Sodium Dodecyl Sulfate Micellar Solutions Research Articles

Dynamic light scattering of an ionic SDS micellar solution under an AC electric field

The phase separation behavior of near-critical ionic sodium-dodecyl-sulfate (SDS) micellar solution under a sinusoidal electric field was investigated by phase-contrast optical microscopy and by the small-angle dynamic light scattering method. The sinusoidal electric field significantly deformed the concentration domains and shifted the phase separation temperature. The autocorrelation function under a sinusoidal electric field was measured in the vicinity of a phase separation temperature range of 0.10 K < Tp – T < 0.97 K, where Tp – T is the temperature distance from the phase separation temperature in quiescent state Tp. The correlation function with an oscillatory part in the longer correlation time region was observed. The occurrence of the oscillatory mode, which depended on both the applied field frequency and the ambient temperature, indicates deformation of concentration fluctuation domains by dynamical coupling between the phase separation and the applied sinusoidal electric field.

Microviscosity Dependence of Magnetic Isotope Effect on Radical Pair Decay Rates in SDS Micellar Solution

Abstract The microviscosity dependences of the magnetic field and magnetic isotope effects on disappearance of radical pairs (RPs) comprising benzophenone ketyl and alkyl radicals were investigated in sodium dodecyl sulfate (SDS) micellar solutions. The increase in microviscosity of the SDS micelle by adding MgCl2 caused not only a deceleration in the escape rate of the component radicals from the micelle but also a small magnetic isotope effect on the RP decay rate. The small magnetic isotope effect was explained by an increase in the correlation time of the radical motion, which is coupled with the anisotropic hyperfine interaction modulating the spin-lattice relaxation of RP.

Micellar electrokinetic chromatography of polychlorinated biphenyl congeners using a polymeric surfactant as the pseudostationary phase

Micellar electrokinetic chromatography (MEKC) of highly hydrophobic compounds is generally difficult using sodium dodecyl sulfate micellar solutions. The polymeric surfactant, polysodium undecyl sulfate (poly-SUS) has been used to separate moderately to highly hydrophobic polychlorinated biphenyl (PCB) congeners by MEKC in the absence of cyclodextrins. Parameters such as concentration of acetonitrile (ACN), polymeric surfactant concentration, and the effect of pH were examined. Optimum MEKC conditions to get baseline resolution of nine PCBs was 7.5 m M borate in 40% (v/v) ACN fraction buffered at pH 9.2 using 0.5% (w/v) poly-SUS. The applied voltage was 30 kV and the temperature was maintained at 25°C. Elution order for each PCB congener was found to be dependent on the degree of chlorination and hydrophobic character.

Diffusion Coefficients of Three Organic Solutes in Aqueous Sodium Dodecyl Sulfate Solutions

Tracer diffusion coefficients of phenol, toluene, and benzoic acid in aqueous solutions of sodium dodecyl sulfate (SDS) were measured by the Taylor dispersion technique. In addition, the viscosities and densities of the SDS solutions were measured. For phenol and toluene, the effect of micelle formation on the diffusion coefficient is pronounced. When the SDS concentration is below the critical micelle concentration (cmc), the diffusion coefficients are almost independent of the SDS concentration. However, above the cmc there is a rapid decrease in the diffusion coefficients, and the apparent diffusion coefficients of the two solutes are the weighted average of free solute diffusion and the micelle diffusion. A model is presented to describe the diffusion behavior of the two solutes in aqueous micellar solutions of SDS. The interaction between the two solutes and the micelles has been investigated and the fraction of each solute that is solubilized by the micelles is estimated from the measured apparent diffusion coefficient. For benzoic acid, the diffusion coefficient is dependent on the joint contribution of the benzoic acid molecules that are solubilized by the micelles as well as the corresponding benzoate ions. The effect of micelle formation on the diffusion coefficient of benzoic acid is not as pronounced as for phenol and toluene.

A monolayer complex of Cu2(OH)3C12H25SO4 directly precipitated from an aqueous SDS solution.

A layered complex with the chemical composition of Cu2(OH)3C12H25OSO3 was obtained through direct precipitation from a sodium dodecyl sulfate micellar solution of Cu(II) at a nearly neutral condition (pH approximately equals 6.8). From the XRD, 13C CPMAS NMR, and the spin probe ESR observations, a modified botallackite structure with a monolayer alkyl phase was proposed for the complex. Magnetic susceptibility measurements for the complex showed that there exist at least two exchange couplings: one is positive, and its magnitude is larger than that of the other, which is negative (J approximately equals -8 K). Although the cupric ions of the complex are paramagnetic, most of those are ESR silent and only the ESR signals from defects could be observed even at 298 K. A spin clustering model has been employed to explain the magnetic properties of the complex.

Distribution of nonionic compounds between the gas phase and sodium dodecyl sulfate micelles

Regression analysis of the influence of the structure of nonionic organic compounds on their partition coefficients (K gm) between the sodium dodecyl sulfate (SDS) micelles and the gas phase in aqueous micellar SDS solutions was performed using the descriptors characterizing the mechanisms of interaction between these compounds and SDS micelles. For alkanes and compounds with hydroxyl groups, as well as for aromatic and aliphatic compounds without hydroxyl groups, the log(K gm) values are described by separate regression equations, which is due to specific features of intermolecular interactions for these types of organic compounds in the case of their solubilization by SDS micelles.

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.

Influence of Changes in the Interfacial Electrical Potential on a Ligand Substitution Reaction in Aqueous Sodium Dodecyl Sulfate Micellar Solutions

The ligand substitution reaction between Fe(CN)5H2O3- and β-Co(trien)2(pzCO2)2+ (trien = triethylenetetraammine; pzCO2 = pyrazinecarboxylate) was studied in aqueous salt and sodium dodecyl sulfate micellar solutions. In homogeneus aqueous solutions, an increase in the concentration of the background electrolytes resulted in a decrease in the observed rate constant. This was explained by considering the influence of the salts on the activity coefficients of the participants in the reaction using a Guggenheim−Guntleberg-type equation. In sodium dodecyl sulfate micellar solutions, the effect of the variation of the surfactant concentration operated mainly through its influence on the approaching process between the two oppositely charged reactants. When the surfactant concentration is high enough to ensure the total incorporation of the Co(III) complex molecules into the micellar pseudophase, the decrease in the electrical component of the free energy of activation (controlled by changes in the interfacial electrical potential, ΔΨ) is responsible for the increase in the observed rate constant when [SDS] increases. The addition of salts and alcohols to the sodium dodecyl sulfate micellar reaction media provokes an increase in the observed rate constant, this increase being greater the higher the [additive]. This can be explained considering that the presence of these additives results in a diminution of the electric component of the free energy of activation due to a decrease in |ΔΨ| of the negatively charged micelles.

The effect of an external heavy atom on the sensitized room temperature phosphorescence in aqueous micellar solutions of sodium dodecylsulphate

The process of triplet–triplet excitation energy transfer between a triphaflavine molecule (donor) and molecules of polycyclic aromatic hydrocarbons (PAH) (acceptor) in micelles of sodium dodecylsulphate was studied. The sensitized room-temperature phosphorescence was shown to occur in the presence of external thallium “heavy” ions for pyrene and benz[a]anthracene. The decay rate constants of PAH triplet states, as well as the quenching rate constants of these states by thallium ions in the case of a direct excitation of PAH in their absorption band and by triplet–triplet energy transfer from triphaflavine were determined and discussed.

Phosphorescence of molecules of polycyclic aromatic hydrocarbons in aqueous micellar solutions of sodium dodecylsulfate at room temperature

Deactivation of the excited states of pyrene, benzanthracene, and fluorene molecules in aqueous micellar solutions of sodium dodecylsufate is studied using steady and pulsed fluorimetry. Quenching of the singlet states of polyatomic hydrocarbons by thallium ions is considered. Effective, micellar, and biomolecular constants for the quenching rate are obtained. Phosphorescence constants for the aforementioned compounds are determined. Reasons behind the possibility of observing phosphorescence of polyaromatic compounds in micellar solutions at room temperature are ascertained.

Determination of Parabens in Cosmetics without Previous Extraction by Micellar Liquid Chromatography

A simple and rapid micellar liquid chromatography method for the determination of p-hydroxybenzoic acid esters (methyl-, ethyl-, n-propyl-, and n-butylparaben) in cosmetics (bath foam, milk lotion, hand cream, cream base, and shampoo) is described. The samples are solved with n-propanol, further diluted with more n-propanol or with an aqueous sodium dodecyl sulphate (SDS) micellar solution, and injected. Separations are performed with a micellar mobile phase containing 0.1M SDS, 2.5% n-propanol, 10mM phosphate (pH 3), and with an octadecyl silica column (C 18 ). Calibrations are linear (correlation coefficient r > 0.999) and the limits of detection range from 0.03 to 0.3 ng paraben. The determination of parabens at concentrations well below the levels used in cosmetic formulations is possible. Repeatabilities range from 0.2 to 1.1% for 35 ng paraben.

Use of the Brönsted equation in the interpretation of micellar effects in kinetics. Study of the reaction [Fe(CN)5(4-CNpy)]3-+CN-⇌Fe(CN)64-+4-CNpy in SDS micellar solutions

A study of the reaction [Fe(CN)5(4-CNpy)]3-+CN-⇄Fe(CN)64-+4-CNpy was carried out in sodium dodecyl sulfate (SDS) micellar solutions. We conclude that the well known pseudophase model, an extension of the Olson–Simonson treatment to micellar solutions, is equivalent to the Bronsted equation in regard to rationalization of the micellar effects on reactivity. The equivalence follows from the fact that both pseudophase and Bronsted approaches can be used to rationalize kinetic data, as well as from thermodynamic considerations.

Vibrational cooling kinetics ofS1trans-stilbene in sodium dodecyl sulfate micellar solution observed with picosecond time-resolved resonance Raman spectroscopy

Microscopic solvation environments and ultrafast intermolecular energy transfer kinetics of trans-stilbene were studied in a sodium dodecyl sulfate (SDS) micellar solution and in a dodecane solution. The UV absorption spectrum showed no evidence of aggregate formation in the micellar solution. The agreement of the fluorescence lifetimes suggests that the microscopic environments in two solutions are similar. Picosecond time-resolved Raman spectroscopy showed that the vibrational cooling kinetics of S1 trans-stilbene are faster in the SDS micellar solution than in dodecane. These results are explained well by a simple model of solute–solvent energy transfer and solute vibrational cooling proposed earlier. Picosecond time-resolved Raman spectroscopy can be an effective method in studying solvation structure and its dynamics. © 1998 John Wiley & Sons, Ltd.

Vibrational cooling kinetics of S1 trans-stilbene in sodium dodecyl sulfate micellar solution observed with picosecond time‐resolved resonance Raman spectroscopy

Microscopic solvation environments and ultrafast intermolecular energy transfer kinetics of trans-stilbene were studied in a sodium dodecyl sulfate (SDS) micellar solution and in a dodecane solution. The UV absorption spectrum showed no evidence of aggregate formation in the micellar solution. The agreement of the fluorescence lifetimes suggests that the microscopic environments in two solutions are similar. Picosecond time-resolved Raman spectroscopy showed that the vibrational cooling kinetics of S1 trans-stilbene are faster in the SDS micellar solution than in dodecane. These results are explained well by a simple model of solute–solvent energy transfer and solute vibrational cooling proposed earlier. Picosecond time-resolved Raman spectroscopy can be an effective method in studying solvation structure and its dynamics. © 1998 John Wiley & Sons, Ltd.

Separation of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography with aqueous short-chain alcohol solvent

Micellar electrokinetic capillary chromatography (MEKC) with aqueous organic solvent has been developed to separate polycyclic aromatic hydrocarbons (PAHs). Methanol, ethanol or propanol as an organic modifier was added to sodium dodecyl sulfate (SDS) micellar solution in order to increase the solubility of very hydrophobic solutes in mobile phase. Both methanol and ethanol can be used as co-solvents for the separation of PAHs. Use of ethanol resulted in a shorter analysis time than use of methanol. The separations of some PAHs were unsatisfactory using propanol although the analysis time was much shorter than with ethanol. The influence of ethanol content, SDS concentration and temperature on the separations was studied. Benzene and nine polycyclic aromatic hydrocarbons were successfully separated using 50 mM SDS–20 mM phosphate–5 mM borate, containing 40% (v/v) ethanol at 35°C. The relative standard deviation (R.S.D.) of t R ranged from 0.5 to 1.5% for six repeat injections.

Effect of the Micellar Electric Field on Electron-Transfer Processes. A Study of the Metal-to-Metal Charge Transfer within the Binuclear Complex Pentaammineruthenium(III)−(μ-Cyano)pentacyanoruthenium(II) in Micellar Solutions of Sodium Dodecylsulfate (SDS) and Hexadecyltrimethylammonium Chloride (CTACl)

The metal-to-metal charge-transfer band within the binuclear complex pentaammineruthenium(III)−(μ-cyano)pentacyanoruthenium(II), a Robin−Day class II complex, was studied in solutions containing sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium chloride (CTACl). The redox potentials of both ruthenium centers were also measured. From the optical and electrochemical (redox) data, both the reorganization free energy and the reaction free energy corresponding to the electron transfer were obtained. It was found that in solutions containing the anionic surfactant the relevant parameters for the electron-transfer process, that is, the free energies of reorganization and reaction, are quite similar to those corresponding to aqueous electrolyte solutions. In the case of the solutions containing the cationic surfactant, these parameters are quite different from those of the aqueous electrolyte solutions. The results are interpreted taking into account the effects of the micellar electric field on both the binuclear complex and the medium (solvent) surrounding it. These effects depend on the (average) position of the binuclear complex in relation to the micelle: in the case of cationic micelles the binuclear complex penetrates the Stern layer. When the micelles are anionic, the binuclear complex is, on the average, outside this layer, but a residual influence of the micellar field seems to be operative.

A study on one-electron oxidation of phenothiazine derivatives BV piperidine oxoammonium ion in SDS micelle

N-Substituted phenothiazines were oxidized by 2,2,6,6-tetramethy-4-acetyloxypiperidine oxoammonium hexachloroantimonate (TAPO) to the corresponding radical cations in sodium dodecyl sulfate (SDS) micellar solution. The radical cations of phenothiazine derivatives were generated and stabilized by the anionic micelle in queous solution. An electron transfer mechanism has been proposed.

Spin coherence effects observed in the OD ESR spectra of radical pairs with strong hyperfine interaction

The optically detected ESR technique is used to record the spectra of a radical pair generated in the photolysis of 2,4,6-trimethylbenzoyl diphenylphosphine oxide in a micellar sodium dodecylsulfate solution. Along with the signals of the radicals of the pair, additional resonances have been detected in the spectrum, whose signal is inverted with respect to the fundamental ones. It is shown that the inverted lines consist of narrow and wide components, which arise from the effects of crossing and anticrossing of pair spin energy levels, respectively.

Effect of counterion size on the viscosity behaviour of sodium dodecyl sulphate micellar solutions

Abstract The present studies were performed to see the influence of counterion size on the viscosity behaviour of 0.3M sodium dodecyl sulphate micellar solutions at 30° C. Some symmetrical quaternary ammonium salts (R4NBr where R=H, CH3, C2H5, n-C3H7 or n-C4H9) and two organic salts (thiamine hydrochloride and guanidine hydrochloride, THCl and GuHCl)) were used for deriving the counterions. The viscosity decreased, increased and again decreased as the concentration of R4NBr was progressively increased (no initial fall was detected with (n-C4H9)4NBr). The |ηr| was always higher with the combination SDS-(C2H5)4NBr than with SDS-(n-C3H7)4NBr. The results are interpreted in the light of adsorption/intercalation of the counterions or their electrostrictive/hydrophobic nature. Similar reasoning is invoked for THCl addition. The viscosity results of GuHCl addition are discussed with reference to its water structure breaking nature.

Viscosities of Sodium Dodecyl Sulfate Solutions in Aqueous Ammonium Salts

Viscosity measurements have been performed on 0.3 M sodium dodecyl sulfate (SDS) micellar solutions containing different ammonium salts, NH4X (X = OH, Cl, Br, I, NO3, or SCN) at different temperatures (25 to 40 °C). The viscosity decreased, increased, and again decreased as the salt concentration was increased. This behavior was explained in the light of micellar growth/breakdown, the nature of X, and intermicellar interactions. It was also found that, depending on coion species of the added salt, the viscosities of SDS/NH4X micellar solutions differ considerably, indicating the effect of hydrophobic interaction on micelle size or viscosity.