Structural information from multilamellar liposomes at full hydration:: Full q-range fitting with high quality x-ray data

We present a method for analyzing small angle x-ray scattering data on multilamellar phospholipid bilayer systems at full hydration. The method utilizes a modified Caille theory structure factor in combination with a Gaussian model representation of the electron density profile such that It accounts also for the diffuse scattering between Bragg peaks. Thus the method can retrieve structural information even if only a few orders of diffraction are observed. We further introduce a procedure to derive fundamental parameters. such as area per lipid, membrane thickness, and number of water molecules per lipid, directly from the electron density profile without the need of additional volumetric measurements. The theoretical apparatus is applied to experimental data on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine liposome preparations.