Stabilization of all-aqueous droplets by interfacial self-assembly of fatty acids bilayers.

All-aqueous microdroplets produced by liquid-liquid phase separation have emerged as promising models of artificial cells, and offer new approaches for the solvent-free encapsulation of fragile solutes. Yet, the lack of a membrane on such droplets makes them intrinsically unstable against coarsening, and precludes a fine control over chemical localization, as solutes can freely diffuse through the interface. Herein, we report the construction of stable and impermeable water-in-water emulsions via the interfacial self-assembly of mixed sodium oleate/1-decanol bilayers on dextran-rich droplets produced by segregative liquid-liquid phase separation with poly(ethylene glycol). Lipids spontaneously self-assemble as multilamellar structures at the surface of the droplets as revealed by freeze-fracture transmission electron microscopy and small-angle X-ray scattering. We further demonstrate that the lipid-based membrane is impermeable to oligonucleotides and proteins, but also to a low molecular weight dye, so that a strict chemical encapsulation can be achieved by spontaneous partitioning within the droplets before membrane self-assembly. Taken together, our results highlight the ease of production of fatty acid-stabilized all-aqueous emulsions droplets able to encapsulate a range of solutes without the need of oil or organic solvents, paving the way to the construction of robust membrane-bounded, polymer-rich artificial cells.

Cytidine- and guanosine-based nucleotide-lipids.

Hybrid nucleotide-lipids composed of a lipid covalently attached to purine and pyrimidine nucleobases exhibit supramolecular properties. The novel cytidine and guanosine derivatives are promising bioinspired materials, which can act as supramolecular gelators depending on both the nucleobase and the presence of salts. These supramolecular properties are of broad interest for biomedical applications.

Preparation of Swellable Hydrogel-Containing Colloidosomes from Aqueous Two-Phase Pickering Emulsion Droplets.

The fabrication of stable colloidosomes derived from water-in-water Pickering-like emulsions are described that were produced by addition of fluorescent amine-modified polystyrene latex beads to an aqueous two-phase system consisting of dextran-enriched droplets dispersed in a PEG-enriched continuous phase. Addition of polyacrylic acid followed by carbodiimide-induced crosslinking with dextran produces hydrogelled droplets capable of reversible swelling and selective molecular uptake and exclusion. Colloidosomes produced specifically in all-water systems could offer new opportunities in microencapsulation and the bottom-up construction of synthetic protocells.

Highly confined stacks of graphene oxide sheets in water.

Since the discovery of graphene oxide (GO), the most accessible of the precursors of graphene, this material has been widely studied for applications in science and technology. In this work, we describe a procedure to obtain GO dispersions in water at high concentrations, these highly dehydrated dispersions being in addition fully redispersible by dilution. With the availability of such concentrated samples, it was possible to investigate the structure of hydrated GO sheets in a previously unexplored range of concentrations, and to evidence a structural phase transition. Tentatively applying models designed for describing the small-angle scattering curve in the Smectic A (or [Formula: see text]) phase of lyotropic systems, it was possible to extract elastic parameters characterising the system on the dilute side of the transition, thereby evidencing the relevance of both electrostatic and steric (Helfrich) interactions in stabilising aqueous lamellar stacks of GO sheets.

Self-Assembling Behavior of Glycerol Monoundecenoate in Water.

The self-assembling properties of glycerol esters in water are well known. Still, few data on glycerol monoesters of undecylenic acid are available. The aim of this study was to highlight the behavior of glycerol monoundecenoate (GM-C11:1) in different diluted and concentrated states. Its self-assembling properties in water and upon solid inorganic surfaces were investigated in the diluted state using surface tension experiments, atomic force microscopy, and cryogenic transmission electron microscopy studies. In the concentrated state, the gelling properties in the presence of water were investigated using polarized light microscopy, differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) experiments. GM-C11:1 at 100 mg/L self-assembles at the liquid/air interfaces as aggregates of approximately 20 nm in diameter, organized into concentric forms. These aggregates are spherical globules composed of several molecules of GM-C11:1. At higher concentrations (1000 and 104 mg/L), GM-C11:1 is able to uniformly coat liquid/air and liquid/solid interfaces. In bulk, GM-C11:1 forms spontaneously aggregates and vesicles. In a more concentrated state, GM-C11:1 assembles into lamellar Lß and Lα forms in water. By cross-referencing SAXS and DSC findings, we were able to distinguish between interlamellar water molecules strongly bound to GM-C11:1 and other molecules remaining unbound and considered to be "mobile" water. The percentage of water strongly bound was proportional to the percentage of GM-C11:1 in the system. In this case, GM-C11:1 appears to be an effective molecule for surface treatments for which water retention is important.

Sequestration of Proteins by Fatty Acid Coacervates for Their Encapsulation within Vesicles.

Encapsulating biological materials in lipid vesicles is of interest for mimicking cells; however, except in some particular cases, such processes do not occur spontaneously. Herein, we developed a simple and robust method for encapsulating proteins in fatty acid vesicles in high yields. Fatty acid based, membrane-free coacervates spontaneously sequester proteins and can reversibly form membranous vesicles upon varying the pH value, the precrowding feature in coacervates allowing for protein encapsulation within vesicles. We then produced enzyme-enriched vesicles and show that enzymatic reactions can occur in these micrometric capsules. This work could be of interest in the field of synthetic biology for building microreactors.

Clouding in fatty acid dispersions for charge-dependent dye extraction.

The clouding phenomenon in non-ionic surfactant systems is a common feature that remains rare for ionic detergents. Here, we show that fatty acid (negatively charged) systems cloud upon cooling hot dispersions depending on the concentration or when adding excess guanidine hydrochloride. The clouding of these solutions yields the formation of enriched fatty acid droplets in which they exhibit a polymorphism that depends on the temperature: upon cooling, elongated wormlike micelles transit to rigid stacked bilayers inside droplets. Above this transition temperature, droplets coalesce yielding a phase separation between a fatty acid-rich phase and water, allowing extraction of dyes depending on their charge and lipophilicity. Positively charged and zwitterionic dyes were sequestered within the droplets (and then in the fatty acid-rich upper phase) whereas the negatively charged ones were found in both phases. Our results show an additional case of negatively charged surfactant which exhibit clouding phenomenon and suggest that these systems could be used for extracting solutes depending on their charge and lipophilicity.

Self-Assembly of Bilayer Vesicles Made of Saturated Long Chain Fatty Acids.

Saturated long chain fatty acids (sLCFA, e.g., C14:0, C16:0, and C18:0) are potentially the greenest and cheapest surfactants naturally available. However, because aqueous sodium soaps of sLCFA are known to crystallize, the self-assembly of stable bilayer vesicles has not been reported yet. Here, by using such soaps in combination with guanidine hydrochloride (GuHCl), which has been shown recently to prevent crystallization, we were capable of producing stable bilayer vesicles made of sLCFA. The phase diagrams were established for a variety of systems showing that vesicles can form in a broad range of composition and pH. Both solid state NMR and small-angle neutron scattering allowed demonstrating that in such vesicles sLCFA are arranged in a bilayer structure which exhibits similar dynamic and structural properties as those of phospholipid membranes. We expect these vesicles to be of interest as model systems of protocells and minimal cells but also for various applications since fatty acids are potentially substitutes to phospholipids, synthetic surfactants, and polymers.

pH-Cleavable Nucleoside Lipids: A New Paradigm for Controlling the Stability of Lipid-Based Delivery Systems.

Lipid-based delivery systems are an established technology with considerable clinical acceptance and several applications in human. Herein, we report the design, synthesis and evaluation of novel orthoester nucleoside lipids (ONLs) for the modulation of liposome stability. The ONLs contain head groups with 3'-orthoester nucleoside derivatives featuring positive or negative charges. The insertion of the orthoester function in the NL structures allows the formation of pH-sensitive liposomes. ONL-based liposomes can be hydrolyzed to provide nontoxic products, including nucleoside derivatives and hexadecanol. To allow the release to be tunable at different hydrolysis rates, the charge of the polar head structure is modulated, and the head group can be released at a biologically relevant pH. Crucially, when ONLs are mixed with natural phosphocholine lipids (PC), the resultant liposome evolves toward the formation of a hexadecanol/PC lamellar system. Biological evaluation shows that stable nucleic acid lipid particles (SNALPs) formulated with ONLs and siRNAs can effectively enter into tumor cells and release their nucleic acid payload in response to an intracellular acidic environment. This results in a much higher antitumor activity than conventional SNALPs. The ability to use pH-cleavable nucleolipids to control the stability of lipid-based delivery systems represents a promising approach for the intracellular delivery of drug cargos.

From nucleobases to nucleolipids: an ITC approach on the thermodynamics of their interactions in aqueous solutions.

Hybrid constructions based on nucleosides and lipophilic components, known as nucleolipids, have become an extremely interesting class of molecules, especially for their potential biomedical applications. In this matter, it seemed important to define the nature and estimate the strength of their interaction with polynucleotides by different ways. We report in this work a systematic investigation through isothermal titration calorimetry of the thermodynamics of the association and dissociation of adenine and thymine derivatives, not previously performed. Then we use the results obtained on these simple systems as a basis for comparison with the binding of phospholipids functionalized with adenosine and thymidine to polyadenylic or polyuridylic acids applying the same experimental technique.

Fully deuterated magnetically oriented system based on fatty acid direct hexagonal phases.

There is strong demand in the field of NMR for simple oriented lipid supramolecular assemblies, the constituents of which can be fully deuterated, for specifically studying the structure of host protonated molecules (e.g., peptides, proteins...) in a lipid environment. Also, small-angle neutron scattering (SANS) in fully deuterated oriented systems is powerful for gaining information on protonated host molecules in a lipid environment by using the contrast proton/deuterium method. Here we report on a very simple system made of fatty acids (dodecanoic and tetradecanoic) and ethanolamine in water. All components of this system can be obtained commercially as perdeuterated. Depending on the molar ratio and the concentration, the system self-assembles at room temperature into a direct hexagonal phase that is oriented by moderate magnetic fields of a few tesla. The orientation occurs within the magnetic field upon cooling the system from its higher-temperature isotropic phase: the lipid cylinders of the hexagonal phase become oriented parallel to the field. This is shown by solid-state NMR using either perdeuterated fatty acids or ethanolamine. This system bears strong interest for studying host protonated molecules but also in materials chemistry for building oriented solid materials.

Steric-induced effects on stabilizing a lamellar structure.

We investigate the behavior of multilamellar phases composed of lecithin and a commercial cosurfactant (Simusol), which is a mixture of ethoxylated fatty acids. Using X-ray scattering and a new procedure to fit the data, relevant parameters characterizing the lamellar structure were determined as a function of membrane composition, varying from 100% of lecithin to 100% of Simulsol. Scattering data illustrating the swelling of the lamellae for different amounts of cosurfactant are presented with the respective behavior of the Caillé parameter. With this experimental approach, we show that the incorporation of ethoxy brushes onto the lipid surface enhances repulsive interactions arising from membrane fluctuations and changes the interactions at the interface between bilayers.

Tuning molecular interactions in lipid-oligonucleotides assemblies via locked nucleic acid (LNA)-based lipids.

Hybrid nucleotide-lipids containing locked nucleic acid (LNA) show enhanced hybridization properties with complementary single strand RNAs compared to DNA lipid analogues. The LNA adenosine lipid features unique binding properties with a high binding affinity for poly-uridine and the entropically driven formation of a stable complex (K(d) ≈ 43 nM). Enhanced hybridization properties of LNA-based lipids should be applicable for the development of oligonucleotide (ON) delivery systems or as small molecule binders to RNA for novel therapeutic strategies.

Amino acid-nucleotide-lipids: effect of amino acid on the self-assembly properties.

Hybrid amphiphiles composed of a lipid covalently linked to biomolecules are attracting considerable attention, owing to their unique physicochemical and biological properties. Herein, we have synthesized novel amino acid-nucleotide-lipids (ANLs), presenting phenylalanine and thymidine residues and saturated or unsaturated diacyl glycerol lipid moieties to investigate the effect of the specific aminoacid moieties on both aggregation properties and interactions of ANLs with single strand polyA RNA. Physicochemical studies (DLS, cryo-TEM, and small angle X-ray scattering) indicate that phenylanaline amino acids inserted at the 5' position of the nucleotide-lipids stabilize multilamellar systems, whereas unilamellar vesicles are formed preferentially in the case of nucleotide-lipids (NLs). Both NLs and ANLs exhibit weak interactions with complementary polyA RNA as revealed by isothermal titration calorimetry investigations. The multilamellar vesicles obtained with ANLs could be used as a versatile carrier, suitable for both hydrophobic and hydrophilic therapeutic molecules.

Unexpected bilayer formation in Langmuir films of nucleolipids.

Langmuir monolayers have been extensively investigated by various experimental techniques. These studies allowed an in-depth understanding of the molecular conformation in the layer, phase transitions, and the structure of the multilayer. As the monolayer is compressed and the surface pressure is increased beyond a critical value, usually occurring in the minimal closely packed molecular area, the monolayer fractures and/or folds, forming multilayers in a process referred to as collapse. Various mechanisms for monolayer collapse and the resulting reorganization of the film have been proposed, and only a few studies have demonstrated the formation of a bilayer after collapse and with the use of a Ca(2+) solution. In this work, Langmuir isotherms coupled with imaging ellipsometry and polarization modulation infrared reflection absorption spectroscopy were recorded to investigate the air-water interface properties of Langmuir films of anionic nucleolipids. We report for these new molecules the formation of a quasi-hexagonal packing of bilayer domains at a low compression rate, a singular behavior for lipids at the air-water interface that has not yet been documented.

From Brittle to Pliant Viscoelastic Materials with Solid State Linear Polyphosphonium - Carboxylate Assemblies.

A polystyrenylphosphonium polymer was synthesized and complexed with various carboxylic acid derivatives to form new solid-state polyelectrolyte-surfactant assemblies. The properties of these ionic materials were highly dependent on the nature of the anion and included a brittle material, a rubbery ball that bounces, or a sticky fiber. The values for the equilibrium modulus, storage modulus, and loss modulus were dependent on the composition of the carboxylic acid and the number of electrostatic interactions. Small-angle X-ray scattering studies on the supramolecular assemblies confirmed a bilayer structure for two of the assemblies.

Multiscale structural characterizations of fatty acid multilayered tubes with a temperature-tunable diameter.

It is known that 12-hydroxystearic acid coupled via ion-pairing with a counterion, such as ethanolamine, self-assembles into supramolecular multilayer tubes that exhibit a peculiar temperature-tunable diameter variation. At a given temperature threshold (T(Ø↑)), there is a large increase of the tube diameter by almost a factor of 10. We investigate here the nature of the counterion on the self-assembly of such tubes and the variation of their diameter with the temperature. Eight different counterions are used to produce tubes via ion-pairing with 12-hydroxystearic acid. We systematically measure structural parameters at different scales coupling phase contrast microscopy and small-angle neutron scattering (SANS), in combination with thermodynamic studies using differential scanning calorimetry (DSC). The temperature T(Ø↑) is found to depend sensitively on the nature of the counterion. One could not identify any DSC peak associated with the diameter variation. However, a detailed line-shape analysis of the SANS spectra reveals that a significant softening of the elastic properties of the multilayer tube walls occurs at T(Ø↑), for all counterions investigated. Depending on both the temperature and the nature of the counterion, the interlayer spacing in the multilayered structure (respectively, the bilayer thickness) varies in a range from 240 to 440 Å (respectively, from 22 to 42 Å), but those variations appear not to be related to T(Ø↑). Altogether, our results show that the variation of the diameter is correlated to the nature of the counterion and to the elastic properties of the bilayer stack.

Self-assembly, foaming, and emulsifying properties of sodium alkyl carboxylate/guanidine hydrochloride aqueous mixtures.

Unsaturated fatty acids may be extracted from various agricultural resources and are widely used as soaps in the industry. However, there also exist a large variety of saturated and hydroxy fatty acids in nature, but their metal salts crystallize at room temperature in water, hampering their use in biological and chemical studies or for industrial applications. Addition of guanidine hydrochloride (GuHCl) to sodium salt of myristic acid has been shown to prevent its crystallization in water, forming stable flat bilayers at room temperature. Herein, we extend this finding to two other saturated fatty acids (palmitic and stearic acids) and two hydroxyl fatty acids (juniperic and 12 hydroxy stearic acids) and study more deeply (by using small angle neutron scattering) the supramolecular assemblies formed in both saturated and hydroxyl fatty acid systems. In addition, we take the advantage that crystallization no longer occurs at room temperature in the presence of GuHCl to study the foaming and emulsifying properties of those fatty acid dispersions. Briefly, our results show that all fatty acids, even juniperic acid, which is a bola lipid, are arranged in a bilayer structure that may be interdigitated. Depending on the nature of the fatty acid, the systems exhibit good foamability and foam stability (except for juniperic acid), and emulsion stability was good. Those findings should be of interest for using saturated long chain (and hydroxyl) fatty acids as surfactants for detergency or even materials chemistry.

Self-assembly and foaming properties of fatty acid-lysine aqueous dispersions.

We report on dispersions of fatty acid-lysine salts in aqueous solutions which are further used to produce foams. The alkyl chain length is varied from dodecyl to stearic. In aqueous solutions, the lysine salt of the dodecyl chain yields an isotropic solution, probably micelles, whereas for longer alkyl chains, vesicles formed but crystallized upon resting at room temperature or when kept at 4 degrees C. Solid-state NMR showed that in vesicles fatty acids are embedded in a lamellar arrangement passing from a gel to a fluid state upon heating; the transition temperature at which it occurs was determined by DSC. Those results are confirmed by small-angle neutron scattering which also give additional information on the bilayer structure. Incredibly stable foams are obtained using the palmitic acid/Lys salt whereas for other alkyl chain length, poor or no foam is formed. We conclude that the foamability is related to the phase behavior in aqueous solution.