Micellar Solutions Of Cetyltrimethylammonium Bromide Research Articles

Photoinduced Reversible Change of Fluid Viscosity

We report a reversible photoinduced fluid viscosity change. A small amount of a "photoswitchable" azobenzene-modified cationic surfactant (4-butylazobenzene-4'-(oxyethyl)trimethylammonium bromide, AZTMA) was added to a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal). The trans-AZTMA solution had a remarkably high viscosity as a result of the entangled network of wormlike micelles. UV light irradiation on the trans-AZTMA solution remarkably decreased the viscosity of the solution because the bulky structure of cis-AZTMA is likely to disrupt the network structure of wormlike micelles. This photoinduced viscosity change is perfectly reversible between the trans- and cis-AZTMA solutions.

Microrheology of Wormlike Micellar Fluids from the Diffusion of Colloidal Probes

The microrheology of cationic micellar solutions has been investigated as a function of added organic salts using quasielastic light scattering (QELS). Two organic salts, sodium p-toluene sulfonate and sodium salicylate, were used to induce microstructural changes in cetyl trimethylammonium bromide (CTAB) micelles. The mean-squared displacement (MSD) of polystyrene probe particles embedded in CTAB micellar solutions was monitored by QELS in the single-scattering regime. Through the use of the generalized Stokes-Einstein relationship, the frequency-dependent complex shear moduli of each fluid were estimated from the Laplace transform of the corresponding MSD. The salt-induced transition from nearly spherical to elongated wormlike micelles and consequent changes in fluid response from viscous to viscoelastic are clearly captured by microrheology.

Properties of the Silica Layer during the Formation of MCM-41 Studied by EPR of a Silica-Bound Spin Probe

The properties of the silica layer during the formation of the mesoporous material MCM-41 were investigated by electron paramagnetic resonance (EPR) experiments carried out on a specifically designed, organo(trialkoxy)silane spin probe, SL1SiEt. Minute amounts of the spin probe were co-condensed with the silica source, tetraethyl orthosilicate (TEOS), in the synthesis of MCM-41 with cetyltrimethylammonium bromide (CTAB) under basic conditions. The mobility and location of the spin probe were followed in the CTAB micellar solution before the reaction, in the reaction mixture and in the final ordered material. It was found that the EPR spectra of hydrolyzed SL1SiEt throughout the room temperature part of the reaction are characteristic of a fast tumbling species, indicating that the silica is highly fluid prior to drying. After filtering, a slow motion type spectrum was observed, showing that the spin-label experiences considerable motional hindrance. The liquidlike behavior could be restored upon stirring the material in water. When the reaction is performed with a hydrothermal stage, the spectrum of SL1SiEt in the final product is the same as that of the room temperature synthesized material, but the addition of water did not restore the high mobility, due to a higher degree of silica cross-linking. The location of SL1SiEt throughout the formation process was obtained from electron spin-echo envelope modulation (ESEEM) measurements on MCM-41 prepared with CTAB deuterated either at the N-methyl or the alpha position and in a reaction carried out in D2O. Comparing the deuterium modulation depth, k(2H), induced by CTAB-alpha-d2, CTAB-d9, or D2O in CTAB micellar solutions of a number of reference spin probes with those of SL1SiEt revealed that the hydrolyzed SL1SiEt is located near the polar heads of the surfactant in the absence of base and TEOS. This supports the postulation of charge matching at the interface as a driving force for the formation of the mesostructure. Similar experiments carried out on reaction mixtures containing SL1SiEt showed a decrease of k(2H) from CTAB-alpha-d2 and CTAB-d9 compared to the micellar solution, exhibiting practically no time dependence. This indicates that the spin probe is pulled away from the micelle-water interface into the loosely linked, forming silica network. After drying, the modulation depth induced by CTAB-alpha-d2 and CTAB-d9 increases, showing that, once the water is removed, the silica walls contract around the micelles, pushing the silica-linked spin probe into the organic phase within the mesopores.

Structural transitions of cetyltrimethylammonium bromide micelles in aqueous media: Effect of additives

The effect of organic additives ( n-octanol, n-octanoic acid, n-octylamine and n-octane) on the sphere-to-rod transitions in aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB, 0.25 M) was examined by viscosity, conductance, sound velocity and small angle neutron scattering (SANS) measurements. Nonpolar additive n-octane solubilize in the core of micelles which retain sphericity, while additives with polar substituents like octanol, octanoic acid and octylamine forms the additive–CTAB mixed micelles which causes micellar growth. Octanol and octanoic acid is more effective in promoting the sphere-to-rod transition as compared to octylamine. These results are well supported by SANS measurements. The structural transformation is explained by hydrophobic interactions and electrostatic effects between the additives and CTAB micelle.

Protolytic Photodissociation and Proton-Induced Quenching of 1-Naphthol and 2-Octadecyl-1-Naphthol in Micelles

Kinetics of excited-state proton-transfer reactions and proton-induced fluorescence quenching of 1-naphthol (1N) and 2-octadecyl-1-naphthol (2O1N) in micellar solutions of cetyltrimethylammonium bromide (CTAB), polyoxyethylene(23) lauryl ether (Brij 35), and sodium dodecyl sulfate (SDS) was studied by using stationary and time-resolved fluorescence techniques. The ground-state acidity constant of 2O1N in cationic micelles of CTAB was found to be significantly smaller than that of the parent compound (ΔpK = 0.5). However, similar rate and equilibrium constants of the protolytic dissociation were obtained for 1N and 2O1N in the singlet excited state. Effects of nonionic micelles of Brij 35 closely resemble those of CTAB. In anionic micelles of SDS, the protolytic photodissociation was much slower for 2O1N than for 1N. The protonation rate for the excited anions in micellar solutions increases by approximately 2 orders of magnitude in the series CTAB, Brij 35, SDS. Excited-state kinetics was rationalized wit...

Determination of Anticonvulsant Drugs in Pharmaceutical Preparations by Micellar Liquid Chromatography

A micellar liquid chromatographic method for quality control of pharmaceutical preparations (capsules, pills, tablets, injections, drops, and suppositories) containing the anticonvulsant drugs acetazolamide, carbamacepine, chlordiazepoxide, diazepam, ethosuximide, phenytoin, phenobarbital, and zopiclone has been developed. This methodology involves the use of micellar solutions of cetyltrimethylammonium bromide (CTAB) as mobile phases and UV detection. The proposed approach is rapid and reproducible. Sample preparation only requires dissolution with micellar solvent and adequate dilution with the mobile phase before injection into the chromatographic system.

Photoinduced intermolecular electron transfer between Coumarin dyes and electron donating solvents in cetyltrimethylammonium bromide (CTAB) micelles: evidence for Marcus inverted region

The photoinduced electron transfer between different Coumarin dyes and aromatic amines in cetyltrimethylammonium bromide (CTAB) micellar solution has been reported using both steady state and time resolved fluorescence quenching measurement. The location of the dye molecules in micelles has been confirmed by the time resolved fluorescence anisotropy measurement. The plot of the observed K q values in the CTAB micellar solution with the free energy change (Δ G ∘) for electron transfer reaction show an inversion in the observed rate as predicted by Marcus theory. The two-dimensional electron transfer model has been employed to interpret the Marcus inverted region.

Rheological and Photorheological Effects of 6-Alkyl Coumarins in Aqueous Micellar Solutions

Viscosities of aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) and Triton X-100 were measured in the presence and absence of coumarin derivatives, mainly 6-alkyl coumarins with alkyl substituents between methyl and cetyl. The coumarins generally increased the viscosity; the extent of the increase was specific: alkyl chains of medium length showed the largest effects. In situ photodimerization of the coumarins led to a further rise in the viscosity for short alkyl substituents but to a drop in the viscosity in CTAB for long alkyl substituents. Thermodynamic parameters of micelle formation, determined from surface tension measurements, correlate with rheological changes and indicate an increased hydration of the micelles in the cases exhibiting a high viscosity.

Catalytic Hydrolysis of p‐Nitrophenyl Acetate by Copper Ion Complexes of Diamine‐Based Ligands in CTAB Micellar Solution

The catalytic hydrolysis of p‐nitrophenyl acetate (PNPA) by copper ion complexes of diamine‐based ligands in cetyltrimethylammonium bromide (CTAB) micellar solution was investigated kinetically at 25°C. A binary complex kinetic model for metallomicellar catalysis was suggested to treat quantitatively the catalytic hydrolysis of PNPA. The results indicated that copper ion complexes of diamine‐based ligands in CTAB micellar solution catalyze the hydrolysis of PNPA to different extents and the catalytic mechanism is believed to involve copper coordinated water deprotonization to form a nucleophile for nucleophilic attack.

A micellar liquid chromatographic method for quality control of pharmaceutical preparations containing tricyclic antidepressants

Micellar liquid chromatography methods for quality control of pharmaceutical preparations (capsules, pills, tablets, injections) containing the tricyclic antidepressants amineptine, amitriptiline, clomipramine, doxepin, imipramine, melitracen and nortriptyline alone or together with other CNS drugs like diazepam, medazepam and perphenazine are described. The methods using micellar solutions of cetyltrimethylammonium bromide as mobile phases and UV detection are rapid and reproducible. Due to the versatility of interactions in micellar liquid chromatography, it is possible determine highly hydrophobic compounds such as TCAs in a short time using mobile phases containing low organic solvent concentrations and usual flow rates, in contrast with the RP-HPLC methods proposed for these compounds. Samples preparation only requires solution and adequate dilution with the mobile phase before injection into the chromatographic system.

Role of the functional group position in producing viscoelasticity in micellar solutions: A 1H NMR study

Abstract1H NMR spectra of cetyltrimethylammonium bromide (CTAB) micellar solutions in the absence and presence of sodium anthranilate (NaAn) have been recorded. Studies were performed at a fixed CTAB concentration in the presence of different NaAn concentrations. The specificity of the functional group attached to the salt in producing changes (i.e., viscoelasticity) in CTAB micellar solutions was explored. It was concluded that the nature of the salt counterion together with its intercalation/adsorption in the head group region is the principal cause of viscoelasticity.

Flow-Induced Microstructure in Aqueous Cationic Surfactant Solution in the Presence of Structure-Enhancing Additives.

In the present article, we report the flow-induced microstructure in a dilute wormlike micellar solution of cetyltrimethylammonium bromide (CTAB). The additive is sodium salicylate (NaSal) to enhance the supramolecular structure formation. The flow-induced microstructures in surfactant solution were reproduced by the in situ gelation of the substrate. A silicon alkoxide of tetramethylorthosilicate (TMOS) in aqueous hydrochloric acid was used as a silica precursor to capture the microstructure. The captured flow-induced structures in the wormlike micellar solution show alignment to the direction of flow under a weak flow. Meanwhile, at high shear rates, flow-induced coagulation or layer fluctuations occur. The flow-induced morphologies are dependent on the surfactant concentration, molar ratio of NaSal to CTAB, and flow intensity. SEM images taken from the direct observations through in situ gelation are consistent with the rheological responses such as shear thinning or shear thickening behavior.

Micellar effects on the electrochemistry of dopamine and its selective detection in the presence of ascorbic acid

The electrochemistry of dopamine (3-hydroxytyramine) was studied by cyclic voltammetry at a glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles at different pH. The anodic peak potential ( E pa) and peak current ( I pa) were found to be remarkably dependent on the charge and the concentration of the surfactant. The E pa and I pa change abruptly around the critical micellar concentration (CMC) of the surfactants and reach a plateau above the CMC. The E pa at the plateau shifts to more positive values in the cationic CTAB micellar solution, e.g. from 180 mV vs SCE in aqueous solution at pH 6.8 to 410 mV in CTAB micelle, whilst it shifts to less positive values in the anionic SDS micellar solution, e.g. 150 mV at pH 6.8. Therefore, the overlapped anodic peaks of dopamine and ascorbic acid in the mixture of the two compounds in aqueous solutions can be separated in CTAB micelles since the micelle shifts the E pa of ascorbic acid to less positive values. The two peaks are separated by ca. 400 mV at pH 6.8 in CTAB micelle, hence dopamine can be determined in the presence of 100 times excess of ascorbic acid. In SDS micelle and in the presence of ascorbic acid, the I pa of dopamine is greatly enhanced due to the catalytic oxidation of the latter that enables quantitative determination of both compounds.

Solubilization of short chain phenylalkanoic acids by a cationic surfactant, cetyltrimethylammonium bromide

The solubilization of short chain phenylalkanoic acids by the aqueous micellar solution of cetyltrimethylammonium bromide (CTAB) has been studied as a function of surfactant concentration. The micelle-water partition coefficient, K x , and the standard free energy change of solubilization, Δ G° p, of these additives in the CTAB micelles was determined by using both differential spectroscopic and conductance data at 25.0°C. The critical micelle concentration (CMC) of CTAB in the presence of small amount of these additives was determined by conductivity method. The relative solubility and approximate number of additive molecules per micelle was also estimated at a particular concentration of the surfactant.

Resonance Raman investigation of nickel microperoxidase-11.

Resonance Raman and UV-visible absorption spectra show that nickel(II) microperoxidase-11 (NiMP-11) is four-coordinate in aqueous solution in the pH range from 1.0 to 13.0. In aqueous solutions of NiMP-11 in the absence of cetyltrimethylammonium bromide (CTAB), NiMP-11 is aggregated. In CTAB micellar solutions, where aggregation of NiMP-11 does not occur, the Raman spectra of NiMP-11 are similar to that of nickel(II) cytochrome c (NiCyt-c). The presence of the peptide segment shifts the equilibrium heavily in favor of the nonplanar form, just as does the entire protein component in the case of NiCyt-c. This further elucidates the structural mechanism by which the protein segment ruffles the heme, most likely modulating the redox potential as indicated for the cytochromes c3 [Ma, J.-G., et al. (1998) Biochemistry 37, 12431-12442]. Furthermore, the hydrophobic environment that is provided by the CTAB micelle is found to be crucial to the native folding of the pentapeptide and formation of two hydrogen bonds in the peptide backbone. These two H-bonds act to contract the peptide segment exerting the force on the macrocycle that causes the ruffling and makes the redox potential more negative than if the heme were to remain planar. The structure of the heme and pentapeptide may also be associated with redox-linked triggering of the formation and release of cytochrome-protein complexes.

Micellar effects on the oxidative electrochemistry of lipophilic vitamin C derivatives

The anodic oxidation of ascorbic acid (VC) and its lipophilic derivatives ascorbyl-6-caprylate (VC-8),‡ 6-laurate (VC-12) and 6-palmitate (VC-16) have been studied by cyclic voltammetry at a glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles. The peak potentials (Epa) and peak currents (ipa) have been found to be remarkably dependent on the lipophilicity of the VCs and on the character and concentration of the surfactant. Making VC lipophilic remarkably shifts its peak potential to negative values, the Epa being 200, 70, –85 and –125 mV (vs. SCE) in aqueous solution at pH 6.8 for VC, VC-8, VC-12 and VC-16, respectively. In micellar solutions the Epa and ipa change abruptly around the critical micellar concentration (CMC) of the surfactants and reach a plateau above the CMC. The Epa at the plateau is shifted to more positive values in SDS micelles. It is shifted to more negative values in CTAB micelles except in the case of VC-16, whose Epa is shifted to the positive direction. The effectiveness of the micellar effect decreases in the order VC > VC-8 > VC-12 > VC-16. Sharp current maxima appeared in CTAB micellar solution below its CMC for VC-8, VC-12 and VC-16, demonstrating adsorption of these lipophilic VCs at the electrode surface and formation of premicellar aggregates. The electron-transfer rate constants and diffusion coefficients have been calculated from the cyclic voltammograms. From these data it is concluded that the hydrophobic/lipophilic interaction of the hydrocarbon tail and the electrostatic interaction of the ascorbate anion moiety of the VCs are the dominant factors controlling their electrochemical behaviour in micellar solutions.

Shear Thickening of an Aqueous Micellar Solution of Cetyltrimethylammonium Bromide and Sodium Tosylate

In this experimental study we give results concerning the shear thickening behavior exhibited by an aqueous cationic surfactant solution of CTAB in the presence of added NaTOS. We carefully investigate the rheological characteristics of this phenomenon corresponding to a shear induced state (SIS), the reproductibility and also the transient regimes. We show that with steady experiments there exist no hysteresis effect. Finally we give the evolution of the shear thickening characteristics against temperature.

Relaxation of Excited Eu(III) Complexes in Cetyltrimethylammonium Bromide Micellar Solutions

Relaxation of Excited Eu(III) Complexes in Cetyltrimethylammonium Bromide Micellar Solutions

Measurement of the Solubility of Benzene in Micellar Solution by NMR

The solubilities of benzene in micellar solutions of cetyltrimethylammonium bromide (CTAB)/D 2O and decyltrimethylammonium bromide (DTAB)/D 2O, and in D 2O have been determined by 1 H NMR spectroscopy. The average solubility of benzene in 0.15 M CTAB/D 2O was found to be 3.35 ± 0.05% (wt/wt) (benzene/0.15 M CTAB/D 2O), 1.18 ± 0.09% (wt/ wt) (benzene/0.15 M DTAB/D 2O) in 0.15 M DTAB/D 2O, and 0.074 ± 0.004% (wt/wt) (benzene/D 2O) in D 2O. Values of ΔG = -5.0 kcal/mol and -4.8 kcal/mol were determined for the free energy of transfer of benzene from D 2O to micelle for 0.15 M CTAB/D 2O and 0.15 M DTAB/D 2O micellar solutions, respectively.

The effect of the nature of the surfactant on the location of 6-R-2,2,4-trimethyl-1,2-dihydroquinolines in micelles

The locus of solubilization of 6-R-2,2,4-trimethyl-1,2-dihydroquinoline molecules (R=Me, OEt) in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) has been determined by comparing the UV spectra of micellar solutions of the dihydroquinolines and their solutions in solvents of various polarities. The parameterRpv (defined as the ratio of the absorbance of the long-wave band maximum to that at the adjacent valley) decreases with an increase in the solvent polarity in the order:n-heptane > 2-propanol > ethanol > H2O. In SDS micellar solutions,Rpv is close to the corresponding value in water and does not depend on [SDS]. In CTAB micellar solutions,Rpv is essentially greater than in water and increases with [CTAB]. Thus, the solubilized dihydroquinoline molecules in SDS micelles reside in the Stern layer, and in CTAB micelles they are located both in the interior of the micelle and in the Stern layer; in this case the micelle packing begins from the core.