Reverse Micellar Phase Research Articles

From microemulsion phase diagrams to hydrophilicity and hydration controlled adsorption: a dissipative particle dynamics modelling study of phospholipid assembly in bio oils.

We explore here the assembly and adsorption response of a ternary bio oil-phospholipid-water system via dissipative particle dynamics (DPD) simulations. The mesoscale, particle-based modelling approach allows the examination of large-scale self-assembly response of dipalmitoylphosphatidylcholine (DPPC) phospholipids in a model bio oil solvent (modelled by triglycerides) in the presence of varying amounts of water. We report the reverse micellar and microemulsion assembly phase diagrams of the ternary mixture, verifying the model against literature data. The results show water content vs phospholipid concentration dependent transitions in reverse micellar to network-like and various lamellar phases in bulk assembly. Examination of the DPPC adsorption to smooth, homogeneous adsorbate surfaces of differing polarity reveals that phospholipid adsorption response transitions between discrete assemblies on polyethylene-like hydrophobic to continuous coating on mica-like hydrophilic substrates as the function of phospholipid and water concentrations. The significance of the work is that the presented model for phospholipid assembly in apolar solvents is capable of predicting accurately large scale assembly response and morphology changes including adsorption response in terms of system variables. The presented parametrization and verification information of the model enable readily extending the approach to other systems. The work provides computational access for tuning lipid-based microemulsion systems and their adsorption.

Phase behavior of soybean phosphatidylcholine and glycerol dioleate in hydrated and dehydrated states studied by small-angle X-ray scattering.

Soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) form liquid crystal nanostructures in aqueous environments, and their mixtures can effectively encapsulate active pharmaceutical ingredients (API). When used in a subcutaneous environment, the liquid crystalline matrix gradually hydrates and degrades in the tissue whilst slowly releasing the API. Hydration dependent SPC/GDO phase behavior is complex, non-trivial, and still not fully understood. A deeper understanding of this system is important for controlling its function in drug delivery applications. The phase behavior of the mixture of SPC/GDO/water was studied as a function of hydration and lipid ratio. Small-angle X-ray scattering (SAXS) was used to identify space groups in liquid crystalline phases and to get detailed structural information on the isotropic reverse micellar phase. The reported pseudo ternary phase diagram includes eight different phases and numerous multiphase regions in a thermodynamically consistent way. For mixtures with SPC as the predominant component, the system presents a reverse hexagonal, lamellar and R3m phase. For mixtures with lower SPC concentrations, reverse cubic (Fd3m and Pm3n) as well as intermediate and isotropic micellar phases were identified. By modeling the SAXS data using a core-shell approach, the properties of the isotropic micellar phase were studied in detail as a function of concentration. Moreover, SAXS analysis of other phases revealed new structural features in relation to lipid-water interactions. The new improved ternary phase diagram offers valuable insight into the complex phase behavior of the SPC/GDO system. The detailed structural information is important for understanding what APIs can be incorporated in the liquid crystal structure.

Mixed Surfactant‐Based Reverse Micellar Extraction Studies of Bovine Lactoperoxidase

AbstractThe suitability of reverse micellar extraction for recovery of bovine lactoperoxidase (LP) from aqueous solution was evaluated using systems formed by ionic and nonionic surfactant mixtures. The influence of ionic surfactant concentration, organic solvent, and pH on the extraction of LP into the reverse micellar phase was studied. The Tween® series surfactants with Aerosol‐OT (bis‐(2‐ethylhexyl) sulfosuccinate) showed better extraction of LP in the reverse micelles (RM) compared to the Triton® and Span® series of surfactants. Complete extraction of LP from an aqueous phase of initial concentration 25 mg L−1 occurred with the RM formed by 90 mM Aerosol‐OT/8 mM Tween® 80 in isooctane. The optimal pH, ionic strength, and positively charged ionic surfactant concentration for back extraction were also studied and a maximum of 95.5% back extraction efficiency and 66% LP activity recovery was obtained for a pH of 10.5,1 M KCl and 60 mM cetyltrimethylammonium bromide system.

Properties and Phase Behavior of Water-in-Diesel Microemulsion Fuels Stabilized by Nonionic Surfactants in Combination with Aliphatic Alcohol

We investigate the properties and phase behavior of the water–diesel fuel–Neonol AF 9-6/2-ethylhexanol system, which is regarded as a promising microemulsion fuel. A pseudoternary diagram of the system has been obtained. In the diesel fuel/water (DF/W) ratio ranging from 98:2 to 50:50 and the emulsifier concentration of 8–40 vol %, a region of microemulsions has been distinguished, generating particular interest as an alternative fuel. In the region under study, a reverse micellar phase L2 has existed predominantly. Fish-cut diagrams have been obtained for the DF/W ratios in the emulsifier concentration–temperature coordinates. An increase in the water fraction in microemulsions significantly has narrowed the range of their stability. The critical changes of microemulsion properties have been identified using the fish-cut diagrams. We have established the empirical relationship among the phase inversion temperature, the emulsifier concentration in the phase inversion point, and the water fraction in micro...

Adsorption Behavior of Curcumin onto Cetyltrimethylammonium Chloride Reverse Micelles Immobilized on a Glass Surface As Studied by Polarized Visible Attenuated Total Reflection Spectrometry with a Glass Slab Optical Waveguide.

Polarized visible attenuated total reflection spectrometry with a glass slab optical waveguide revealed that when a hydrophobic dye, curcumin, was adsorbed onto the cetyltrimethylammonium chloride (CTAC) reverse micelles immobilized on a glass surface, in an undissociated form, the curcumin was perpendicular to the surface plane, while in a dissociated form, the curcumin was parallel to the plane. This implies that the former may be located in the CTAC monolayer while the latter may be located in the reverse micellar water phase immobilized on the plane.

A New Phase Transfer Strategy to Convert Protein-Capped Nanomaterials into Uniform Fluorescent Nanoclusters in Reverse Micellar Phase.

A new phase transfer strategy to convert aqueous phase protein-protected nanomaterials into fluorescent nanoclusters in the reverse micellar environment is introduced using bovine serum albumin (BSA)-protected silver nanoclusters (AgNCs) and nanoparticles (AgNPs) as an example. The basic pH employed in the fabrication of protein-protected nanoclusters induces the the protein capping to be negatively charged and facilitates the transfer process of the nanomaterials from aqueous phase to a cationic gemini surfactant (16-2-16)/hexane/hexanol/water reverse micelle (RM) phase. The original fluorescence characteristics of the seed nanocluster is retained after the transfer process. Strikingly, when both the nanomaterials (AgNCs and AgNPs) coexist in the aqueous feed solution, they are exclusively converted into uniform nanoclusters in the RM extract with enhanced fluorescence intensity.

A New Thermodynamic Approach for Protein Partitioning in Reverse Micellar Solution

Reverse micellar systems are nanofluids with unique properties that make them attractive in high selectivity separation processes, especially for biological compounds. Understanding the phase behavior and thermodynamic properties of these nanosystems is the first step in process design. Separation of components by these nanosystems is performed upon contact of aqueous and reverse micellar phases. Due to the complexities of components molecular interactions, phase behavior studies of these solutions are different from regular liquid-liquid systems, and few thermodynamic models have been developed to describe distribution of extract between phases. In this study, a thermodynamic model with φ-φ approach and use of equations of states (EOS) is developed for the first time to describe the protein phase equilibria in reverse micellar systems. The developed model assumes that some reverse micelles act as active surfaces which can adsorb protein molecules. Also, the non-ideal behavior of micellar solution was modeled by three EOS, i.e. vdW, PR, and SRK. Results showed that SRK EOS shows the best match with experimental data of Bovine Serum Albomin (BSA) extraction from aqueous solution using reverse micellar solution of CTAB, a cationic surfactant. In addition, results indicate that the proposed thermodynamic model can describe the changes in electrostatic forces and increase in active surfaces on equilibrium protein extraction. Also, the standard deviation shows an excellent match between experimental data and model predictions.

Phase behavior in the biologically important oleic acid/sodium oleate/water system

The phase behavior in the oleic acid/sodium oleate/normal saline (0.15M NaCl aqueous solution) system has been determined. For this purpose visual inspection of samples between crossed polarizers, and Small Angle X-ray diffraction was used to identify the various phases and their unit cell dimensions. A rich phase behavior was observed for the ternary system, featuring reverse micellar, micellar cubic, hexagonal, and cubic phases, and large regions with lamellar phases. As expected the ratio the ‘oleic acid/sodium oleate’ determines the pH and as a consequence the phase behavior. The results could be modeled by an extended Henderson–Hasselbalch (HH) equation, which takes into account the electrostatic potential at the aqueous lipid interface. The knowledge obtained is important for understanding the lipolysis of triglycerides, as the phase behavior of the end-product of the reaction regulates how well the insoluble product can be dispersed and consequently the kinetics of the process.

Disposable non-enzymatic blood glucose sensing strip based on nanoporous platinum particles

We introduce a disposable non-enzymatic glucose sensor that uses nanoporous Pt instead of enzymes since nanoporous Pt is an ideal electrode material for the electrochemical sensing of glucose. In this work, a nanoporous Pt electrode composed of Pt nanopore-containing particles is formed by simply dispensing a mixture of nanoporous Pt particles and a binding polymer onto a conducting circuit screen-printed on polyimide film; the nanoporous Pt particles were prepared by chemically reducing a Pt precursor in a reverse-micellar phase. This dispensing method is more cost-effective and scalable for mass production in comparison to electroplating. Electrodes based on nanoporous Pt particles dispensed in the manner were tested as non-enzymatic disposable glucose sensors; they exhibited good linearities and acceptable performance in phosphate-buffered saline (PBS) solution at pH 7.4. In human whole blood, the sensors also properly responded to glucose levels. Error grid analysis reveals that most of the data are distributed regions A and B (A: 64%, A+B: 98%).

Reverse micellar extraction of lactoferrin from its synthetic solution using CTAB/n-heptanol system.

The partitioning of Lactoferrin (LF) into the reverse micellar phase formed by a cationic surfactant, cetyltrimethylammonium bromide (CTAB) in n-heptanol from the synthetic solution of LF was studied. The solubilization behaviour of LF into the reverse micellar phase and back extraction using a fresh stripping phase were improved by studying the effect of processing parameters, including surfactant concentration, solution pH, electrolyte salt concentration and addition of alcohol as co-solvent. Forward extraction of 100% was achieved at CTAB concentration of 50mM in n-heptanol solvent, pH of 10 and 1M NaCl. The electrostatic force and hydrophobic interaction have major influence on LF extraction during forward and back extraction respectively. The size of the reverse micelles and their corresponding water content were measured at different operating conditions to assess their role on the LF extraction. The present reverse micellar system has potential to solubilise almost all the LF into the reverse micelles during forward extraction and could able to allow back extraction from the reverse micellar phase with addition of small amount of co-solvent.

MATHEMATICAL MODELLING OF BACKWARD EXTRACTION MIXED REVERSE MICELLE OF AMOXICILLIN BY SURFACE RESPONSE METHODOLOGY (RSM)

One of important factor in reverse micelle extraction is backward transfer. It is important to investigate the favourable conditions for backward transfer from reverse micellar phase to an organic phase. The back extraction of amoxicillin was studied using mixed reverse micelle with combination sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and TWEEN 85. Backward extraction was optimized via response surface methodology (RSM). For mathematical modelling, Central Composite Design (CCD) was used to studies the significant of independent variables: pH of stripping solution (5-8), KCl concentration (2.0 -16.0 g/L) and backward extraction time (5-35 minutes) on the response of the process. Optimized backward extraction for maximized final mass of amoxicillin extracted into aqueous were pH of stripping solution (6.58), backward time (19.8 minutes) and concentration of KCl (11.02 g/L) on the response of the process. Result showed that the experimental data was fitted well to a second-order polynomial model.

Relationship between Structure and Fluctuations of Lipid Nonlamellar Phases Deposited at the Solid–Liquid Interface

The structure and dynamics of nanostructure films formed by mixtures of soy phosphatidylcholine and glycerol dioleate at the silicon-aqueous interface were studied by grazing incidence neutron spin echo spectroscopy (GINSES), specular and off-specular neutron reflectometry, and small-angle X-ray diffraction. Reverse hexagonal (HII) and micellar cubic phase (Fd3m) layers at the solid-liquid interface have been identified with neutron reflectometry measurements. A preferred orientation of the liquid crystalline (LC) domains was observed only for the anisotropic HII phase. The size of the LC domains was found to be about 1 micrometer as estimated from the width of the diffraction peaks. GINSES revealed that the cubic phase forms rather rigid films. In comparison, the HII film was more flexible, appearing as a modified undulation spectrum of the cylinders due to the interaction with the substrate.

Addition of n-Alcohols Induces a Variety of Liquid-Crystalline Structures in Surfactant-Rich Cores of Dispersed Block Copolymer/Surfactant Nanoparticles.

Poly(acrylamide)-b-complex salts made from a symmetric poly(acrylate-b-acrylamide) block copolymer, where the acrylate charges are neutralized by cationic surfactant counterions, form kinetically stable aqueous dispersions of hierarchical aggregates with a liquid-crystalline complex salt core and a diffuse hydrated shell. By the addition of suitable amounts of long-chain alcohols, such as octanol or decanol, the structure of the internal phase can be varied, producing micellar cubic, hexagonal, lamellar, or reverse hexagonal liquid-crystalline phases. In addition, a disordered reverse micellar phase forms at the highest content of octanol. These core structures are the same as those previously obtained for macroscopic homopolymer poly(acrylate) complex salt/water/n-alcohol systems at the corresponding compositions. The poly(acrylamide)-b-complex salt dispersions are kinetically stable for several weeks, with their colloidal properties and internal structures remaining unchanged. The methodology described here establishes an easy and robust protocol for the preparation of colloidal nanoparticles with variable but controlled internal structures.

Extraction of ovalbumin with gemini surfactant reverse micelles – Effect of gemini surfactant structure

Abstract So far, the protein with high solubility in water (such as bovine serum albumin) has been always chosen as the model protein in the studies on reverse micellar extraction; to recover the protein with considerable hydrophobicity from organic phase may not be easy. Noticing that the surfactants used have been mostly conventional ionic surfactants, in the present study, we extract ovalbumin (OVA), a typical globular protein exhibiting emulsifying and foaming capabilities and forming gels upon heating, with a series of gemini surfactant (C m - s -C m ⋅2Br with m being 12, s being 2, 8, 12 or m being 16, s being 5, 8) reverse micelles. Results show that C 12 - s -C 12 ⋅2Br reverse micelle can load more OVA than C 16 - s -C 16 ⋅2Br reverse micelle. Under optimum condition, ca. 90% of OVA can be transferred from water into all these gemini surfactant reverse micelles, while the backward extraction efficiency (i.e. the recovery of OVA from reverse micellar phase) is dependent on gemini surfactant structure; about 59–73% of OVA can be transferred back into water from C 12 -2-C 12 ⋅2Br, C 16 -5-C 16 ⋅2Br and C 16 -8-C 16 ⋅2Br reverse micelles, but very little OVA can be recovered from C 12 -8-C 12 ⋅2Br and C 12 -12-C 12 ⋅2Br reverse micelles.

Detailed investigation of nano-emulsions obtained from the Remcopal 4/decane/water system

Abstract We have investigated the phase behavior of the Remcopal 4/decane/water system. Direct lamellar phase (L α ), reverse hexagonal (H 2 ) liquid crystals, and reverse micellar phase L 2 were identified. Then, nano-emulsions have been formulated by the phase inversion temperature (PIT) method and characterized by various techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), conductivity, and small angle X-ray scattering (SAXS). For oil/surfactant ratios comprising between 2.3 and 5.7, a domain of nano-emulsion, stable between 20 and 27 °C, which extend up to 95 wt.% of water, is formed. The size of nano-emulsions is around 100 nm of diameters. It increases with the oil/surfactant ratio. The conductivity and the SAXS analyzes show that there is a strong relation between the joint presence of a dispersion of the lamellar phase L α , the sponge phase L3, and the formation of the nano-emulsions. Finally, the obtained nano-emulsions have been used as building blocks to prepare porous silica. Surprisingly, materials with a pore size in the micrometer range have been recovered.

Effect of fatty acids on self-assembly of soybean lecithin systems

With the increasing interest in natural formulations for drug administration and functional foods, it is desirable a good knowledge of the phase behavior of lecithin/fatty acid formulations. Phase structure and properties of ternary lecithin/fatty acids/water systems are studied at 37°C, making emphasis in regions with relatively low water and fatty acid content. The effect of fatty acid saturation degree on the phase microstructure is studied by comparing a fully saturated (palmitic acid, C16:0), monounsaturated (oleic acid, C18:1), and diunsaturated (linoleic acid, C18:2) fatty acids. Phase determinations are based on a combination of polarized light microscopy and small-angle X-ray scattering measurements. Interestingly, unsaturated (oleic acid and linoleic acid) fatty acid destabilizes the lamellar bilayer. Slight differences are observed between the phase diagrams produced by the unsaturated ones: small lamellar, medium cubic and large hexagonal regions. A narrow isotropic fluid region also appears on the lecithin–fatty acid axis, up to 8wt% water. In contrast, a marked difference in phase microsctructure was observed between unsaturated and saturated systems in which the cubic and isotropic fluid phases are not formed. These differences are, probably, a consequence of the high Krafft point of the C16 saturated chains that imply rather rigid chains. However, unsaturated fatty acids result in more flexible tails. The frequent presence of, at least, one unsaturated chain in phospholipids makes it very likely a better mixing situation than in the case of more rigid chains. This swelling potential favors the formation of reverse hexagonal, cubic, and micellar phases. Both unsaturated fatty acid systems evolve by aging, with a reduction of the extension of reverse hexagonal phase and migration of the cubic phase to lower fatty acid and water contents. The kinetic stability of the systems seems to be controlled by the unsaturation of fatty acids.

Compact polar moieties induce lipid-water systems to form discontinuous reverse micellar phase.

The role of molecular interactions in governing lipid mesophase organization is of fundamental interest and has technological implications. Herein, we describe an unusual pathway for monoolein/water reorganization from a bicontinuous mesophase to a discontinuous reverse micellar assembly, directed by the inclusion of polar macromolecules. This pathway is very different from those reported earlier, wherein the Fd3m phase formed only upon addition of apolar oils. Experiments and molecular dynamics simulations indicate that hydrophilic ternary additives capable of inducing discontinuous phase formation must (i) interact strongly with the monoolein head group and (ii) have a compact molecular architecture. We present a detailed investigation that contrasts a monoolein-water system containing polyamidoamine (PAMAM) dendrons with one containing their linear analogs. The Fd3m phase forms only on the addition of PAMAM dendrons but not their linear analogs. Thus, the dendritic architecture of PAMAM plays an important role in determining lipid mesophase behavior. Both dendrons and their linear analogs interact strongly with monoolein through their amine groups. However, while linear polymers adsorb and spread on monoolein, dendrons form aggregates that interact with the lipid. Dendrons induce formation of an intermediate reverse hexagonal phase, which subsequently restructures into the Fd3m phase. Finally, we demonstrate that other additives with compact structures that are known to interact with monoolein, such as branched polyethylenimine and polyhedral silsesquioxane cages, also induce the formation of the Fd3m phase.

Facile dispersion and control of internal structure in lyotropic liquid crystalline particles by auxiliary solvent evaporation.

Submicron sized, structured lyotropic liquid crystalline (LLC) particles, so-called hexosomes and cubosomes, are generally obtained by high energy input dispersion methods, notably ultrasonication and high-pressure emulsification. We present a method to obtain dispersions of such LLC particles with a significantly reduced energy input, by evaporation of an auxiliary volatile solvent immiscible with water, e.g. cyclohexane or limonene. The inner structure of the particles can be precisely controlled by the addition of a nonvolatile oil, such as α-tocopherol or tetradecane consistently with bulk phase diagrams,. Two different lyotropic surfactants were employed, industrial grade monolinoleine (MLO) and soy bean phosphatidylcholine (PC). The lyotropic surfactant and oil phase modifier were first dissolved in the volatile solvent to give a liquid reverse micellar (L2) phase, which requires significantly less energy input to be dispersed in an aqueous solution of secondary emulsifier compared to the corresponding gel-like bulk mesophase. The auxiliary volatile solvent was then removed from the emulsion by evaporation at room temperature, yielding LLC particles of the desired inner structure, Pn3̅m, H2, or Fd3̅m. The obtained particles were characterized by small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). Our method enables fine-tuning of the final particle size through the volatile-to-nonvolatile volume ratio and processing conditions.

Reverse micellar extraction of fungal glucoamylase produced in solid-state fermentation culture.

Partial purification of glucoamylase from solid-state fermentation culture was, firstly, investigated by reverse micellar extraction (RME). To avoid back extraction problems, the glucoamylase was kept in the original aqueous phase, while the other undesired proteins/ enzymes were moved to the reverse micellar organic phase. The individual and interaction effects of main factors (i.e., pH and NaCl concentration in the aqueous phase, and concentration of sodium bis-2-ethyl-hexyl-sulfosuccinate (AOT) in the organic phase) were studied using response surface methodology. The optimum conditions for the maximum recovery of the enzyme were pH 2.75, 100 mM NaCl, and 200 mM AOT. Furthermore, the optimum organic to aqueous volume ratio (Vorg/Vaq) and appropriate number of sequential extraction stages were 2 and 3, respectively. Finally, 60% of the undesired enzymes including proteases and xylanases were removed from the aqueous phase, while 140% of glucoamylase activity was recovered in the aqueous phase and the purification factor of glucoamylase was found to be 3.0-fold.

Positron Lifetime and Electrical Conductivity Studies of Bicontinuous Phase in (TTAB+Pentanol)/Water/n-Octane Reverse Micellar System

Reverse micellar (L2) phase in (TTAB+pentanol)/water/n-octane, mapped by using optical method, was investigated by preparing mixtures of 30%, 40%, 50%, 60% and 70% by weight of (TTAB+pentanol)(1:1) in n-octane. Positron annihilation studies were performed in these mixtures as a function of water concentration. Around water concentrations of 13.8%, 11.1%, 8.4%, 7.9% and 9.1% respectively, ortho-positronium pick-off lifetime τ3 shows oscillatory behaviour whereas positronium formation I3 exhibits abrupt change. These changes have been attributed to the setting in of bicontinuous phase. Electrical conductivity measurements support these results. Positron annihilation technique can thus distinguish between droplet-like and bicontinuous structures in L2 phase.