Pivotal surfaces in inverse hexagonal and cubic phases of phospholipids and glycolipids

Data on the location and dimensions of the pivotal surfaces in inverse hexagonal (HII) and inverse cubic (QII) phases of phospholipids and glycolipids are reviewed. This includes the HII phases of dioleoyl phosphatidylethanolamine, 2:1 mol/mol mixtures of saturated fatty acids with the corresponding diacyl phosphatidylcholine, and glucosyl didodecylglycerol, and also the QII230/G gyroid inverse cubic phases of monooleoylglycerol and glucosyl didodecylglycerol. Data from the inverse cubic phases are largely compatible with those from inverse hexagonal HII-phases. The pivotal plane is located in the hydrophobic region, relatively close to the polar–apolar interface. The area per lipid at the pivotal plane is similar in size to lipid cross-sectional areas found in the fluid lamellar phase (Lα) of lipid bilayers.