  We present a novel 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 new 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.
