We have determined the structure of tubules formed upon Ca2+ addition to vesicles formed from a number of (asymmetric) sodium di-n-alkyl phosphates using X-ray diffraction. The tubules that had been visualized by electron microscopy were previously assumed to be an inverted hexagonal phase. However, we have gained strong evidence that they are anhydrous crystals as can be deduced from the high-angle region of the X-ray diffraction patterns. In these crystals the chains are highly ordered (three-dimensionally) and molecules are packed parallel to each other, not forming a lamellar phase but small packs which form regular two-dimensional lattices. Besides the Ca2+ salts, also the Na+ salts of these surfactants have been studied in water by X-ray diffraction. We find that the crystal lattices of the Na+ salts possess a highly crystalline layered structure at room temperature. Furthermore, they transform to L-alpha phases. For the various di-n-alkyl phosphates these transitions occur at different temperatures, which are lower for the more asymmetric di-n-alkyl phosphates. Finally, information was obtained about interdigitation or tilting of the alkyl chains of the asymmetric phosphates in the crystalline phase based on d spacings.
|Number of pages||3|
|Publication status||Published - Jul-1992|
- HEXAGONAL LIPID PHASES
- DIDODECYLPHOSPHATE VESICLES