Ayako Goto

The distribution of alkyl paraben in aqueous sodium lauryl sulfate micellar solutions: III. The gel filtration of solubilized systems

Abstract The apparent distribution coefficients, K a , for methyl-, ethyl-, and butylparabens between the sodium lauryl sulfate (SLS) micellar and aqueous phases were measured from the elution curves of SLS and alkyl paraben obtained by the tail analysis on Bio Gel P-4. The results show that the K a was a linear function of the molar fraction of alkyl paraben in the micellar phase ( X s m ). In view of this relationship, the distribution coefficients, K t , were estimated from the K a values on the basis of ideal solution theory. The free energy change of a solubilizate for a transition from the aqueous to micellar phase, ΔG t , was calculated from the K t . The solubilized system was analyzed thermodynamically on the basis of the ΔG t . The results show that an approximately linear relationship exists between the ΔG t and the carbon number of the alkyl paraben. Furthermore, the CMC decreasing effect which describes stabilization of micelle on solubilization was confirmed experimentally to be correlated with ΔG t .

The solution state of nonionic surfactant micelles in aqueous solution

Abstract A gas chromatography procedure has been developed for the analysis of hexaoxyethylene n -lauryl ether (C 12 E 6 ), a nonionic surfactant. The sensitivity is about 0.013 mg of C 12 E 6 in 1 ml of aqueous sample. It is simpler than conventional methods. The gas chromatographic method was used in conjunction with tail analysis (analysis of tail parts of elution curves) from Sephadex G-200 to investigate the solution state of nonionic surfactant micelles in aqueous solution. The tail analysis for the elution curve of C 12 E 6 solution gave the elution volume of C 12 E 6 micelle, V m , and the monomer concentration, C f . The V m values decreased with surfactant concentration at low concentrations and became nearly constant at high concentrations. The decrease of V m suggests that the micellar size increases. The C f values increased toward a limiting concentration, as surfactant concentration was increased. These results suggest that nonionic surfactant systems exhibit a continuous self-association at low concentrations. It was furthermore assumed that the monomer concentration and the micellar size are approximately constant at high concentrations. The micellar weight at high concentrations was estimated to be 270,000 by the application of the Laurent-Killander equation.

Calorimetnc studies on the state of water in aerosol ot reversed micelles

Abstract The state of water in the Aerosol OT (AOT) / isooctane reversed micelle solutions was studied by a microcalorimeter of conduction type. The molar enthalpy changes of water were obtained by mixing AOT solutions of various R values with those at R of zero, where R means the molar ratio of water to surfactant, AOT. The observed enthalpy values at larger were endothermic, whereas those at smaller R were exothermic. An enthalpy curve against R was drawn by adding consecutively the enthalpy changes, showing a maximum at R of 2. This feature was qualitatively discussed in terms of the state of water in reversed micelles.

Effect of alkylparabens on the solution state of sodium lauryl sulfate micelle. IV. Gel filtration of solubilized systems

Abstract Incorporation of methyl-, ethyl-, and butylparabens into sodium lauryl sulfate (SLS) micelle was examined by measurement of ultraviolet spectra, conductance, degree of counterion binding to the micelle, and elution volume of micelles solubilizing alkylparabens. The results show that alkylparabens penetrated only a little into the palisade layer. This phenomenon was closely related to the diluted charge density of micellar surface and the decrease of micellar volume by the solubilization. The factors for stabilization of the micelle by solubilization of alkylparabens were assumed as reduction of the free energy of a micelle due to the diluted surface charge density on a micelle, the entropy of mixing of the mixed micelle, and the decrease of activity coefficient of SLS molecule in the mixed micelle, γ ∗m , which may be considered as geometrical factors. Among these geometrical factors the hydrophobic interaction between alkylparaben and the hydrocarbon part of SLS micelle will be of importance.

IUPAC-NIST Solubility Data Series. 90. Hydroxybenzoic Acid Derivatives in Binary, Ternary, and Multicomponent Systems. Part I. Hydroxybenzoic Acids, Hydroxybenzoates, and Hydroxybenzoic Acid Salts in Water and Aqueous Systems

The solubility data for well-defined binary, ternary, and multicomponent systems of solid-liquid type are reviewed. One component, which is 2-, 3-, and 4-hydroxybenzoic acids, 4-hydroxybenzoate alkyl esters (parabens), or hydroxybenzoic acid salts, is in the solid state at room temperature and another component is liquid water, meaning that all of the systems are aqueous solutions. The ternary or multicomponent systems include organic substances of various classes (hydrocarbons of several structural types, halogenated hydrocarbons, alcohols, acids, ethers, esters, amides, and surfactants) or inorganic substances. Systems reported in the primary literature from 1898 through 2000 are compiled. For seven systems, sufficient binary data for hydroxybenzoic acids or parabens in water are available to allow critical evaluation. Almost all data are expressed as mass and mole fractions as well as the originally reported units, while some data are expressed as molar concentration.

IUPAC-NIST Solubility Data Series. 90. Hydroxybenzoic Acid Derivatives in Binary and Ternary Systems. Part II. Hydroxybenzoic Acids, Hydroxybenzoates, and Hydroxybenzoic Acid Salts in Nonaqueous Systems

The solid-liquid solubility data for well defined nonaqueous binary and ternary systems are reviewed. One component includes hydroxybenzoic acid, hydroxybenzoate, and hydroxybenzoic acid salt, and another component includes a variety of organic compounds (hydrocarbons, alcohols, halogenated hydrocarbons, carboxylic acids, esters, et al.) and carbon dioxide. The ternary systems include mixtures of organic substances of various classes and carbon dioxide. The total number of compilation sheets is 270 for six types of system. Almost all data are expressed as mass percent and mole fraction as well as the originally reported units, while some data are expressed as molar concentration. Critical evaluation was carried out for the binary nonaqueous systems of 2-, 3-, and 4-hydroxybenzoic acids and hydroxybenzoates (methylparaben, ethylparaben, propylparaben, and butylparaben) in alcohols, 1-heptane, and benzene.

FLOCCULATION OF SODIUM BIS(2-ETHYLHEXYL) SULFOSUCCINATE REVERSED MICELLES IN ISOOCTANE

Abstract The observation of reversed micelle in AOT[sodium bis(2-ethylhexyl) sulfosuccinate] /isooctane solution was carried out by a freeze-fracture transmission electron microscope. The micrograph of 5w/v% AOT/isooctane solution at R=1 ([H 2 O]/[AOT]) showed that the microparticles of reversed micelles with the size less than 10 nm existed individually and they were scarcely changed by dilution with isooctane. On the other hand, the micrograph of 5%w/v AOT solution at R=20 was greatly different from that at R=1. Large particles with size less than 200 nm were observed. They appeared to be flocs of reversed micelles which flocculated loosely. The flocculation was also confirmed by a cryo-transmission electron microscope (cryo-TEM). The extent of the flocculation was decreased by dilution of the AOT solution at R=20 with isooctane. This phenomenon was supported by measuring T 1 of solubilized water with 1 H-NMR spectroscopy. It is concluded that the AOT reversed micelles were observed visually and the flocculation of AOT reversed micelles was directly proved. It was confirmed that the flocculation occurred easily in higher AOT and water concentrations before percolation occurred.

Effect of glycyrrhizin on the phosphatidylcholine-water system ESR and calorimetric study

Abstract ESR and DSC study was carried out to reveal the effect of glycyrrhizin (GR) on dipalmitoylphosphatidylcholine (DPPC) membrane. Temperature dependence of the TEMPO parameter showed that the pretransition of DPPC bilayer almost disappeared but the main transition was moved to higher temperature by the addition of GR. It was clearly ascertained by the fact that a broad endothermic peak was observed overlapping with the original one in the DSC curve. The shift to higher temperature is rare and suggests that the structure of the bilayer is stabilized by GR; nevertheless the membrane was dissolved. The order parameter of the spin-labeled phosphatidylcholine in this system was examined. It showed that the motion of the alkyl chain of DPPC is hindered by GR. From these results, a model of the fragmented bilayer is proposed and a discussion is given on the stability of the structure.

Physical organic studies on bimolecular reactions in reversed micelles: addition of cyanide ion to the N-methyl-3-caribamoylpyridinium ion in hexadecyltrimethylammonium bromide reversed micelles

The bimolecular reaction of cyanide (CN–) ion with N-methyl-3-carbamoylpyridinium (S+) ion, in the water pool of the reversed-micellar system water/hexadecyltrimethylammonium bromide (HTAB)/chloroform–iso-octane (3 : 2, v/v) has been studied at various temperatures (15–40 °C) by measuring spectrophotometrically the decrease of the absorption due to S+(265 nm) and the increase of the absorption due to the addition product (340 nm). The results of the reaction series were examined throughout with respect to the molar ratio of water to HTAB, R. Since the rate and equilibrium constants of the bimolecular reaction are affected by the method in which the concentrations of reactants are defined or by fixing the extent of reaction space, the water pool is assumed to be the sole reaction space and the rate and equilibrium constants in the water pool, K2w and Kw, which are based on the modified concentrations of the reaction species, have been evaluated. It is found that terms of K2w and Kw, the smaller the value of R, the more the addition reaction is enhanced. From the relationships between Kw and K2wvs. temperature, the standard and activation enthalpies of reaction, ΔH⊖ and ΔH‡, respectively, have been calculated. The behaviour of ΔH⊖ and ΔH‡ as well as Kw and K2w is found to differ in reactions which have R below and above ca. 3. To explain the enhancement of the reaction due to the specific field effect of the water pool and the retardation of the reaction due to electrostatic interactions among S+ ions, the involvement of CN– and HTAB ions is proposed. The differing behaviour in the reactions is more clearly manifested in the thermodynamic and kinetic diagrams of enthalpy vs. entropy, which give separate plots corresponding to R both below and above ca. 3. In addition, the effect of varying the CN– ion concentration is discussed and is found to be consistent with the situation described above.

The addition of cyanide ion to N-alkyl-3-carbamoylpyridinium ion in hexadecyltrimethylammonium bromide reversed micelles: the effects of alkyl chain length

The addition of cyanide (CN–) ion to N-alkyl-3-carbamoylpyridinium ion (alkyl derivatives) with various alkyl chains in water pools of the reversed micellar system, water/hexadecyltrimethylammonium bromide (HTAB)/chloroform–iso-octane (3 : 2, v/v) has been determined spectrophotometrically. The results of the reaction series are examined with respect to the molar ratio of water to HTAB, R, and the CN– ion concentration in the water pool, [CN–]aq, in order to study the effect of the alkyl chain length of the alkyl derivatives on the addition reaction in HTAB reversed micelles. The rate constant, k2w, and the equilibrium constant, Kw, are evaluated on the basis of the dispersed water pools in the micellar system as the space for reaction.Based on the behaviour of k2w and Kw with R, the present results are obtained. The addition reaction proceeds favourably with decreasing R and with increasing alkyl chain length of the alkyl derivatives. Furthermore, the reaction tends not to be affected significantly by water content in the reversed micelles with increasing alkyl chain length.The effect of CN– ion concentration in water pools on kw and k2w suggests that the reverse reaction for the longer alkyl derivatives is highly affected by CN– ion concentration compared to that for the shorter alkyl derivatives.The behaviour of k2w and Kw with R and [CN–]aq is interpreted mainly on the basis of the different localizations of respective alkyl derivatives in the water pool.