Method for obtaining structure and interactions from oriented lipid bilayers

Precise calculations are made of the scattering intensity 1(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)not equal0 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-alpha phase. These results illustrate the advantages of oriented samples compared to powder samples.