Membrane fusion is a natural and essential phenomenon in many cellular processes, including the entry of pathogens into host cells, the transfer of genetic material or the transport of newly synthesized membrane constituents. It is defined as the process by which two different lipid membranes merge into a single continuous bilayer. Scientific community is very active in recent years to better understand the molecular events responsible for the intermembrane fusion. The control of the fusion between vesicles or bacterial membranes is a major issue in the development of drug delivery systems, the control of chemical reactions (bioreactors) or the development of artificial cell systems (Bottom-up approach of Synthetic Biology). Another interest in Synthetic Biology is to improve the efficiency of genome transplantation, which needs fusion events and remains, to date, poorly controlled. The model systems studied are phospholipid-based vesicles in order to mimic most biological membranes. The originality of this work is to incorporate a nucleotide lipid to promote and optimize the membrane fusion. This phenomenon is governed by the Watson-Crick base-pairing interactions between the complementary vesicles. Indirect techniques (dynamic light scattering, differential scanning calorimetry, Small Angle X-ray Scattering) have clearly shown the existence of a mixed post-fusion bilayer. We will discuss the role of the membrane composition, the fluidity of the bilayer or the size of the vesicles on the fusion events. The existence and the role of micro-domains, also known as rafts, will also be discussed.

The graphene oxide (GO) is widely used as a graphene precursor. It has been recently evidenced that this object can form different lyotropic liquid crystals phases observed in highly anisotropic colloids. The confinement of GO sheets, a two-dimensional (2D) crystal is herein aim of study. The binary GO water is studied to describe the liquid crystallinity of concentrated dispersions, characterized through complementary techniques as X-ray Scattering and Polarized Optical Microscopy. Concentrated GO dispersions were achieved by implementing rigorous procedures, based on high rate centrifugation (where concentrations between 15 and 20 % (mass) were achieved) followed by dehydration (dispersions up to 100 % were characterized), avoiding the formation of aggregates. Some phase transitions were detected in concentrated domains, never studied before. The Dynamic Light Scattering was used to characterize the GO sheets dimensions.

In current biomedically oriented research, the development of a biomimetic nanoparticle platform is of interest to provide a molecular toolbox (i.e., allowing easy modular exchange of its parts depending on actual needs while being nontoxic and allowing real-time recognition and tracking using various methods, such as fluorescence). We report the development of germanium(IV) oxide-polysaccharide composite particles possessing these properties. The nanoparticles are based on a crystalline germanium oxide core with a size range of 20–30 and 300–900 nm. Two new simple coating techniques were compared for the preparation of the photoluminescent polysaccharide-coated germanium(IV) oxide nanoparticles. The germanium(IV)-based core allows for in situ polysaccharide attachment via direct chelation. In addition, the nanoparticles were coated with thin layer of silicon oxide. After coating, 3-(triethoxysilyl)propyl isocyanate was grafted onto the surface, and the polysaccharides were immobilized on the particle surface via a covalent urethane linkage, which allows for an even more stable polysaccharide coating than that obtained via chelation. This approach provides access to a new material platform for biological track and image applications.

Water activity and its relationship with interactions stabilising lamellar stacks of mixed lipid bilayers in their fluid state are investigated by means of osmotic pressure measurements coupled with small-angle X-ray scattering. The (electrically neutral) bilayers are composed of a mixture in various proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. For highly dehydrated samples the osmotic pressure profile always exhibits the "classical" exponential decay as hydration increases but, depending on Simulsol to lecithin ratio, it becomes either of the "bound" or "unbound" types for more water-swollen systems. A simple thermodynamic model is used for interpreting the results without resorting to the celebrated but elusive "hydration forces".

Structure and interactions stabilising the lamellar stack of mixed lipid bilayers in their fluid state are investigated by means of small-angle X-ray scattering. The (electrically neutral) bilayers are composed of a mixtures of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. The soft confinement of the bilayer hydrophilic components is varied by changing hydration and bilayer composition, as well as the length of the cosurfactant polar head. Structural transitions are observed at low hydration, in the stacking order for the longer cosurfactant, and in the mixed bilayers for the shorter one. At higher hydration, the swelling of the lamellar stacks occurs with a significant, but continuous evolution in the mixed bilayer structure. The bilayer structural changes are discussed in analogy with the so-called "brush-to-mushroom" transition induced by lateral confinement, relevant for long linear polymers grafted onto rigid surfaces, taking also into account the role of vertical confinement.

Simultaneous measurements of small-angle neutron scattering and dynamic light scattering have been performed on a binary mixture of partially miscible liquids, 2,6-dimethylpyridine and water. At critical composition the temperature dependence of the correlation length of fluctuations in composition is strongly affected by the addition of nanoparticles of a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide. A crossover between Ising-type critical behavior and mean-field critical behavior is observed when the correlation length is equal to the size of the nanoparticles.

New "bottom-up" fabrication techniques are now effectively explored for the production of nanostructured functional materials, and specifically for nanophotonic devices and metamaterials (1). Expected benefits from bottom-up approaches include assembling true threedimensional metamaterials and synthesizing resonators with sizes appropriate for the optical range. Nanochemistry and self-assembly appear as interesting nanofabrication tools. Among the promising self-assembled systems are the diblock copolymers made of two molecular chains of distinct chemical nature linked together, which present solid state spontaneous structures with long-range order and tunable characteristic sizes between 10 and 50 nm. In particular, alternating lamellar and hexagonally-ordered cylindrical structures are described in many diblock copolymer systems. These are, however, organic materials exhibiting moderate susceptibilities and low optical constant contrast. Therefore, in their native state, they should be considered essentially as 'optically neutral' templates, used to spatially organize 'active' entities.

The use of agricultural resources for industrial purposes will undoubtedly be one of the major challenges of the 21st century, either from the energetic point of view by the progressive replacement of fossil fuels or with respect to non-energy uses by making available new organic “biosynthons” to the chemicals industry. In such a context, we demonstrate here the strong potential of dispersions of saturated fatty acids and their hydroxylated derivatives, extracted from biological compounds of plant origin, as a new class of green surfactants.

Using Fluorescence Recovery After Photobleaching, we investigate the Brownian motion of DNA rod-like fragments in two distinct anisotropic phases with a local nematic symmetry. The height of the measurement volume ensures the averaging of the anisotropy of the in-plane diffusive motion parallel or perpendicular to the local nematic director in aligned domains. Still, as shown in using a model specifically designed to handle such a situation and predicting a non-Gaussian shape for the bleached spot as fluorescence recovery proceeds, the two distinct diffusion coefficients of the DNA particles can be retrieved from data analysis. In the first system investigated (a ternary DNA-lipid lamellar complex), the magnitude and anisotropy of the diffusion coefficient of the DNA fragments confined by the lipid bilayers are obtained for the first time. In the second, binary DNA-solvent system, the magnitude of the diffusion coefficient is found to decrease markedly as DNA concentration is increased from isotropic to cholesteric phase. In addition, the diffusion coefficient anisotropy measured within cholesteric domains in the phase coexistence region increases with concentration, and eventually reaches a high value in the cholesteric phase.

The structure of a complex between hydrated DNA and a non-cationic lipid is studied, including its phase diagram. The complex is spontaneously formed by adding DNA fragments (ca. 150 base pairs in length) to non-cationic lipids and water. The self-assembly process often leads to highly ordered structures. The structures were studied by combining X-ray scattering, fluorescence and polarized microscopy, as well as freeze-fracture experiments with transmission electron microscopy. We observe a significant increase of the smectic order as DNA is incorporated into the water layers of the lamellar host phase, and stabilization of single phase domains for large amounts of DNA. The effect of confinement on DNA ordering is investigated by varying the water content, following three dilution lines. A rich polymorphism is found, ranging from weakly correlated DNA-DNA in-plane organizations to highly ordered structures, where transmembrane correlations lead to the formation of columnar rectangular and columnar hexagonal superlattices of nucleotides embedded between lipid lamellae. From these observations, we suggest that addition of DNA to the lamellar phase significantly restricts membrane fluctuations above a certain concentration and helps the formation of the lipoplex. The alteration of membrane steric interactions, together with the appearance of interfacial interactions between membranes and DNA molecules may be a relevant mechanism for the emergence of highly ordered structures in the concentrated regime.

The use of agricultural resources for industrial purposes will undoubtly be one of the major challenges of the 21 st century. Organic biosynthons used in chemistry should progressively replace those coming from fossil fuels. Our work on dispersions of fatty acids and hydroxylated derivatives forms part of these efforts in that it seeks to demonstrate the potential contribution of fatty acids (which may be extracted from plants) as a new class of surface active agents. Dispersions of fatty acid and their hydroxyl derivatives are thus studied in solution in order to generate a new class of surface active agents for foaming and emulsifying properties.

We study the effect of the soft confinement by fluid lipid bilayers on the spatial organisation of DNA molecules in a DNA-zwitterionic lipid hydrated lamellar complex. The confinement is increased by dehydrating the complex in a controlled way, which leads to a decrease of the water channel thickness separating the periodically stacked bilayers. Using grazing-incidence small-angle X-ray scattering on an oriented thin film, we probe in situ as dehydration proceeds the structure of the DNA-lipid complex. A structural phase transition is evidenced, where an apparently disordered phase of DNA rods embedded within the one-dimensionally ordered lipid lamellar phase observed at high hydration is replaced by a 2D hexagonal structure of DNA molecules intercalated between the lipid bilayers. Copyright (C) EPLA, 2010

. The dynamic behaviour of three hydrophilic probes (two dyes and one fluorescently-labelled protein) inserted in the water layers of lyotropic lamellar phases has been studied by confocal fluorescence recovery experiments. Two different, ionic (AOT/NaCl/ H 2 O and non-ionic ( C 12 E 5 /hexanol/ H 2 O host systems were studied. The confinement effect has been carefully monitored using the swelling properties of the lamellar phases. In all cases, we measure the evolution of the probe diffusion coefficient in the layer plane D ⊥ versus the separation between the membranes d w . Depending on the composition of the lamellar phase, this distance can be continuously adjusted from 500Å to about 20Å. For all systems, we observe a first regime, called dilute regime, where the diffusion coefficient decreases almost linearly with 1/ d w . In this regime, the Faxén theory for the friction coefficient of a spherical particle symmetrically dragged between two rigid walls can largely explain our results. More unexpectedly, when the membranes are non-ionic, and also quite flexible ( C 12 E 5 /hexanol in water), we observe the existence of a second, concentrated (or confined) regime, where the diffusion coefficient is nearly constant and different from zero for membrane separations smaller than the particle size. This new regime can be heuristically explained by simple arguments taking into account the membrane fluidity.

We studied the micelle formation of a diblock copolymer of styrene and ethylene oxide in mixtures of 2,6-dimethylpyridine (2,6-lutidine) and water. Micelles are formed in a broad solvent composition range with a volume fraction of water ranging from 0.05 to 0.85, where neither polystyrene nor polyethylene oxide homopolymers are soluble. The diffusion behavior of pure solvent mixtures and in solutions of copolymer micelles is reported. In LTD/water mixtures, two diffusive processes corresponding to self-difusion and two modes belonging to mutual diffusion and diffusion of solvent clusters have been found. In copolymer solutions, the mode of copolymer micelle diffusion replaces the mode of solvent cluster diffusion. Quasielastic light scattering, small-angle neutron scattering, and pulsed-field gradient NMR have been employed in our study.

We report X-ray resonant scattering experiments performed on the prototype liquid-crystalline compound MHPOBC doped with a chemical probe containing a resonant atom (selenium). We determined directly for the first time the microscopic 3- and 4-layer structure of the ferrielectric subphases ( SmCFI1* and SmCFI2*) present in MHPOBC. Despite the low fraction of the selenium probe, the resonant signal is strong enough to allow an unambiguous determination of the basic structure of the ferrielectric subphases. These experiments demonstrate that the resonant scattering technique can be extended to liquid crystalline materials without resonant element and may stimulate new studies. A non-resonant Bragg reflection was also found in the SmCFI1* phase in pure MHPOBC, consistent with the 3-layer distorted model, but never detected before.

We study asymmetric block copolymers with the simple diblock AB architecture, in the case where the longer block A is both hydrophobic and "soft", whereas the shorter block B is hydrophilic and "hard". Materials with such a particular combination of physico-chemical and mechanical properties have distinctive advantages, in particular for designing water-compatible adhesive materials. The phase diagram is established, combining NMR and SAXS characterisations of the materials. The swelling with water is monitored through gravimetry and "time-resolved" SAXS. Indications of maintained adhesive properties in a wet environment are given.

We report the direct observation, using freeze-fracture transmission electron microscopy, of topological melting in a lyotropic system in the vicinity of a smectic-cholesteric (N*) phase transition. The proliferation of dislocations leads to at least one, and possibly two intermediate phases, characterised by orientational ordering of the dislocation loops and the subsequent unbinding of the screw-dislocation lines.

There is considerable interest in constructing supramolecular hollow tube architectures based on amphiphilic molecules. This can be achieved by using relatively expensive synthetic lipids. Herein, we report on the facile preparation of self-assembled microtubes from a novel low-cost lipid mixture that does not require a previous chemical synthesis step and consists of the ethanolamine salt of 12-hydroxy-stearic acid in water. Tubes of more than 10 microm in length spontaneously form upon cooling from an isotropic solution. They exhibit inner and outer diameters of 400 and 600 nm, respectively, and their walls consist of concentric stacked bilayers of fatty acid salts, each separated by a layer of water.