Structure and interaction potentials in solid-supported lipid membranes studied by x-ray reflectivity at varied osmotic pressure

Highly oriented solid-supported lipid membranes in stacks of controlled number $N \simeq 16$ (oligo-membranes) have been prepared by spin-coating using the uncharged lipid model system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The samples have been immersed in aqueous polymer solutions for control of osmotic pressure and have been studied by X-ray reflectivity. The bilayer structure and fluctuations have been determined by modelling the data over the full q-range. Thermal fluctuations are described using the continuous smectic Hamiltonian with the appropriate boundary conditions at the substrate and at the free surface of the stack. The resulting fluctuation amplitudes and the pressure-distance relation are discussed in view of the inter-bilayer potential

Waveguide-enhanced scattering from thin biomolecular films

An X-ray diffraction experiment on multilamellar membranes incorporated into an X-ray waveguide structure is reported. In the device, the lipid bilayers are confined to one side by the silicon substrate and to the other side by an evaporated thin metal cap layer. Shining a highly brilliant X-ray beam onto the system, resonantly enhanced, precisely defined and clearly distinguishable standing-wavefield distributions (modes) are excited. The in-plane structure of the acyl chain ordering is then studied by grazing incidence diffraction under simultaneously excited modes. A significant gain in signal-to-noise ratio as well as enhanced spatial resolution can be obtained with such a setu

X-ray reflectivity of solid-supported, multilamellar membranes

We have investigated the structure of solid-supported, multilamellar membranes by X-ray reflectivity. The density profile is obtained by fitting the full $q$-range to a model using the bilayer Fourier coefficients as fitting parameters. The effect of hydration and the substrate boundary condition are discussed in view of the well-known Landau-Peierls effect and its implications for structure determination. The resulting bilayer density profile agrees remarkably well with previously published data of a molecular dynamics (MD) simulation for 1,2-oleoyl-palmitoyl-sn-glycero-3-phosphocholine (OPPC)

Solid-supported lipid multilayers: Structure factor and fluctuations

We present a theoretical description of the thermal fluctuations in a solid-supported stack of lipid bilayers, for the case of vanishing surface tension $\gamma = 0$ and in the framework of continuous smectic elasticity. The model is successfully used to model the reflectivity profile of a thin (16 bilayers) DMPC sample under applied osmotic pressure and the diffuse scattering from a thick (800 bilayers) stack. We compare our model to previously existing theories

Dewetting of solid-supported multilamellar lipid layers

Thin multilamellar assemblies of neutral lipid bilayers deposited on silicon substrates are shown to be unstable upon hydration. We analyze the stability of these systems taking into account a reduction of the fluctuation-related components of the bilayer interaction potential. The sizes of the patterns observed are consistent with a spinodal dewetting process