Structure of lipid bilayers

The quantitative experimental uncertainty in the structure of fully hydrate d, biologically relevant, fluid (L-alpha) phase lipid bilayers has been too large to provide a firm base for applications or for comparison with simul ations. Many structural methods are reviewed including modern liquid crysta llography of lipid bilayers that deals with the fully developed undulation fluctuations that occur in the L-alpha phase. These fluctuations degrade th e higher order diffraction data in a way that, if unrecognized, leads to er roneous conclusions regarding bilayer structure. Diffraction measurements a t high instrumental resolution provide a measure of these fluctuations. In addition to providing better structural determination, this opens a new win dow on interactions between bilayers, so the experimental determination of interbilayer interaction parameters is reviewed briefly. We introduce a new structural correction based on fluctuations that has not been included in any previous studies. Updated measurements, such as for the area compressib ility modulus, are used to provide adjustments to many of the literature va lues of structural quantities. Since the gel (L-beta') phase is valuable as a stepping stone for obtaining fluid phase results, a brief review is give n of the lower temperature phases. The uncertainty in structural results fo r lipid bilayers is being reduced and best current values are provided for bilayers of five lipids. (C) 2000 Elsevier Science B.V. All rights reserved .