Small-angle neutron scattering from multilamellar lipid bilayers: Theory, model, and experiment

Small-angle neutron scattering data obtained from fully hydrated, multilamellar phospholipid bilayers with deuterated acyl chains of different length are presented and analyzed within a paracrystalline theory and a geometric model that permit the bilayer structure to be determined under conditions where the lamellar layers are coupled and fluctuating. This theory provides structural information in the region of the solid-fluid bilayer phase transition without invoking the usual decoupling of the scattering intensity function into form and structure factors. Results are presented as a function of temperature for the lamellar repeat distance, the hydrophobic bilayer thickness, as well as the thickness of the aqueous and polar head group region. In addition to these geometric parameters the analysis permits determination of molecular cross-sectional area, number of interlamellar water molecules, as well as estimates for response functions such as lateral area compressibility. The results, which are compared to experimental data obtained by other techniques, provide indirect information on interlamellar undulation forces, renormalization of bilayer bending rigidity, and unbinding phenomena in multilamellar stacks.