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Influence d'inclusions sur les paramètres élastiques de membrane non-ioniques

Abstract : Replacing small amounts of nonionic surfactant by an ionic one does not modify structural and elastic parameters of a reverse lamellar phase because of counterions self-screening. On the other hand, as the surface charge density increases in a direct lamellar phase, steric repulsions between in-plane charges "iron" membranes fluctuations, leading to a decrease of the periodicity. The Caillé parameter eta decreases, whereas the membrane rigidity increases, in good agreement with Fogden et al. predictions. The smectic compressibility modulus Bbar increases because of electrostatic repulsions and then decreases slightly either because of a renormalization of the membrane thickness due to counterions condensation or because of fluctuations correlations predicted by Lukatsky et al. A hydrophobic-hydrophilic-hydrophobic peptide, globally neutral was inserted in lamellar and sponge phases. In these phases, it lies on the membrane and its hydrophilic part is organized in a rigid alpha helix. Its insertion leads to a decrease of the Caillé parameter eta but steric repulsions still stabilize the phase and the periodicity remains unchanged. The decrease of eta is explained either by an increase of the effective membrane thickness, or by the Sens and Turner model. The peptide also induces a rigidification of the membrane. Because of their restrictive hypotheses, existing models cannot account for the spectacular rigidification, which is well correlated to the increase of the membrane thickness. The light-harvesting complex LH2 was inserted in the Q230 cubic phase of monoolein. We investigated the absorption and fluorescence properties of this oligomeric membrane protein. The insertion of LH2 in the cubic phase induced modifications in the pigments binding sites. Despite these significant structural perturbations, the protein seems to keep an oligomeric structure. These observations ruled out crystallization trials in the cubic phase for this protein, leading to some caution in the use of the cubic phase as a crystallization matrix. We also showed that LH2 was denaturated in sponge phases of surfactants.
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Contributor : Tsapis Nicolas <>
Submitted on : Tuesday, January 7, 2003 - 6:00:09 PM
Last modification on : Thursday, July 1, 2021 - 5:32:04 PM
Long-term archiving on: : Tuesday, September 11, 2012 - 7:15:10 PM


  • HAL Id : tel-00002241, version 1


Nicolas Tsapis. Influence d'inclusions sur les paramètres élastiques de membrane non-ioniques. Biophysique []. Université Pierre et Marie Curie - Paris VI, 2000. Français. ⟨tel-00002241⟩



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