Extending SDP Modeling to the Inverted Hexagonal Phase

Abstract

The SDP (Scattering Density Profile) technique was developed to model the X-ray and neutron scattering profiles of lipid bilayers. The lipids were divided up into coarse grained components, with the probability of a component being found at a given point in the bilayer represented by an appropriate function. Most of the lipid component probability densities were modeled as Gaussians, with the hydrocarbon tail region represented by an error function. Building on this powerful method developed by others, we have extended it to the inverted hexagonal phase. As the technique was originally developed for use for lipids with phosphatidylcholine head groups, we have also modified it for use with phosphatidylethanolamine head groups. We have been able to generate models whose Fourier components agree well with the amplitudes acquired from X-ray diffraction. Additionally, the Luzzati interface from the models is close to the experimentally determined electron density peak, as one would expect for these systems.