Properties of water in triton N-42 reverse micelles during the solubilization of HCl solutions according to FT-IR and photon correlation spectroscopy

FT-IR and photon correlation spectroscopy methods are used to study the distribution of free (bulk) and bound (hydration) water in Triton N-42 reverse micelles under the conditions of injection solubilization of hydrochloric acid solutions. The amount of each type of water is calculated depending on the solubilization capacity (V _s/V _o) and HCl concentration in the aqueous pseudophase. According to the IR spectroscopy data, the distribution of water is largely determined by the solubilization capacity of the micellar solution, while the fraction of bulk water exceeds significantly the value calculated by the geometric approach based on the photon correlation spectroscopy data. The difference shows that there is bulk water in the surface layer formed by oxyethyl groups of Triton N-42 molecules in spherocylindrical micelles.     

The kinetics of synthesis and mechanism of coagulation of gold nanoparticles in Triton N-42 reverse micelles

The reduction of Au(III) with hydrazine monohydrate in micellar Triton N-42 solutions was shown to be an autocatalytic reaction. Its rate constants were calculated. The growth of a gold nucleus proceeded as a result of surface reduction until the polar micelle nanocavity was completely filled. Calculations according to the Derjaguin-Landau-Verway-Overbeck theory showed that the fate of nanoparticles formed depended on interparticle interaction energy. At a small radius of particles, high surface potential, and fairly thick surfactant surface layer, stable systems were formed. The coagulation zones were calculated depending on the structural parameters of nanoparticles and micelles. If a nanoparticle grew larger than 6.1 nm at a surface potential lower than 10 mV and surface layer thickness ～1.6 nm, the potential well depth exceeded 3/2 kT in magnitude, and coagulation occurred in the system.     

FT-IR study of the properties of water in Triton N-42 inverse micelles

The distribution of free (bulk) and bound (hydration) water in Triton N-42 inverse micelles has been studied. The percent of bulk water changes from 12% to 27% when solubilization capacity* (V _s /V _o ) increases from 0.5 vol.% to 3.5 vol.%. Triton N-42 inverse micelles contain hydration water of two types: 1) water bound with hydroxyl groups and secondary-bound with ethoxy groups and 2) water primary-bound with ethoxy groups. The quantity of water of each type is calculated as a function of solubilization capacity. The polar group of the surfactant molecule is hydrated by approximately six H₂O molecules when V _s /V _o = 3.5 vol.%.     

The preparation of gold nanoparticles in triton N-42 reverse micelles after preliminary concentration from acid sulfate-chloride solutions

The distribution of Au(III) between an acid (3 mol/l HCl) aqueous phase and a micellar Triton N-42 solution in n-decane was studied as a function of the concentration of Na₂SO₄ (0–3.55 mol/l). The high distribution coefficients (200–500) allow 50-fold absolute concentration to be performed at a 90% extraction. Au⁰ nanoparticles were obtained by the injection solubilization of a reducing agent (hydrazine) into micellar extracts. At low solubilization capacities (≤1 vol %) and high reducing agent concentrations (≥0.2 mol/l) in Triton N-42 micelles, stable systems of Au⁰ nanoparticles suitable for the spectrophotometric determination of gold were obtained. At high solubilization capacities and low hydrazine concentrations, reduction was accompanied by coagulation and sedimentation processes. These processes were studied by spectrophotometry and the static and dynamic light scattering methods.     

Generation of silver and lead chromate nanoparticles in Triton N-42 and AOT reversed-micellar solutions

A process is proposed for manufacturing silver and lead nanoparticles in Triton N-42 and AOT solutions in decane. The completion of nanoparticle formation and solution stability were studied spectrophotometrically as functions of the parameters of reversed-micellar systems (the nature and proportion of the surfactant, solubilization capacity, reagent concentrations, and their ratios). Atomic absorption spectroscopy (AAS) and X-ray powder diffraction (XRD) showed that the nanoparticles isolated from Triton N-42 and AOT solutions compositionally correspond to and are isostructural to Ag₂CrO₄ and PbCrO₄. Mean nanoparticle sizes are 15–30 nm as determined by transmission electron microscopy (TEM).     

Compressed CO2-enhanced solubilization of 1-butyl-3-methylimidazolium tetrafluoroborate in reverse micelles of Triton X-100

We carried out the first study about the effect of a compressed gas on the properties of reverse micellar solutions with ionic liquid (IL) polar cores. And the properties of compressed CO2/cyclohexane/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/Triton X-100 (TX-100) system were investigated at 288.2, 293.2, 298.2, 308.2 K and different pressures by using phase behavior measurement, small-angle x-ray scattering, and UV-Vis techniques. The concentration of the surfactant in the solution was 0.3 mol/l (M). It was found that compressed CO2 could enhance solubilization of the IL in the reverse micelles considerably at suitable pressures, and formation of the reverse micelles could be controlled easily by pressure. Increase of CO2 pressure resulted in decrease of the micellar sizes at fixed [bmim][BF4]-to-surfactant molar ratios (w), and the size of the reverse micelles increased with the increase of w values. The polarity of the IL cores increased continuously with increasing w value.     

Study of water properties during Pt(IV) and Au(III) extraction by triton N-42 reverse micelles from acid sulfate-chloride solutions

FT-IR spectroscopy is used to study the distribution of bulk (free) and hydration (bound) water during the extraction of Pt(IV) and Au(III) from acid sulfate-chloride media by Triton N-42 reverse micelles. The bulk water fraction in Triton N-42 micelles reduces from 44% to 23% with an increase in the sodium sulfate concentration up to 3.5 mol/l in the feed. A decrease in the total concentration of micellar water and bulk water fraction complies well with an increase in the Pt(IV) and Au(III) distribution coefficients and concentration during the extraction by Triton N-42 reverse micelles.     

Effect of dioctyl sulfide on the kinetics of oxidative dissolution of gold nanoparticles in triton N-42 reverse micelles

The effect of additions of hydrophobic dioctyl sulfide (L) on the kinetics of dissolution of gold nanoparticles in the interaction with a dispersed aqueous hydrochloric solution of H₂O₂ in Triton N-42 reverse micelles (decane was the dispersion medium) was studied spectrophotometrically. The process consists of a two-stage oxidation Au⁰ → AuCl₂⁻ → AuCl₄⁻ at the surface of gold particles; the first stage occurs in two ways: a spontaneous reaction and an autocatalytic reaction involving AuCl₄⁻ ions. With small additions of L (c _L < c _Au), only spontaneous oxidation of Au(0) to Au(I) takes place because Au(I) is completely bound in an inert complex AuLCl. When unbound L is exhausted, the newly formed AuLCl is accumulated in micellar shells, changes the properties of the medium inside the micelles, and affects the rate constant of the autocatalytic reaction, which increases with increasing c _L. At high concentrations of L, the coagulation of particles occurs instead of their dissolution, because of the deterioration of the protective properties of micellar shells as a result of the ingression and accumulation of dioctyl sulfide molecules on account of selective adsorption on gold particles. The rate constants of all stages of dissolution and coagulation are determined.     

Enhanced solubilization of bovine serum albumin in reverse micelles by compressed CO2

The effect of compressed CO2 on the solubilization of bovine serum albumin (BSA) in water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micelles was studied by observing phase behavior and recording UV-visible spectra under different conditions. The pH values within the water cores of reverse micelles at different CO2 pressures were also determined. The solubilization capacity of the reverse micelles for the protein increased considerably as CO2 pressure increased within the low-pressure range, but decreased at higher CO2 pressures, so that the micelles eventually lost their ability to solubilize the protein. The effect of CO2 on the stability of the reverse micelles played an important role in the relationship between pressure and protein solubility. A "multicomplex" model was proposed to explain these effects. The different solublization capacities within different pressure ranges demonstrates the unique advantage of using compressed CO2 in the extraction of proteins with reverse micelles.     

Physicochemical investigation of the solubilization of ytterbium nitrate in AOT reverse micelles and liquid crystals

A wide investigation of the solubilization of the water-soluble salt Yb(NO₃)₃ in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles and AOT liquid crystals has been carried out. After saturation of water/AOT/organic solvent w/o microemulsions with pure Yb(NO₃)₃, the Yb(NO₃)₃/AOT composites were prepared by complete evaporation under vacuum of the volatile components (water and organic solvent) of the salt-containing microemulsions. It was observed that these composites can be totally dissolved in pure n-heptane or CCl₄, allowing the solubilization of a noticeable amount of Yb(NO₃)₃ in quite dry apolar media. By UV–vis–NIR, FT-IR, and ¹H NMR spectroscopies, some information on the state of Yb(NO₃)₃ within AOT reverse micelles were acquired, whereas by small angle X-ray scattering (SAXS), it has been ascertained that Yb(NO₃)₃ is quite homogeneously distributed as very small clusters among the reverse micelles. An analysis of SAXS and wide-angle X-ray scattering spectra of Yb(NO₃)₃/AOT composites leads to the hypothesis that, also in these systems, Yb(NO₃)₃ is dispersed in the surfactant matrix as very small clusters.     

高压CO~2对反胶束溶解蛋白质性质的影响

在308.15K下,研究了表面活性剂琥珀酸二(2-乙基己基)酯磺酸钠(Aerosol-Ot,简称AOT)的浓度和水的含量不同时,溶解的CO~2对反胶束溶解牛血清蛋白(BSA)的性质和异辛烷中AOT反胶束稳定性的影响。实验表明,在适当条件下,CO~2可以使反胶束溶液中的蛋白质全部析出。本研究对有关机理进行了初步分析。     

Spectral properties of carbocyanine dyes in solutions of reverse AOT micelles

Spectral and luminescence studies of an anionic carbocyanine dye in solutions of reverse AOT micelles have shown that the dye in micelle pools can occur only in the form of the trans-monomer; although aggregated forms of the dye including J aggregates can be present in micellar solution, they all are localized in the organic phase, not micellar pools.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 1, 2005, pp. 21–25.Original Russian Text Copyright © 2005 by Brichkin, Kurandina, Nikolaeva, Razumov.     

Complexes of the proton and its hydrates with carbamoylphosphine oxide in wet dichloroethane solutions

To better understand the complex equilibria involved in the UNEX process for acidic solvent extraction of radionuclides, the interaction of a carbamoylphosphine oxide ligand (L) with the proton of hydrated chlorinated cobalt(III)dicarbollide acid, H[Co(C2B9H8Cl3)2], has been studied in wet 1,2-dichlorethane (DCE) solution using IR and NMR (13C and 31P) spectroscopy. The formation of two groups of complexes has been determined. The first group contains three complexes with 1:1 composition of acid to ligand (Scheme 1). The second group of complexes has 1:2 composition in the equilibrium, shown in Scheme 2. Within each group, the complexes differ in composition only by the number of incorporated water molecules. The equilibria (Schemes 1 and 2) are both very sensitive to the content of self-associated water in solution and are driven by its concentration, which is unsteady and depends on the solution preparation history. The simultaneous presence of both anhydrous (I, II) and hydrated (III, IIIa, IV) proton solvates indicates that the enthalpies of carbamoylphosphine oxide complex formation with H+, H3O+, and H5O2(+) are very close to each other.     

Excited-state proton transfer behavior of 7-hydroxy-4-methylcoumarin in AOT reverse micelles

The excited-state proton transfer and phototautomerization of 7-hydroxy-4-methylcoumarin (7H4MC) dye has been studied in the confined water pools of AOT reverse micelles using steady-state and time-resolved fluorescence measurements. In the "dry" reverse micelles ([water]/[AOT], w(0) = 0), only the neutral form of the dye is present both in the ground and the excited states. At higher w(0) values, three prototropic forms, namely, neutral, anionic, and tautomeric, can be identified in the excited state, although only the neutral form of the dye is present in the ground state. From steady-state fluorescence results and time-resolved area-normalized emission spectra (TRANES), it is indicated that the anionic and tautomeric forms of the dye are the excited-state reaction products and that they arise apparently independently from the excited neutral form of the dye. In bulk water, however, there is no evidence of the tautomeric species and only the anionic form is observed in the excited state. The fluorescence quenching results of the three forms of 7H4MC by the different quenchers, potassium iodide, aniline, and N, N-dimethylaniline, suggest that the distribution of 7H4MC molecules in the reverse micelles is not diverse but that the different prototropic forms arise from the same population of the excited dye in the interfacial region.     

Micellar solubilization of biopolymers in hydrocarbon solvents. I. a structural model for protein-containing reverse micelles

Three proteins (horse liver alcohol dehydrogenase, ribonuclease, lysozyme) were solubilized in hydrocarbon with the help of reverse micelles formed by aqueous di(2-ethyl-hexyl) sodium sulfosuccinate (AOT). Sedimentation and diffusion coefficients of the micellar aggregates were measured with an analytical ultracentrifuge. Partial specific volumes were also evaluated from density measurements. The molecular weight of the protein-containing reverse micelles (M _t ) could thus be determined for each protein system at various w₀ values (w₀ - [H₂O]/[AOT]). For horse liver alcohol dehydrogenase at w₀ = 46.4, for example,M _t is ca. 2,670,000 Daltons; for lysozyme at wo = 22.5,M _t is ca. 323,000 Daltons and increases by increasing w₀. On the basis of these experimentally determined molecular weights, a structural model for the protein-containing reverse micelle is proposed. The model is based upon the assumption that the protein is confined in the water pool of a spherical micelle, and that the inner core volume is the sum of the protein volume and the volume of all water molecules present in a micelle. It is possible then to calculate the micellar structure at each w₀ value. For example, in the case of ribonuclease at w₀ = 20, the inner core radius is ca. 37.5 A, and a layer of water of ca. 22 A separates the protein surface from the surfactant layer. The possible implications of this model for the reactivity of enzymes solubilized in hydrocarbons by reverse micelles are discussed.     

Structure, stability, and hydration of a polypeptide in AOT reverse micelles

In this communication, we provide theoretical evidence that the folded structure of a simple peptide, alanine zwitterionic octapeptide, or A8, unstable in solution, becomes stable in a reverse micelle (RM) of appropriate size. Our molecular dynamics simulations were carried out for realistic models of sodium 2-ethylhexylsulfosuccinate RM in isooctane, simulated for an extended period of time. For the RM of the smaller size, we find that a helical structure is stable for the whole length of the simulation. On the contrary, the peptide very quickly takes an extended structure in larger micelles.     

The location of tryptophan, N-acetyltryptophan and alpha-chymotrypsin in reverse micelles of AOT: a fluorescence study

The spectroscopic properties of alpha-chymotrypsin (alpha-Chym), L-tryptophan (Trp) and N-acetyl-L-tryptophan (NAT) solubilized in hydrated reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate in iso-octane were followed by fluorescence as a function of the amount of intramicellar water and initial pH. The lack of pH dependence observed for Trp in these systems, as opposed to what occurs in bulk water, and the similarities found for the protein in both media foresee different locations of these probes. In reverse micelles, fluorescence quenching studies using acrylamide emphasize the existence of structural alterations within the protein when its global charge changes from positive (pH = 7) to negative (pH = 10). The ensemble of the data points to an interfacial location of the zwitterionic Trp, an intermediate region of less tightly bound water for the location of the anionic Trp and NAT and an almost bulk water environment for alpha-Chym.     

Structure and ordering kinetics of micelles in triblock copolymer solutions in selective solvents

We have used small-angle x-ray scattering (SAXS), and small-angle neutron scattering (SANS) to study the micelle structure of a polystyrene-block-poly(ethene-co-butene)-block-polystyrene triblock copolymer in dilute - semidilute solutions in solvents selective for either the outer styrene block (dioxane) or for the middle block (heptane or tetradecane). Measurements of equilibrium structure factors showed that micelles were formed in both types of selective solvents. In the case of dioxane, the micelles are isolated whereas in the case of heptane or tetradecane, a bridged micellar structure may be formed at higher copolymer concentrations. In both cases we observed an ordered cubic structure of insoluble domains (micellar cores) at high concentrations (> 8 %). The micellar scattering function was fit to the Percus-Yevick interacting hard-sphere model. The temperature dependence of the core radius, the hard-sphere interaction radius and the volume fraction of hard spheres were obtained. We also used synchrotron-based time-resolved SAXS to examine the kinetics of ordering of the micelles on a cubic lattice for many different temperature jumps into the ordered cubic phase starting from the disordered micellar fluid phase in different solvents at different concentrations. The time evolution of the structure changes was determined by fitting the data with Gaussians to describe the structure factor of the ordered Bragg peaks and the Percus-Yevick structure factor was used to describe the micellar fluid. The time dependence of the peak intensities and widths as well as of the micellar parameters will be presented. The results showing the kinetics of the transformation from the fluid to the ordered phase were analyzed using the Mehl-Johnson-Avrami theory of nucleation.     

Magnetic modulation of the luminescence of pyrene-N,N-dimethylaniline exciplexes in solutions of reverse micelles

An external magnetic field was found to enhance the luminescence of pyrene-N,N-dimethylaniline exciplexes in a solution of reverse micelles containing water, OT Aerosol, and pentanol (0.6%, B=30 mT). The field dependence of the relative change in the intensity of the exciplex fluorescence does not reach saturation for fields with magnetic induction up to 30 mT, which is not observed in polar homogeneous solutions. These results may be attributed to the circumstance that a significant fraction of pyrene (up to 30%) is localized in the interphase of the reverse micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1918–1920, August, 1990.