An inverse face-centered cubic phase formed by diacylglycerol-phosphatidylcholine mixtures.

Fully hydrated unsaturated diacylglycerol-phosphatidylcholine mixtures are found to adopt an inverse face-centered cubic phase, of crystallographic cubic aspect 15. The same behavior is observed for either the 1,2- or 1,3-isomer of the diacylglycerol. This Q15 cubic phase, of probable space group Fd3m (Q227), occurs between an inverse hexagonal (HII) phase and an inverse micellar (L2) solution, with increasing diacylglycerol concentration, which implies that the mean curvature of the interface is more negative than that of the HII phase. This behavior is quite different from that of the more usual bicontinuous inverse cubic phases Pn3m (Q224), Im3m (Q229), and Ia3d (Q230), which normally occur between the lamellar L alpha and the HII phases. One possible structure for the Fd3m cubic phase has recently been proposed (Mariani, P., Luzzati, V., & Delacroix, H. (1988) J. Mol. Biol. 204, 165-189), consisting of tetrahedrally arranged clusters of inverse micelles surrounded by a continuous cage of tetrahedrally connected water/lipid (inverse) channels.