Method for obtaining structure and interactions from oriented lipid bilayers

Precise calculations are made of the scattering intensity I(q) from an oriented stack of lipid bilayers using a realistic model of fluctuations. The quantities of interest include the bilayer bending modulus K_c, the interbilayer interaction modulus B, and bilayer structure through the form factor F(q_z). It is shown how K_c and B may be obtained from data at large q_z where fluctuations dominate. Good estimates of F(q_z) can be made over wide ranges of q_z by using I(q) in q regions away from the peaks and for q_r≠0 where details of the scattering domains play little role. Rough estimates of domain sizes can also be made from smaller q_z data. Results are presented for data taken on fully hydrated, oriented DOPC bilayers in the L_α phase. These results illustrate the advantages of oriented samples compared to powder samples.