Surfactant Dioctyl Sulfosuccinate Research Articles

Enhancing the tribological performance of PLA-based biocomposites reinforced with graphene oxide

Poly(lactic acid) (PLA) reinforced with graphene has gained substantial interest as a biomaterial, where the tribological and mechanical behavior of PLA/graphene composites are major concerns. This study aims to develop PLA-based biocomposites reinforced with graphene oxide (GO) that have enhanced tribological capabilities. First, homogenous dispersions of GO and GO treated with the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) were retained. Then, poly(L-lactic acid) (PLLA) biopolymer and PLLA/GO, PLLA/GO(AOT), PLA/GO(AOT), and PLLA/polyethylene glycol (PEG)/GO biocomposite samples were produced via hot pressing, and their tribological behavior was examined in detail. The worn surface characteristics were examined using scanning electron microscopy (SEM), 3D confocal microscopy, and atomic force microscopy (AFM). Results showed that GO reinforcement considerably affected the sliding wear behavior of PLA. Contrary to anticipated, surface treatment of GO does not improve the PLLA/GO wear resistance; rather, it increases the wear rate. PEG positively affects the sliding wear performance of PLLA/GO. PLLA/GO and PLLA/PEG/GO biocomposites exhibited the lowest wear rate at normal loads of 5 and 8 N, respectively, which was decreased by about 50% compared to unreinforced PLLA samples. With the addition of GO, the wear mechanisms of the PLA-based biocomposites changed from adhesive wear to abrasive wear. These findings might increase the applicability of PLA-based biocomposites where tribological performance is the main concern, such as biodegradable implants for load-bearing bone fractures or scaffolds, opening up new opportunities for their use.

Enhancing Structural and Thermal Properties of Poly(lactic acid) Using Graphene Oxide Filler and Anionic Surfactant Treatment.

Graphene has attracted extensive attention in various fields due to its intriguing properties. In this work, nanocomposite films based on poly(lactic acid) (PLA and PLLA) polymers filled with graphene oxide (GO) were developed. The impact of treating GO with the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) on the properties of the resulting nanocomposites was investigated. To determine the morphological, optical, and structural properties of the obtained materials, physicochemical analyses were performed, including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. Additionally, the thermal properties and wettability of neat polymers and nanocomposites were thoroughly investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and contact angle analysis. It was observed that GO was well dispersed throughout the PLA and PLLA matrix, leading to stronger interface bonding. The results demonstrate that the untreated and treated GO improved the crystallinity and thermal stability properties of the PLA and PLLA. However, the AOT-treated GO has significantly higher performance compared to the untreated GO in terms of crystallinity, melting temperature (increased by ~15 °C), and wettability (the contact angle decreased by ~30°). These findings reveal the high performance of the developed novel composite, which could be applied in tissue engineering as a scaffold.

Structural Insights into Self-Assembled Aerosol-OT Aggregates in Aqueous Media Using Atomistic Molecular Dynamics.

In water, the surfactant dioctyl sulfosuccinate (Aerosol-OT or AOT) exhibits diverse aggregate structures, ranging from micelles to lamella. An atomic-level understanding, however, of the formation and structure of these aggregates is lacking. Herein, using atomistic molecular dynamics (MD) with microsecond-long simulations, self-assembly of AOT in water is studied for concentrations of 1, 7.2, and 20 wt % at 293 K and for 7.2 wt % at 353 K. Assembly proceeds through stepwise association and dissociation of single AOT molecules, and the fusion and fission of AOT clusters. At 293 K, AOT self-assembles into either (i) spherical micelles (1 wt %), (ii) biphasic systems consisting of rod-like and prolate spheroidal micelles (7.2 wt %), or (iii) bilayers (20 wt %). We hypothesize that the observed rod-like structure is a precursor to lamellar microdomains found experimentally in biphasic dispersions. Increasing temperature to 353 K at 7.2 wt % results in a system consisting of prolate micelles but no rod-like micelles. Simulated phase behavior agrees with previously published experimental observations. Individual aggregates formed during self-assembly are identified using graph theory. Structural metrics of these aggregates like the radius of gyration, shape anisotropy, and prolateness are presented. Trends in structural metrics quantitatively reflect how shapes and sizes of AOT aggregates vary with surfactant concentration and temperature. These simulations provide deeper insight into open questions in the scientific community and demonstrate a method to generate physics-based micelle structures that can be used to rationalize experimental observations.

Fish Waste Based Lipopeptide Production and the Potential Application as a Bio-Dispersant for Oil Spill Control.

There is a growing acceptance worldwide for the application of dispersants as a marine oil spill response strategy. The development of more effective dispersants with less toxicity and higher biodegradability would be a step forward in improving public acceptance and regulatory approvals for their use. By applying advances in environmental biotechnology, a bio-dispersant agent with a lipopeptide biosurfactant produced by Bacillus subtilis N3-1P as the key component was formulated in this study. The economic feasibility of producing biosurfactant (a high-added-value bioproduct) from fish waste-based peptone as a nutrient substrate was evaluated. Protein hydrolyzate was prepared from cod liver and head wastes obtained from fish processing facilities. Hydrolysis conditions (i.e., time, temperature, pH and enzyme to substrate level) for preparing protein hydrolyzates were optimized by response surface methodology using a factorial design. The critical micelle dilution (CMD) value for biosurfactant produced from the fish liver and head waste generated peptones was 54.72 and 47.59 CMD, respectively. Biosurfactant product generated by fish liver peptone had a low critical micelle concentration of 0.18 g L–1 and could reduce the surface tension of distilled water to 27.9 mN/m. Structure characterization proved that the generated biosurfactant product belongs to the lipopeptide class. An alternative to the key surfactant dioctyl sulfosuccinate sodium (DOSS) used in Corexit 9500 has been proposed based on a binary mixture of lipopeptides and DOSS that exhibited synergistic effects. Using the standard baffled flask test, a high dispersion efficiency of 76.8% for Alaska North Slope oil was achieved at a biodispersant composition of 80/20 (v/v) of lipopeptides/DOSS. The results show that fish waste can be utilized to produce a more effective, environmentally acceptable and cost-efficient biodispersant that can be applied to oil spills in the marine environment.

Influence of Electrolyte and Temperature on the Aggregation Behaviour of Mixed System Consisting Drug and Anionic Surfactant

At present work, the interaction of amphiphilic drug promazine hydrochloride (PMZ) with anionic surfactant sodium dodecyl sulfate (SDS) and imipramine hydrochloride (IMH) with anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) in the absence and presence of 50 mmol.kg−1 inorganic salt is investigated in aqueous medium at different temperatures. For this, conductometric measurements were carried out to evaluate the critical micelle concentrations (CMC) of drug and surfactant. Ideal critical micelle concentration (CMC id) and interaction parameter (β) has also been evaluated. The deviations obtained in values of CMC and CMC id indicate the interaction between drug and surfactant. Other micellar mole fraction parameters such as X1 Rub (Rubingh), X1 Mot (Motomura), X1 Rd (Rodenas) and X1 ideal (ideal mole fraction) are also evaluated based on different proposed models. Other thermodynamic parameters of micellization such as, standard free energy of micellization , standard enthalpy of micellization , and standard entropy of micellization are also evaluated based upon the equations already present in literature to understand the interactions prevailing in the studied systems.

An Asymmetric Electrochemical System with Complementary Tunability in Hydrophobicity for Selective Separations of Organics.

Conducting polymers modified with redox-active moieties or amphiphilic surfactants are promising adsorbent materials for the separation of neutral organic species from water. We develop an asymmetric system combining a polyvinylferrocene–polypyrrole hybrid (PVF–PPy) and an amphiphilic surfactant dioctyl sulfosuccinate (AOT)-doped polypyrrole (PPy(AOT)) that have complementary hydrophobicity tunability in response to electrochemical modulations. Both materials are hydrophobic in their respective neutral states, exhibiting high affinities toward organics. Upon application of a mild potential to oxidize PVF–PPy and reduce PPy(AOT), these polymers can be simultaneously rendered hydrophilic, thereby driving desorption of organics and regeneration of the materials. The asymmetric system can be used in a cyclic fashion, through repeated electrical shorting of the two electrodes to program the capture of organics from a large volume of feed solution, and application of a potential (above 0.9 V) to stimulate the release of the adsorbed organics into a small volume of desorption solution. The asymmetric configuration has multiple benefits, including suppression of water parasitic reactions, high energetic efficiency, and selectivity for target organic species. Therefore, the electrode system has the potential to reduce the energy consumption in the mitigation of organic contaminants over conventional methods, with the additional ability to recover valuable organic products, opening up new possibilities for addressing the water–energy nexus.

Oxygen vacancies in concave cubes Cu2O-reduced graphene oxide heterojunction with enhanced photocatalytic H2 production

A novel composite heterojunction based on concave cubes Cu2O-reduced graphene oxide (Cu2O-RGO) was synthesized via one-pot hydrothermal method. The anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) can act as the soft template to build the novel Cu2O-based microstructure. The ascorbic acid serves as reductant and etching agent in the Cu2O growing process. The facet etching of Cu2O and reduction of GO can take place simultaneously in the reaction system. The concave cubes Cu2O with average edge length of ~ 1.55 µm were well-dispersed on the surface of RGO. The Cu2O-RGO (2 wt%) heterojunction exhibited superior photocatalytic performance and recyclability with the highest amount of H2 yields of 64.3 µmol/g, which was fivefold more than the pure Cu2O (12.8 µmol/g). The enhanced photocatalytic performances were attributed to the oxygen vacancies in Cu2O and a flexible conducting channel supported by RGO. Furthermore, the synergistic effect of Cu2O and graphene caused broader absorption in visible light region and lower recombination of photogenerated electron–hole pairs. It is believed that the Cu2O-RGO heterojunction could provide an alternative method to design excellent photocatalysts for energy application.

Association behavior of a mixed system of the antidepressant drug imipramine hydrochloride and dioctyl sulfosuccinate sodium salt: Effect of temperature and salt

Herein, we have checked the interaction between the imipramine hydrochloride (IMH, an antidepressant drug) and anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) mixed system through a conductometric method in aqueous medium along with electrolyte solutions at different temperatures (288.15 to 303.15 K). Considerable changes were obtained in the different physicochemical parameters estimated in the current system. The AOT has an exceptional surface activity together with a very low critical micelle concentration (cmc) value as compared with other anionic surfactants, therefore, having much less toxicity. The deviations between observed cmc and ideal critical micelle concentration (cmcid) values point to an interaction between IMH and AOT. The value of cmc of the mixed system reduces through the increase of the mole fraction of AOT. With a rise in the temperature, the cmc value of pure IMH along with IMH–AOT mixtures increases first and then decreases with a further rise in the temperature. In the presence of 50 mmol·kg−1 NaCl, the observed cmc of the individual constituents along with IMH–AOT mixtures was clearly lower than that in an aqueous system. The micellar mole fraction values according to different proposed models X1Rub (Rubingh), X1Mot (Motomura), X1Rd (Rodenas) and X1ideal (ideal mole fraction) were estimated and the results obtained reveal the high contribution of AOT in the mixed micellization and the values increase through the rise in the mole fraction of AOT. At all studied temperatures the magnitudes of free energy of micellization (∆Gm0), interaction parameter (β) along with excess free energy (∆Gex) evaluated for the current studied system were obtained to be negative. The value of the activity coefficients (f1 and f2) were also computed by employing the method specified in the literatures. The negative values of enthalpy (ΔHm0) of the systems at lower temperature indicate the micellization is exothermic while at higher temperature negative values of ΔHm0 becomes positive, which means the micellization process becomes endothermic. The values of entropy (ΔSm0) were found to be positive in all cases. All of the estimated results imply a strong interaction among the studied constituents.

Superhydrophobic, Surfactant‐doped, Conducting Polymers for Electrochemically Reversible Adsorption of Organic Contaminants

AbstractPolymeric adsorbents show great potential for the replacement of activated carbon for removing a wide range of toxic organic pollutants from wastewater streams since they do not suffer from costly regeneration needs and high attrition rates. Herein, an electrochemically regenerable polymeric adsorbent based on an intrinsically conducting polymer (CP), polypyrrole (PPy), doped with anionic surfactant dioctylsulfosuccinate (AOT), denoted PPy(AOT), for mitigating organic pollutants in wastewater is reported. A facile electropolymerization protocol to synthesize highly porous PPy(AOT) is developed, with an adsorption capacity of greater than 570 mg pollutant/g polymer in its superhydrophobic oxidized state. It is demonstrated that the hydrophobicity of PPy(AOT) and hence its affinity for organics can be modulated electrochemically through the re‐orientation of AOT dopants, which can be exploited to regenerate the adsorbent and use it repeatedly for multiple adsorption/desorption cycles. It also explores the interactions between the adsorbed organic molecules and the surfactant‐doped CP adsorbent using a combined density functional theory and molecular dynamics approach to elucidate the mechanism of electrochemical modulations of hydrophobicity and affinity of the material. The physicochemical insights are significant for developing broader applications of such material in drug delivery, sensing, self‐cleaning surfaces, microfluidics, and artificial muscles.

Influence of lanthanum precursors on the heterogeneous La/SnO2–TiO2 nanocatalyst with enhanced catalytic activity under visible light

Surfactant controlled synthesis of La/SnO2–TiO2 nanocomposite was studied by using anionic surfactant dioctyl sulfosuccinate sodium salt (DOSS) synthesized via sol–gel method followed by hydrothermal method by using different lanthanum precursors. The structural investigation, thermal degradation, kinetics, thermodynamics properties, crystallite size, morphology, surface and photocatalytic properties of synthesized samples were studied by using different characterization techniques i.e. Thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FTIR), Particle Size Analyzer (PSA), Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Ultraviolet–Visible spectrophotometer (UV–VIS). Band gap calculations and optical properties of both SnO2–TiO2 and La/SnO2–TiO2 were studied by using UV–Visible spectroscopy. The performance of both SnO2–TiO2 and La/SnO2–TiO2 nanocomposites as a photocatalytic agent was also investigated for the degradation of methylene blue (MB) under the illumination of sunlight.

Encapsulation of α-tocopherol and β-carotene in concentrated oil-in-water beverage emulsions stabilized with whey protein isolate

ABSTRACTThe stabilization of flavor emulsions is a challenge for the industry of functional beverages. In this work, whey protein isolate was used as the stabilizing agent in concentrated orange oil-in-water emulsions. A 23 factorial design was performed, varying the ratio of orange oil/water (30–60%), the concentration of whey protein (1–15%), and the concentration of the surfactant dioctyl sulfosuccinate sodium (0–100 mg L−1). Analyses of surface tension, film formation, zeta potential, particle size, and turbidity were performed. Stable emulsions containing 60% of oil phase were prepared. β-Carotene and α-tocopherol were successfully encapsulated, without affecting the emulsion's stability.

Biodegradation of crude oil and dispersants in deep seawater from the Gulf of Mexico: Insights from ultra-high resolution mass spectrometry

During the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, three million liters of chemical dispersants (Corexit 9500 and 9527) were directly applied at the discharging wellhead at 1500m water depth. Such a deep-water large-scale application was unprecedented and the effect of dispersants on oil biodegradation is not yet completely understood. The present study explores the biodegradation of oil, dispersant, dispersed oil or dispersed oil and nutrients at the molecular level using ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR–MS) following a laboratory experiment with Gulf deep water. Oil-derived molecular formulae exhibited a specific molecular fingerprint and were mainly observed in the mass range <300Da. The relative abundance of heteroatom-containing (N, S, and P) compounds decreased over time in the oil-only treatments, indicating that they may have served as nutrients when oil-derived hydrocarbons were metabolized. Relative changes over time in the molecular composition were less pronounced in the dispersed oil treatments compared to the oil-only treatments, suggesting that dispersants affected the metabolic pathways of organic matter biodegradation. In particular, dispersant addition led to an increase of S-containing organic molecular formulae, likely derived from the surfactant di-octyl sulfosuccinate (DOSS). DOSS and several dispersant-derived metabolites (with and without S) were still detectable after six weeks of incubation, underscoring that they were not rapidly biodegraded under the experimental conditions. FT-ICR–MS fragmentation studies allowed tentatively assigning structures to several of these molecules, and we propose that they are degradation products of DOSS and other dispersant components. The present study suggests preferential degradation, transformation and enrichment of distinct dispersant molecules, highlighting the need to include these compounds when tracking Corexit-derived compounds in the environment.

Water-in-ionic liquid microemulsion formation in solvent mixture of aprotic and protic imidazolium-based ionic liquids.

We report that water-in-ionic liquid microemulsions (MEs) are stably formed in an organic solvent-free system, i.e., a mixture of aprotic (aIL) and protic (pIL) imidazolium-based ionic liquids (ILs) containing the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT). Structural investigations using dynamic light, small-angle X-ray, and small-angle neutron scatterings were performed for MEs formed in mixtures of aprotic 1-octyl-3-methylimidazolium ([C8mIm(+)]) and protic 1-alkylimidazolium ([CnImH(+)], n = 4 or 8) IL with a common anion, bis(trifluoromethanesulfonyl)amide ([TFSA(-)]). It was found that the ME structure strongly depends on the mixing composition of the aIL/pIL in the medium. The ME size appreciably increases with increasing pIL content in both [C8mIm(+)][TFSA(-)]/[C8ImH(+)][TFSA(-)] and [C8mIm(+)][TFSA(-)]/[C4ImH(+)][TFSA(-)] mixtures. The size is larger for the n = 8 system than that for the n = 4 system. These results indicate that the shell part of MEs is composed of both AOT and pIL cation, and the ME size can be tuned by pIL content in the aIL/pIL mixtures.

MoO2/Multiwalled Carbon Nanotubes (MWCNT) Hybrid for Use as a Li-Ion Battery Anode

A molybdenum dioxide/multiwalled carbon nanotubes (MoO2/MWCNT) hybrid composed of spherical flowerlike nanostructures of MoO2, interconnected by MWCNTs has been prepared by a one-step hydrothermal route. The growth of MoO2 nanoparticles into spherical floral shapes with a monoclinic crystalline structure is steered by the dioctyl sulfosuccinate surfactant. The one-dimensional electron transport pathways provided by MWCNTs, which are in direct contact with MoO2 nanostructures, impart an enhanced reversible lithium storage capacity (1143 mA h g(-1) at a current density of 100 mA g(-1) after 200 cycles), high rate capability (408 mA h g(-1) at a high C-rate of 1000 mA g(-1)) and good cycling stability to the MoO2/MWCNT hybrid relative to neat MoO2. Surface potential mapping of the electrodes by Kelvin probe force microscopy, revealed a lower localized work function for the MoO2/MWCNT hybrid as compared to the neat oxide. This makes the MoO2/MWCNT hybrid more easily oxidizable than neat MoO2. Such a distinctive topology achieved for the MoO2/MWCNT hybrid, wherein the MWCNTs prevent the agglomeration of MoO2 nanostructures and thus preserve good electrical connectivities, makes it different in terms of both morphology and performance from all previously reported MoO2-based anode materials to date.

Substrate-induced coagulation (SIC) of nano-disperse alumina in non-aqueous media: The dispersibility and stability of alumina in N-methyl-2-pyrrolidinone

This work investigated colloidal properties such as the zeta-potential, the electrophoretic mobilities and the wetting behaviour of alumina dispersed in non-aqueous media. Non-aqueous dispersions of alumina were prepared in the solvent N-methyl-2-pyrrolidinone (NMP). The wetting behaviour of alumina in NMP was characterized by the powder contact angle method and the Wilhemy plate method. The behaviour of the dispersion should provide information for the development of a substrate-induced coagulation (SIC) coating process of nano-sized alumina in non-aqeous media. SIC is a dip-coating process that coats pretreated but chemically different surfaces with nano-sized particles. It was found that the anionic surfactant dioctyl sulfosuccinate (AOT) had no stabilizing effect on alumina dispersed in NMP.

Microemulsion Systems with Rhodium Tris(3‐sulfophenyl)phosphine Trisodium Salt Complex for Product Isolation and Catalyst Recycling in the Hydrogenation of Dimethyl Itaconate

AbstractMicroemulsion systems with the nonionic surfactant p‐tert‐octylphenoxy polyethoxyethanol (OP9.5EO), the anionic surfactant dioctyl sulfosuccinate sodium salt (DOSS) and the narrow range nonionic surfactant alkyl polyethylene glycol ether (C10EO5) were used as solvent systems in the catalytic hydrogenation of dimethyl itaconate (DMI) catalysed by the water soluble catalyst complex Rh‐TPPTS in order to achieve product isolation and catalyst recycling. The DOSS systems, which are more sensitive to the substrate and catalyst addition allowed for the hydrogenation to proceed with an initial hydrogenation rate about three times higher than with the nonionic surfactants, when the surfactant concentration was 15 wt%. Systems with 3 wt% surfactant were used in order to accomplish catalyst recycling. With a biphasic DOSS mixture a turnover number (TON) of 1,200 mol of DMI hydrogenated per mol of catalyst (Rh) was obtained in 3 consecutive runs. A three‐phase system for the OP9.5EO mixture allowed the catalyst to be recycled 3 times and a TON of 1,500 in 4 runs was obtained. A TON of 800 in 2 runs was obtained using a three‐phase C10EO5 mixture.

Increasing the Luminescent Quantum Yield of CdS Nanoparticles Having Broadband Emission

Studies of the quantum yield (QY) of CdS quantum dots (QDs) with broadband luminescence are presented. These QDs are synthesized using the classic inverse micelle method employing the surfactant dioctyl sulfosuccinate sodium salt in heptane. Previous studies have shown that the QY of these materials is in the range of 10–13%. We have found that dehydration and UV photolysis roughly double the QY to typically , while only slightly redshifting the emission. Dehydration is accomplished by cooling the samples to to remove the water from the inverse micelles. The addition of trialkylamines to dehydrated, photolyzed solutions results in a further improvement in QY to 37%. This effect is independent of amine chain length over the range studied.

The Surface and Thermodynamic Properties of Ethoxylated Sodium Monoalkyl Sulfosuccinate Surfactants

A series of ethoxylated sodium monooctyl sulfosuccinates [E(n)SMOSS] and ethoxylated sodium monolauryl sulfosuccinates [E(n)SMLSS] have different units of ethylene oxide (n = 9, 14, 23) were synthesized. The surface and thermodynamic properties of these surfactants have been compared with sodium dioctyl sulfosuccinate surfactant (SDOSS) as a commonly used surfactant. The surface tension measurements at 25, 35, 45, and 55°C were used to determine of the critical micelle concentration (CMC) and surface active properties of these surfactants. The effect of the ethylene oxide (EO) unit and the alkyl chain length on the surface properties for the prepared surfactants was studied. The results show that the ethoxylated sodium monoalkyl sulfosuccinates generally have lower values of CMC than that of sodium dioctyl sulfosuccinate. The values of surface active parameters indicate that the ethoxylated sodium monooctyl sulfosuccinates and ethoxylated sodium monolauryl sulfosuccinates surfactants have adsorption properties better than the sodium dioctyl sulfosuccinate surfactant as a resulted presence of ethylene oxide in molecules of the prepared surfactants. The thermodynamic parameters show that the (EO) unites in the chemical structure of ethoxylated sodium monoalkyl sulfosuccinate surfactants improve their micellization and adsorption properties.

Improving activity and stability of cutinase towards the anionic detergent AOT by complete saturation mutagenesis

Cutinase is an enzyme suitable for detergent applications as well as for organic synthesis in non-aqueous solvents. However, its inactivation in the presence of anionic surfactants is a problem which we have addressed by creating a complete saturation library. For this, the cutinase gene from Fusarium solani pisi was mutated to incorporate all 19 possible amino acid exchanges at each of the 214 amino acid positions. The resulting library was screened for active variants with improved stability in the presence of the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT). Twenty-four sites in cutinase were discovered where amino acid replacements resulted in a 2-11-fold stability increase as compared to the wild-type enzyme.

Use of reverse micelles in membrane protein structural biology

Membrane protein structural biology is a rapidly developing field with fundamental importance for elucidating key biological and biophysical processes including signal transduction, intercellular communication, and cellular transport. In addition to the intrinsic interest in this area of research, structural studies of membrane proteins have direct significance on the development of therapeutics that impact human health in diverse and important ways. In this article we demonstrate the potential of investigating the structure of membrane proteins using the reverse micelle forming surfactant dioctyl sulfosuccinate (AOT) in application to the prototypical model ion channel gramicidin A. Reverse micelles are surfactant based nanoparticles which have been employed to investigate fundamental physical properties of biomolecules. The results of this solution NMR based study indicate that the AOT reverse micelle system is capable of refolding and stabilizing relatively high concentrations of the native conformation of gramicidin A. Importantly, pulsed-field-gradient NMR diffusion and NOESY experiments reveal stable gramicidin A homodimer interactions that bridge reverse micelle particles. The spectroscopic benefit of reverse micelle-membrane protein solubilization is also explored, and significant enhancement over commonly used micelle based mimetic systems is demonstrated. These results establish the effectiveness of reverse micelle based studies of membrane proteins, and illustrate that membrane proteins solubilized by reverse micelles are compatible with high resolution solution NMR techniques.