AN FD3M LYOTROPIC CUBIC PHASE IN A BINARY GLYCOLIPID WATER SYSTEM/

The lyotropic cubic phase of space group Fd3m has been observed for th e first time in a purely binary amphiphile/water system, consisting of fully-hydrated synthetic 1,2-di-O-alkyl-3-O-(alpha-or beta-D-xylopyra nosyl)-sn-glycerols. These glycolipids are saturated analogues of natu rally-occurring membrane lipids, with the polar headgroup chemically m odified to render it less hydrophilic. A number of chain lengths of th ese alpha- and beta-anomers in the range from C12 to C19 have been stu died, and we find that the Fd3m cubic phase is suppressed when the cha in length is reduced to C14 or shorter. The relative intensities of th e X-ray Bragg peaks are similar to those of previously observed Fd3m p hases, which have been shown to have an inverse micellar structure, im plying that the glycolipid Fd3m cubic phase described here also consis ts of the same complex packing of inverse Micelles.