SMALL-ANGLE NEUTRON-SCATTERING FROM MULTILAMELLAR LIPID BILAYERS - THEORY, MODEL, AND EXPERIMENT

Small-angle neutron scattering data obtained from fully hydrated, mult ilamellar phospholipid bilayers with deuterated acyl chains of differe nt length are presented and analyzed within a paracrystalline theory a nd a geometric model that permit the bilayer structure to be determine d under conditions where the lamellar layers are coupled and fluctuati ng. This theory provides structural information in the region of the s olid-fluid bilayer phase transition without invoking the usual decoupl ing of the scattering intensity function into form and structure facto rs. Results are presented as a function of temperature for the lamella r repeat distance, the hydrophobic bilayer thickness, as well as the t hickness of the aqueous and polar head group region. In addition to th ese geometric parameters the analysis permits determination of molecul ar cross-sectional area, number of interlamellar water molecules, as w ell as estimates for response functions such as lateral area compressi bility. The results, which are compared to experimental data obtained by other techniques, provide indirect information on interlamellar und ulation forces, renormalization of bilayer bending rigidity, and unbin ding phenomena in multilamellar stacks.