Cationic Surfactant Cetyltrimethylammonium Chloride Research Articles

Experimental study on drag-reducing channel flow with surfactant additives––spatial structure of turbulence investigated by PIV system

The turbulent frictional drag of water can be reduced dramatically by adding small amounts of drag-reducing materials, such as polymers or surfactants. As a percentage drag reduction of 80% can easily be achieved, this technique is thought to be the most practical method of reducing turbulent frictional drag. In this work, a double pulse particle image velocimetry (PIV) system was used to clarify the spatial velocity distribution of surfactant solution flow in a two-dimensional channel. A type of cationic surfactant cetyltrimethyl ammonium chloride (C 16H 33N(CH 3) 3Cl) mixed with the same weight of counter-ion material NaSal (HOC 6H 4COONa) was used as a drag-reducing additive to water at a mass concentration of 40 ppm. Instantaneous velocity distribution taken by PIV was examined to clarify the effect of surfactant. It was found that the instantaneous velocity distribution taken in water flow exhibits penetration from the low-speed fluid region into the high-speed region, which is one of the important events of turbulence energy production and turbulent mixing. Although this structure is commonly observed in water flow, it was not found in drag-reducing flow under the same Reynolds number. The strong vorticity fluctuation near the wall also disappeared and the integral length scale in streamwise direction of turbulent fluctuation had a smaller value in surfactant solution flow.

Spin casted mesoporous silica coatings for medical applications

Self-assembling organic/inorganic sol–gel systems were used to prepare mesoporous silica coatings that can qualify for medical applications. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC) or an amphiphilic triblock copolymer were utilized as templates or structure-directing agents, and tetraethylorthosilicate (TEOS) as the silica precursor. Thin films could be applied on different substrates (glass, silicon, and titanium) by spin casting of the sol–gels. X-Ray diffraction analyses indicated that well ordered hexagonally packed mesostructures with unit cells of 3 and 13 nm, when CTAC and triblock copolymer were used, respectively, could be fabricated. Parameters such as CTAC/TEOS molar ratio and gel formation time highly affected the resulting structure, so the optimum values were established. A competition occurs between the formation of cylindrical mesochannels on the substrate and homogeneous nucleation of the silica in the sol–gel solution to form spherical particles. Therefore, a growing presence of silica particles on the spin casted coatings happens as the gel formation time is increased above ∼60 s, which results in poorer mesoporous films. When a triblock copolymer was used as template, a preferred alignment of the mesostructure was observed independently of the substrate. The removal of the organic template to hollow the pores was accomplished by photocalcination (selective ultraviolet irradiation). The resulting mesoporous silica coatings were able to induce apatite formation after 1 week of immersion in a simulated body fluid in physiological conditions, which is a sound indication of a bioactive behavior when tested in vivo. These results indicate that the coatings prepared by the methodology described in this work may be valid candidates to be used on implants.

On-line sample concentration in micellar electrokinetic chromatography using cationic surfactants

Two on-line sample concentration techniques, sample stacking and sweeping, were evaluated using cationic surfactants as pseudostationary phases in micellar electrokinetic chromatography. As cationic surfactant micelles, tetradecyltrimethylammonium bromide and cetyltrimethylammonium chloride were employed. About 10-fold and 1000-fold increases in detection sensitivity in terms of peak heights were observed by sample stacking and sweeping, respectively, without suppression of the electroosmotic flow. In particular, the concentration limits of detection ( S/ N=3) for test naphthalenesulfonic acids obtained with sweeping were from 0.96 to 0.47 ppb with UV detection without any preconcentration procedure.

Aligned bioactive mesoporous silica coatings for implants.

Ongoing research is reported aimed at preparing mesoporous silica coatings on various substrates for medical applications by a biomimetic approach (self-assembling of organic/inorganic sol-gel systems into ordered structures). Tetraethylorthosilicate (TEOS) was selected as the silica precursor, and amphiphilic triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), and the cationic surfactant cetyltrimethyl ammonium chloride (CTAC), as structure-directing agents. The mesochannels diameter could be adjusted by changing the directing agent, and a preferred alignment of the mesostructure was observed independently of the used substrate (glass, silicon, Ti or Ti6Al4V). Three different treatments (thermocalcination, photocalcination, and solvent extraction) have been also studied to remove the organic templates, of which photocalcination showed to be the most versatile. When soaked in a simulated body fluid, mesoporous silica coatings induced apatite formation after seven days.

Effect of hydrolysed metal cations on the liquid–liquid extraction of silica fines with cetyltrimethylammonium chloride

Silica fines of <5 μm were liquid–liquid extracted from aqueous suspension containing cationic surfactant cetyltrimethylammonium chloride (CTAC) to the isooctane–water interface region. The silica depression on addition of hydrolysable metal cations Fe(III), Al(III) and La(III) was investigated to clarify the role of such cations in the hydrophile–lipophile transition of the silica fines together with CTAC. At an addition of only 5 μM CTAC, the silica fines were completely recovered in the dense emulsion phase from metal salt-free suspension in the entire pH range investigated. In contrast, addition of 1-mM total metal cations caused silica depression in a certain pH range, specific for the metal salt used. Speciation distribution diagrams for the respective metal–H 2O systems indicate that decreases in percentage recoveries of the silica in the lower pH range are in line with increases in concentrations of the metal hydroxo complexes. Furthermore, the silica depression disappears when the pH approaches the point-of-zero charge of the hydroxide precipitate. In these pH ranges, the neutral to negative metal precipitates are also extracted into the oil–water interface during the liquid–liquid extraction. It seems that the lipophilic-to-hydrophobic transition, that is, depression by metal-salt addition of silica fines in cationic liquid–liquid extraction is controlled by the presence of metal-hydroxide species and their charges, attributable to the hydroxide coating on the silica surface.

FT-EPR Study of Spin-correlated Radical Pairs Formed by Electron Transfer Quenching of Porphyrin Triplets in Micellar Solution

The spin-correlated radical pairs (SCRPs) formed by photoinduced electron transfer from zinc tetrakis(4-sulfonatophenyl)porphyrin ( ZnTPPS ) to quinones in micelles of the cationic surfactant cetyltrimethylammonium chloride ( CTAC ) were studied by means of Fourier transform EPR (FT-EPR). It is shown that variation of the power of the microwave pulse allows the separation of EPR signals arising from SCRPs and free radicals. The measured kinetics of radical formation can be accounted for in terms of a statistical model taking into account the non-uniform distribution of the solutes over the micelles. The rate constant of electron transfer quenching (kq) of the ZnTPPS triplet state by duroquinone (DQ) is found to be 1.05 × 106 s−1. The FT-EPR measurements gave information also on the kinetics of the homogeneous electron transfer reaction DQ − + DQ → DQ + DQ − in CTAC solution in which the DQ − anion radicals were generated by light-induced electron transfer from ZnTPPS . It is found that the dependence of the rate of this reaction on quinone concentration deviates from the linear relationship found in homogeneous solutions. A statistical model is proposed to account for the data. Based on this model, the rate constant of the self-exchange reaction (k ex ) is 4.1 × 106 s−1. From results obtained with duroquinone and benzoquinone as acceptors, it is concluded that ZnTPPS is located at the micelle/water interface.

Electron spin resonance and optical spectroscopy of tubular aluminophosphate materials containing framework vanadium

A series of aluminophosphate materials without (UHM-1) and with variable amounts of vanadium (VUHM-1) have been synthesized in the presence of a cationic surfactant cetyltrimethylammonium chloride and an organic base tetramethylammonium hydroxide. Powder X-ray diffraction and electron probe microanalysis show that both UHM-1 and VUHM-1 with V/Al ratios up to 0.05 possess disordered arrays of tubular channels which mimic the hexagonal MCM-41 structure. The overall P/Al ratio is about half of the initial unity ratio in the gel mixture, especially for VUHM-1. This indicates incomplete condensation of phosphorus oxide and a non-ideal aluminophosphate framework; this seems associated with poorer thermal stability than microporous aluminophosphate and mesoporous aluminosilicate MCM-41. Electron spin resonance and diffuse reflectance ultraviolet-visible spectroscopies reveal that in as-synthesized VUHM-1 the vanadium exists as monoatomically dispersed square pyramidal VO 2+ ions and as tetrahedral V 5+ ions which are consistent with a framework location for the vanadium.

Characterization of Aluminophosphate-Based Tubular Mesoporous Molecular Sieves

A series of aluminophosphate-based tubular mesoporous molecular sieves without (UHM-1) and with substituted silicon (UHM-3) have been synthesized at room temperature in the presence of a cationic surfactant cetyltrimethylammonium chloride (CTACl) and an organic base tetramethylammonium hydroxide (TMAOH). Characterization by powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), N2 adsorption, and 27Al, 31P, and 29Si magic-angle-spinning (MAS) NMR spectroscopies has been carried out to understand both the pore structures and the local atomic arrangements of these solid products. The synthesis of UHM-1 and UHM-3 is successful only at room temperature within the following molar gel composition: Al2O3:(0.6−3.4) P2O5:(0.0−1.0) SiO2:(0.24−0.50) CTACl:(8.5−47.0) TMAOH:(200−642) H2O. The presence of TMAOH is essential to maintain the gel pH at 8.5 or above. The pH greatly influences the nature of the final “crystalline” products, particularly the coordination of aluminum and phosphorus. XRD, EPMA, TEM, and N2 adsorption measurements show that these solid products have a unique composition and disordered tubular mesopores with an average pore diameter of about 35 Å in the calcined form. The overall P/Al ratio of UHM-1 is less than unity, especially in gels of higher pH, indicating incomplete condensation of phosphorus and a nonideal aluminophosphate framework. This may account for their poorer thermal stability relative to microporous aluminophosphate molecular sieves and aluminosilicate-based MCM-41 materials. 27Al and 31P MAS NMR reveal that aluminum in UHM-1 with a P/Al ratio of 0.60 synthesized at a gel pH of 8.5 is present in both tetrahedral and octahedral environments while phosphorus is present in a tetrahedral environment and also as hydroxylated species. As the P/Al ratio of UHM-1 decreases together with increasing gel pH, the relative amounts of tetrahedral aluminum and tetrahedral phosphorus decrease. This change suggests some Al−O−P linkages in the tetrahedral regions of the UHM-1 samples, and an increasing octahedral aluminum content at lower P/Al ratio indicates that octahedral aluminum alone can construct a tubular mesoporous structure. After incorporation of silicon into UHM-1, 29Si, 27Al, and 31P MAS NMR of UHM-3 reveal that silicon is atomically dispersed and that the relative amounts of tetrahedral aluminum and tetrahedral phosphorus increase monotonically with increasing silicon incorporation. Virtually all the aluminum is tetrahedral, and all the phosphorus is tetrahedral after silicon incorporation reaches a Si/Al ratio of unity. This indicates more ordered atomic arrangements of tetrahedral silicon, aluminum, and phosphorus via oxygen bridges in UHM-3 than in UHM-1. The incorporation of silicon appears to make the aluminophosphate framework more flexible and facilitates the formation of an aluminophosphate-based mesoporous structure.

Electron Spin Resonance and Electron Spin Echo Modulation Spectroscopy of Aluminophosphate-Based Mesoporous Molecular Sieve Containing Framework Manganese

Aluminophosphate-based mesoporous molecular sieves with variable amounts of framework manganese have been synthesized at room temperature using cationic surfactant cetyltrimethylammonium chloride as a structure-directing agent. Powder X-ray diffraction shows that all solid products with a d spacing of about 0.42 nm are structurally similar to silica-based MCM-41 materials. After calcination at 500 °C to decompose the surfactant these products still show a single broad diffraction peak with a d spacing of 0.36 nm and high surface area (830−930 m2/g), indicating that the products are relatively thermally stable. Electron probe microanalysis shows that the incorporation of Mn2+ causes an increase of the framework P/Al ratio from about 0.6 for manganese-free samples to about 0.7 for manganese-containing samples; these values are lower than 1.0 for an ideal aluminophosphate framework. This increase in P/Al ratio may account for the improved thermal stability of aluminophosphate mesoporous molecular sieves upon...

Micellar effect on the photoinduced electron-transfer reactions of ruthenium(II)–polypyridyl complexes with phenolate ions. Effect of cetyltrimethylammonium chloride

Although the emission spectra and excited-state lifetime of Ru(bpy) 3 2+ (bpy=2,2′-bipyridine), Ru(dmbpy) 3 2+ (dmbpy=4,4′- dimethyl-2,2′-bipyridine) and Ru(phen) 3 2+ (phen=1,10-phenanthroline) are little affected by the addition of the cationic surfactant cetyltrimethylammonium chloride (CTAC), an appreciable shift in λ max em , emission intensity and emission lifetime are observed for Ru(dtbpy) 3 2+ (dtbpy=4,4′-di-tert-butyl-2,2′-bipyri dine) and Ru(dpphen) 3 2+ (dpphen=4,7-diphenyl-1,10-phenanthroline). These results point out the importance of hydrophobic interactions over the coulombic repulsion thereby bringing the ruthenium(II) complexes close to the cationic micelles. The rate of luminescence quenching of five *Ru(NN) 3 2+ complexes, with alkyl-substituted phenolate ions in the presence of CTAC, follows different trends depending on the nature of the ligand in Ru(NN) 3 2+ as well as the quencher. The micellar inhibition is explained by considering ArO - being strongly associated with CTAC leaving Ru(NN) 3 2+ in the aqueous phase. The micellar catalysis at high [CTAC] with Ru(dtbpy) 3 2+ and Ru(dpphen) 3 2+ may be due to the operation of predominant hydrophobic interaction over the electrostatic repulsion.

Separation of phenylenediamine, phenol and aminophenol derivatives by micellar electrokinetic chromatography Comparison of the role of anionic and cationic surfactants

A mixture of phenylenediamine, aminophenol and phenol derivatives was studied with capillary zone electrophoresis (CZE) at different pHs. The use of acidic or alkaline pH did not give separations with a good resolution. Next, separation was performed using micellar electrokinetic capillary chromatography (MEKC), first with the anionic surfactant sodium dodecyl sulfate (SDS) and second with the cationic surfactant cetyl trimethylammoniumchloride (CTACl). In both cases, a study of pH, surfactant concentration and ionic strength of the electrolyte as function of the capacity factor allowed for the determination of the optimum conditions. Since separation was obtained with both surfactants, we studied the distribution coefficient to determine the affinities of the solutes for the aqueous medium and the different surfactants.

Solubilization of Lecithin Vesicles by a Cationic Surfactant: Intermediate Structures in the Vesicle-Micelle Transition Observed by Cryo-Transmission Electron Microscopy

The morphological change of lecithin vesicles during solubilization with the cationic surfactant cetyltrimethylammonium chloride (CTAC) was studied by means of cryo-transmission electron microscopy (cryo-TEM). The observed changes in aggregate size and structure were in most respects similar to those observed for systems containing lecithin and nonionic surfactants. Addition of low concentrations of CTAC to sonicated small unilamellar vesicles do as previously found for nonionics, give rise to a significant increase in the vesicle size. The growth of vesicles was monitored in time resolved cryo-TEM measurements and was clearly shown to proceed through an intermediate state comprising open bilayered discs. Contrary to other systems the addition of CTAC to the present system gives rise, at a certain concentration range, to the formation of a new intermediate structure. The samples stabilize in vesicles or open fragments of bilayers filled with holes to form a mesh-structure. Such structures, previously not documented by cryo-TEM, may be viewed as intermediates between bilayers and cylindrical micelles. The effects of CTAC on aggregate size and structure described above pertain to systems containing 100 mM NaCl. In the absence of salt the vesicle growth at low surfactant concentrations is strongly supressed, and only a dissolution of vesicles directly into mixed cylindrical micelles is observed.

Characterization of a Truncated Form of Recombinant Porcine Growth Hormone Generated in Vitro During Solubilization of Inclusion Bodies

During the development of a novel solubilization procedure (1) for bacterial inclusion bodies (IB′s) using the cationic surfactant cetyltrimethylammonium chloride (CTAC; (CH 3) 3N +C 16H 33Cl) significant proportions of an apparently truncated, lower molecular weight (MW) variant form of recombinant pig growth hormone (rPGH) were observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis relative to pig pituitary derived GH. The formation of this rPGH-like species, designated P-band, was found to occur in vitro during solubilization of IB′s by CTAC and was dependent on pH and temperature of solubilization, but was not due directly to the use of CTAC, as purified soluble rPGH of the correct MW could not be converted to P-band by exposure to CTAC alone. The bacterial proteolysis suspected as being responsible for the in vitro formation of P-band could not be inhibited by the use of a "cocktail" of defined antiproteolytic agents but was inhibited by pH and temperature, and by solubilization of IB′s in 5% SDS, 6 M gnHCl or 7.5 M urea. Detailed characterization of the structure of P-band by N-terminal amino acid sequencing, electrospray mass spectrometry, radio-receptor binding assay, peptide mapping, and C-terminal peptide sequencing confirmed that P-band was approximately 950 mass units smaller than normal rPGH and lacked eight C-terminal amino acids. A significant finding was that P-band is unable to bind to the pig liver-membrane GH receptor in a competitive radioreceptor assay. Analysis of the relative secondary and tertiary structure of P-band by circular dichroism spectra, intrinsic tryptophan-dependent fluorescence, and average surface hydrophobicity (2) suggested small but measurable changes to the overall structure of P-band relative to normal rPGH. Consequently, our results also suggest that the C-terminal portion of rPGH, including in particular the last eight amino acids, is of major importance in the binding of rPGH to the pig liver membrane GH receptor.

Production of methionyl-minus ovine growth hormone in Escherichia coli and one-step purification

The overproduction of ovine growth hormone (oGH) in Escherichia coli is described, achieved in part by alteration of the codon usage for nine of the first 15 amino acids (aa) of the mature hormone. Recombinant oGH (re-oGH), representing 12% of the total cellular protein, was isolated from inclusion bodies by solubilisation using the cationic surfactant cetyltrimethylammonium chloride (CTAC). The hormone was refolded and subsequently purified to greater than 95% homogeneity in a single step using preparative reverse phase high performance liquid chromatography. The aa sequence analysis revealed that the N-terminus of the E. coli-derived polypeptide was identical to that of pituitary-derived oGH, and re-oGH displayed potent somatotropic activity in vivo.

Photoinduced electron transfer from porphyrins to quinones in micellar systems: an FT-EPR study

The photoinduced electron transfer from zinc tetrakis (4-sulfonatophenyl) porphyrin (ZnTPPS) to duroquinone (DQ) in several micellar solutions was investigated with Fourier transform-electron paramagnetic resonance (FT-EPR). The measurements give information on the formation and decay of free radicals, following pulsed-laser excitation of ZnTPPS, with nanosecond time resolution. It was found that the characteristics and time evolution of the EPR spectra depend strongly on surfactant properties. In particular, long-lived [ZnTPPS 3−… DQ −] spin-correlated radical pairs (lifetime > 1 μs) were observed in solutions of the cationic surfactant cetyltrimethylammonium chloride (CTAC). By contrast, radical pair lifetimes in anionic and neutral micelles are shorter than 100 ns. The experimental data can be rationalized in terms of the Coulombic and hydrophobic interactions that determine the spatial organization and stability of the different species (reactants and products) in the microheterogenous systems.