Characteristics of a liquid/liquid optical waveguide using sheath flow and its application to detect molecules at a liquid/liquid interface.

The formation conditions and characteristics of a liquid/liquid optical waveguide (LLW) were studied using a two-phase sheath flow, where the inner organic phase flow acted as the core and the outer aqueous flow acted as the clad. In immiscible solvent systems, i.e., toluene/water and diethyl ether/water systems, the LLWs were formed in the range of higher than ca. 600 of the Reynolds number (Re), where the linear velocity of the organic solvent was much higher than that of the aqueous solution. On the other hand, in a miscible solvent system, i.e., a tetrahydrofuran/water system, a stable LLW was formed in the range of a much lower Re than in immiscible systems. Moreover, the molecules at the toluene/water interface of the LLW were observed with both fluorescence and absorbance measurement systems. In particular, the change in the fluorescence spectrum of 1-anilino-8-naphthalenesulfonate (ANS) at the interface within 1 ms was observed by this method, indicating the usefulness of the LLW for a fast kinetic study of a liquid/liquid interface.     

Entrapment of enzyme in water-restricted microenvironment for enzyme-mediated catalysis under microemulsion-based organogels

Nonaqueous enzymology has emerged as a major area of biotechnology research and development. Enzymes in organic solvents offer great potential for the biocatalysis of a wide range of chemical processes that cannot occur in water. One of the most commonly used methods for carrying out enzymatic conversions in organic solvents is enzymes solubilized in water-in-oil (w/o) microemulsions or water containing reverse micelles. In reverse micelles, enzyme molecules are solubilized in discrete hydrated micelles formed by surfactants within a continuous phase, i.e., nonpolar organic solvent. Under appropriate conditions, these solutions are homogeneous, thermodynamically stable, and optically transparent. However, there are very few examples of preparative-scale enzyme-catalyzed synthesis in water-in-oil microemulsion. One reason is that despite the advantages offered by microemulsion media, product isolation and enzyme reuse from such singlephase liquid medium is more complex than in competing methodologies in which the catalyst is present as a separate solid phase. Therefore, the approach simplifying product isolation, and enzyme reuse from microemulsion-based media, has been the use of a gelled microemulsion system, especially gelatin silica nanocomposite.     

Interfacial tension of evaporating emulsion droplets containing amphiphilic block copolymers: effects of solvent and polymer composition

Evaporating droplets of volatile organic solvent containing amphiphilic block copolymers may undergo hydrodynamic instabilities that lead to dispersal of copolymer micelles into the surrounding aqueous phase. As for related phenomena in reactive polymer blends and oil/water/surfactant systems, this process has been ascribed to a nearly vanishing or transiently negative interfacial tension between the water and solvent phases induced by adsorption of copolymer to the interface. In this report, we investigate the influence of the choice of organic solvent and polymer composition for a series of polystyrene-b-poly(ethylene oxide) (PS-PEO) diblock copolymers, by in situ micropipette tensiometry on evaporating emulsion drops. These measurements suggest that the sensitivity to the organic solvent chosen reflects both differences in the bare solvent/water interfacial tension as well as the propensity of the copolymer to aggregate within the organic phase. While instabilities coincident with an approach of the interfacial tension nearly to zero were observed only for copolymers with PEO content greater than 15 wt.%, beyond this point the interfacial behavior and critical concentration needed to trigger surface instability were found to depend only weakly on copolymer composition.     

Limonene in Arizona liquid systems used in countercurrent chromatography. I Physicochemical properties

Limonene is a biorenewable cycloterpene solvent derived from orange peel waste. Its potential as a “green” solvent to replace heptane was recently evaluated. Countercurrent chromatography (CCC) is a preparative separation technique using biphasic liquid systems. One liquid phase is the mobile phase; the other liquid phase is the stationary phase held in place by centrifugal fields. A particular range of special proportions of the heptane/ethyl acetate/methanol/water system is called the Arizona (AZ) liquid system when the heptane/ethyl acetate ratio is exactly the same as the methanol/water ratio. A continuous polarity decrease is obtained between the most polar A composition (ethyl acetate/water or 0/1/0/1 v/v) and the least polar Z composition (heptane/methanol or 1/0/1/0 v/v), replacing heptane by limonene and methanol by ethanol produce biphasic liquid systems much more environmentallyfriendly than the original AZ compositions. The chemical compositions of the two liquid phases of 12 AZ limonene/ethyl acetate/ethanol/water proportions were fully determined by Karl-Fisher titration of water and by gas chromatography for the organic solvents. The results were compared with the compositions of the corresponding AZ mixtures containing heptane and methanol. Significant differences in ethyl acetate and ethanol distribution between phases of the two systems with identical volume proportions were established. The ratio of the upper phase over the lower phase volumes and the phase density difference are important in CCC, there are also significant differences between the classic and “green” AZ systems that are discussed.     

A two-state model for selective solubilization of benzene-limonene mixtures in sodium dihexyl sulfosuccinate microemulsions

When surfactants are used to solubilize oil, the oil to be solubilized is often a mixture of components with differing properties, for example, solubilization of drug molecules in microemulsion formulations, remediation of organic polluted aquifers using surfactants, and so forth. Previous research has demonstrated that selective solubilization of one organic component over the other may occur if the organic components are dissimilar. In this research, we investigated selective solubilization from benzene-limonene mixtures in Winsor type I and III microemulsion systems containing water, sodium di-n-hexyl sulfosuccinate, and NaCl. The effect of the oil phase composition and the electrolyte concentration on the selectivity was studied. It was found that the selectivity toward benzene was highest at low electrolyte and benzene concentrations, decreasing as the electrolyte or benzene concentration increased. The results are discussed on the basis of the two-state solubilization theory and by correlating the curvature of the surfactant film in the microemulsion with changes of the electrolyte concentration and the oil phase composition. A simple mathematical model is developed for the selectivity, which combines the two-state solubilization theory and the net-average curvature model of microemulsion solubilization to yield close agreement with the experimental data.     

Oxidation in three-liquid-phase microemulsion systems using "Balanced Catalytic Surfactants"

A series of "Balanced Catalytic Surfactants" (BCS) [(Cn)2N(C1)2]2MoO4 (n = 8, 9, 10, 12) based on amphiphilic double-tailed quaternary ammonium with molybdate as a counterion has been developed for the dark singlet [4 + 2] cyclooxygenation of organic substrates in three-liquid-phase microemulsion systems. These cationic surfactants form three-liquid-phase microemulsion systems at room temperature in the presence of an appropriate organic solvent and water without addition of any cosurfactant or electrolyte. Comparative peroxidation of rubrene points out the specific advantages of these three-phase media over phase transfer catalysis in two phase systems and on conventional one-phase microemulsions based on sodium molybdate: (i) only three constituents, (ii) low amounts of surfactants, (iii) insensitivity to water dilution, (iv) fast separation of the three phases, (v) straightforward recovery of the product and the surfactant from the oil and microemulsion phases, respectively. The preparative peroxidation of alpha-terpinene and 1,4,5-trimethylnaphtalene was performed in the ternary systems [(C8)2N(C1)2]2MoO4/water/tert-butyl acetate or benzene. The reusability of the catalyst, the catalytic nature of the BCS, and the ability of the systems to oxidize poorly reactive substrates were demonstrated showing the broadness of the applicability of such systems.     

二烷基磷(膦)酸萃取剂钠盐微乳液的热力学函数

测定了二烷基磷(膦)酸钠盐(NaDEHP,NaEHEHP和NaDTMPP)-醇-有机溶剂-水(或盐溶液)皂化萃取体系微乳液的ΔG~0~→~1(醇从油相转移到界面相的标准自由能变),探讨了萃取剂类型,有机溶剂类型,烷烃碳链长度,醇碳链长度,温度及水相金属离子浓度对热力学函数的影响规律     

Effect of ionic surfactants on the phase behavior and structure of sucrose ester/water/oil systems

The phase behavior and structure of sucrose ester/water/oil systems in the presence of long-chain cosurfactant (monolaurin) and small amounts of ionic surfactants was investigated by phase study and small angle X-ray scattering. In a water/sucrose ester/monolaurin/decane system at 27 degrees C, instead of a three-phase microemulsion, lamellar liquid crystals are formed in the dilute region. Unlike other systems in the presence of alcohol as cosurfactant, the HLB composition does not change with dilution, since monolaurin adsorbs almost completely in the interface. The addition of small amounts of ionic surfactant, regardless of the counterion, increases the solubilization of water in W/O microemulsions. The solubilization on oil in O/W microemulsions is not much affected, but structuring is induced and a viscous isotropic phase is formed. At high ionic surfactant concentrations, the single-phase microemulsion disappears and liquid crystals are favored.     

Phase diagrams and chemical physical properties of dodecyl sulfobetain/alcohol/oil/water microemulsion system

The HLB plane equation was deduced according to the mass balance relation in microemulsion systems for the first time. The δ-γ fishlike phase diagram was plotted and the composition of the interfacial layer was calculated for dodecyl sulfobetain/alcohol/oil/water microemulsion system. The solubilities of dodecyl sulfobetian and alcohol and the solubilization capacity for the middle-phase microemulsion were examined. The effects of different alcohols, oils, and aqueous solution composition (NaCl content and pH values) on the phase behavior and the related parameters were also investigated. The phase behavior for dodecyl sulfobetain-based microemulsion system was compared with corresponding phase behavior for lauric-N-methylglucamide-based and sodium dodecyl sulfatebased systems. The text was submitted by the authors in English.     

蒽在SDS/BA/H2O体系中的光谱特征

用紫外-可见吸收光谱和荧光发射光谱研究了蒽在不同组成和结构的十二烷基硫酸钠(SDS)/苯甲醇(BA)/H20微乳液中的光谱特征,探讨了微乳液组成和结构对蒽光谱特征的影响,阐述了蒽在微乳液中的定位。结果表明,蒽位于O/W微乳液的膜相和油核;在SDS/BA/H2O W/O微乳液中,蒽定位于油连续相。     

混合溶剂体系中牛肝β-半乳糖苷酶催化5-氟-2'-脱氧尿苷区域选择性半乳糖基化反应

研究了混合溶剂体系中有机溶剂种类和含量对牛肝β-半乳糖苷酶催化5-氟-2'-脱氧尿苷区域选择性半乳糖基化反应的影响.结果表明,在含10%(体积分数)有机溶剂体系中,该酶稳定性差,失活严重.减少有机溶剂含量可显著减轻其对该酶的毒害作用.然而,有机溶剂的添加对酶促糖基化反应的区域选择性的影响很小(均保持在99%以上).牛肝...     

Determination of Surfactants Using Ion Pair Extraction of Near-infrared Laser Dyes

Abstract

Ionic surfactants and near-infrared laser dyes formed complexes which were extracted into organic solvents as ion pairs. Surfactants were determined spectrophotometrically by measuring the near-infrared absorbance and fluorescence of the ion pair in the organic solvent. Several of the commercially available near infrared dyes have been found suitable for surfactant determination in water using this technique. The excess near-infrared dye coextracted into the organic solvent was determined by blank extractions. The calibration curves were linear within two orders of magnitude of surfactant concentrations. Non-linear calibration curves are obtained for wider concentration range of surfactants. This method using the recently developed near-infrared laser diode intracavity technique was applied to the determination of SDS in water. Lower detection limits and ease of operation are the major advantages of using this new laser diode technique. The extraction efficiency of different solvent systems was evaluated.     

Enhancement of dissolution rate of mitotane and warfarin prepared by using microemulsion systems

Micronization is the most effective way to enhance the dissolution rate of poorly water-soluble drugs and bioavailability in human body. Microemulsion systems were applied to micronize mitotane and warfarin by cooling method and solvent diffusion process. The triangle phase diagram of the ternary benzyl alcohol+sodium dodecyl sulfate (SDS)+water system was investigated at six different temperatures to determine an appropriate operational microemulsion regime for crystallization. The particle sizes of mitotane and warfarin re-crystallized from microemulsion systems were greatly reduced (to ～1 μm) compared with that of the commercial ones. Consequently, the dissolution rate coefficients of re-crystallized mitotane and warfarin were significantly improved by, respectively, 7.5 and 13.3 times larger than that of the commercial ones. The crystal structures of re-crystallized mitotane and warfarin were the same as the commercial ones based on the XRD and DSC measurements. In addition, it is interesting to observe the variation of morphology of re-crystallized mitotane as a function of the composition of the SDS and the drug concentrations.     

Rapid determination of water- and fat-soluble vitamins with microemulsion electrokinetic chromatography

A rapid, reliable and reproducible method based on microemulsion electrokinetic chromatography (MEEKC) for simultaneous determination of 13 kinds of water- and fat-soluble vitamins has been developed in this work. A novel microemulsion system consisting of 1.2% (w/w) sodium lauryl sulphate (SDS), 21% (v/v) 1-butanol, 18% (v/v) acetonitrile, 0.8% (w/w) n-hexane, 20mM borax buffer (pH 8.7) was applied to improve selectivity and efficiency, as well as shorten analysis time. The composition of microemulsion used as the MEEKC running buffer was investigated thoroughly to obtain stable separation medium, as well as the optimum determination conditions. Acetonitrile as the organic solvent modifier, pH of the running buffer and 1-butanol as the co-surfactant played the most important roles for the separation of the fat-soluble vitamins, water-soluble vitamins and stabilization of system, respectively. The 13 water- and fat-soluble vitamins were baseline separated within 30 min. The system was applied to determine water- and fat-soluble vitamins in commercial multivitamin pharmaceutical formulation, good accuracy and precision were obtained with recoveries between 97% and 105%, relative standard derivations (RSDs) less than 1.8% except vitamin C, and acceptable quantitative results corresponding to label claim.     

Formulation and physicochemical characterization of imwitor 308 based self microemulsifying drug delivery systems

Self Microemulsifying Drug Delivery Systems (SMEDDS) are a novel alternative to the conventional transdermal delivery systems. SMEDDS are water-free systems, made up of oils and surfactants that can readily form a microemulsion upon dilution within an aqueous medium. Before SMEDDS can be used as a drug delivery system it is necessary to investigate the internal microstructure of the resulting microemulsion. Novel Imwitor 308 based SMEDDS were prepared and investigated. Phase behaviour of the comprising components was investigated through the construction of pseudoternary phase diagrams. The formed systems were characterized using visual inspection, measurement of electrical conductivity, viscosity and droplet size. Amongst the pseudoternary systems investigated, IPM/Cremophor EL (50% w/w)/Imwitor (50% w/w) and Myritol 318/Tween 85 (64% w/w)/ Transcutol P (20% w/w)/Imwitor (16% w/w) possessed the largest microemulsion area. Electrical conductivity and viscosity studies depict structural transitions from w/o microemulsion to bicontinuous or o/w microemulsion around 20-35% water. This was further supported by the droplet size and Fourier transform (FT)-IR measurements. The FT-IR data suggests that below the percolation threshold (ψ(C)) the water molecules are mainly bounded to the surfactant head group (bound water). Above this value, water molecule move to the outer phase of the microemulsion mainly interacting with each other though hydrogen bounding (free water). It was also found that pseudoternary systems with water content of less than 30% were stable at 32°C. Such systems may form stable microemulsion upon contact with the skin. Absorption of water may also result in a supersaturated solution with enhanced transdermal flux.     

Organic and bioorganic reactions in microemulsions

During the last two decades reactions in microemulsions have developed into an emerging technology. In most instances oil-continuous microemulsions (w/o systems) have been used and the water droplets have proven useful as “minireactors” for various types of syntheses. This review discusses recent advances in the fields of organic and bioorganic reactions in microemulsions. In preparative organic synthesis microemulsions are of interest to overcome incompatibility problems between nonpolar organic compounds and inorganic salts. For this purpose, microemulsions can be regarded as an alternative to two-phase systems with added phase transfer reagents. Properly formulated microemulsions may also accelerate organic reactions, various mechanisms of such rate enhancements are discussed. Transition from a homogeneous solvent system to a microemulsion may also affect the regioselectivity of organic reactions due to orientation of reactants at the oil-water interface. In bioorganic synthesis, microemulsions are of interest as a reaction medium for several reasons: (i) nonpolar substrates can be dissolved in high concentrations, (ii) thermodynamic equilibria of condensation/hydrolysis reactions can be shifted by adjusting water content, (iii) enzymes are sometimes found to be more stable and more active than in aqueous buffer. Lipases are the most widely used enzymes and reactions have been performed in different types of microemulsion systems. This review presents general aspects of enzymatic catalysis in microemulsions followed by a discussion of recent advances in preparative work focusing on lipase catalyzed processes.     

液/液界面新溶剂体系的电化学研究

用循环伏安法测定了离子在水-异硫氰酸烯丙脂(AIT)体系中的标准转移Gibbs能△_o~w G_(tr,i)~0。对含有AIT的混合溶剂的研究, 发现了一系列电位窗比较宽的水/有机溶剂体系, 讨论了溶剂效应对△_o~w G_(tr,i)~0的影响。     

Enzymatic hydrolysis of starch in water-immiscible organic solvent,two-phase systems

Enzyme-catalyzed hydrolyzations of starch by α-amylase have been studied in various two-phase systems, consisting of water and a water-immiscible organic solvent. The hydrolytic conversion of soluble starch to malto-oligosaccharides by α-amylase was greatly accelerated in 10% (v/v) water content of water-dodecane two-phase systems. However, a rapid inactivation of the enzyme has been observed in these systems. Addition of surfactant to these systems, such as polyoxyethylene (20) sorbitan monopalmitate (Tween 60) or bis(2-ethylhexyl) sodium sulfosuccinate (AOT), was effective for the enzyme stability. Effects of enzyme immobilization on the stability of α-amylase, using Ca-alginate and chitosan beads, also have been studied. The stability of immobilized enzyme was clearly enhanced in a 5–10% (v/v) water content two-phase system, whereas the free enzyme was inactivated within 41 h, remaining at a relative activity of 47–76% after 41 h of treatment. Furthermore, scanning electron micrographs (SEM) were taken to observe the effect of the two-phase system on the hydrolysis of starch. Potato starch granules have been extremely swelled and burst out in the stirred 10% (v/v) water content system, which did not contain enzymes.     

States of water located in the continuous organic phase of 1-butyl-3-methylimidazolium tetrafluoroborate/Triton X-100/triethylamine reverse microemulsions.

We demonstrate a novel ionic liquid (IL) microemulsion, consisting of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and nonionic surfactant Triton X-100 prepared in triethylamine which is used either as an organic solvent or a Lewis base. The effects of small amounts of added water on the microstructure of the IL microemulsion are investigated by various techniques. UV/Vis spectroscopic analysis and FTIR spectra indicate that these water molecules are not solubilized into the IL pools of the microemulsions. 1H NMR spectra further show that the added water binds with triethylamine to form a surrounding OH- base environment. Some of OH- ions enter the palisade layers of the IL microemulsions and a continuous base interface is created. The unique solubilization behavior of water reveals that it is possible to use the triethylamine microemulsions as a template to prepare metal hydroxides as well as metal oxides in the microemulsions, which is not possible when using traditional microemulsions.     

Effect of Interfacial Alcohol Concentrations on Oil Solubilization by Sodium Dodecyl Sulfate Micelles

Alcohol partitioning and its effect on oil solubilization in Winsor Type I microemulsion systems was investigated. The microemulsion systems consisted of sodium dodecyl sulfate (SDS), pentanol, isopropanol (IPA), and dodecane, with either deionized water or an aqueous solution of 50 mM CaCl(2). Alcohol partitioning between aqueous, oil, and interfacial phases of the microemulsion was described using a pseudophase model in which the alcohol was assumed to self-associate in the oil phase. Partitioning in these miroemulsions was consistent with pentanol self-association in the oil phase. IPA did not self-associate but co-associated with pentanol in the oil phase. IPA concentrations as high as 20 g/kg of water had no effect on pentanol partitioning. The partition coefficient for pentanol between aqueous and interfacial phases was about 220 on a mole fraction basis. However, pentanol saturated the interfacial phase at a mole ratio of 3 : 1 pentanol to SDS. Addition of pentanol beyond that sufficient to saturate the interface resulted in large amounts of pentanol partitioning into the oil, reaching concentrations in excess of 25 g dL(-1) of oil phase. Dodecane solubilization increased linearly with pentanol mole fraction in the interface up to the 3 : 1 pentanol-to-SDS saturation level. The fact that dodecane solubilization was unaffected by pentanol at concentrations beyond those necessary for interfacial saturation suggests that pentanol behaves as a cosurfactant and not a cosolvent in these microemulsion systems. Copyright 2000 Academic Press.