Lyotropic liquid crystals of 1-, 2-, or 3-dimensional periodicity spontaneously assemble when lipids are mixed with solvent under various conditions of temperature, pressure and hydration. Although biomembranes are generally based on the fluid lamellar phase, there is increasing evidence that curved membrane structures such as the inverse cubic phases may be present in cell membranes, and/or may facilitate cellular processes such as endo- and exocytosis, and fusion.
We have studied the effect of chain branching on the phase behaviour of a series of synthetic β-D-glucosides derived from Guerbet alcohols, whose total hydrocarbon chain length ranged from C8 to C24. A wide range of liquid-crystalline phases was observed, with the C16 Guerbet glucoside (i.e. b-Glc-C10C6) forming an Ia3d cubic phase of space group in excess aqueous solution, which is very unusual behaviour.
Monoacylglycerols have proved to be invaluable for in-cubo crystallization of membrane proteins. We have studied the effect of hydrostatic pressure on the La – Ia3d cubic transition of monolinolein at a range of hydration. Pressure is found to stabilize the lamellar phase over the cubic phase, and at fixed pressure, increasing the water content causes the coexistence region to move to lower temperature.
We have previously shown that by addition of weakly-polar amphiphiles such as diacylglycerols to phospholipids, one can tune the interfacial curvature to be strongly inverse, leading to the formation of a discontinuous cubic phase of spacegroup Fd3m, with a structure based upon a complex close packing of inverse micelles. We have investigated the effect of hydrostatic pressure on the structure and stability of this phase, and have discovered a number of novel effects. We also discovered a lyotropic phase of space group P63/mmc, whose structure is based upon a 3-D hexagonal packing of quasi-spherical inverse micelles, in a hydrated mixture of dioleoylphosphatidylcholine, dioleoylglycerol, and cholesterol.