Native and modified glucose oxidase in reversed micelles

The enzymatic activity of the native and modified glucose oxidase (GOx) from Aspergillus niger in the system of reversed micelles of Aerosol OT in octane was investigated. Two forms of the modified enzyme were studied: a hydrophobized form obtained by the attachment of palmitic chains to lysine amino groups by the reaction with palmitic acid ester of N-hydroxysuccinimide and a glycosylated (hydrophilized) form obtained by the attachment of the cellobiose moieties. The native glucose oxidase and its derivatives, while incorporated into micelles in a surfactant concentration range from 0.05 to 0.3 M, display an enzymatic activity, which is comparable with the activity in aqueous solution. The dependence of the enzymatic activity on hydration degree of surfactant (the molar ratio of water to surfactant, W₀) does not indicate the formation of qualitatively new associated forms of the enzyme subunits inside the micelles. The apparent size of Aerosol OT micelles obtained by dynamic light scattering gradually increases from 10±3 nm at low W₀ up to 25±5 nm at high W₀. Incorporation of the native and hydrophobized glucose oxidase into micelles does not affect their mean size. Kinetic analysis shows that the enzyme specificity is about an order of magnitude greater in the system of reversed micelles as compared with aqueous solution.     

Transport of charged Aerosol OT inverse micelles in nonpolar liquids

Surfactants such as Aerosol OT (AOT) are commonly used to stabilize and electrically charge nonpolar colloids in devices such as electronic ink displays. The electrical behavior of such devices is strongly influenced by the presence of charged inverse micelles, formed by excess surfactant that does not cover the particles. The presence of charged inverse micelles results in increased conductivity of the solution, affecting both the energy consumption of the device and its switching characteristics. In this work, we use transient current measurements to investigate the electrical properties of suspensions of the surfactant Aerosol OT in dodecane. No particles are added, to isolate the effect of excess surfactant. The measured currents upon application of a voltage step are found to be exponentially decaying, and can be described by an analytical model based on an equivalent electric circuit. This behavior is physically interpreted, first by the high generation rate of charged inverse micelles giving the suspension resistor like properties, and second by the buildup of layers of charged inverse micelles at both electrodes, acting as capacitors. The model explains the measurements over a large range of surfactant concentrations, applied voltages, and device thicknesses.     

Activation and stabilization of enzymes entrapped into reversed micelles

Observations of the activity of two hydrolyzing enzymes—protease and α-amylase—entrapped inside the reversed micelles formed by surfactants in hexane, benzene, and cyclohexane are reported. The surfactants chosen for this study are: Tween 80, a nonionic surfactant, Cetyl pyridinium chloride, a cationic surfactant, and two anionic surfactants, sodium lauryl sulfate and Aerosol OT. Tween 80 enhances the activity of both protease and α-amylase. Sodium lauryl sulfate and Aerosol OT, which are ionic surfactants, enhance the activity of protease, but inhibit the activity of α-amylase. Cetyl pyridinium chloride, however, enhances the activity of α-amylase, but inhibits the activity of protease. Enhanced activity is generally severalfold greater in comparison to the activity observed in the usual aqueous system in the absence of reversed micelles. It has also been observed that the enhanced activity of the enzymes entrapped inside the reversed micelles remains preserved for a much longer period of time in comparison to the activity in the usual aqueous systems. These observations, which support the view that with proper choice of surfactant and the organic solvent, reversed micelles act like a microreactor that provides a favorable aqueous microenvironment for enzyme activity, have biotechnological overtones.     

Coexisting aggregates in mixed aerosol OT and cholesterol microemulsions

Dynamic light scattering and NMR spectroscopic experimental evidence suggest the coexistence of two compositionally different self-assembled particles in solution. The self-assembled particles form in solutions containing water, Aerosol OT (AOT, sodium bis(2-ethylhexyl) sulfosuccinate) surfactant, and cholesterol in cyclohexane. In a similar series of studies carried out in 1-octanol only one aggregate type, that is, reverse micelles, is observed. Dynamic light scattering measurements reveal the presence of two different types of aggregates in the microemulsions formed in cyclohexane, demonstrating the coexistence of two compositionally distinct structures with very similar Gibbs energies. One particle type consists of standard AOT reverse micelles while the second type of particle consists of submicellar aggregates including cholesterol as well as small amounts of AOT and water. In microemulsions employing 1-octanol as the continuous medium, AOT reverse micelles form in a dispersed solution of cholesterol in 1-octanol. Although the size distribution of self-assembled particles is well-known for many different systems, evidence for simultaneous formation of two distinctly sized particles in solution that are chemically different is unprecedented. The ability to form microemulsion solutions that contain coexisting particles may have important applications in drug formulation and administration, particularly as applied to drug delivery using cholesterol as a targeting agent.     

The Dipole Moment of Reverse Micelles according to Computer Simulation Data

Sodium 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxybutane-2-sulfonate (Aerosol OT) reverse micelles in isooctane have been simulated, and the mean-square dipole moment has been calculated. The formed isolated micelles have been classified according to aggregate radius and surface area per one surfactant molecule. It has been shown that, for micelles with a constant surface density of surfactant anion charges, the meansquare dipole moment rises with the aggregate size faster than the squared radius does. Dipole moment values obtained within the atomistic model for a reverse micelle are much higher than the values presented in the literature for the primitive model.     

Solution behaviour of Aerosol OT in non-polar solvents

The aggregational behaviour of Aerosol OT in non-polar solvents and the applications of these systems in various areas have been reviewed. Aerosol OT forms reverse micelles in oils without using any cosurfactant and the reverse micellar solution can dissolve large amounts of water with the formation of discrete droplet microemulsion or bicontinuous microemulsions. Due to their simplicity in the sense of the smallest number of components in the reverse micellar systems, these systems have been widely studied and have also been divergently applied. This review gives a detailed account of various aspects of Aerosol OT reverse micelles namely their aggregational, structural, conformational, dynamic and applications reported in the literature to date.     

Solvation dynamics of formamide and N,N-dimethylformamide in aerosol OT reverse micelles

The solvation dynamics of formamide and N,N-dimethylformamide in Aerosol OT reverse micelles has been investigated in this work. The solvation dynamics of formamide and N,N-dimethylformamide in the reverse micelles is more than 100 times slower than that of the pure solvents. The solvation dynamics of formamide in the reverse micelle solution depends strongly on the molar ratio between formamide and Aerosol OT (w = [polar solvent]/[Aerosol OT]), but that of N,N-dimethylformamide in the reverse micelle solution shows a tiny w dependence. We have estimated the interaction energies of the geometry-optimized clusters of a simple model of the Aerosol OT polar headgroup (CH3SO3-) and formamide or N,N-dimethylformamide by ab initio calculations (the second-order M?ller-Plesset perturbation theory) to find their interactions. The interaction energies of the mimic clusters estimated by the ab initio calculations and the features of the slow solvation dynamics and w dependence in formamide and N,N-dimethylformamide reverse micelles are discussed.     

Role of environment on the activity and stability of α-amylase incorporated in reverse micelles

α-amylase (3.2.1.1) was solubilized in reverse micelles formed by Triton X-100 in xylene. Although the enzyme shows decrease in specific activity in reverse micellar medium, it possesses significantly high stability in comparison to bulk aqueous medium. Water/Surfactant ratio (Wo) was found to play a crucial role in both activity and stability of the enzyme. The optimum water/surfactant ratio for the catalytic function of an enzyme in reverse micelles is 36, while the enzyme is stable at Wo 12 for a considerably long period, and at Wo above 20 the enzyme gets inactivated within a day. Glycerol and CaCl₂ improve the stability in both aqueous and reverse micellar medium. Thus the interior of the reverse micelles acts as a microreactor and provides favorable environment for the enzyme activity and stability.     

Partial purification of glutaryl-7-ACA acylase from crude cellular lysate by reverse micelles

Glutaryl-7-ACA acylase was partially purified from the cellular lysate ofPseudomonas sp. NCIMB 40409 by means of reverse micelles-water two-phases extractions. The tetrameric enzyme can be solubilized inside the reverse micelles formed by anionic (Aerosol OT, AOT) and cationic (tetradecyltrimethylammoniumbromide, TDAB) surfactants with retention of the enzymatic activity. With TDAB reverse micelles system, the acylase was partially extracted from the aqueous phase and, after backward transfer into a second water phase, a twofold purification factor was achieved. On the other hand, with the AOT micellar system, in conditions were most of the proteins but acylase, were extracted by the organic micellar solution, a sixfold increase of the specific activity of the acylase remaining in the aqueous phase was obtained.     

纳米铜颗粒-酶-复合功能敏感膜生物传感器

用水合联肼作还原剂研制成亲水纳米铜颗粒,用琥珀酸二异酯磺酸钠／丙三醇／正庚烷反胶束体系合成出憎水纳米铜颗粒,并通过透射电镜和紫外光谱考察了制得的纳米颗粒样品,用憎水纳米铜颗粒及亲水纳米铜颗粒与聚 烯醇缩丁醛构成复合固酶膜基质,用溶胶－凝胶法固定葡萄糖氧化酶,构建葡萄糖生物传感器,实验结果表明,纳米铜颗粒可大幅度提高固定化酶的催化活性,响应电流从相应浓度的几十纳安增强到几千纳安,从理论和实验上证明了     

Synthesis and Stabilization of Gold Nanoparticles in Reverse Micelles of Aerosol OT and Triton X-100

Mechanisms of the formation and stabilization of gold nanoparticles in reverse micelles of micro-emulsions based on Triton X-100 (TX-100) and Aerosol OT (AOT) are studied. The instability of AOT-based microemulsions is shown to be caused by the oxidative degradation of gold nanoparticles in micelle water pools. Methods are proposed for the stabilization of these microemulsions. It is revealed that the mean size of gold nanoparticles synthesized in TX-100 reverse micelles in the presence of sodium sulfite is markedly smaller than that of particles prepared in AOT reverse micelles. This is explained by the fact that gold clusters are formed in the micelle shell rather than in the water pool. In the shell, the clusters are stabilized by oxyethylene groups of TX-100 molecules.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 534–540.Original Russian Text Copyright © 2005 by Spirin, Brichkin, Razumov.     

Phenidone Oxidation during Photoinitiated Chemical Reduction of AgBr Nanocrystals in Water Pools of Reverse Micelles

Photoinitiated chemical reduction of AgBr nanocrystals (synthesized in water pools of reverse micelles of Aerosol OT and sodium dodecyl sulfate) with phenidone was shown to yield 1-phenyl-3-hydroxypyrazole along with reduced silver. This becomes possible because of irreversible oxidation of phenidone (1-phenyl-3-pyrazolidone) used as a reducing agent, and the rate of 1-phenyl-3-hydroxypyrazole accumulation significantly increases in the presence of a silver halogenide. The formation of the dissociated form of 1-phenyl-3-hydroxypyrazole becomes more probable with decreasing diameter of the water pool of reverse micelles formed by both surfactants.     

Structure and rheology of reverse micelles in dipentaerythrityl tri-(12-hydroxystearate)/oil systems

We report the formation of reverse rod-like micelles and their rheological properties in novel nonionic surfactant, dipentaerythrityl tri-(12-hydroxystearate) (designated as WO-6)/oil systems without external water addition. Small-angle X-ray scattering (SAXS) was used to investigate the structure of the micelles and their flow properties were studied by rheological measurements. We found that WO-6 spontaneously self-assembles into reverse micelles in a variety of organic solvents at ambient conditions, their structure depending on solvent molecular architecture, surfactant concentration, and temperature. Rod-like micelles with a maximum length of ca. 12 nm and a cross section diameter of ca. 2 nm were observed in cyclohexane. When cyclohexane was replaced with a linear chain octane, the length and the cross section diameter were simultaneously increased. With a further increase of hydrocarbon chain length of solvent oils from octane to hexadecane, the rod-like micelles grew axially, keeping the cross section diameter (ca. 3 nm) virtually constant. Increasing surfactant concentration also favored one-dimensional micellar growth. On the other hand, micelles shrunk with the rise of temperature, which is similar to a rod-to-sphere transition, and is essentially the opposite temperature dependence to that often observed in aqueous micellar systems. A structural picture drawn by SAXS is well supported by rheology; the relative (zero-shear) viscosity of the WO-6/oil systems was found to be markedly greater than that expected for a dispersion of spherical particles due to the elongated micellar structure, despite quantitative inconsistency with semi-empirically predicted values for rigid rod-like particles.     

Functionalization of (CdSe)ZnS nanoparticles in reverse micelles of Aerosol OT

A method is optimized for in situ functionalization and activation of (CdSe)ZnS nanoparticles in reverse micelles of Aerosol OT, as well as their conjugation with antibodies. The efficiency of particle functionalization depends on the method of micellar solution formation. Fluorescence remains practically unchanged, provided that NH₂ groups of polymers bonded to the nanoparticles are activated by glutaric aldehyde. All operations of antibody conjugation should be carried out in reverse micelles for the maximum preservation of the fluorescence properties of the particles. Nanoparticles are isolated from reverse micelles using a mixture of acetone with a solution composed of 50 mM NaHCO₃ and 200 mM NaCl. The optimum medium for dissolving the precipitate of the particles consists of NaHCO₃ (50 mM), bovine serum albumin (0.1%), and Twin 85 (0.05%). The modified particles were subjected to photoactivation in an aqueous medium at room temperature and daylight.     

Distribution of Polyphenols and a Surfactant Component in Skin during Aerosol OT Microemulsion-Enhanced Intradermal Delivery

As for most other polyphenols, intradermal delivery of curcumin and resveratrol is limited; however, it was significantly improved by a microemulsion using Aerosol OT (Aerosol OT microemulsion) and Tween 80 (Tween 80 microemulsion) as surfactants. Aerosol OT microemulsion was more effective and the incorporation ratio of these polyphenols into skin by Aerosol OT microemulsion was five-fold or ten-fold that by Tween 80 microemulsion. To clarify the mechanism of the enhancement we examined the distribution of these polyphenols and the surfactant component, Aerosol OT, using excised guinea pig skin and Yucatan micropig (YMP) skin. During permeation, polyphenols distributed deep in the skin. In particular, a small molecule, resveratrol, was mainly present in the dermis in YMP skin. Aerosol OT also distributed deep in the skin. These findings suggest the possible involvement of the interaction of surfactant molecules with skin components in the enhanced delivery process of polyphenols. The distribution ratio between the dermis and epidermis of the polyphenols, including quercetin, in the presence of Aerosol OT microemulsion decreased with the increase of molecular weight in YMP skin, suggesting the possibility that distribution to the dermis is regulated by the molecular size.     

Comparison of charge separation in direct and reverse micelles

The photoelectron transfer from zinc porphyrin or chlorophyll to various dialkyl viologens occurs from the triplet state of the sensitizer in oil-in-water cetyltrimethylammonium chloride (CTAC) micelles and in water-in-oil Aerosol OT micelles. The charge separation following the photoelectron transfer is due to the entrance of reduced viologens into the micellar core in oil-in-water CTAC micelles and to bimolecular exchange between water pools in reverse micelles     

Molecular dynamics study of micellization thermodynamics in AOT/hexane system

The thermodynamics of reverse micelle formation from an ionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT), in hexane is studied by molecular dynamics simulation. A change in the Gibbs free energy upon the addition of one AOT molecule to a reverse micelle is calculated as depending on aggregation number N by the thermodynamic integration method. This dependence has a minimum at N ≈ 20 and maximum at N ≈ 35 and predetermines the monotonically decreasing character of the standard chemical potential of AOT in a micelle with the increase of the aggregation number. The simulation results predict the formation of reverse AOT micelles with an average aggregation number of ≈30, which is in good agreement with experimental data.     

Activity and Conformation of Yeast Alcohol Dehydrogenase (YADH) Entrapped in Reverse Micelles

Yeast alcohol dehydrogenase (YADH) solubilized in reverse micelles of aerosol OT (i.e., AOT or sodium bis (2-ethyl hexyl) sulfosuccinate) in isooctane has been shown to be catalytically more active than that in aqueous buffer under optimum conditions of pH, temperature, and water content in reverse micelles. Studies of the secondary structure conformational changes of the enzyme in reverse micelles have been made from circular dichroism spectroscopy. It has been seen that the conformation of YADH in reverse micelles is extremely sensitive to pH, temperature, and water content. A comparison has been made between the catalytic activity of the enzyme and the α-helix content in the conformation and it has been observed that the enzyme is most active at the maximum α-helix content. While the β-sheet content in the conformation of the entrapped enzyme was found to be dependent on the enzyme–micelle interface interaction, the α-helix and random coil conformations are governed by the degree of entrapment and the extent of rigidity provided by the micelle core to the enzyme structure.     

Enthalpies of reaction of calcium chloride and sodium oxalate in aqueous solution of Tween 80

The heats of mixing of dilute calcium chloride and sodium oxalate solutions in water and aqueous solutions of a nonionogenic surfactant, namely, polyoxyethylene (20) sorbitan monooleate (Tween 80) containing 1–5 wt % of the dissolved substance were measured at 298.15 K. The heats of dilution of calcium chloride solutions were determined, and the enthalpies of precipitation of calcium oxalate in water and surfactant solutions were calculated. The surfactant concentration was found to have almost no effect on the enthalpies of the processes under study; rather, it modifies the shape of the resultant deposit by preventing the agglomeration of calcium oxalate particles.