Stabilization of a bicontinuous cubic phase from polymerizable monoacylglycerol and diacylglycerol

Technological applications of lipids may be possible through stabilization of various liquid-crystalline phases. One important approach to stabilized self-assembling materials utilizes polymerization of liquid-crystalline phases composed of reactive lipids. Polymerization of lipids has been utilized to modify the chemical and physical properties of lamellar assemblies (e.g., lipid monolayers, multilayers, and bilayer vesicles). In addition, polymerization of the lipid region of three-dimensional nonlamellar lipid-phase structures has recently been reported, including the reversed bicontinuous cubic (Q II ) phase, belonging to the space group Pn3m and the reversed hexagonal (H II ) phase. Here we show that an easily prepared polymerizable monoacylglycerol combined in a 9/1 molar ratio with the corresponding polymerizable 1,2-diacylglycerol forms nonlamellar phases upon hydration at room temperature. Phase investigation using cross-polarized light, 2 H NMR spectroscopy, and X-ray diffraction showed that the lipid mixture formed a well-defined cubic phase from at least 5 to 45°C. The X-ray diffraction pattern corresponded to a cubic phase with Ia3d symmetry and a unit cell size of 131 A at 25 °C. Polymerization to high conversion of this cubic phase was accomplished via the thermal decomposition of H 2 O 2 . The resultant polymers dissolved in organic solvent, indicating they were not cross-linked. The visual clear character, cross-polarized light test, and X-ray diffraction showed that isotropic architecture was maintained up to at least 70 °C after sample polymerization. The diffusion coefficient of water (23°C) within the polymerized cubic phase, determined by pulsed field gradient NMR spectroscopy, was 1.2 0.2 x 10 -10 m 2 /s, a value consistent with retention of the cubic phase during and after the polymerization. The biocompatible and mesoporous nature of the polymerized cubic phase suggests it could be used as the host for incorporation of synthetic or biological molecules in a manner that has already proven especially useful in microporous solids.