Non-bilayer phases are thought to be of considerable biological relevance. Whenever there is a topological change in the membrane, corresponding to events such as membrane fusion, non-bilayer structures are assumed to be adopted locally. Several complex three-dimensional lyotropic liquid crystal phases are already known, such as the bicontinuous cubic phases, but for many years only a single example was found – a cubic phase of spacegroup Fd3m – of a structure based upon a complex close packing of inverse micelles. A novel lyotropic liquid crystal phase has been discovered and its structure has been solved. The new phase belongs to spacegroup P63/mmc, whose structure is based upon a hexagonal close packing of identical quasi-spherical inverse micelles. [147].
The equilibrium phase behaviour of binary Phospholipid: Diacylglycerol [172] and ternary Phospholipid:Diacylglycerol:Cholesterol mixtures in excess water have been investigated as a function of hydrostatic pressure and temperature using synchrotron x-ray diffraction. By changing hydration and hydrocarbon chain unsaturation, and by varying the mole ratio of the mixtures, the interfacial curvature of the system can be tuned and a plethora of phases are found to be adopted by the various mixtures.
There is a scarcity of knowledge regarding the kinetics and mechanisms of lyotropic phase transitions; such transitions are relevant in understanding fundamental cellular processes such as membrane fusion and fission. Time resolved x-ray diffraction experiments, using pressure as the trigger mechanism have been employed in order to investigate lamellar – non-lamellar transition kinetics in cholesterol/ phospholipid/diacylglycerol model membrane systems and preliminary results are presented.