Neutron reflectivity of supported membranes incorporating terminally anchored polymers: Protrusions vs. blisters

The effect of terminally anchored chains on the structure of lipid bilayers adsorbed at the solid/water interface was characterized by neutron reflectivity. In the studied system, the inner leaflet, closer to the substrate, consisted of head-deuterated 1,2-distearoyl-sn-glycero-3-phosphorylcholine (DSPC) and the outer leaflet comprised a mixture of DSPC and polyethylene glycol (PEG) functionalized 1,2-distearoyl-sn-glycero-3-phosphoethanolamine. The DSPC headgroups were deuterated to enhance sensitivity and demarcate the bilayer/water interface. The effect on the inner and outer headgroup layers was characterized by w 1/2, the width at half-height of the scattering length density profile. The inner headgroup layer was essentially unperturbed while w 1/2 of the outer layer increased significantly. This suggests that the anchored PEG chains give rise to headgroup protrusions rather than to blister-like membrane deformations. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mapping the location of grafted PNIPAAM in mesoporous SBA-15 silica using gas adsorption analysis.

The thermoresponsive polymer poly-N-isopropylacrylamide (PNIPAAM) was grafted in mesoporous SBA-15 silica. The grafting process consists of three steps: (i) increasing the amount of surface silanol groups of SBA-15 by hydroxylation, (ii) attachment of an anchor (1-(trichlorosilyl)-2-(m/p-(chloromethylphenyl)ethane) and finally (iii) the polymerization of the monomers (NIPAAM) onto the anchor. After each step, the materials were characterized regarding the porosity, using inert gas (argon, nitrogen) physisorption measurements. Also, the structure was investigated by small-angle X-ray diffraction analysis and thermogravimetric analysis was used for determination of the amount of grafted material. A total of 17% by weight of organic material was introduced in the porous host and the structure was preserved during the grafting process. Physisorption measurements revealed that the anchor is mainly located in the intrawall pores present in SBA-15. Consequently, the polymer is preferentially located in the intrawall pores or in the vicinity thereof. The final mesopore volume is 0.47 cm(3) g(-1) as compared to 0.96 cm(3) g(-1) for the pure SBA-15. The surprisingly large loss of mesopore volume and an almost constant mesopore diameter is consistent with a partial sealing of the mesopore volume in the composite materials. The potential thermocontrol combined with the large mesoporosity and the possible "storage space" provided by the sealed mesopore volume leads to a material with possibilities for various applications

X-ray structure, thermodynamics, elastic properties and MD simulations of cardiolipin/dimyristoylphosphatidylcholine mixed membranes

tCardiolipins (CLs) are important biologically for their unique role in biomembranes that couple phos-phorylation and electron transport like bacterial plasma membranes, chromatophores, chloroplasts andmitochondria. CLs are often tightly coupled to proteins involved in oxidative phosphorylation. The firststep in understanding the interaction of CL with proteins is to obtain the pure CL structure, and the struc-ture of mixtures of CL with other lipids. In this work we use a variety of techniques to characterize the fluidphase structure, material properties and thermodynamics of mixtures of dimyristoylphosphatidylcholine(DMPC) with tetramyristoylcardiolipin (TMCL), both with 14-carbon chains, at several mole percentages.X-ray diffuse scattering was used to determine structure, including bilayer thickness and area/lipid, thebending modulus, KC, and SXray, a measure of chain orientational order. Our results reveal that TMCL thick-ens DMPC bilayers at all mole percentages, with a total increase of ∼6˚A in pure TMCL, and increases ALfrom 64˚ A2(DMPC at 35◦C) to 109˚A2(TMCL at 50◦C). KCincreases by ∼50%, indicating that TMCL stiffensDMPC membranes. TMCL also orders DMPC chains by a factor of ∼2 for pure TMCL. Coarse grain moleculardynamics simulations confirm the experimental thickening of 2˚A for 20 mol% TMCL and locate the TMCLheadgroups near the glycerol-carbonyl region of DMPC; i.e., they are sequestered below the DMPC phos-phocholine headgroup. Our results suggest that TMCL plays a role similar to cholesterol in that it thickensand stiffens DMPC membranes, orders chains, and is positioned under the umbrella of the PC headgroup.CL may be necessary for hydrophobic matching to inner mitochondrial membrane proteins. Differentialscanning calorimetry, SXrayand CGMD simulations all suggest that TMCL does not form domains withinthe DMPC bilayers. We also determined the gel phase structure of TMCL, which surprisingly displaysdiffuse X-ray scattering, like a fluid phase lipid. AL= 40.8˚ A2for the ½TMCL gel phase, smaller than theDMPC gel phase with AL= 47.2˚ A2, but similar to ALof DLPE = 41˚ A2, consistent with untilted chains in gelphase TMCL