Biomimetic systems such as giant unilamellar vesicles (GUVs) are increasingly used for studying protein/lipid interactions due to their size (similar to that of cells) and to their ease of observation by light microscopy techniques. We use GUVs to understand in vitro, using purified proteins and biomimetic membranes, the interplay between specific proteins and lipids with actin in the organisation of the linkage between the cytoskeleton and the plasma membrane. These components contribute to the anchoring of a cell in its environment as they are localized in membrane protrusions. The protein Ezrin, a membrane cytoskeleton linker involved in the cellular morphogenesis and motility, provides a direct link between the plasmic membrane of cells and the actin cytoskeleton through its interaction with phosphatidylinositol(4,5) bisphosphate (PIP2), a lipid which plays important physiological roles in cellulo. We will first show zeta potential measurements and confocal microscopy images that quantify the incorporation of PIP2 in the membrane of GUVs, and then present results on the interaction of ezrin with PIP2-containing GUVs.

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We have investigated the nonlinear rheology of a soft composite transient network made of a solution of surfactant wormlike micelles (WM) in the semidilute regime that are reversibly bridged by telechelic polymers. The samples are well described, in the linear regime, as two Maxwell fluids components blends, characterized by two markedly different characteristic times. The slow mode is mainly related to the transient network of entangled WM, and the fast mode to the network of telechelic chains. In this paper we investigate the nonlinear viscoelasticity and show that the nonlinear behavior reflects as well the behavior of two coupled networks. On one hand, stress relaxation experiments and time-resolved stress response following the application of a constant shear rate show that, in the weakly nonlinear regime, these novel composite networks stiffen. A fourfold increase of the elastic modulus with respect to the linear value is reached for strain amplitude of about 200%. This strain hardening is due to the nonlinear stretching of the telechelic polymer chains. On the other hand, the samples exhibit shear banding in the highly nonlinear regime, similarly to pure semidilute solutions of WM.

Palladium nanowires (of length a few tens of nanometers) are synthesized in a hexagonal mesophase formed by a quaternary system (Pd-doped water, surfactant, cosurfactant, and oil) by electron beam irradiation. The mesophases can be doped by high concentrations of palladium (0.1 M) without any disturbance of the structure of the mesophases which allows the quantitative synthesis of 1D Pd nanostructures. We found an increase in the average length of the nanowires with the amount of cosurfactant (pentanol) that assists the reduction/growth processes. The electrocatalytic oxidation of ethanol was selected as a test reaction in alkaline medium where Pd is known to be among the best electrode materials. We found that the Pd nanowires exhibit both a very important electrocatalytic activity for ethanol oxidation and a very high stability.

Bimetallic Pd-Au nanostructures were synthesized in the soft templates provided by surfactant hexagonal mesophases. The nanostructures are constituted by a core rich in gold and a Pd porous shelf. The electrocatalytic activity of these nanostructures for ethanol oxidation in basic medium was compared with that of alloyed Pd-Au nanoparticles synthesized in solution. The Pd-Au alloy is active toward the oxidation of ethanol in an alkaline medium but is not durable in realizing this process. The Pd-shell-Au-core nanostructures synthesized in mesophases are promising for application in direct ethanol fuel cells as they exhibit a very good electrocatalytic activity and a high stability.