Rheology of Ultraswollen Bicontinuous Lipidic Cubic Phases.

Rheological studies of liquid crystalline systems based on monopalmitolein and 5 or 8% of 1,2 distearoylphosphatidylglycerol are reported. Such cubic phases have been shown to possess unusually large water channels because of their ability of accommodating up to 80 wt % of water, a feature that renders these systems suitable for crystallizing membrane proteins with large extracellular domains. Their mechanical properties are supposed to be substantially different from those of traditional cubic phases. Rheological measurements were carried out on cubic phases of both Pn3m and Ia3d symmetries. It was verified that these ultraswollen cubic phases are less rigid than the normal cubic phases, with the Pn3m being softer that the Ia3d ones. Furthermore, for the Pn3m case, the longest relaxation time is shown to decrease logarithmically with increasing surface area per unit volume, proving the critical role of the density of interfaces in establishing the macroscopic viscoelastic properties of the bicontinuous cubic phases. [ABSTRACT FROM AUTHOR]