Water In Reverse Micelles Research Articles

Comparative Study on the Structure of Water in Reverse Micelles Stabilized with Sodium Bis(2-ethylhexyl) Sulfosuccinate or Sodium Bis(2-ethylhexyl) Phosphate in n-Heptane

The microstructure of water solubilized in H2O/surfactant/n-heptane ternary systems has been investigated by employing 1H-NMR and FT-IR spectroscopic techniques. Two reverse micellar systems were prepared and studied, i.e., sodium bis(2-ethylhexyl) sulfosuccinate in n-heptane (H2O/AOT/n-heptane) and sodium bis(2-ethylhexyl) phosphate in n-heptane (H2O/NaDEHP/n-heptane). 1H-NMR data showed that the chemical shift of water protons for the AOT and NaDEHP reverse micelles varied downfield and upfield, respectively, with an increase of the water content. The opposite shift directions with increasing water content are interpreted as due to a composition change of the solubilized water associated with head-groups and sodium counterions in reverse micellar systems. On the basis of deconvolution results of FT-IR spectra, a four-component model is proposed to interpret the FT-IR and 1H-NMR results.

Influence of Water on the Primary Photosynthetic Activity of Rhodospirillum Rubrum in Reverse Micelles

The effect of water on the primary photosynthetic activity of purple bacterium Rhodospirillum rubrum was studied in Hexadecane-Tween-Spane (HTS)- and phospholipid (PLC)-reverse micelles. Reverse micelles offer the possibility of modulating the amount of water to which enzymes and multienzymatic complexes are exposed. Fast bacteriochlorophyll (BChl) fluorescence induction kinetics and reaction centre absorption changes at 820 nm were used as an assay for the functional transfer of bacterial cells into HTS-reverse micelles and bacterial photosynthetic complexes (BPC) into PLC-reverse micelles. Both the bacterial cells and BPC showed an increase in the rate of primary photosynthetic activity by increasing the concentration of water in the reverse micelles. The bacterial cells could be kept viable for many hours in HTS-reverse micelles in presence of 6% (v/v) water. NMR studies indicated that the photosynthetic activity was affected by the availability of water in reverse micelles. The bacterial cells in HTS or BPC in PLC reverse micelles could be used to further understand the influence of water on the organisation and function of photosynthetic complexes.

Intramolecular charge transfer at reverse micelle–water pool interface: p- N, N-dimethylaminobenzoic acid in AOT/cyclohexane/water reverse micelle

Photoinduced intramolecular charge transfer (ICT) of p- N, N-dimethylaminobenzoic acid (DMABOA) in AOT/cyclohexane/H 2O reverse micelle was investigated and compared with that in CTAB/1-heptanol/H 2O reverse micelle. It is proposed that the DMABOA molecule exists at the AOT reverse micelle–water pool interface with its carboxylic group heading toward the water pool while the dimethylaminophenyl moiety buried in the micellar phase. Dual fluorescence of DMABOA that is indicative of the ICT reaction in the excited state was observed over the investigated water pool size, W of 3–17, in the AOT reverse micelle. The ICT emission of DMABOA in the AOT reverse micelle–water pool interface was found to be much weaker than that in the CTAB reverse micelle–water pool interface, and was attributed to the parallel direction of the electric field at the AOT reverse micelle–water pool interface to the charge transfer.

Microstructure Studies of Primary Amine N1923/n-heptane/Alcohol/Water Reverse Micelles

The microstructural characteristics of primary amine N1923/n-heptane/alcohol/water reverse micelles have been investigated by means of the dilution method and FT-IR spectroscopic and TEM techniques. Some structural parameters have been obtained. The broad bands obtained for water, alcohol, and primary amine N1923 bands have been resolved by both Gaussian and Lorentzian curve-fitting programs, and the vibrational characteristics, particularly the peak area and relative content corresponding to each peak, have been analyzed and assigned. It has been observed that the aqueous core of the reverse micelle droplet is composed of bound water and bulk water while a little free water remains at the interface. The hydration number of RNH3+ increases with the addition of water; however, it almost remains a constant under the conditions of various alcohols with the same content of water. All that has been obtained is very significant for the study of the mechanism of amine extraction systems.

Micropolarity of sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles prepared in supercritical ethane and near-critical propane

The micropolarity of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles prepared in supercritical ethane and near-critical propane has been determined in terms of a solvent polarity parameter, ET(30) values, by using absorption probes, 1-ethyl-4-methoxycarbonyl pyridinium iodide and 2,6-diphenyl-4-(2,4,6-triphenylpyridinio)-phenolate as a functions of pressure and the molar ratio of water to AOT, W0, at a constant temperature of 310 K. The micropolarity comparable to that of ethanol was observed for reverse micelles containing water of W0 = 2. The micropolarity increased with the water content and became independent of pressure after the system changed to a one-phase reverse micelle solution. For a given W0 value, no difference in the micropolarity was noticed in the micelles prepared in ethane and propane. Phase behaviour investigations have revealed that complete dissolution of 50 mM AOT occurred at 20 MPa in supercritical ethane, while a much lower pressure of 1 MPa was required in near-critical propane. The amount of water solubilized in reverse micelles formed in supercritical ethane was relatively low, reaching a W0 value of 7 at 36 MPa. In contrast, the amount of water solubilized in near-critical propane reverse micelles was W0 = 11 at a much lower pressure of 6 MPa. A higher pressure was required to solubilize larger amount of water in reverse micelles prepared in both ethane and propane.

Structural aspects in self-assembled systems of polyoxyethylene surfactants, as studied by the spin probe technique

Typical examples of structural characterization of self-assembled systems by the spin probes technique, selected from our representative results accumulated in the last years of systematic studies, are presented. The choice of the examples has aimed at emphasizing the potentiality of this technique in the study of self-assembled systems, in general, and of those of PEO surfactants, in particular. By using specific ESR parameters (the nitrogen hyperfine splitting (hfs), a N, the rotational correlation time, τ c, the order parameter, S) of a variety of properly chosen nitroxides, problems such hydration degree and profile of the PEO chains, ordering and order profile along these chains, their penetrability by the oil solvent, role of the terminal OH in the micellization, as well as differences in these quantities vs . the nature of the aggregate (micelle, reverse micelle, lamellar phase, etc.), nature of the surfactants (conventional or triblock copolymer), solubilizates (water in reverse micelles or various alcohols in micelles) and temperature have been discussed.

Kinetic model for enzymatic hydrolysis in reverse micelles

A bound water model is developed for the interpretation of kinetic data of b-galactosidase in reverse micelles. Assessing the kinetic parameters of p-nitrophenyl-b-D-galactopyranoside hydrolysis in aqueous and reverse micellar system reveals that the major effect on hydrolytic rate is owing to the amount of free water in reverse micelles, not the enzyme molecules' structural change.

The contribution of water to the selectivity of pyruvate kinase for Na+ and K+.

For many years it has been known that K+ is an essential activator of pyruvate kinase [Kachmar, J. F. & Boyer, P. D. (1953) J. Biol. Chem. 200, 669-683] and that Na+ induces relatively small enhancements of activity. The effect of these two alkali metal ions on the activity of pyruvate kinase entrapped in the low water environment of reverse 'micelles formed with cetyltrimethylammonium, hexanol, n-octane and various water concentrations was studied. In reverse micelles with 3.6% water, the activity with 7 mM Na+ is more than 82 times higher than in aqueous solution with an equivalent Na+ concentration. As the concentration of water in reverse micelles is raised, the activating effect of relatively low concentrations of Na+ (or K+) decreases simultaneously to a more than 100-fold increase in the concentration of Na+ or K+ required for attaining half-maximal activation. Similar results were obtained with NH4+, Rb+ and Cs+. Therefore, the amount of water in the system is critical for observing activation by alkali metal ions. In fact, the concentration of Na+ required for half-maximal activation in standard aqueous media is higher than the concentrations that can be experimentally assayed. As evidenced from fluorescence and kinetic data, it appears that the entrapment of pyruvate kinase in reverse micelles does not produce gross structural alterations. Therefore, it is suggested that in conventional aqueous systems, the basis of the high discrimination between Na+ and K+ by pyruvate kinase is the higher energy required for desolvating Na+. Nevertheless, at all the water concentrations studied, the activities reached with K+ were higher than with Na+ which suggests that the Na+ form of the enzyme has a lower catalytic capacity than the K+-enzyme complex.

Organic reactions in micro-organized media: Why and how?

Abstract

Continuous Assay for Acid Phosphatase Using Phenyl Phosphate

A continuous spectrophotometric assay for the determination of the initial rate of an acid phosphatase-catalyzed reaction in an acidic environment, using phenyl phosphate as a substrate, is presented. The method is based on the continuous determination of phenol, a product of the enzymatic hydrolysis, by the kinetic measurement of its absorbance. The method allows for the direct estimation of acid phosphatase activity in an acidic solution. This is possible without interrupting the reaction by alkalization or precipitation required for commonly used end-point colorimetric detection procedures for phosphate or phenol, and without the use of any coupled assays. The method has been developed for acid phosphatase activity determination in an aqueous solution and in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)–isooctane–water reverse micelles in a broad pH range (pH 3.8 to 8.8). The proposed procedure has been used for the determination of kinetic constants (Kmandkcat) for human prostatic acid phosphatase in aqueous solutions, and in AOT–isooctane–water reverse micelles, at pH 3.8, 4.5, and 5.7.

Water in oil colloïdal droplets used as microreactors

This review presents the main results of the studies carried out in reverse micelles during last few years. The reader can point out the ability of reverse micelles in acting as a microreactor, in the various cases. Because of the ability of changing the size of such reactor by increasing the amount of solubilized water in reverse micelles and by changing the location of the reactants, the kinetic rate constant of chemical reactions can be changed by several order of magnitude.This property favors the formation of nanosize monodispersed crystallites. By changing the water content, the size of the clusters increases and their surface can be modified. Percolation process induced by cytochrome c addition in dilute reverse micelles is reported. It is shown that this is due to electrostatic interactions between the protein and the water in oil interface. Reverse micelles are able to solubilize enzyme keeping its activity and play an important role as protecting agents in the chemical modification of the enzyme.

Lipase-Catalyzed Reactions in Reverse Micelles Formed by Soybean Lecithin

Reverse micelles formed by soybean lecithin in isooctane were used as a reaction medium for both the lipase-catalyzed hydrolysis as well as the synthesis of lipids. Neither reaction appears to follow Michaelis-Menten kinetics and it is suggested that the rates are diffusion controlled. The hydrolysis of para-nitrophenylpalmitate (PNPP) and, in particular, the pH-dependency of the lipase-catalyzed hydrolysis was then examined. The highest rate of reaction occurred at pHopt = 5–5.5, which was the same in water and lecithin reverse micelles, as well as in reverse micelles formed by bis(2-ethylhexyl)-sulfosuccinate (AOT) in isooctane. The dependence of the reaction rate on the water content of the micellar system was investigated for the same reaction. The maximal rate was found at an extremely low water content, i.e. at Wo = 2.2 (Wo = [H2O]/[Lecithin]). The temperature stability of the lipase in lecithin reverse micelles was also studied and found to be greater than in aqueous solutions. Studies of the depen...

Interfacial water structure in lecithin—oil—water reverse micelles

Lecithin dissolved in organic solvents forms reverse micellar aggregates which can solubilize water. Using NMR and FTIR techniques it has been found that water in lecithin reverse micelles remains mainly in three different states, namely water hydrated to monomeric lecithin, water bound to the lecithin aggregates and free water in the aqueous core of the aggregates. The composition of each of the various states of water depends on the amount of water solubilized in the micelles. It has been estimated that the maximum amount of water bound per lecithin molecule is between 4 and 5 in the aggregated system.

ChemInform Abstract: STRUCTURE AND STATE OF WATER IN REVERSED MICELLES. 3

Chemischer InformationsdienstVolume 8, Issue 39 Physical Inorganic Chemistry ChemInform Abstract: STRUCTURE AND STATE OF WATER IN REVERSED MICELLES. 3 M. WONG, M. WONGSearch for more papers by this authorJ. K. THOMAS, J. K. THOMASSearch for more papers by this authorT. NOWAK, T. NOWAKSearch for more papers by this author M. WONG, M. WONGSearch for more papers by this authorJ. K. THOMAS, J. K. THOMASSearch for more papers by this authorT. NOWAK, T. NOWAKSearch for more papers by this author First published: September 27, 1977 https://doi.org/10.1002/chin.197739010AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue39September 27, 1977 RelatedInformation