Keishiro Shirahama

The CMC-decreasing effects of some added alcohols on the aqueous sodium dodecyl sulfate solutions

Abstract The critical micelle concentration (CMC) of sodium dodecyl sulfate in water at 25°C was measured as a function of the concentration of the added alcohols (C2C4) including all isomers. On addition of alcohols, the CMC decreases. The CMC depression becomes more marked, the stronger the hydrophobicity of the added alcohol. As a measure of the hydrophobicity of the alcohols, the free energy of transfer of an alcohol molecule from pure liquid to the extremely diluted aqueous solution was employed. The logarithm of the CMC-decreasing effect vs. this free-energy plot gives a line which expresses the CMC-decreasing effect in terms of a limiting slope of a log (CMC) vs. mole fraction of the added alcohol plot. In order to explain the above phenomena, the factors that affect the CMC decrease may be considered as reduction of the free energy of a micelle due to the diluted surface charge density on a micelle, the hydrophobic interaction to the hydrocarbon exposed to water, and the entropy of mixing of a mixed micelle on addition of alcohol, and they contribute in this order.

Binding isotherms of sodium dodecyl sulfate to protein polypeptides with special reference to SDS-polyacylamide gel electrophoresis.

To clarify the mode of interaction between sodium dodecyl sulfate (SDS) and protein polypeptides with special reference to SDS-polyacrylamide gel electrophoresis, the binding of SDS to several protein polypeptides was investigated by the equilibrium dialysis technique. Each of the binding isotherms was characterized by the presence of two phases: an initial gradual increase in the amount of binding to 0.3-0.6 g/g (first phase) and a subsequent steep increase to 1.2-1.5 g/g (second phase). The binding was completed at a concentration of SDS below the critical micelle concentration. Throughout the first and second phases, the isotherms obtained were different for each kind of protein. On the basis of experiments with bovine serum albumin and ribonuclease (EC 3.1.4.22], the isotherms were profoundly affected by the method used for modification of the sulfhydryl groups. The claim of Reynolds and Tanford (Proc. Natl, Acad. Sci. U.S., 66, 1002 (1970)) that the isotherms are virtually identical for many kinds of proteins was not supported by the present data. Changes in the gross and local conformations were examined with reference to the isotherms by measurements of CD spectrum, free boundary electrophoresis, and gel filtration. The results obtained were collectively interpreted based on the model of SDS-protein polypeptide complexes proposed by the present authors (J. Biochem., 75, 309 (1974)).

The binding equilibrium of sodium dodecyl sulfate to poly(ethylene oxide) in 0.1 M sodium chloride solution at 30°C

SummaryThe binding equilibrium of sodium dodecyl sulfate (SDS) to poly(ethylene oxide) in 0.1 M sodium chloride solution at 30°C was determined by using a dialysis technique. The binding isotherm was characterized by a sudden uprise near 1 mM SDS and a saturation tendency towards the cinc (1.5 mM).The completion of binding in such a narrow concentration range is attributable to a strong cohesion between bound surfactant molecules, and to a smallness of the surfactanr cluster which is considered as distributed along the polymer chain.ZusammenfassungEs wurden die Bindungsgleichgewichte des Natriumdodecylsulfats mit Poly(äthylenoxyd) in 0.1 M Natrium-chlorid-Lösung bei 30°C durch die Dialysemethode bestimmt. Die Bindunsisotherme werden von der plötzlichen Zunahme nahe 1 mM Tensid und der Sättigungstendenz zu der cmc (1.5 mM) charakterisiert. Es wurde gefolgert, daß das Zustandekommen der Bindung in einem so engen Konzentrationsberich der starken Kohäsion zwischen den gebundenen Tensidmolekülen und der Kleinheit des Tensidbüschels, welches längs der Polymerkette werteilt ist, zugeschrieben werden kann.

The effect of 1-alkanols on ionization of sodium dodecyl sulfate micelles

Abstract For an aqueous sodium dodecyl sulfate solution including small amounts of l-alkanols (C4−C7), it is confirmed that a linear relation is valid between d ln ( x f ) dy f (CMC-depressing power of the alkanol) and K (partition coefficient of the alkanol between bulk water and micelle phases). From the linear relation, we estimate a constant value of θ defined as −d ln ( x f ) dy f = θ·K; θ (=0.69) is independent of the kind of alkanol and xf and yf are mole fractions of monomerically dissolving surfactant and alkanol, respectively: xf corresponds to the critical micelle concentration (CMC) of the surfactant. Some aspects of θ are discussed from the viewpoint that θ reflects an interaction of the surfactant and the alkanol in their mixed micelles. The effects of solubilized alkanol on the degree of ionization of ionic micelles (α) and on the electrical potential at the micellar surface (φ) are numerically estimated on the basis of θ and through thermodynamic relations. In the relations, a factor like the “osmotic coefficient” is introduced to correct the nonideality of monomer and micellar surfactant species, in place of the familiar activity coefficient. From this factor it is found that solubilized alkanol causes an increase in α (i.e., ∂α/∂ym > 0) but has little influence on ψ (i.e., ∂ψ/∂ym ≈ 0), where ym is the mole fraction of the alkanol in the micellar phase.

Swelling of poly(N-isopropylacrylamide) gels in water-aprotic solvent mixtures

The swelling volume of poly(N-isopropylacrylamide) (PIPAAm) gel in aprotic solvents (acetonitrile (AcN)-, tetrahydrofuran (THF)-, 1,4-dioxane (DO)- and dimethylsulfoxide (DMSO))-water mixtures was measured at 25°C. The gel swollen in water shrank first and then reswelled with addition of the aprotic solvents. At an intermediate mole fraction (XDMSO) range of DMSO-water mixtures, the gel demonstrated a “reentrant” swelling phenomenon the hydrated gel shrank first on addition of a small amount of solvent, showed a typical wide reentrant transition, and gradually reswelled in the range near pure solvent. On the other hand, the gels in AcN-, THF-, and DO-water mixtures demonstrated a “reentrant-convex” swelling phenomenon: the gels reswelled after a reentrant phase transition in low Xorg (XAcN, XTHF and XDO), showed a maximum swelling in the intermediate Xorg region, and shrank again gradually in the high Xorg region. Such a swelling behavior of the gel was interpreted by correlating with solution properties of the aqueous aprotic solvent mixtures.The strength of hydrogen bonding around amide groups of the homopolymer was examined in pure solvents (water, THF, and DMSO) and in all proportion of aqueous THF to observe the relation with swelling behavior of gel by spectrum analysis of the amide I and II bands of Fourier Transform Infrared Spectroscopy (FT-IR). The swelling properties of gels in solvents and the aqueous mixtures were well correlated with the peak shifts of amide groups of the homopolymer.

Binding of hexadecylammonium surfactants to water-soluble neutral polymers

The binding of hexadecyltrimethylammonium bromide and hexadecyldimethyl-2-hydroxyethylammonium bromide to neutral polymers was measured by a potentiometric titration method using surfactant selective electrodes. Binding to poly(vinyl alcohol) was slightly cooperative, while that to poly(ethylene oxide) lacked the co-operativity. Poly(vinyl pyrrolidone) did not bind them at all. Binding affinity as estimated by a distribution coefficient of the cationic surfactants between the bulk and polymer phases is about 2 orders of magnitude smaller than that of anionic sodium dodecyl sulfate. The heat of binding was estimated from the temperature dependence of the distribution coefficient and found to be endothermic. It is imagined that the cationic surfactants are simply partitioned between the aqueous bulk phase and the polymer coil phase which is regarded as aqueous organic mixed solvent.

Interactions of amphiphilic drugs withα-,β-, andγ-cyclodextrins

The association of several amphiphilic drugs with α-, β-, and γ-cyclodextrins has been measured by use of drug-sensitive electrodes. Drugs investigated are hydrochlorides of chlorpromazine, dibucaine, tetracaine, and procaine, and valethamate bromide. Each drug forms the drug:cyclodextrin=1∶1 complex with α- and β-cyclodextrin, and both the 1∶1 and 2∶1 complex with γ-cyclodextrin, except valethamate which only forms the 1∶1 complex. The strength of the 1∶1 complex formations is in the order of βCyD>α-CyD>γ-CyD. The association constant of the 2∶1 complex in drug-γ-CyD is larger than that of 1∶1 complex. The free energy change of the conplex formation has a positive correlation with that of the micelle formation of drugs. The deviation from this relation is explained in terms of fittability of the bulky hydrophobic group of drugs into the cyclodextrins cavity. The free energy change for the complex formation between chlopromazine or valethamate and β-CyD is governed by the enthalpy term and not by the entropy term which controls the surfactant-β-CyD interactions.

Interaction between poly(styrene sulfonate) and dodecylpyridinium chloride in ethanol-water mixed solvents

Abstract Binding of dodecylpyridinium chloride to poly(styrene sulfonate) in ethanol-water mixed solvent was measured by a surfactant-selective electrode which consists of polymeric materials only and thus shows a good electrode performance even in mixed solvent. It was found that both intrinsic binding and the cooperative effect were reduced by added ethanol. This is ascribed to replacement of water molecules hydrophobically hydrated around the hydrophobic moieties of the polymer and the surfactant with ethanol molecules. This tendency is correlated with the free energy change of a surfactant molecule when transferred from water to an ethanol-water mixed solvent, which was also measured by the same surfactant electrode as used in the binding study.

The interaction of mixed surfactants with polyelectrolytes

Abstract The interactions between a linear polymer, sodium poly(2-acrylamide-2-methylpropane sulfonate), and two cationic surfactants, dodecylpyridinium chloride and tetradecylpyridinium chloride and their mixtures with different ratios, were studied by a potentiometric titration method using a surfactant-selective electrode. The ideal mixing/ideal cooperative binding model we had proposed previously was applied to successfully predict the binding isotherms of the mixed surfactant systems and the critical aggregation concentrations of the binding. The binding of surfactant mixtures to polymers is similar to the ideal mixed micelle formation and a sort of synergetic effect was found during the binding process.

A Formulation of Chemical Kinetics in Micellar Solutions

Reaction kinetics in the presence of micelles is formulated on the basis of a microheterogeneous reaction in accordance with a current model of micellar catalysis. The necessary molecular parameters are the radius of the hydrocarbon core of a spherical micelle, the thickness of a reaction surface layer, the surface and zeta potentials, and a distribution coefficient of a hydrophobic substrate. The derived expression was applied to the hydrolysis reaction of methylorthobenzoate in the presence of sodium dodecylsufate micelle to describe reaction properties such as a rate-surfactant concentration profile, inhibition by added electrolyte, and activation energy. The micellar effect on the reaction rate was explained by a simple concentration effect of the reactants; the stabilization of the transition state by the micellar surface potential need not be taken into consideration. Inhibition of the orthoester hydrolysis by a cationic surfactant is also predicted.