Tsuyoshi Asakawa

Influence of external environment on microviscosity in micelles

Abstract N,N,N′,N′ -Tetramethyldiaminodiphenylketoimine hydrochloride was used as a probe to determine the microviscosity in micelles of sodium dodecyl sulfate (SDS). The fluorescence intensity of the probe increased with an increasing concentration of SDS up to its critical micelle concentration, and then it became nearly constant. The microviscosity in the SDS micelles was estimated to be 5 cP. Addition of urea or NaCl, a change from H 2 O to D 2 O, or a variation in temperature produced different effects on the probe in the micelle and bulk phase, respectively. Addition of urea and substitution of D 2 O for H 2 O increased the microviscosity. The microviscosity in the micelles decreased as the temperature rose. The increment in the fluorescence intensity in the micelle solution was small up to 0.3 M NaCl and then the intensity increased steeply with addition of more NaCl. This abrupt change corresponded to a sphere-rod transition in the micelle form.

Critical micelle concentration in mixtures of N-acyl amino acid surfactants

Abstract The critical micelle concentrations (CMC) were determined in the mixed solutions of N-lauroyl amino acid sodium salts. The results suggested that steric hindrance of its amino acid residue was not always significant on formation of the mixed micelle. In addition, a model was proposed to predict the CMC in the mixed system without an adjustable parameter. It was found that the model was applicable to the systems that deviated significantly from ideal mixing.

Fluorine nuclear magnetic resonance of fluorocarbon and hydrocarbon surfactant mixtures

Etudes des interactions dans les micelles mixtes fondees sur le deplacement chimique de 19 F du groupe CF 3 dans les systemes mixtes de tensioactifs fluorocarbure et hydrocarbure. Cas des perfluorooctanesulfonate de Li ou de Na et des decyl- ou -laurylsulfate de sodium

Hydrophobicity and surface activities of sodium salts of N-dodecanoyl amino acids

Abstract Surface tensions of N-dodecanoyl amino acids were measured in 100 mM NaOH solution at 45.0°C. The dependence of the surface tension γ on the surfactant concentration (CA−) was expressed by the equation γ = γ0 - RTΓmln(1 + KCA). The saturated adsorbed amount of surfactant at the air-water interface Γm varied somewhat with different amino acid side chains. The hydrophobicity of an amino acid was defined by using the critical micelle concentration (CMC(X)) of its N-dodecanoyl derivative as Δg = ln CMC(X) − ln CMC(glycinate). A progressive increase in hydrophobicity produced an increase in K and in the surface pressure at CMC (πCMC). A linear relationship existed between Δg and efficiency in surface tension reduction, pC20, i.e., the logarithm of reciprocal of the concentration when γ0 − γ is 20 mN/m. It was found that the amino acid side chains in the surfactants did not have a hydrophobic interaction with the dodecanoyl grup.

Effect of amino acid surfactants on phase transition of poly(N-isopropylacrylamide) gel

The volume phase transition behavior of a poly(N-isopropylacrylamide) gel (NIPA gel) in solutions of N-acyl amino acid surfactants were studied as a function of surfactant concentration. The addition of a surfactant beyond the critical micelle concentration (cmc) produced elevation in the transition temperature of the NIPA gel and its swelling. The changes in the volume phase transition temperature and in the swelling of the NIPA gel became more significant with the decreasing size of the amino acid side chain. This result could almost be explained only by the binding amount of surfactant onto the NIPA gel regardless of molecular structure of the amino acid. The binding amount increased in the order of sodium N-lauroyl-glycinate>-alaninate>-valinate>-leucinate>or=-phenylalaninate. For an N-acyl amino acid surfactant to bind onto the NIPA gel, to increase the transition temperature, and to facilitate swelling of the gel, the steric hindrance of the amino acid side chain was more effective than its hydrophobicity.

Solubilization of octafluoronaphthalene by mixed micelles of fluorocarbon and hydrocarbon surfactants in aqueous solutions

Solubilization of octafluoronaphthalene (OFN) by fluorocarbon and hydrocarbon surfactants in aqueous solutions has been examined to investigate the effects of mixing surfactants and added salt. Diethylammonium perfluoronanoate (DEAPFN) micelles have the most solubilization power toward OFN. The difference in micellar solubilization power will be caused by the hydrophobicity of ionic groups and micellar size. Large positive synergistic effects on solubilization behavior were observed in the DEAPFN-diethylammonium tetradecyl sulfate mixed micellar systems. Solubilization of OFN depended on the concentrations of added salt and the aggregation number, that is, the micellar size.

Isotachophoretic analysis of surfactants

The qualitative and quantitative determination of anionic surfactants (sodium and lithium alkylsulfate, sodium dodecylbenzenesulfonate, sodium di-2-ethylhexyl sulfosuccinate, sodium and lithium perfluoroalkylcarboxylate, and lithium perfluorooctanesulfonate) were investigated by a capillary tube isotachophoresis using a potential gradient detector. The leading electrolyte solution was the mixture of acetonitrile and aqueous solution of histidine buffer containing calcium chloride. The terminating electrolyte solution was the aqueous solution of sodium octanoate. These electrolytes were effective for the analysis of the mixtures of strongly acidic surfactants.

Aggregation Behavior of Fluorooctanols in Hydrocarbon Solvents.

The association behaviors of three 1-octanols (1-octanol:  C8OH; 1,1,2,2-tetrahydrotridecafluorooctanol:  TFC8OH; and 1,1-dihydropentadecafluorooctanol:  DFC8OH) in two hydrocarbon solvents (n-hexane and benzene) were examined by vibration spectroscopy from 288.15 to 318.15 K. From the analysis of results with a mass action model, it was found that dimers and tetramers of 1-octanols coexisted with monomers in the n-hexane solution. These aggregates were formed by hydrogen bonding between the OH groups of 1-octanols. In the n-hexane solutions, an increase in the fluorination number of the 1-octanol molecule enhanced the intermolecular hydrogen bonding between the OH groups, but reduced the amounts of polymeric species. Conversely, in the benzene solution, the NIR experiment suggested that the OH groups of 1-octanols did not interact with other OH groups, but with the benzene molecules instead. It was found from (19)F NMR chemical shift measurements that the fluorooctanols in the benzene solution aggregated by interaction between the fluorocarbon chains instead of by hydrogen bonding.

Influence of sphere-rod transition in micelle shape on thermal cis-trans isomerization of 4-dimethylamino-4′-nitroazobenzene

Abstract The rate constant of thermal cis to trans isomerization of 4-dimethylamino-4′-nitroazobenzene (DMNA) was measured in sodium dodecyl sulfate (SDS) solutions in the presence of NaCl. The rate constant decreased abruptly above a threshold NaCl concentration which corresponded to a sphere-rod transition in micelle shape of SDS. Micro-viscosity of the micelle also increased at NaCl concentration above the threshold value, while a discontinuous change in micro-polarity of the micelle was not found at the transition point. The rate constant of cis-DMNA in the spherical micelle was larger than that in the rod-like micelle.

Aggregation and pH Responsive Behavior of Thioester Surfactants and Formation of Disulfide Linkages in Aqueous Solutions

pH responsive surfactants, [C12H25N(CH3)2(CH2)nSCOCH3]Br (C12nSAc, n = 4, 11, 12), were prepared, and their properties in aqueous solution were examined. The critical micelle concentration (cmc) and critical vesicle concentration (cvc) were determined based on changes in conductivity, as well as by fluorescence measurements, and light scattering methods. A significant increase in the light scattering intensities of the C12nSAc (n=11, 12) systems suggested that the growth of aggregates was accompanied by considerable counterion binding with increasing surfactant concentration. The diameter of C1211SAc, recorded by the dynamic light scattering measurements, was about 9.6 ±1.0 nm, which was slightly smaller than that for didodecyldimethylammonium bromide (DDAB) vesicles. The thioester group was easily hydrolyzed upon the addition of NaOH, while it was hardly hydrolyzed with the addition of HCl. The time course of alkaline hydrolysis was examined by the conductivity measurements and high-performance liquid chromatography analysis. [C12H25N(CH3)2(CH2)11SS(CH2)11N(CH3)2C12H25]2Br (2C1211SS) was generated in the C1211SAc alkaline solution because of air oxidation. The C1211SAc alkaline solution gradually became an opaque blue color with increasing light scattering at 346 nm, indicating the remarkable growth of vesicles. The chemical structure of 2C1211SS was consistent with that of a disulfide linked double tailed surfactant, similar to DDAB. The disulfide linkage between the double tailed surfactants will contribute to the stabilization and growth of vesicles.