Inverted micelle

Alternatively, inverted micelles can also be formed in water-free medium. If no water is present in a two-component system, the difference between the solubility parameters of the hydrocarbon tail of the surfactant and the organic solvent contributes to inverted micelle formation. A large negative enthalpy change is the driving force to form spontaneous inverted micellization, in contrast with aqueous systems. 

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Lianos P and Thomas J K 1986 Cadmium sulfide of small dimensions produced in inverted micelles Chem. Phys. Lett. 125 299... 

Zulauf M and Eicke FI 1979 Inverted micelles and microemulsions in the ternary system Fl20/aerosol-OT-isoctane as studied by photon correlation spectroscopy J. Phys. Chem. 83 480... 

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

The lipases demonstrated very high stability in media partially or totally composed of organic solvent. In such media, the lipases catalyze esterification, transesterification, and resolution of enantiomers [19,45,75,97-100]. Nevertheless, several biphasic systems (organic-aqueous) are used for hydrolysis of lipid and fats [7,34,101]. Kinetic studies in biphase media or in inverted micelles demonstrate that the lipase behavior is different... 

Figure 7.22b shows that hydrophilic molecules, those with log Kj < 1, are much more permeable in octanol than in olive oil. The same may be said in comparison to 2% DOPC and dodecane. Octanol appears to enhance the permeability of hydrophilic molecules, compared to that of DOPC, dodecane, and olive oil. This is dramatically evident in Fig. 7.7, and is confirmed in Figs. 7.8c and 7.22b. The mechanism is not precisely known, but it is reasonable to suspect a shuttle service may be provided by the water clusters in octanol-based PAMPA (perhaps like an inverted micelle equivalent of endocytosis). Thus, it appears that charged molecules can be substantially permeable in the octanol PAMPA. However, do charged molecules permeate phospholipid bilayers to any appreciable extent We will return to this question later, and will cite evidence at least for a partial answer. 

Zulauf, M and Eicke, H.F. "Inverted Micelles and Microemulsions in the Ternary System H20/Aerosol OT/Isooctane as Studied by Photon Correlation Spectroscopy," J. Phvs. Chem.. 1979, 82(4), 480 486. 

Figure 22.1 The amphiphilic nature of phospholipids in solution drives the formation of complex structures. Spherical micelles may form in aqueous solution, wherein the hydrophilic head groups all point out toward the surrounding water environment and the hydrophobic tails point inward to the exclusion of water. Larger lipid bilayers may form by similar forces, creating sheets, spheres, and other highly complex morphologies. In non-aqueous solution, inverted micelles may form, wherein the tails all point toward the outer hydrophobic region and the heads point inward forming hexagonal shapes.

Based on the above results and discussion, the mechanism for the rhythmic oscillations at the oil/water interface with surfactant and alcohol molecules may be explained in the following way [3,47,48] with reference to Table 1. As the first step, surfactant and alcohol molecules diffuse from the bulk aqueous phase to the interface. The surfactant and alcohol molecules near the interface tend to form a monolayer. When the concentration of the surfactant together with the alcohol reaches an upper critical value, the surfactant molecules are abruptly transferred to the organic phase with the formation of inverted micelles or inverted microemulsions. This step should be associated with the transfer of alcohol from the interface to the organic phase. Thus, when the concentration of the surfactant at the interface decreases below the lower critical value, accumulation of the surfactant begins and the cycle is repeated. Rhythmic changes in the electrical potential and the interface tension are thus generated. 

Upon immersion in acidic water (pH = 1) these unimolecular inverted micelles form vesicles in which the dendrimer component has a highly distorted conformation with an axial ratio of 1 8 for the highest generations. The amphiphilic dendrimers within the aggregates in solution are thought to have a flattened shape similar to those proposed for dendrimers at the air-water interface (section 16.2.1). 

Crooks et al. reported the transfer of amine-functionalized poly(amidoamine) dendrimers into toluene containing dodecanoic acid [198], The method is based on the formation of ion pairs between the fatty acids and the terminal amine-groups. These dendrimer-fatty acid complexes resemble unimolecular inverted micelles and could be used as phase transfer vehicles for the transport of Methyl Orange, an anionic dye molecule, into an organic medium. 

The pharmaceutical and fine chemical industry might use pure hydrogenase or partially purified enzyme preparations in bioconversion applications such as regio and stereoselective hydrogenation of target compounds (van Berkel-Arts et al. 1986). Enzymes are able to catalyse such stereospecific syntheses with ease. However, the cofactors for the NAD-dependent oxidoreductases are expensive. The pyridine nucleotide-dependent hydrogenases such as those from Ralstonia eutropha and hyperthermophilic archaea (Rakhely et al. 1999) make it possible to exploit H2 as a low-cost reductant. The use of inverted micelles in hydrophobic solvents, in which H2 is soluble, has advantages in that the enzymes appear to be stabilized. 

Figure 9.15 Enzymes in aqueous (light-coloured) and hydrophobic (shaded) phases. (A) A protein in the periplasm (PP) of a cell (OM = outer membrane, CM = cytoplasmic membrane) (B) membrane-bound protein in a lipid bilayer (C) hydrophilic protein in an inverted micelle (D) interaction between enzyme and substrates in aqueous micelles (E) graph of catalytic activity as a function of micelle concentration.

Fig. 21. Schematic illustration of phase-transfer catalysis using an amine-terminated den-drimer-encapsulated nanoparticle complexed with a fatty acid (present in the organic phase). The fatty acid surrounds the dendrimer, yielding a monodisperse inverted micelle which is soluble in the organic phase. After catalysis, the catalyst can be reclaimed by changing the pH of the aqueous phase...

Toluene solutions of Pd encapsulated within dendrimer-templated inverted micelles have been tested for catalytic activity by examining their effectiveness towards hydrogenation of allyl alcohol in organic solvents [19]. The reaction product was confirmed to be n-propanol by H NMR spectroscopy, and the turnover frequency, calculated from the rate of hydrogen uptake, was 760 mol H2 (mol Pd) h at 20 °C. This value compares favorably with the value of 218 mol H2 (mol Pd) h obtained for the same reaction carried out in water using Pd nanoparticles encapsulated in hydroxy-terminated dendrimers. 

A structure formed by the reversible association of am-phiphiles in apolar solvents. In inverted micelles, the polar portion of the amphiphile is concentrated in the interior of the macrostructure. Such association usually occurs with aggregation and is not typically characterized by a definite nucleation stage. Thus, inverted micelles (also referred to as inverse or reverse micelles) often fail to exhibit critical micelle concentration behavior. See Micelle... 

INVERTED MICELLE REVERSE TRANSCRIPTASE VIRAL POLYMERASES Reversible adiabatic change,... 

Cao LX, Huang SH, Shulin E (2004) ZnS/CdS/ZnS quantum dot quantum well produced in inverted micelles. J Colloid Interface Sci 273 478-482... 

Lianos P, Thomas JK (1986) Cadmium-Sulfide of Small Dimensions Produced in Inverted Micelles. Chem Phys Lett 125 299-302... 

Lianos P, Thomas JK (1987) Small Cds Particles in Inverted Micelles. J Colloid Interface Sci 117 505-512... 

Zulauf M, Eicke HE (1979) Inverted Micelles and Microemulsions in the Ternary-System H2o-Aerosol-Ot-lsooctane as Studied hy Photon Correlation Spectroscopy. 

Micelles are spontaneously formed by most surfactants (especially single-chained ones) even at fairly low concentrations in water, whereas at higher surfactant concentrations, with or without the addition of an oil (e.g. octane) or co-surfactant (e.g. pentanol), a diverse range of structures can be formed. These various structures include micelles, multibilayers (liquid crystals), inverted micelles, emulsions (swollen micelles) and a range of microemulsions. In each case, the self-assembled structures are determined by the relative amounts of surfactant, hydrocarbon oil, co-surfactant (e.g. pentanol) and water, and the fundamental requirement that there be no molecular contact between hydrocarbon and water. 

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