Reverse Micelle System Research Articles

Photophysical features of coumarin 120 in reverse micelles

The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV–Vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (kr) and non-radiative rate constants (knr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.

Synthesis of highly stable cyanine-dye-doped silica nanoparticle for biological applications

Cyanine dyes are widely used in biological labeling and imaging because of their narrow near infrared emission, good brightness and high flexibility in functionalization, which not only enables multiplex analysis and multi-color imaging, but also greatly reduces autofluorescence from biological matter and increases signal-to-noise ratio. Unfortunately, their poor chemical- and photo-stability strongly limits their applications. The incorporation of cyanine dyes in silica nanoparticles provides a solution to the problem. On one hand, the incorporation of cyanine dyes in silica matrix can enhance their chemical- and photo-stability and increase brightness of the nanomaterials. On the other hand, silica matrix provides an optimized condition to host the dye, which helps to maintain their fluorescent properties during application. In addition, the well-established silane technique provides numerous functionalities for diverse applications. However, commercially available cyanine dyes are not very stable at high alkaline conditions, which will gradually lose their fluorescence over time. Our results showed that cyanine dyes are very vulnerable in the reverse micelle system, in which they will lose their fluorescence in less than half an hour. The existence of surfactant could greatly promote degradation of cyanine dyes. Fluorescent silica nanoparticles cannot be obtained at the high alkaline condition with the existence of surfactant. In contrast, the cyanine dyes are relatively stable in Stöber media. Owing to the fast formation of silica particles in Stöber media, the exposure time of cyanine dye in alkaline solution was greatly reduced, and highly fluorescent particles with good morphology and size distribution could be obtained via Stöber approach. However, the increasing water content in the Stöber could reduce the stability of cyanine dyes, which should be avoided. This research here provides a clear guidance on how to successfully synthesize cyanine dye-doped silica nanoparticles with good morphology, size distribution, stability and brightness.

Scalable synthesis of sub-100 nm hollow carbon nanospheres for energy storage applications

Sub-100 nm hollow carbon nanospheres with thin shells are highly desirable anode materials for energy storage applications. However, their synthesis remains a great challenge with conventional strategies. In this work, we demonstrate that hollow carbon nanospheres of unprecedentedly small sizes (down to ∼32.5 nm and with thickness of ∼3.9 nm) can be produced on a large scale by a templating process in a unique reverse micelle system. Reverse micelles enable a spatially confined Stober process that produces uniform silica nanospheres with significantly reduced sizes compared with those from a conventional Stober process, and a subsequent well-controlled sol–gel coating process with a resorcinol–formaldehyde resin on these silica nanospheres as a precursor of the hollow carbon nanospheres. Owing to the short diffusion length resulting from their hollow structure, as well as their small size and microporosity, these hollow carbon nanospheres show excellent capacity and cycling stability when used as anode materials for lithium/sodium-ion batteries.

Dyeing Properties of Cotton with Reactive Dye in Nonane Nonaqueous Reverse Micelle System.

In this study, we explored the dyeing behavior of cotton with reactive dyes in poly(ethylene glycol)-based reverse micelle system in nonaqueous alkane medium of nonane (C9H20). Calibration of dyeing databases for both conventional aqueous-based dyeing method and nonaqueous nonane reverse micellar dyeing method was initially established, along with simulated dyeing of standard samples with known concentrations. Several color difference formulae were used to conduct computer color matching (CCM), by matching the color between batch samples and the standard samples, for both dyeing methods. Excellent color matching results were achieved as both dyeing methods showed that the CCM-predicted concentrations were nearly the same as the known concentrations. It indicates that utilizing nonane as a solvent to facilitate reverse micellar dyeing of cotton can achieve good color matching when compared with that of the conventional aqueous-based dyeing system. Relative unlevelness indices were used to evaluate the evenness of the dyed samples. Good to excellent levelness results were obtained, comparable to that of the conventional aqueous-based dyeing system. Color fastness to laundering of nonane reverse micellar dyed samples was found to be good for industrial applications. In addition, during the reverse micellar dyeing process, only very low level of volatile organic compound content was detected and 98% nonane could be recovered simply by fractional distillation. The results in this study explored the practical usage of nonane nonaqueous reverse micellar approach on the dyeing of cotton with the use of reactive dyes.

Amyloid Beta Peptide Folding in Reverse Micelles.

Previously published experimental studies have suggested that when the 40-residue amyloid beta peptide is encapsulated in a reverse micelle, it folds into a structure that may nucleate amyloid fibril formation (Yeung, P. S.-W.; Axelsen, P. H. J. Am. Chem. Soc. 2012, 134, 6061 ). The factors that induce the formation of this structure have now been identified in a multi-microsecond simulation of the same reverse micelle system that was studied experimentally. Key features of the polypeptide-micelle interaction include the anchoring of a hydrophobic residue cluster into gaps in the reverse micelle surface, the formation of a beta turn at the anchor point that brings N- and C-terminal segments of the polypeptide into proximity, high ionic strength that promotes intramolecular hydrogen bond formation, and deformation of the reverse micelle surface to facilitate interactions with the surface along the entire length of the polypeptide. Together, these features cause the simulation-derived vibrational spectrum to red shift in a manner that reproduces the red-shift previously reported experimentally. On the basis of these findings, a new mechanism is proposed whereby membranes nucleate fibril formation and facilitate the in-register alignment of polypeptide strands that is characteristic of amyloid fibrils.

Small-Angle Neutron Scattering Studies on an Idealized Diesel Biofuel Platform

Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) were used to characterize the microstructure of a reverse micelle system consisting of ethanol, water, and surfactant in n-hexadecanes as an analytical framework to understand the structure and stability of a model platform for biofuel formulations. Best-fit modeling of SANS scattering data suggested that the micelles are better described as ellipsoids rather than spheres, with the (geometric) diameters of stable micelles increasing from 2.4 to 7.5 nm as a function of the increasing water content as well as surfactant concentration. Fitted diameters from DLS measurements followed similar trends, but DLS measurements overestimated the interior of the micelles by roughly 2–3 nm because DLS measurements are based on the full hydrodynamic radius, including the surfactant shell. SANS only detects the nanopool interior, a significant advantage. The choice of surfactant altered the stability at temperatures below 10 °C, but the micelles rea...

Large-Scale, Facile Transfer of Oleic Acid-Stabilized Iron Oxide Nanoparticles to the Aqueous Phase for Biological Applications.

Fe3O4 nanoparticles synthesized via thermal decomposition in the organic phase have attracted tremendous research interest because of their unique morphology, size dispersion, and crystallinity. However, their poor water dispersibility strongly limited their development in biomedical applications. Therefore, a phase-transfer strategy through which hydrophobic nanoparticles with good performance in the aqueous phase can be obtained is an extremely critical issue. Herein, we present a large-scale, facile, highly efficient strategy for the phase transfer of oleic acid-coated Fe3O4 nanoparticles via a reverse-micelle-based oxidative reaction. The reverse micelle system improves the efficiency of the interface oxidative reaction and prevents the aggregation of nanoparticles during the reaction, facilitating the transfer of Fe3O4 nanoparticles from the organic phase to the aqueous phase. The transferred Fe3O4 nanoparticles are used as a T2 contrast agent to perform magnetic resonance imaging of CNE2 cells (nasopharyngeal carcinoma cell line). In addition, the free carboxyl groups on the surface of transferred nanoparticles can also be programmed to permit the conjugation of other molecules, in turn allowing nanoparticles to be extended in biological targeting or biological recognition applications. Therefore, this strategy offers a promising platform for the large-scale, highly efficient phase transfer of oleic acid-capped nanoparticles and may become a new paradigm to promote the development of diverse nanoparticles for widespread biomedical applications.

Decomposition of formic acid over silica encapsulated and amine functionalised gold nanoparticles

Formic acid has recently attracted considerable attention as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage. Here, we show that silica encapsulated and amine functionalised gold nanoparticles are highly active catalysts for the production of hydrogen by vapour phase decomposition of formic acid. The core-shell catalysts are prepared in a reverse micelle system that makes it possible to control the size of the Au nanoparticles and the thickness of the SiO2 shells, which has a large impact on the catalytic activity. The smallest gold nanoparticles are 2.2±0.3nm in diameter and have a turnover frequency (TOF) of up to 958h−1 at a temperature of 130°C. Based on detailed in situ ATR-FTIR studies and results from kinetic isotope labelling experiments we propose that the active site is a low-coordinated and amine functionalised Au atom, while H-assisted formate decomposition into CO2 and H2 is the rate limiting step.

<b>Optimization of protein extraction process from jackfruit seed flour by reverse micelle system

The extraction of protein from flour of jackfruit seeds by reverse micelles was evaluated. Reverse micelle system was composed of sodium dodecyl sulfate (SDS) as surfactant, butanol as solvent, and water. The effects of stirring time, temperature, molar ratio H 2 O SDS -1 , concentration of butanol (mass percentage) and flour mass were tested in batch systems. Based on the adjusted linear regression model, only butanol concentration provided optimum extraction conditions (41.16%). Based on the analysis of surface response, the best extraction yield could be obtained at 25°C, stirring time of 120 min, mass of flour of 100 mg, and a ratio H 2 O SDS -1 of 50. Experimental results showed that a 79.00% extraction yield could be obtained.

USPIO assisting degradation of MXC by host/guest-type immobilized laccase in AOT reverse micelle system.

The laccase and ultrasmall superparamagnetic iron oxide nanoparticles (USPIO) have been assembled inside the tubular mesoporous silica via co-adsorption technology to prepare host/guest-type immobilized laccase, which is applied to degrade methoxychlor (MXC) in aqueous and reverse micelle environments. The effects of various parameters on degradation of MXC were studied. Under the optimum conditions, the degradation rate could reach maximum value of 45.6% and remain at 20.8% after seven cycles. Moreover, the addition of small molecular compound 2, 2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) to the system could greatly improve the degradation efficiency. The MXC degradation process is a first-order reaction, and the activation energy of MXC degradation catalyzed by immobilized laccase (41.46kJmol(-1)) is relatively lower than that catalyzed by free laccase (44.91kJmol(-1)). Based on the degradation products measured by gas chromatograph-mass spectrometer (GC-MS) and nuclear magnetic resonance (NMR), the degradation mechanism of MXC has also been proposed.

Characterization of Cetyltrimethylammonium Bromide/Hexanol Reverse Micelles by Experimentally Benchmarked Molecular Dynamics Simulations.

Encapsulation of small molecules, proteins, and other macromolecules within the protective water core of reverse micelles is emerging as a powerful strategy for a variety of applications. The cationic surfactant cetyltrimethylammonium bromide (CTAB) in combination with hexanol as a cosurfactant is particularly useful in the context of solution NMR spectroscopy of encapsulated proteins. Small-angle X-ray and neutron scattering is employed to investigate the internal structure of the CTAB/hexanol reverse micelle particle under conditions appropriate for high-resolution NMR spectroscopy. The scattering profiles are used to benchmark extensive molecular dynamics simulations of this reverse micelle system and indicate that the parameters used in these simulations recapitulate experimental results. Scattering profiles and simulations indicate formation of homogeneous solutions of small approximately spherical reverse micelle particles at a water loading of 20 composed of ∼150 CTAB and 240 hexanol molecules. The 3000 waters comprising the reverse micelle core show a gradient of translational diffusion that reaches that of bulk water at the center. Rotational diffusion is slowed relative to bulk throughout the water core, with the greatest slowing near the CTAB headgroups. The 5 Å thick interfacial region of the micelle consists of overlapping layers of Br(-) enriched water, CTAB headgroups, and hexanol hydroxyl groups, containing about one-third of the total water. This study employs well-parametrized MD simulations, X-ray and neutron scattering, and electrostatic theory to illuminate fundamental properties of CTAB/hexanol reverse micelle size, shape, partitioning, and water behavior.

Modulation of anionic reverse micellar interface with non-ionic surfactants can regulate enzyme activity within the micellar waterpool

In this contribution, we have studied the effect of replacing anionic surfactant 1,4-bis(2-ethylhexyl)sulphosuccinate (AOT) by nonionic surfactant(s) of varying hydrophilic-lipophilic balance (HLB) on the structure, dynamics and activity of water encapsulated in reverse micelles (RMs) formed in a biocompatible oil isopropyl myristate (IPM). The sizes of the RM droplets are measured using dynamic light scattering (DLS) technique, while the structure of water in the RM waterpool is determined using FTIR spectroscopy. The solvation dynamics in these systems is obtained by time-resolved fluorescence spectroscopy using ammonium 8-anilino-1-naphthalenesulfonate (ANS) as the fluorophore. We spectroscopically measure the enzymatic activity of α-chymotrypsin on the substrate Ala-Ala-Phe-7-amido-4-methyl-coumarin (AMC) in these mixed RM systems. It has been found that the rate could either be enhanced or reduced depending on the HLB of the added Brij(s). Such result could be found useful in modulating the reaction for specific applications.

Mixed reverse micellar extraction and effect of surfactant chain length on extraction efficiency

Abstract This study investigated the effect of surfactant chain length on mixed reverse micellar extraction of cellulase. The mixed reverse micelle systems were formed by biosurfactant rhamnolipid and a nonionic surfactant tween (tween-20, tween-40, tween-60, or tween-80). Electron spin resonance (ESR) method was used in order to find the suitable chain length of tween and the best ratio of rhamnolipid/tween mixture. The key parameters such as pH and temperature in forward and backward extraction were studied, and the results showed that mixed reverse micelle with different surfactant chain length had different pH sensitivities. Rhamnolipid/tween-80 system was more sensitive to pH than other systems, and rhamnolipid/tween-20 system was the least sensitive to pH among four systems. The experimental results also showed that chain length had limited sensitivity to temperature. Rotation correlation time of cellulase solutions (original and extraction) were investigated, which proved the superiority of longer chain length system (rhamnolipid/tween-80 system).

Solution-grown GeO2 nanoparticles with a nearly 100% yield as lithium-ion battery anodes

Germanium oxide (GeO2) nanoparticles were synthesized with a nearly 100% production yield in a nonionic reverse micelle system at ambient temperature as high performance lithium-ion battery anodes.

Removal of Amoxicillin Antibiotic from Aqueous Solution Using an Anionic Surfactant

A novel separation technique based on an aqueous surfactant extraction to remove organic contaminants from aqueous solutions was investigated. A model was developed regarding the kinetic partitioning of amoxicillin and regarding the mechanism governing the forward transfer of amoxicillin in a reverse micelle system. Results were interpreted in terms of a two-film theory for flat interface. To confirm the relevance of the developed separation technique, it was applied to the elimination of amoxicillin by adsorption on an anionic surfactant, sodium dodecyl sulfate. The effects of various parameters such as contact time, pH, temperature, and initial concentration of sodium dodecyl sulfate were investigated at an agitation speed of 350 rpm. The percentage of maximum adsorption capacity of amoxicillin was found to be 87.7 % for the following optimal conditions: amoxicillin concentration of 4 mg/L, 40 min contact time, pH 4, 50 °C, and 0.01 g/L initial sodium dodecyl sulfate concentration. The results showed that the pseudo-first-order model provides most adequate correlation of experimental data compared to the pseudo-second-order model. Three statistical functions were used to estimate the error deviations between experimental and theoretically predicted kinetic adsorption values, including the average relative error deviation (ARED), the sum of the squares of the errors (SSE), and the standard deviation of residuals (S res). The results showed that, both Freundlich equation and pseudo-first-order equation provide the best fit to experimental data. Adsorption isotherm data appeared to be accurately described by a Freundlich model. The thermodynamic parameters (∆G, ∆H, and ∆S) showed that the process was feasible, spontaneous, and exothermic.

Activation of Dioxygen by a TAML Activator in Reverse Micelles: Characterization of an Fe(III)Fe(IV) Dimer and Associated Catalytic Chemistry.

Iron TAML activators of peroxides are functional catalase-peroxidase mimics. Switching from hydrogen peroxide (H2O2) to dioxygen (O2) as the primary oxidant was achieved by using a system of reverse micelles of Aerosol OT (AOT) in n-octane. Hydrophilic TAML activators are localized in the aqueous microreactors of reverse micelles where water is present in much lower abundance than in bulk water. n-Octane serves as a proximate reservoir supplying O2 to result in partial oxidation of Fe(III) to Fe(IV)-containing species, mostly the Fe(III)Fe(IV) (major) and Fe(IV)Fe(IV) (minor) dimers which coexist with the Fe(III) TAML monomeric species. The speciation depends on the pH and the degree of hydration w0, viz., the amount of water in the reverse micelles. The previously unknown Fe(III)Fe(IV) dimer has been characterized by UV-vis, EPR, and Mössbauer spectroscopies. Reactive electron donors such as NADH, pinacyanol chloride, and hydroquinone undergo the TAML-catalyzed oxidation by O2. The oxidation of NADH, studied in most detail, is much faster at the lowest degree of hydration w0 (in "drier micelles") and is accelerated by light through NADH photochemistry. Dyes that are more resistant to oxidation than pinacyanol chloride (Orange II, Safranine O) are not oxidized in the reverse micellar media. Despite the limitation of low reactivity, the new systems highlight an encouraging step in replacing TAML peroxidase-like chemistry with more attractive dioxygen-activation chemistry.

Synergetic Catalysis of Non-noble Bimetallic Cu–Co Nanoparticles Embedded in SiO2 Nanospheres in Hydrolytic Dehydrogenation of Ammonia Borane

Ultrafine non-noble bimetallic Cu–Co nanoparticles (∼2 nm) encapsulated within SiO2 nanospheres (Cu–Co@SiO2) have been successfully synthesized via a one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDS, XPS, PXRD, ICP, and N2 adsorption–desorption methods. In each core–shell Cu–Co@SiO2 nanosphere, several Cu–Co NPs are separately embedded in SiO2. Compared with their monometallic counterparts, the bimetallic core–shell nanospheres CuxCo1–x@SiO2 with different metal compositions show a higher catalytic performance for hydrogen generation from the hydrolysis of ammonia borane (NH3BH3, AB) at room temperature, due to the strain and ligand effects on the modification of the surface electronic structure and chemical properties of Cu–Co NPs in the SiO2 nanospheres. Especially, the Cu0.5Co0.5@SiO2 nanospheres show the best catalytic performance among all the synthesized CuxCo1–x@SiO2 catalysts in the hydrolytic dehydrogenation of AB. In addition, the activation energy (Ea) of C...

The influence of rutile particles on photo-induced activity of the sol–gel TiO2/ITO photo-anode

The rutile effect on structural and photo-electrochemical properties and photo-induced activity were studied. Thin TiO2 layers were prepared by the sol–gel method using a reverse micelles system as a molecular template and deposited on the conductive ITO substrate by a dip-coating technique. Pure anatase or mixed anatase/rutile phase were obtained during the calcination step as a result of the selected temperature. The crystallographic structure was determined by Raman spectroscopy and XRD analysis. The positive influence of the presence of rutile particles in the thin layer on the photo-induced properties was verified. It was found that the mixed crystallographic phase of anatase and rutile can exhibit much higher photo-induced activity than pure anatase or the pure rutile form. The reason for this is that the excited electrons can easily transfer from the anatase surface states to rutile as well as from the anatase conduction band to rutile, which improves the electron-transfer rate. The electron transport between connected anatase and rutile particles can support the photo-excited charge separation and thus reduce the recombination rate.

Kinetics of Protein Extraction in Reverse Micelle

Sodium bis (2-ethylhexyl) sulfosuccinate (AOT)-sodium dodecyl sulfate (SDS)/isooctane-octanol reverse micelle extraction was tested an efficient and effective approach to separate peanut protein from full-fat peanut powder. Here, important kinetic factors including pH, ion strength, and temperature were studied during reverse micelle backward extraction. The extraction conditions were obtained by response surface experiments as follows: pH 7.5, ion concentration 1.1 mol/L at temperature 35°C. Under these optimum extraction conditions, the extraction rate of protein reached 79.03%. A model on the kinetic partitioning of peanut protein was also developed. The backward extraction in this reverse micelle system was controlled by interfacial resistance instead of diffusion resistance in reverse micelle and aqueous phase with the total mass transfer rate of 0.8×10−5 m3·s−1. A two-film theory may be the mechanism for flat interface. Results of mass transfer process are helpful for creating an reverse micelle extraction process, and used for purification of peanut proteins, promoting the development of food industry.

Core–shell nanospheres Pt@SiO2 for catalytic hydrogen production

Ultrafine platinum nanoparticles (NPs) embedded in silica nanospheres (Pt@SiO2) have been synthesized in a NP-5/cyclohexane reversed-micelle system followed by NaBH4 reduction. The as-synthesized core–shell nanocatalysts Pt@SiO2 were characterized by scanning electron microscopy, transmission electron microscopes, X-ray powder diffraction analysis, energy dispersive X-ray spectrometer and nitrogen adsorption–desorption investigations. Interestingly, the as-synthesized core–shell nanocatalysts Pt@SiO2 showed an excellent catalytic performance in hydrogen generation from the hydrolysis of ammonia borane (BH3NH3, AB) at room temperature. Especially, the catalytic performance of the Pt@SiO2 remained almost unchanged after the five recycles and even after the heat treatment (673K), because the silica shells inhibit aggregation or deformation of the metal cores. Besides, the kinetic studies showed that the catalytic hydrolysis of AB was first order with respect to the catalyst concentration and zero order with respect to the substrate concentration, respectively. The excellent catalytic activity and stability of Pt@SiO2 can make it have a bright future in the practical application.