Use Of Reverse Micelles Research Articles

Investigated the effects of surfactant concentration on cobalt ferrite nanoparticles synthesized in reverse micelles

The use of reverse micelles as nanoscale hydrophilic voids of microemulsions in the manufacture of ferrites has been recognized since the 1960s, but there has been very little attention on the structural and magnetic properties with respect to surfactant concentration. This paper investigates the influence of surfactant sodium dodecyl sulphate (SDS) concentrations on cobalt ferrite (CoFe2O4) nanoparticles prepared by reverse micelles at annealing temperatures 250°C and 500°C. Samples with varied cobalt to SDS ratios (Co: SDS = 1: 0.33, 1: 0.5, 1: 0.66) were subjected to XRD, TGA, TEM, FTIR and VSM Studies. All the samples exhibited single-phase spinel structures with crystalline diameters ranging from 10 to 18 nm. As the SDS concentration increased the crystallite size decreased. The TEM images showed the particle size in the range of 7.6 -17.7 nm. VSM investigations show the ferromagnetic behavior of the sample. The observed increase in coercivity with respect to annealing temperature for the same concentration reflects the single-domain nature of the nano particles. This underscores the crucial role of annealing conditions in customizing cobalt ferrite nanoparticles as a suitable application in longitudinal magnetic recording media.

Site specific NMR characterization of abeta-40 oligomers cross seeded by abeta-42 oligomers.

Extracellular accumulation of β amyloid peptides of 40 (Aβ40) and 42 residues (Aβ42) has been considered as one of the hallmarks in the pathology of Alzheimer's disease. In this work, we are able to prepare oligomeric aggregates of Aβ with uniform size and monomorphic structure. Our experimental design is to incubate Aβ peptides in reverse micelles (RMs) so that the peptides could aggregate only through a single nucleation process and the size of the oligomers is confined by the physical dimension of the reverse micelles. The hence obtained Aβ oligomers (AβOs) are 23 nm in diameter and they belong to the category of high molecular-weight (MW) oligomers. The solid-state NMR data revealed that Aβ40Os adopt the structural motif of β-loop-β but the chemical shifts manifested that they may be structurally different from low-MW AβOs and mature fibrils. From the thioflavin-T results, we found that high-MW Aβ42Os can accelerate the fibrillization of Aβ40 monomers. Our protocol allows performing cross-seeding experiments among oligomeric species. By comparing the chemical shifts of Aβ40Os cross seeded by Aβ42Os and those of Aβ40Os prepared in the absence of Aβ42Os, we observed that the chemical states of E11, K16, and E22 were altered, whereas the backbone conformation of the β-sheet region near the C-terminus was structurally invariant. The use of reverse micelles allows hitherto the most detailed characterization of the structural variability of Aβ40Os.

A new liquid phase microextraction method-based reverse micelle for analysis of dexketoprofen in human plasma by HPLC-DAD

A new liquid phase microextraction method was developed by used reverse micelle-based coacervates as microextraction agents for the separation of dexketoprofen (DKT) from human plasma before its determination by high-performance liquid chromatography with photodiode-array detection (HPLC-DAD). The change in the concentration of dexketoprofen in the plasma of the male and female patients was successfully monitored by using this method. The proposed method involves the use of reverse micelles of decanoic acid (DA) are dispersed in tetrahydrofuran (THF) and aqueous system. After addition of the DA and THF to the aqueous sample phase, the formation of micelles of nano and molecular size was observed in an ultrasonic bath. The solution was centrifuged, and the DKT extracted into the DA phase was analyzed by HPLC-DAD. Some analytical parameters that important in the developed procedure were examined in detail. The limit of detection (LOD), the limit of quantification (LOQ), the intraday, and inter day relative standard deviation (RSD, %) of the developed method in the plasma sample were found to be 12.8 ng mL−1, 38.8 ng mL−1, 1.7 and 3.9%, respectively. Additional/recovery studies were performed in plasma samples with proposed method, and quantitative recoveries were obtained in the range of 97–100%. The developed microextraction method was applied to human plasma that taken from volunteer patients for the determination of DKT.Graphical abstract

A regression analysis with laboratory validation for the use of reverse micelles to achieve desired nanosized catalytically active sites

Nano-sized catalytic sites can be synthesized using reverse micelles to systematically deposit active metal species onto catalyst supports. The size of these metallic sites is influenced by the synthesis conditions, namely the water to surfactant molar ratio, the surfactant concentrations, and the surfactant type. These parameters can be adjusted to create tunable micro-structures that are catalytically active for specific chemical reactions. From a literature search, the size of catalytic sites was compiled against their respective synthesis conditions. A regression analysis was performed to investigate which parameters had significant effects on the size of the catalytic site. Initial laboratory tests were then carried out using the regression results to develop nano-nickel sites deposited onto TiO2. According to the model, specific surfactant/solvent combinations (i.e. AOT/cyclohexane) and the water to surfactant molar ratio had profound impacts on the size of the produced catalytic site.

Reverse Micelles as Templates for the Fabrication of Size-Controlled Nanoparticles: A Physical Chemistry Experiment

Synthesis and characterization of nanomaterials yields opportunities for instruction of related topics in solution chemistry and materials science, as well as spectroscopy connecting to band theory, the particle in a box quantum mechanical model, and thermodynamics. In collaboration with an undergraduate research assistant, we have developed a synthesis experiment that investigates the use of reverse micelles as reaction templates for the preparation of size-controlled nanomaterials through simple, controlled precipitation reactions. This experiment is designed for an undergraduate physical or inorganic chemistry laboratory course. The proposed method boasts several advantageous features, including simplicity, functionality both at low temperature and in the presence of oxygen, applicability to a wide variety of compounds including semiconductors and colloidal metals, and precise control of particle size. To demonstrate our method, we chose CdSe as a model system due to its readily observable size-dependent optical effects. The particles produced are well-controlled and show high optical quality. Additionally, the use of reverse micelles allows us to further broaden the scope of this assessment, incorporating other key topics including ligand–metal chelation, nucleation/growth kinetics, thermodynamics, surfactant chemistry, and hydrodynamics.

Structural Characterization of Biocompatible Reverse Micelles Using Small-Angle X-ray Scattering, 31P Nuclear Magnetic Resonance, and Fluorescence Spectroscopy

The most critical problem regarding the use of reverse micelles (RMs) in several fields is the toxicity of their partial components. In this sense, many efforts have been made to characterize nontoxic RM formulations on the basis of biological amphiphiles and/or different oils. In this contribution, the microstructure of biocompatible mixed RMs formulated by sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri- n-octylphosphine oxide (TOPO) surfactants dispersed in the friendly solvent methyl laurate was studied by using SAXS and 31P NMR and by following the solvatochromic behavior of the molecular probe 4-aminophthalimide (4-AP). The results indicated the presence of RM aggregates upon TOPO incorporation with a droplet size reduction and an increase in the interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edge excitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the external nonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogen bond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionic surfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches, i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of the interfacial fluidity of RMs, a parameter that is difficult to measure directly.

Reverse micelles enhance the formation of clathrate hydrates of hydrogen

HypothesisClathrate hydrates of hydrogen form at relatively low pressures (e.g., ca. 10 MPa) when a co-former compound is added. In that case, however, the gravimetric amount of stored hydrogen drops to less than 1 wt% from ca. 5.6 wt% without a co-former. Another factor hindering the entrapment of hydrogen into a clathrate matrix appears to be of a kinetic origin, in that the mass transfer of hydrogen into clathrates is limited by the macroscopic scale of the gas–water interfaces involved in their formation. Thus, the enhanced formation of binary (hydrogen + co-former) hydrates would represent a major achievement in the attempt to exploit those materials as a convenient means for storing hydrogen. ExperimentsHere, we present a simple process for the enhanced formation of binary hydrates of hydrogen and several co-formers, which is based on the use of reverse micelles for reducing the size of hydrate-forming gas–water interfaces down to tens of nanometers. This reduction of particle size allowed us to reduce the kinetic hindrance to hydrate formation. FindingsThe present process was able to (i) enhance the kinetics of the formation process; and (ii) assist clathrate formation when using water-insoluble coformers (e.g., cyclopentane, tetrahydrothiophene).

High Antifungal Activity against Candida Species of Monometallic and Bimetallic Nanoparticles Synthesized in Nanoreactors.

Among all novel challenges nowadays worldwide, infectious disease is probably one of the most important. It is well-known that common treatments used include high doses of antibiotics, which are very invasive therapies for patients. These treatments are more intensive when the infection is related to multidrug resistant microorganisms. In this sense, in this work we report the use of reverse micelles to form less than 5 nm gold, silver, and gold-silver nanoparticles (NPs) with biological activity against five opportunistic Candida strains responsible of several diseases in human beings. As a result, we evaluate the interface properties and droplet-droplet interactions of micelles founding high fluidity in the polar head of the surfactant, necessary to form a flexible interaction channel in the "dimmer" micelle-micelle. In this condition, we form monodispersed, highly reactive NPs with sizes less than 5 nm with high antifungal activity against C. parapsilosis, C. Krusei, C. glabrata, C. guillermondii, and C. albicans, with minimum inhibitory concentrations (MIC50) less than 0.7 ppm in all cases, the lowest reported to the best of our knowledge. These are very promising results to develop alternative therapies to treat fungal diseases in humans, animals, and plants, or to coat conventional surfaces in surgery rooms.

Reverse Micelles as a Tool to Probe the Synergy Between Confinement and Osmolytes with Respect to Protein Hydration Properties

There is a rapidly growing awareness not only that dynamics are essential for protein function but that functionally important protein motions are tightly coupled to hydration shell dynamics. The dynamics of hydration waters are in turn a function of both confinement conditions and the presence of surrounding cosolutes/osmolytes. Mimicking the combination of confinement and osmolyte levels for proteins in the in vivo cell environment is challenging. Here we present results obtained through the use of reverse micelles as a unique medium chosen to represent this crowded environment of proteins. The effects on the hydration properties of proteins encapsulated within reverse micelles are presented, and compared with confinement within Sol-gels. The addition of biologically relevant osmolytes to the reverse micelles and Sol-gels is used to expose potential synergy between confinement and osmolyte with respect to impact on hydration.

Use of Reverse Micelles for the Simultaneous Extraction of Oil, Proteins, and Glucosinolates from Cruciferous Oilseeds

Cruciferous oilseeds are important sources of oil, proteins, and glucosinolates (GLs), potentially available when biorefinery processes are used. The proposed extraction technology is based on the use of reverse micelles (RMs) made with cetyltrimethylammonium bromide (CTAB) dispersed in organic solvent. The physicochemical properties of this extraction system and the good water solubility of many high value compounds, such as GLs and some proteins, permit the simultaneous extraction of oil, and these products from cruciferous oilseed meals. This procedure is based on three main steps: (i) seed conditioning; (ii) solid-liquid extraction by RM solution; and (iii) back-transfer of the RM solution for recovery of the extracted compounds. The method makes it possible to simultaneously extract almost the same amount of oil as with pure organic solvents used in the current extraction plants and more than 90% of soluble proteins and GLs. It is a promising biorefinery technology alternative to traditional oil extraction processes.

Submicronic particles of manganese carbonate prepared in reverse micelles: A new electrode material for lithium-ion batteries

A new preparation procedure based on the use of reverse micelles is used in the synthesis of manganese carbonate. A novel monodispersed form of MnCO 3 is obtained, in which particles with a regular shape and ca. 200 nm edges are observed by electron microscopy. The thermal decomposition at 400 °C of this solid under argon leads to the formation of MnO submicron particles. As-prepared MnCO 3 and the product of calcination, MnO, were tested in lithium cells. The electrochemical reaction with lithium of the new MnCO 3 material takes place by a different conversion reaction than the corresponding oxide. The low molecular-weight of MnCO 3 does not penalize the capacity while giving extra stability due to the formation of lithium carbonate as the main side product, which yields better capacity retention. In contrast to other anodes in recent commercial Li-ion product, the use of MnCO 3 submicron particles avoids the presence of the more toxic and expensive cobalt in the stoichiometry of the active electrode material.

Preparation and characterization of rare-earth-doped Y2O3 luminescent ceramics by the use of reverse micelles

The objective of this project was to study luminescent powders of Y2O3:Eu3+ (5 at%), Y2O3:Tb3+ (5 at%), and Y2O3:Tm3+,Yb3+ (Tm: 2 at%, Yb: 1 at%), prepared by the use of reverse micelles. This report describes the phase stability, crystallite size, and luminescence properties of these powder materials as a function of heat treatment time and temperature. The Y2O3 phase produced during synthesis can be controlled by the heat treatment temperature and time. Monoclinic and cubic phases of Y2O3 are obtainable, with the monoclinic powders produced at the smaller crystallite sizes. Photoluminescence properties of the Y2O3:Eu3+ and Y2O3:Tb3+ were evaluated and sharp emission was observed for the Eu3+ powders at 610 nm and the Tb3+ powders at 544 nm. The maximum emission intensity of both phosphors increased as annealing temperature and time increased. This, however, was not seen for the case of the Y2O3:Tm3+,Yb3+ powders, which exhibited emission at 454 nm. For this phosphor, as heat treatment temperature increased the luminescence intensity decreased.

Collections of Copper Nanocrystals Characterized by Different Sizes and Shapes: Optical Response of These Nanoobjects

The use of reverse micelles makes it possible to produce copper nanocrystals characterized by various sizes and shapes. By increasing the water content, the average size of the metallic nanocrystal...

Membrane separations using reverse micelles in nearcritical and supercritical fluid solvents

The use of reverse micelles coupled with ultrafiltration membranes for the separation of macromolecules dissolved in the cores of the reverse micelles using nearcritical and supercritical fluid solvents is described. This methodology allows one to address the separation of a wide range of polar molecules greatly extending the type of molecules that can be separated using only pure supercritical fluids. The solutes to be separated are initially dissolved in the reverse micellar solution and introduce into the pressure vessel containing the membrane. The surfactant and water core are passed through the membrane while the macromolecule selectivity is based on size and molecular weight. The ability for continuous recycle in an extraction system is discussed.

Probing Porous Polymer Resins by High-Field Electron Spin Resonance Spectroscopy

High-field W-band (95 GHz) electron spin resonance spectroscopy of various spin probes was used to study the structure of highly cross-linked porous polymer resins based on a styrenedivinylbenzene matrix. The pores of these resins were created by template imprinting with reverse micelles solubilized in the mixture of monomers and cross-linkers prior to the polymerization. Functional groups in the resins were introduced by the use of polymerizable cosurfactants in the reverse micelles. Sufficiently large unpolar spin probes exhibit a distribution of mobilities that can be attributed to regions with different degrees of cross-linking in the polymer. The dynamics of a surfactant spin probe is sensitive to the presence of pores and the functionalization of the pore surface with highly polar groups. This effect disappears when the headgroup of the surfactant spin probe is esterified. It can be considered as a structural memory effect related to the use of reverse micelles as templates for imprinting. The result indicates that the pores can be filled or washed selectively.

Synthesis of Semi-Conducting Nanoparticles within a Protein Template

ABSTRACTThe ability to synthesise and tune photoresponsive and photoredox II-VI semi-conductor nanoparticles by quantum confinement is a continuously and rapidly developing area. Chemical methods are useful in producing dispersions of nanoparticles of uniform size in many organic solvents. Such synthetic methods employ the use of reverse micelles [1,2], phospholipid vesicles[3,4] or capping agents[5,6]to restrict particle size and growth to the nanometre regime.The production of super lattice assemblies, through, for example the use of controlled crystallisation [7], Langmuir monolayers[8], Langmuir Blogget films[9], and self assembled short chain dithiol monolayers[10] on gold substrates has also received attention in the past. This latter approach potentially opens the way for self assembled electro-luminescent devices[11].The ability to couple organic self assembly and inorganic nano-synthesis could also provide a route toward the chemical synthesis of an organised array of quantum-confined semiconductors. An aspect of this synthesis with construction approach is the possible coupling of biological templating systems to produce biomimetic materials [12,13]. In fact, an example would be the stabilised CdS nanoparticles in yeast binding to phytochelatin peptides which are secreted in response to metal toxicification [14].

Synthesis and Characterization of CdS Nanoclusters in a Quaternary Microemulsion: the Role of the Cosurfactant

Nanostructured semiconductor particles are currently under intense investigation because of their interesting photophysical and photochemical properties. Several preparation methods have been exploited for this class of materials; among them, the use of reverse micelles or “water-in-oil” microemulsions is a simple and successful preparative route. In this paper, a novel synthetic medium has been exploited, consisting of a quaternary CTAB/n-pentanol/n-hexane/water microemulsion. The presence of cosurfactant (n-pentanol), in addition to water, allows the simultaneous modulation of the water droplets dimensions and their exchange dynamics. Nanoparticles were characterized by UV−vis and photoluminescence spectroscopy, High-Resolution Transmission Electron Microscopy, and Raman spectroscopy. All measurements showed that the mean size of the nanoparticles is governed by the pentanol content of the system. They also possess a narrow size distribution and a good degree of crystallinity. Moreover, pentanol has an ...

Immobilization ofCandida rugosa lipase to nylon fibers using its carbohydrate groups as the chemical link

The aim of this study was to evaluate the immobilization of lipase from Candida rugosa on a nylon support by methods used to attach biomolecules to solid supports through their carbohydrate moieties. The carbohydrate groups were converted to dialdehydes by treatment with sodium periodate. The length of exposure and the periodate amount were optimized to the point where almost total activity retention was obtained. Tests of the immobilized enzyme showed the expressed activity to be significantly higher than the activity obtained with the unimmobilized enzyme. The use of reverse micelles as a way of delivering water to the enzyme was tested and found to give significantly higher activities. The immobilized enzyme activity was also tested with other substrates, one of which was a chiral ester. The immobilized enzyme was found to have high stereoselective efficiency and activity toward racemic methyl methoxyphenyl glycidate, a chiral intermediate used in the manufacture of the drug diltiazem.

Hemoglobin Extraction Using Cosurfactant-Free Nonionic Microemulsions

ABSTRACT Oil-continuous microemulsions provide an effective medium as a liquid membrane for extraction of proteins due to high solubilization and low miscibility in aqueous feed. Unlike the use of reverse micelles, this new method employs a preformulated cosurfactant-free nonionic microemulsion of high water content. The use of nonionic microemulsions for hemoglobin extraction demonstrates the potential for effective separation of proteins, amino acids, and other biochemicals. The extraction can be controlled by adjusting pH and microemulsion composition. It is enhanced by the addition of an appropriate liquid ion exchanger. The extraction results cannot be explained only in terms of ionic interactions.

Strategies for enzymatic esterification in organic solvents: Comparison of microaqueous, biphasic, and micellar systems

The kinetics of butyl butyrate synthesis by a lipase from Mucor miehei in different types of organic media were investigated. The three systems studied were a microaqueous medium containing enzyme in suspension in hexane, a water-hexane two-phase system, and reverse micelles. The synthesis of butyl butyrate was possible in all cases because of a favorable partition of the ester into the organic solvent. A sufficient stirring rate was necessary to achieve good reaction rates in the case of the liquid-liquid biphasic medium. The effect of water content was different according to the type of system used. The dependence of reaction rate and of conversion yield on enzyme and substrate concentrations was also investigated. From an applied point of view, the best performances were obtained with either microaqueous or liquid-liquid two-phase systems. The use of reverse micelles can be advocated only in particular conditions, such as low enzyme concentration, compatible with the specific constraints it involves.