Micellar Solutions Of Cetyltrimethylammonium Bromide Research Articles

Comparative analysis of fluorescent methods selectivity for ecotoxicants environmental monitoring

A comparative analysis of classical and synchronous fluorescent methods selectivity for ecotoxicants determination of polycyclic aromatic hydrocarbons (PAHs) was carried out. PAHs sorption preconcentration from aqueous cetyltrimethylammonium bromide micellar solutions and spectra recording on a viscose matrix were used. In the case of complex environmental samples, the scope of fluorimetric analysis can be expanded by registering synchronous fluorescence spectra obtained by simultaneously scanning the excitation and emission wavelengths with a constant shift: λem - λex = Δλ = const. The composition of PAHs mixture (phenanthrene, anthracene, fluorene, pyrene) was experimentally evaluated by classical fluorescence with selective excitation and synchronous fluorescence. It was concluded that the use of synchronous spectra makes it possible to improve the selectivity of the PAHs fluorescence analysis in a mixture. These methods can be successfully applied to identify individual PAHs in monitoring of environment water bodies.

Hydrolytic reactivity of novel copper(II) complexes with reduced N-salicylate threonine Schiff bases: distinguishable effects of various micelles

Three new bi- or tetranuclear copper (II) complexes (complexes 1, 2 and 3) with reduced N-salicylate threonine were synthesized and characterized by single crystal X-ray diffraction, X-ray powder diffraction, UV–vis, and thermogravimetric analysis. Single-crystal diffraction analysis reveals that these complexes have similar coordination modes and conformations which were linked into multidimensional networks through some weak interactions. These three complexes were employed to promote the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA). Catalytic reactivities of the as-prepared complexes show that in the hydrolysis of p-nitrophenyl acetate (PNPA) these three complexes provide 51, 45, 39-fold rate acceleration as compared to spontaneous hydrolysis of PNPA at pH 7.0, respectively. Under selected conditions, excess three orders of magnitude rate enhancement were observed for the catalytic hydrolysis of another carboxylic ester, p-nitrophenyl picolinate (PNPP). Furthermore, these complexes efficiently promote the PNPA hydrolysis in micellar solution of cetyltrimethylammonium bromide (CTAB) or bis(hexadecylhexmethyl ammonium)ethane bromide (16−6−16) giving rise to excess two orders of magnitude rate enhancement which is approximate 2.0 − 4.0 times higher than that in the buffer. However, the introduction of micelles of n-lauroylsarcosine sodium (LSS) or double-chained C22/8 surfactant did not increase the rate or even inhibited the hydrolysis reaction in contrast with buffered aqueous medium.

Surfactant Micelles Enable Metal‐Free Spirocyclization of Keto‐Ynamides and Access to Aza‐Spiro Scaffolds in Aqueous Media

Micellar solutions of cetyltrimethylammonium bromide (CTAB) surfactant allow the spirocyclization of keto‐ynamides in an aqueous medium without recourse to transition‐metal catalysis, enabling access in water to naturally occurring aza‐spiro compounds with potential in drug discovery. The reaction was monitored by dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo‐TEM), which determined the morphology and change in size of the micelles before and after incorporation of the substrate and achievement of 5‐endo‐dig cyclization inside the micelles.

Influences of Micelle Formation and Added Salts on the Hydrolysis Reaction Rate of p‐Nitrophenyl Benzoate in Aqueous Buffered Media

ABSTRACTThe hydrolysis reaction rate of p‐nitrophenyl benzoate (p‐NPB) has been examined in aqueous buffer media of pH 9.18, containing surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), or sodium dodecyl sulfate (SDS) at 35°C. Although the rate constant [log (k/s−1)] of p‐NPB hydrolysis has once decreased slightly below the critical micelle concentration (CMC) value for CTAB and CTAC, it has begun to increase drastically with micellar formation. With increasing concentrations larger than the CMC value, the log (k/s−1) value has reached the optimal value, i.e., a 140‐ and 200‐fold rate acceleration for CTAB and CTAC, respectively, compared to that without a surfactant. Whereas the anionic surfactant, SDS, has caused only a gradual rate deceleration in the whole concentration range (up to 0.03 mol dm−3). Increases in pH of the buffer have resulted in increases of the hydrolysis rate. In the CTAB micellar solution, the remarkably enhanced rate has been retarded significantly by the addition of only 0.10 mol dm−3 bromide salts. The effects of rate retardation caused by the added salts follows in the order of NaBr > Me4NBr > Et4NBr > Pr4NBr > n‐Bu4NBr. In the absence of surfactant, however, the addition of the bromide salts has accelerated the hydrolysis rate, except for the metallic salt of NaBr, with the order of Me4NBr < Et4NBr < Pr4NBr < n‐Bu4NBr. In the CTAC micellar solution, similar rate retardation effects have been observed in the presence of chloride salts (NaCl, Et4NCl, and n‐Bu4NCl). The effects of added salts have been interpreted from the viewpoints of the changes in activity of the OH− ion and/or the nucleophilicities of the anions from the added salts.

Electroreduction of Nitrobenzene: Nominal Simulation of Voltammogram

For the electrochemical reduction of nitrobenzene in aqueous cationic micellar solution of cetyltrimethylammonium bromide [CTAB] at platinum electrode using cyclic voltammetry, a reversible/quasi reversible charge transfer reaction pertaining to one electron couple of ArNO2/ArNO2.- was indicated (1). Digital simulation was used to evaluate electrochemical kinetic parameters for the mono-electron transfer step (1). An ECE mechanism, Scheme-1 and Figures 1 and 2 and Table-1, is suggested for the previously reported voltammograms (2) featuring nitrobenzene reduction on a coated platinum electrode partially covered by a thin film of dioctadecyldimethylammonium chloride [DODAC]. Table-1: Diffusion coefficients for nitrobenzene (2) Diffusion coefficient (cm2/s) 6.11×10-5 1.09×10-4 Bare Pt DODAC covered Pt, this work References (1) Tariq, M.; Haque, I. U., Science International (Lahore), 2016, 28, 361 (2) Haque, I. U.; Tariq, M., Journal of the Chemical Society of Pakistan, 2011, 33, 529 Figure 1

The physicochemical properties of CTAB solutions in the presence of α-tocopherol

The electrolytic conductivity, electrophoretic mobility and zeta potential (LDV - laser Doppler velocimetry method) as well as the particles size distribution (DLS - dynamic light scattering method) were determined in the cetyltrimethylammonium bromide (CTAB) solutions (0.25–25.00mM) at different concentrations of α-tocopherol (0–11.6mM). The measurements were made at 25°C and 30°C. It was found that α-tocopherol (vitamin E) modifies the physicochemical properties of CTAB micellar solutions – the potential carrier of bioactive substances. The electrolytic conductivity of CTAB solutions was lowered by the addition of α-tocopherol. Particularly, the effect was observed in the concentration range 0.25–2.5mM, i.e. in the vicinity of CMC. The critical micelle concentration (CMC) of CTAB solutions determined from the conductivity data decreased with the increasing vitamin E content due to the mixed aggregates formation. At the same time the electrophoretic mobility and zeta potential increased as a result of higher degree of the mixed aggregates dissociation. This effect was observed for all surfactant concentrations at both temperatures. The hydrodynamic diameter of mixed CTAB/α-tocopherol particles increased from 7–8nm for the CTAB solutions to 50–60nm for those containing vitamin E. The information about the aggregates size and their electrokinetic properties can be useful in predicting the encapsulation of biomolecules in the surfactant micelles and their transport by different membranes.

ひも状ミセル水溶液中でのせん断波の伝播速度と減衰特性

Shear wave speeds of aqueous wormlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) were measured in a surfactant concentration range of 2-50 mM at different counterion to surfactant concentration ratios. Shear waves were excited by the impulsive motion of a flat plate driven by a solenoid-based actuator, and were visualized by using a circular polariscope and a CCD camera. The shear wave speed was determined by tracking the position of a light intensity peak over several frames. Shear wave speeds were found to strongly depend on the surfactant concentration rather than on counterion to surfactant ratios, and were found to increase proportionally to the surfactant concentration in this concentration range. The attenuation factor of the exponential decay of the wave front was not obtained because the stress jump across the wave front was smoothed significantly.

Electrochemical Behavior of Nitrobenzene in Aqueous CTAB

A mechanistic study of the electroreduction of nitrobenzene was undertaken following previously reported voltammetric investigations of nitrobenzene reduction on bare and dioctadecyldimethylammonium chloride (DODAC) covered platinum electrode [1]. The electrochemical reduction of nitrobenzene in aqueous micellar solution of cetyltrimethylammonium bromide (CTAB) at platinum electrode using cyclic voltammetry revealed two distinct cathodic and anodic peaks with interpeak separation of about 60-65 mV indicating a reversible/quasi-reversible charge transfer reaction pertaining to one electron couple of ArNO2/ArNO2 .- as reported in literature [2-6]. Additional interpretation of experimental cyclic voltammogram was done by using digital simulation. Diffusion co-efficient values of nitrobenzene calculated using Randle-Sevcik equation were found close to the reported values [5-6]. References (1) Haque, I. U.; Tariq, M. J. Chem. Soc. Pak. 2011, 33, 529-534. (2) Sripriya, R.; Chandrasekaran, M.; Noel, M. Colloid Polym Sci. 2006, 285, 39-48. (3) Ernst, S.; Ward, K. R; Norman, S. E.; Hardacre, C.; Compton, R. G. Phys. Chem. Chem. Phys. 2013, 15, 6382-6389. (4) Jara-Ulloa, P.; Nunez-Vergara, L. J.; Squella, J. A. Electroanal. 2007, 19, 1490-1495. (5) Smith, W. H.; Bard, A. J. J. Am. Chem. Soc. 1975, 97, 5203-5210. (6) Kaifer, A. E.; Bard, A. J. J. Phys. Chem., 1985, 89, 4876-4880.

S0520202 大振幅せん断振動におけるひも状ミセル水溶液のシアバンド形成過程

The formation process of Shear-bands in a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in the large amplitude oscillatory shear (LAOS) is examined experimentally. A transient response of shear stress after applying a large amplitude sinusoidal strain is measured by rheometer with concentric cylinder. In order to observe the spatial distribution of the optical anisotropy in the flow field, a new visualization technique recently developed by the authors, which can evaluate distribution of both the birefringence and the orientation angle from a photograph taken by the crossed-Nicols method, was applied. The highly-birefringent layer was formed near the moving wall when the strain exceeds 2.3 in the LAOS flow. In the oscillation with the higher strain, the shear-bands are formed but the bands disappeared at when the strain turns to zero. Therefore, the formation and dissipation of the shear-bands are repeated in each cycle of the LAOS flow.

Effect of Urea on the Kinetics of the Alkaline Hydrolysis of Crystal Violet Catalyzed by Aqueous Micellar Solutions of Cetyltrimethylammonium Bromide

Kinetics of alkaline hydrolysis of crystal violet (CV) in micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), both in absence and presence of urea was investigated. The reaction was catalyzed by micelles of CTAB and addition of urea caused a gradual decrease in the rate of the reaction. Kinetic results could be correlated with change in micellization behavior of CTAB by water structure breaking effect of urea. The kinetic profiles have been fitted with the simulated profiles on the basis of pseudophase ion-exchange model and best fits with reasonable parameters could be obtained.

Hydrolytic cleavage of p-nitrophenyl picolinate by mononuclear Zn(II) and Co(II) complexes with imidazole derivative in CTAB micellar solution

One new hydroxyl-functionalized imidazole derivative (L) was synthesized and characterized. Further, the related mononuclear zinc(II) and cobalt(II) complexes were prepared and used as mimic hydrolases to catalyze the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) in buffered aqueous solution and a micellar solution of cetyltrimethylammonium bromide (CTAB). Observations show that for all of catalytic systems, the hydrolysis of PNPP was pH-dependent in the pH range of 7.00–8.20. Besides, hydrolysis rates of PNPP displayed a constant increase with the increasing concentration of substrate. In the case of CoL-containing system, moreover, much greater acceleration for PNPP hydrolysis was observed in comparison with the ZnL-containing system. However, micellar effect of CTAB micelle aggregates on the PNPP hydrolysis was not obvious only showing 1.0 ∼ 1.3 folds rate difference in contrast to buffered aqueous solution.

Physicochemical investigation and spectral properties of Sunset Yellow dye in cetyltrimethylammonium bromide micellar solution under different pH conditions

To mimic binding to biological membranes, the extent of interaction of the efficient food dye Sunset Yellow with a cationic surfactant, cetyltrimethylammonium bromide, was probed by quantifying its absorption and fluorescence emission spectra as a function of premicellar to post‐micellar surfactant concentration. The characteristics of the partition behaviour and spectral‐luminescent properties of Sunset Yellow–surfactant have been evaluated qualitatively as well as quantitatively for various cetyltrimethylammonium bromide concentrations. With the help of mathematical models, the water–micelle partition coefficient, the Sunset Yellow–cetyltrimethylammonium bromide binding constant, the binding capacity, and the degree of counterion binding were calculated at 25 °C under various pH conditions. The solubilisation of Sunset Yellow is also discussed from the thermodynamics viewpoint by considering the standard free energy change of dye solubilisation and the Sunset Yellow–cetyltrimethylammonium bromide binding energy. The high values of all these interactions indicate that the dye, being organic in nature, is partitioned largely from the aqueous environment to the palisade layer of the micelle. The solubilisation of the dye is enhanced by switching the pH to suppress the self‐aggregation of dye molecules. Combined with electrostatic forces, the hydrophobic interactions also play a promising role in the solubilisation of Sunset Yellow in the outer core of the micellar interior.

Organo-Modified Montmorillonite Enhanced Chemiluminescence via Inactivation of Halide Counterions in a Micellar Solution

In this work, it was found that cationic surfactant cetyltrimethylammonium bromide (CTAB)-modified montomorillonite (MMT) can significantly amplify chemiluminescence (CL) from the peroxynitrite system. Transmission electron microscopy (TEM), scanning electron microscope (SEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ζ potential measurements and differential thermogravimetry (DTG) analyses confirmed the geometrical configuration of CTAB at the surface of MMT. In addition, the enhancement mechanism of CTAB-modified MMT on the peroxynitrite CL was discussed by the CL spectrum, the scavengers of reactive oxygen species, and various controlled experiments. The results indicated that the electrostatic attraction between CTA+ cations and MMT could form a CTA+ monolayer at the surface of MMT, resulting in the effective removal of halide counterions in the CTAB micellar solution. Therefore, the inactivation of the halide counterion-quenched CL could generate the intense CL emissions. The success of this work has explored a novel route to the applications of clay nanocomposites in CL field.

Self-healing hydrogels formed in catanionic surfactant solutions

Physical gels with remarkable properties were obtained by copolymerization of acrylamide with the hydrophobic monomer stearyl methacrylate (C18) in a micellar solution of cetyltrimethylammonium bromide (CTAB) containing up to 15 mol% sodium dodecyl sulfate (SDS). The addition of SDS causes the CTAB micelles to grow and thus enables solubilization of C18. The gels exhibit time-dependent dynamic moduli, high elongation ratios at break (1800–5000%), and self-healing, as evidenced by rheological and mechanical measurements and substantiated by dynamic light scattering. As the size of the micelles in the gelation solution increases, both the degree of temporary spatial inhomogeneity and the lifetime of hydrophobic associations in the gels increase while the elongation ratio at break decreases. Although the physical gels were insoluble in water due to strong hydrophobic interactions, they could be solubilized in surfactant solutions thus providing a means of characterization of the network chains. Viscometric and rheological behaviors of polymer solutions show a substantial increase in the associativity of the network chains with rising micelle size, which results in prolonged lifetime of hydrophobic associations acting as physical cross-links in gels. The internal dynamics of self-healing gels could thus be controlled by the associativity of the network chains which in turn depends on the size of CTAB micelles.

Electrodeposition of Nickel from Reverse Micellar Solutions of Cetyltrimethylammonium Bromide

Electrochemical behavior of nickel chloride was investigated in aqueous and reverse micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) on glassy carbon (GC) and copper electrodes by cyclic voltammetric measurements. The electrochemical reduction of nickel ion to metallic nickel has been found to occur with ease on a copper electrode in aqueous solution. Electrodeposition of nickel on a copper substrate was therefore performed from reverse micellar solutions of CTAB/1-butanol/water with different water content using coulometric method at a fixed potential below the reduction potential. Morphology and microstructure of the deposits were examined by scanning electron microscopy; while elemental characterization was carried out by energy dispersive X-ray spectroscopic method and X-ray diffraction technique. The variation in the composition of the reverse micellar solutions brings about changes in the size and distribution of reverse micelles as revealed by dynamic light scattering measurements and consequently influences the morphology of electrodeposited nickel. The mechanism of electrodepostion of nickel from reverse micellar solutions has been elucidated and the organized media have, for the first time, been established as a suitable one for electrodeposition of nickel with tunable microstructure and morphology through systematic variation of the composition of the reverse micellar solutions.

Quantitative Correlation between Counterion (X) Affinity to Cationic Micelles and X-Induced Micellar Growth for X = 2,4-; 2,5-; 2,6- and 3,4-Dichlorobenzoate Ions

A semi empirical kinetic (SEK) method has been used to determine the ratio of cetyltrimethylammonium bromide (CTABr) micellar binding constants of counterion X⁻ and Br⁻ (a reference counterion), i.e. K(X)/K(Br) (=R(X)(Br)). The values of K(X) and K(Br) have been derived from the kinetic parameters obtained in the presence spherical/non-spherical and spherical micelles, respectively. This rather new method gives the respective mean values of R(X)(Br) as 45±2, 25±3, 4.7±0.6 and 119±10 for X=2,4-, 2,5-, 2,6- and 3,4-Cl₂C₆H₃CO₂⁻ (Cl₂Bz'Na). Literature lacks the report on the values of R(X)(Br) for all X except for X=2,6-Cl₂C₆H₃CO₂⁻ (2,6-Cl2Bz'⁻) for which the reported value is 5.0. Rheological properties, such as shear thinning behavior, reveal indirectly the presence of wormlike micelles (WM) in the CTABr micellar solutions containing MX for all X except X=2,6-Cl₂Bz'⁻. The micelles remain spherical within [2,6-Cl₂Bz'⁻] range 0.01-0.34 M at 0.015 M CTABr. The maxima of the plots of zero shear viscosity, η₀, (obtained from the initial plateau region of flow curves, i.e. η vs. γ curve) vs. [MX] (MX=2,4-, 2,5- and 3,4-Cl₂Bz'Na) at 0.015 M CTABr also support indirectly the presence of linear, entangled and branched WM.

Flow-induced structure change of CTAB/NaSal aqueous solutions in step planar elongation flow

Accurately controlled step planar elongation flow generated by a two-dimensional squeezing flow cell was applied to wormlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in water. Opaque regions were observed in the center plane and at the corners of the flow field during squeeze flow. The opaque region in the center plane is caused by planar elongation flow, resulting in elongation-induced structure (EIS), while the corner opaque regions are mainly induced by shear, generating shear-induced structure (SIS). SIS at the corners appeared earlier than EIS in the center plane in the squeezing process, but the strain required to generate EIS is considerably smaller than strain for SIS. In the case of high elongation rate and large strain, flow fluctuations appeared after EIS and SIS occurred. The appearance of both EIS and SIS are related to strain, the Weissenberg number, the Deborah number, and the concentration ratio of CTAB and NaSal in the solution but independent of the initial structure of the micelles in solution.

Rheo-SANS Studies on Shear-Thickening/Thinning in Aqueous Rodlike Micellar Solutions

Shear-induced thickening/thinning phenomena of aqueous rodlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and micellar structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems.

Investigation Micellar Catalysis of p-Nitrophenyl Acetate Hydrolysis with Mn(Niten)2H2O Complex

In this article, a mononuclear Mn(Niten)2H2O complex was prepared to catalyze hydrolysis of p-nitrophenyl acetate (PNPA) in presence of Cetyltrimethylammonium bromide (CTAB) micellar system in different pH range from 6.5–10 at 25°C. These results obtained indicate that the complex exhibits good catalytic function. It also appears the complex accelerates the hydrolytic cleavage of PNPA in cationic CTAB micellar solution which may be due to coordinating ability of substrate to complex, electrostatic interaction between micelles and complex and due to electrostatic interaction between micelles with reactant.

Plasmon-resonant nanoparticles and nanostars with magnetic cores: synthesis and magnetomotive imaging.

Plasmon-resonant gold nanostars (NSTs) with magnetic cores were synthesized by a multistep sequence from superparamagnetic Fe3O4 nanoparticles (NPs) and evaluated as optical contrast agents under magnetomotive (MM) imaging conditions. Core-shell Fe3O4@Au NPs were prepared in nonpolar organic solvents with nanometer control over shell thickness and with good epitaxy to the Fe3O4 surface. Anisotropic growth was performed in micellar solutions of cetyltrimethylammonium bromide (CTAB) under mildly reducing conditions, resulting in NSTs with physical features similar to those produced from colloidal gold seeds. NSTs could be produced below 100 nm from tip to tip, but seed size had a significant impact on growth habit, with larger seed particles producing submicrometer-sized "morning stars". Both NSTs and aggregated core-shell NPs are responsive to in-plane magnetic field gradients and can provide enhanced near-infrared (NIR) contrast under MM conditions, but do so by different mechanisms. NSTs can modulate polarized NIR scattering with minimal translational motion, giving the appearance of a periodic but stationary "blinking", whereas core-shell NP aggregates require lateral displacement for signal modulation. The polarization-sensitive MM imaging modality offers the dual advantage of enhanced signal quality and reduced background signal and can be applied toward the detection of magnetomotive NSTs in heterogeneous biological samples, as illustrated by their detection inside of granular cells such as macrophages.