl-5-nitroaniline, 4-nitrotoluene, 2-nitrotoluene, 4-methyl-3-nitroaniline, 2,4-diaminotoluene, o-toluidine, 1,3-dinitrobenzene, 3-nitroaniline, p-cresol, and 2,4-diaminophenol were identified as photo-transformation intermediates or products.

The interactions of cetyltrimethylammonium with mitochondria: an uncoupler or a detergent?

The interactions of cetyltrimethylammonium (CTA) with mitochondria have been investigated. We confirm, as already observed in a previous paper, that this compound behaves as proton carrier (or uncoupler) of the oxidative phosphorylation, but evidences suggest that this compound enhances the membrane permeability to many other compounds such as sucrose. We conclude therefore that CTA as a detergent enhances membrane permeability to all ions including protons. Some evidences are also given that the inhibitory effect of CTA on the mitochondrial respiratory chain is a consequence of the swelling induced.

Hydrocarbon chain conformation in an intercalated surfactant monolayer and bilayer

Cetyl trimethyl ammonium (CTA) ions have been confined within galleries of layered CdPS3 at two different grafting densities. Low grafting densities are obtained on direct intercalation of CTA ions into CdPS3 to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 A with the interlamellar surfactant ion lying flat forming a monolayer. Intercalation at higher grafting densities was effected by a two-step ion-exchange process to give Cd0.83PS3(CTA)0.34, with a lattice expansion of 26.5 A. At higher grafting densities the interlamellar surfactant ions adopt a tilted bilayer structure.13C NMR and orientation-dependent IR vibrational spectroscopy on single crystals have been used to probe the conformation and orientation of the methylene ‘tail’ of the intercalated surfactant in the two phases. In the monolayer phase, the confined methylene chain adopts an essentially all-trans conformation with most of the trans chain aligned parallel to the gallery walls. On lowering the temperature, molecular plane aligns parallel, so that the methylene chain lies flat, rigid and aligned to the confining surface. In the bilayer phase, most bonds in the methylene chain are in trans conformation. It is possible to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene. These high energy conformers disappear on cooling leaving all fifteen methylene units of the intercalated cetyl trimethyl ammonium ion in trans conformational registry at 40 K.

Interdigitation of an Intercalated Surfactant Bilayer

The cationic surfactant cetyltrimethylammonium (CTA) has been ion-exchange intercalated from an aqueous solution of the surfactant by a two-step process into the galleries of layered cadmium thiophosphate to give Cd0.83PS3(CTA)0.34. Two phases of the intercalated product are observed. One is a phase characterized by a lattice expansion of 26.5 A, in which the methylene chains of the CTA ion adopt a tilted bilayer arrangement. This phase, when left in the reaction media, transforms to a phase characterized by a lattice expansion of 12.5 A with no change in chemical stoichiometry. Using X-ray diffraction and orientation-dependent infrared spectroscopy, it has been possible to establish that the observed collapse of the interlayer spacing is a consequence of the interdigitation of the methylene “tails” of the intercalated CTA ion. Infrared, Raman, and 13C NMR spectroscopies have been used to establish the conformation of the methylene chains in the intercalated normal bilayer and interdigitated bilayer phase...

Ion mediation and surface charge density in phase transition of micelle templated silica

Micelle templated silicas prepared according to the {S+,I−} pathway exhibit phase transitions from lamellar, to hexagonal through the cubic form depending on the lipophilic nature of the anions (Cl−, NO−3, SO2−4), their concentration, and on the presence of cations (Na+, and TMA+) in the synthesis gel. This ion effect is evidenced by the as-synthesized forms of silica mesophases obtained from two series of syntheses, both using cetyltrimethylammonium (CTMA) as surfactant. In the first series, different amounts of various mineral acids HX (X−=Cl−, NO−3 or 1/2SO2−4) were added to the synthesis gel while, in the second one, the concentration of sodium nitrate was varied. The solids were characterized using small angle XRD, transmission electron microscopy, elemental analysis and titration of silanolate groups, CTMA+, and anions of the as-synthesized form. According to chemical analysis, the interface can be described by the following formula {(1−p)S+, pC+, mH2O, nX−, (1−n)I−} where “p” cations C+ and “n” anions X− are inserted in the Helmholtz planes of the electrical interface, respectively. On one hand, these guest ions are competing with cationic surfactants and negative silanolate groups during the synthesis and affect both the long range order and stability of the silica mesophases. On the other hand, they play a mediation role in the electrical balance and in the slight charge density mismatch that control both the interface curvature and the mesophase characteristics.