Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: I. Optimization and separation process.

Ammonium perfluorooctanoate (APFOA) was used as a surfactant for the separation of free unsaturated C18 fatty acids by micellar electrokinetic chromatography. A simple background electrolyte of 50 mM APFOA water/methanol (90:10, v/v) at pH = 10 enabled the repeatable separation of oleic acid, elaidic acid, linoleic acid, and alpha-linolenic acid in less than 20 min. Separation conditions were optimized regarding various parameters (organic solvent, counterion, APFOA concentration, and pH). Because the repulsive interactions between fluorocarbon chains and hydrogenated chains are known to lead to segregation and phase separation, the choice of perfluorinated micelles to separate such perhydrogenated long-chain acids could appear astonishing. Therefore, the critical micelle concentration, the charge density, and the mobility of the micelles have been determined, resulting in a first description of the separation process.

How an organogelator can gelate water: gelation transfer from oil to water induced by a nanoemulsion.

A hydrogel can be formed by an organogelator in the presence of a nanoemulsion. It is expected that this is due to a gelation transfer from oil to water. The system started with an oil-in-water nanoemulsion prepared according to a phase inversion temperature (PIT) process. Into this nanoemulsion consisting of Kolliphor® RH40 and Brij® L4 as surfactants, and Miglyol® 812 as oil and water, we introduced the organogelator 12-hydroxyoctadecanoic acid (12-HOA) in the oil phase. After cooling at room temperature, a slow reversible gelation of the water phase occurred with persistence of the nanoemulsion. This thermally reversible system was investigated using various techniques (rheology, turbidimetry, optical and electron microscopies, scattering techniques). Successive stages appeared during the cooling process after the nanoemulsion formation, corresponding to the migration and self-assembly of the organogelator from the oil nanodroplets to the water phase. According to our measurements and the known self-assembly of 12-HOA, a mechanism explaining the formation of the gelled nanoemulsion is proposed.

In vitro and in vivo cardioprotective and metabolic efficacy of vitamin E TPGS/Apelin.

AIMS: Apelin and vitamin E have been proposed as signaling molecules, but their synergistic role is unknown. The aim of this work was to develop vitamin E TPGS/Apelin system to test their cardioprotective and metabolic efficacy in vitro and in vivo. METHODS: FDA-approved surfactant D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS-1000) and Apelin complex were characterized by physico-chemical methods (CMC determination, dynamic light scattering and circular dichroism). In vitro studies were carried out on H9C2 cardiomyoblasts and isolated murine cardiomyocytes. In vivo studies were performed in isoproterenol- and high-fat diet-induced cardiac remodeling models in mice. RESULTS: We found that vitamin E TPGS/Apelin provide cardioprotective and metabolic efficacy in vitro and in vivo. In vitro studies revealed that vitamin E TPGS/Apelin reduces hypoxia-induced mitochondrial ROS production in cultured cardiomyocytes and H9C2 cardiomyoblasts. In addition, vitamin E TPGS/Apelin confers apoptotic response to hypoxic stress in cells. In a mouse model of isoproterenol-induced cardiac injury, TPGS is not able to affect cardiac remodeling, however combination of vitamin E TPGS and Apelin counteracts myocardial apoptosis, oxidative stress, hypertrophy and fibrosis. Furthermore, combination treatment attenuated obesity-induced cardiometabolic and fibrotic remodeling in mice. CONCLUSION: Together, our data demonstrated the therapeutic benefits of vitamin E TPGS/Apelin complex to combat cardiovascular and metabolic disorders.

Molten fatty acid based microemulsions.

We show that ternary mixtures of water (polar phase), myristic acid (MA, apolar phase) and cetyltrimethylammonium bromide (CTAB, cationic surfactant) studied above the melting point of myristic acid allow the preparation of microemulsions without adding a salt or a co-surfactant. The combination of SANS, SAXS/WAXS, DSC, and phase diagram determination allows a complete characterization of the structures and interactions between components in the molten fatty acid based microemulsions. For the different structures characterized (microemulsion, lamellar or hexagonal phases), a similar thermal behaviour is observed for all ternary MA/CTAB/water monophasic samples and for binary MA/CTAB mixtures without water: crystalline myristic acid melts at 52 °C, and a thermal transition at 70 °C is assigned to the breaking of hydrogen bounds inside the mixed myristic acid/CTAB complex (being the surfactant film in the ternary system). Water determines the film curvature, hence the structures observed at high temperature, but does not influence the thermal behaviour of the ternary system. Myristic acid is partitioned in two "species" that behave independently: pure myristic acid and myristic acid associated with CTAB to form an equimolar complex that plays the role of the surfactant film. We therefore show that myristic acid plays the role of a solvent (oil) and a co-surfactant allowing the fine tuning of the structure of oil and water mixtures. This solvosurfactant behaviour of long chain fatty acid opens the way for new formulations with a complex structure without the addition of any extra compound.

Quenched microemulsions: a new route to proton conductors.

Solid-state proton conductors operating under mild temperature conditions (T < 150 °C) would promote the use of electrochemical devices as fuel cells. Alternatives to the water-sensitive membranes made of perfluorinated sulfonated polymers require the use of protogenic moieties bearing phosphates/phosphonates or imidazole groups. Here, we formulate microemulsions using water, a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) and a fatty acid (myristic acid, MA). The fatty acid acts both as an oil phase above its melting point (52 °C) and as a protogenic moiety. We demonstrate that the mixed MA-CTA film presents significant proton conductivity. Furthermore, bicontinuous microemulsions are found in the water-CTAB-MA phase diagram above 52 °C, where molten MA plays both the role of the oil phase and the co-surfactant. This indicates that the hydrogen-bond rich MA-CTA film can be formulated in the molten phase. The microemulsion converts into a lamellar phase upon solidification at room temperature. Our results demonstrate the potential of such self-assembled materials for the design of bulk proton conductors, but also highlight the necessity to control the evolution of the nanostructure upon solidification of the oil phase.

Reverse aggregate nucleation induced by acids in liquid-liquid extraction processes.

We show in the case of N,N'-dimethyl-N,N'-dioctyl-2-(2(hexyloxy)ethyl)-malonamide (DMDOHEMA) chosen as a typical oil-soluble extractant with surface activity that the free energy of formation of reverse micelles in the solvent phase strongly depends on the presence of polar solutes. Free energies per molecule vary typically from 0 to 2 kT per molecule (5 kJ mol(-1)), depending on the kosmotropic/chaotropic nature of the anion extracted. Variations of the reverse aggregation free energy introduced by acids and other co-extracted solutes as deduced from the critical aggregation concentrations cannot be neglected while modelling extraction. With typical aggregation numbers of 4-6, the free energy of formation of one reverse aggregate varies up to 20 kJ mol(-1), which is four times the typical difference in free energy of one single cation transfer between a "target" and a non-target ion in practical extraction and stripping industrial processes.

How do anions affect self-assembly and solubility of cetylpyridinium surfactants in water.

We report the specific effects of a series of anions (chloride, nitrate, and oxalate) on the solubility and self-assembly of cationic cetylpyridinium surfactants in water. The anion influence on micellization was evidenced by tensiometry and determination of Krafft temperatures. Anions strongly affect these parameters, depending on their position in the lyotropic series as well as on their "bridging" character. Scattering techniques (light, X-rays, and neutrons) were used to characterize the structures of micelles, and by solving a lateral equation of state approach, we show that chaotropic anions can be considered as adsorbed on the pyridinium head groups, inducing a decrease of the surface polarity and a Krafft temperature shift. Mixing different counteranions in various ratios led to a competition with a preferential adsorption at the micellar surface.

Surfactin self-assembles into direct and reverse aggregates in equilibrium and performs selective metal cation extraction.

On tie-lines between water-rich and alkane-rich solutions, it is shown via scattering experiments that natural lipopeptide surfactin self-assembles into direct and reverse micelles in equilibrium. Elongated direct micelles in the aqueous phase are present together with small reverse globular aggregates in the organic phase. These latter are made from hydrated surfactant without any "water pool" in the organic phase. The resulting biphasic system is used for liquid-liquid extraction of model metal cations. It is efficient with iron but not with copper or neodymium. Competitive extractions show high selectivity towards iron.

Ion-specific weak adsorption of salts and water/octanol transfer free energy of a model amphiphilic hexapeptide.

An amphiphilic hexapeptide has been used as a model to quantify how specific ion effects induced by addition of four salts tune the hydrophilic/hydrophobic balance and induce temperature-dependant coacervate formation from aqueous solution. The hexapeptide chosen is present as a dimer with low transfer energy from water to octanol. Taking sodium chloride as the reference state in the Hofmeister scale, we identify water activity effects and therefore measure the free energy of transfer from water to octanol and separately the free energy associated to the adsorption of chaotropic ions or the desorption of kosmotropic ions for the same amphiphilic peptide. These effects have the same order of magnitude: therefore, both energies of solvation as well as transfer into octanol strongly depend on the nature of the electrolytes used to formulate any buffer. Model peptides could be used on separation processes based on criteria linked to "Hofmeister" but different from volume and valency.

Design of double stimuli-responsive polyelectrolyte microcontainers for protein soft encapsulation.

We have designed new double stimuli-responsive polyelectrolyte microcapsules to be useable under physiological conditions to handle biomacromolecules while avoiding the risk of denaturation. They are made of poly(4-vinylpyridine hydrochloride) (PVP) and poly(sodium styrene sulfonate) (PSS). The microcontainers are sensitive to temperature variation, as they irreversibly shrink under heating. In addition, the capsules reversibly swell at pH > 6, making it possible to encapsulate human serum proteins by diffusion through the polymer membrane. Encapsulation efficiency is quantified by fluorescence techniques.

Soft X-ray microscopy to characterize polyelectrolyte assemblies.

Transmission microscopy with soft X-rays (TXM) is applied to image in-situ polyelectrolyte assemblies in aqueous environment. The method is element specific and at this stage exhibits a lateral resolution of 20 nm. With the specific examples of hollow capsules and full spheres made of PAH/PSS polyelectrolyte multilayers, it is shown quantitatively that heat treatment irreversibly reduces the water content in the membrane. These experiments complement those reported recently on the polyion system PDADMAC/PSS, which shows a different glass-transition behavior. Finally, the potential and present limitations of TXM are discussed.

Behavior of temperature-sensitive PNIPAM confined in polyelectrolyte capsules.

Layer-by-layer assembled polyelectrolyte microcapsules are of great interest because they can possibly be used as microcontainers and they show interesting stimuli-responsive properties, which have been recently investigated. Here, we exploit capsules which are made temperature-sensitive by encapsulating poly(N-isopropylacrylamide) (PNIPAM). PNIPAM has a cloud point in water at about 32 degrees C, above which it collapses and is insoluble in water. Further this temperature responsiveness can be tuned by addition of various ions at various concentrations. Here, we present the encapsulation of PNIPAM inside polyelectrolyte microcapsules, and describe the dependence of the lower critical solution temperature (LCST) on the nature and the amount of different salts added. With this information, we demonstrate the ability to tune and finely control the collapse of encapsulated PNIPAM. In this light, this system could be used as a microsensor or drug- delivery system.

Balance of hydrophobic and electrostatic forces in the pH response of weak polyelectrolyte capsules.

A detailed study of the role of solution pH and ionic strength on the swelling behavior of capsules composed of the weak polyelectrolytes poly(4-vinylpyridine) (P4VP) and poly(methacrylic acid) (PMA) with different numbers of layers was carried out. The polyelectrolyte layers were assembled onto silicon oxide particles and multilayer formation was followed by zeta-potential measurements. Hollow capsules were investigated by scanning electron microscopy and atomic force microscopy. The pH-dependent behavior of P4VP/PMA capsules was probed in aqueous media using confocal laser scanning microscopy. All systems exhibited a pronounced swelling at the edges of stability, at pHs of 2 and 8.1. The swelling degree increased when more polymer material was adsorbed. The swollen state can be attributed to uncompensated positive and negative charges within the multilayers, and it is stabilized by counteracting hydrophobic interactions. The swelling was related to the electrostatic interactions by infrared spectroscopy and zeta-potential measurements. The stability of the capsules as well as the swelling degree at a given pH could be tuned, when the ionic strength of the medium was altered.

Microcapsules made of weak polyelectrolytes: templating and stimuli-responsive properties.

Hollow microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are templated on silicon oxide particles using the layer-by-layer adsorption. The colloidal template is removed with a buffer system of hydrofluoric acid and ammonium fluoride. With this buffer system, the template can be dissolved in mild pH conditions, where the polymeric layers are still stable. The morphology and the thickness of the resulting capsules are investigated with atomic force microscopy. The resulting hollow capsules show pH-dependent properties. The shells are stable over a broad pH range and swell and immediately dissolve for pH values below 2.3 and above 11. If the molecular weight of the poly(methacrylic acid) is increased, the enhanced entanglement of the polymers results in a reversible swelling of the capsules at low and at high pH. The swelling degree is probed with confocal laser scanning microscopy. In addition to the pH-dependent size variations, the different ionization degree of poly(methacrylic acid) as a function of pH is used for the selective binding of calcium ions.

Control of drug accessibility on functional polyelectrolyte multilayer films.

A surface coating based on polylysine/hyaluronic acid multilayers was designed and acted as a reservoir for an antiproliferative agent, paclitaxel (Taxol). Absolutely no chemical modification of polyelectrolytes or of the drug was needed and the final architecture was obtained in an extremely simple way using the layer-by-layer method. The paclitaxel dose available for human colonic adenocarcinoma cells HT29 seeded on the films could be finely tuned. Moreover, the accessibility of the drugs was controlled by adding on the top of the drug reservoir a capping made of synthetic polyelectrolyte multilayers. This capping was also required to allow adhesion of HT29 cells. Paclitaxel activity was maintained after embedding in the polyelectrolyte multilayers and cellular viability could be reduced by about 80% 96 h after seeding. The strategy described in this paper could be valuable for various other drug/cell systems.

Entrapment of a weak polyanion and H+/Na+ exchange in confined polyelectrolyte microcapsules.

An approach for the entrapment of a polyanion by polyelectrolyte microcapsules is reported. It is based on a reversal changing of microcapsule wall permeability from neutral to basic pH. Polyelectrolyte microcapsules were templated on latex (polystyrene) particles by the layer-by-layer adsorption of oppositely charged polymers of sodium poly(styrene sulfonate) and poly(allylamine hydrochloride), followed by core removal using tetrahydrofuran. In alkaline conditions, the microcapsules swell and become permeable for polymers. During encapsulation, the addition of salt ions increases the amount of the polymer encapsulated and contributes to its protonation because of redistribution of H+ ions across a semipermeable microcapsule wall. The redistribution of small ions across the microcapsule wall was tuned by adding salt according to the Donnan equilibrium and was characterized by H+ sensitive dyes.

The role of metal nanoparticles in remote release of encapsulated materials.

Laser mediated remote release of encapsulated fluorescently labeled polymers from nanoengineered polyelectrolyte multilayer capsules containing gold sulfide core/gold shell nanoparticles in their walls is observed in real time on a single capsule level. We have developed a method for measuring the temperature increase and have quantitatively investigated the influence of absorption, size, and surface density of metal nanoparticles using an analytical model. Experimental measurements and numerical simulations agree with the model. The treatment presented in this work is of general nature, and it is applicable to any system where nanoparticles are used as absorbing centers. Potential biomedical applications are highlighted.

pH-responsive properties of hollow polyelectrolyte microcapsules templated on various cores.

Hollow polyelectrolyte microcapsules made of poly(allylamine hydrochloride) and sodium poly(styrene sulfonate), templated on various cores, manganese and calcium carbonate particles or polystyrene latexes, were investigated. The polyelectrolyte multilayers respond to a change of pH, leading to a swelling of the capsules in basic conditions and a further shrinking when the pH is reduced to acidic. The nature of the core and the subsequent dissolution process have an influence on this pH responsiveness, and the structuring effect of tetrahydrofuran on the multilayers has been demonstrated. Increasing the molecular weight of the polymers or the number of layers causes also a rigidification of the structure and modifies the pH response.

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases.

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.

Asymmetric synthesis of (alpha-amino)phosphonic acid amphiphiles using chiral P-H spirophosphoranes.

Chiral P-H spirophosphoranes reacted with long-chain prochiral aldimines and, after selective hydrolysis, afforded (alpha-amino)phosphonic acid amphiphiles in both enantiopure forms.