Liquid Crystallinity in Lipid-Water Systems

Following a short review of the three most common liquid crystalline structures occurring in lipid-water systems, viz. the lamellar and the two hexagonal structures, attention is focused on the occurrence of cubic structures in such systems and on the various proposals for the arrangement on the molecular level. It is especially stressed that the tacitly assumed structure of globular aggregates, either of the “oil in water” or “water in oil” type, is often difficult to reconcile with the interpretations of the experimentally obtained X-ray diffraction findings. The different structure proposals are discussed, and the connection between cubic phases of model systems and of systems of biological origin proper are stressed. Due to their optical anisotropy the occurrence of cubic phases in lipid-water systems has often been overlooked.