docusate-sodium and 2-2-4-trimethylpentane

CdS quantum dots (CdS QDs) 4.3 nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0 nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3 M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly.

Topics: Cadmium Compounds; Electrochemical Techniques; Electrodes; Ethanol; Light; Micelles; Octanes; Particle Size; Photosensitizing Agents; Phycoerythrin; Potassium Chloride; Quantum Dots; Selenium Compounds; Succinates; Water

In this study, we investigated the possibility of reversed micelles, widely used as an enzyme reactor for lipases, for the determination of lipoxygenase activity. Although it is rapid and simple, reversed micelles have some limitations, such as interference by UV-absorbing materials and surfactant. Lipoxygenase activity in the reversed micelles was determined by reading the absorbance of the lipid hydroperoxidation product (conjugated diene) at 234 nm. Among surfactants and organic media, AOT and isooctane were most effective for the dioxygenation of linoleic acid in reversed micelles. The strong absorbance of AOT in the UV region is a major obstacle for the direct application of the AOT/isooctane reversed micelles to lipoxygenase activity determination. To prevent interference by AOT, we added an AOT removal step in the procedure for lipoxygenase activity determination in reversed micelles. The lipoxygenase activity was dependent on water content, and maximum activity was obtained at an R-value of 10.

Topics: Enzyme Assays; Kinetics; Lipoxygenase; Micelles; Octanes; Sensitivity and Specificity; Succinates; Surface-Active Agents

Choline acetate is an ionic liquid composed of a kosmotropic anion and a chaotropic cation. According to Hofmeister series, a kosmotropic anion and/or a chaotropic cation could stabilize an enzyme, thereby facilitating the retention of the catalytic activity of the enzyme. In this work, we first report the influence of choline acetate on the activity and stability of lipase in AOT/water/isooctane reverse micelles. The indicator reaction is the lipase-catalyzed hydrolysis of 4-nitrophenyl butyrate. The results show that a low level of choline acetate does not affect the microstructure of the AOT reverse micelles, but the ionic liquid can improve the catalytic efficiency of lipase. Fluorescence spectra show that a high level of choline acetate has an impact on the conformation of lipase, so the activation is mainly due to the influence of choline acetate on the nucleophilicity of water. Infrared spectra demonstrate that choline acetate can form stronger hydrogen bonds with water surrounding lipase, and therefore enhance the nucleophilicity of the water, which makes it easier to attack the acyl enzyme intermediate, thereby increasing the activity of the lipase-catalyzed hydrolysis of the ester. A study on the stability of lipase in AOT reverse micelles indicates that the ionic liquid is able to maintain the activity of lipase to a certain extent. The effect of choline acetate is consistent with that predicted based on Hofmeister series.

Topics: Acetates; Candida; Catalysis; Choline; Fluorescence; Hydrolysis; Ionic Liquids; Lipase; Micelles; Octanes; Protein Conformation; Spectrophotometry, Infrared; Succinates; Water

A study was carried out on the influence of the n-alkyl acid addition on the electric percolation of AOT/iso-octane/water microemulsions ([AOT] = 0.5 M and W= [H(2)O]/[AOT] = 22.2). The observed influence has been explained taking into account the organic nature of these molecules and, hence, their capacity of disturbing the structure of the AOT-film. For these reasons, relationships with their molecular structure (chain length) were analysed.

Topics: Carboxylic Acids; Electric Conductivity; Electrochemistry; Emulsions; Octanes; Succinates; Surface Properties; Water

The thermostability of Cromobacterium viscosum lipase (EC 3.1.1.3) entrapped in AOT (sodium bis-[2-ethylhexyl] sulfosuccinate) reverse micelles was increased by the addition of short-chain polyethylene glycol (PEG 400). Two different approaches were considered: (1) the determination of half-life time and (2) the mechanistic analysis of deactivation kinetics. The half-life of lipase entrapped in AOT/isooctane reverse micelles with PEG 400 at 60 degrees C was 28 h, ninefold higher than that in reverse micelles without PEG 400. The lipase entrapped in both reverse micellar systems followed a series-type deactivation mechanism involving two first-order steps. The deactivation constant for the first step at 60 degrees C in PEG containing reverse micelles was 0.055 h!1, 11-fold lower than that in reverse micelles without PEG, whereas it remained almost constant for the second step. The inactivation energy of the lipase entrapped in reverse micelles with and without PEG 400 was 88.12 and 21.97 kJ/mol, respectively.

Topics: Betaproteobacteria; Enzyme Activation; Enzyme Stability; Enzymes, Immobilized; Lipase; Micelles; Octanes; Polyethylene Glycols; Substrate Specificity; Succinates; Temperature

Structural modifications of AOT/water/isooctane reverse micelles due to incorporation of proteins were studied at various water contents and protein concentrations, using small-angle X-ray scattering (SAXS) experiments under static conditions, rheometry analysis, and SR-SAXS experiments under induced shear flow. Two proteins, lysozyme (pI 11.1, Mw 14,300 Da) and BSA (pI 4.3, Mw 66,700 Da), were chosen as models. SAXS analysis of protein-containing reverse micelles at low water content detected minima in the average micelle size versus protein concentration curve, for both proteins, below and above their isoelectric point. This minimum was attributed to changes in the size distribution of the reverse micelles. SAXS measurements of reverse micelles at high water content have shown them to have a cylindrical form. Incorporation of lysozyme at pH 7 into the cylindrical micelles induced a shape transition to spherical micelles, which was associated with a decreased viscosity. SR-SAXS measurements under induced shear flow and dynamic conditions revealed alignment of the cylindrical micelles in the flow direction. The anisotropy parameter, a measure of the degree of the spatial order, was found to increase with increasing shear rate and to decrease with increasing lysozyme concentration.

Topics: Micelles; Muramidase; Octanes; Proteins; Scattering, Small Angle; Succinates; Surface-Active Agents; Water; X-Ray Diffraction

How water, metabolites and proteins associate and traverse the lipid interface is generally investigated by using probes with spectroscopic handles. Cellular confinement limits the tools of investigation to indirect approaches. Studies of a variety of different probes become important to understand the effects of confinement on chemical reactions and biological function. Confinement of water affects the properties of water and this effect is important for cellular systems. A versatile model system for studying the effect of water confinement on biological processes uses reverse micelles (RMs). Molecular probes are also used to investigate environments that are not readily accessible to direct measurements. Most of the dyes in use contain large hydrophobic chromophores and do not have size and structural flexibility to probe a surface that is both hydrophobic and hydrophilic as common in biological systems. We present the use of vanadium-containing probes for exploration of the fundamental properties of restricted water and lipid interfaces in RMs. The presence of a vanadium atom in these probes provides multiple handles such as chemical shifts, signal linewidth and lifetime experiments in the quadrupolar 51V nuclei as well in 1H and 13C nuclei for investigations. The quadrupolar nuclei have a greater battery of useful spectroscopic parameters and combined with the conventional methods provide multiple handles in one probe. Furthermore, the vanadium-containing probe structure, charge and polarity can be modified for use in various biological settings. Here we introduce the concept and describe a few applications of this approach.

Topics: Cetrimonium; Cetrimonium Compounds; Lipids; Magnetic Resonance Spectroscopy; Micelles; Molecular Structure; Octanes; Organometallic Compounds; Picolinic Acids; Succinates; Vanadates; Water