This study will define the relationship between the molecular structure of lipids, their packing in bilayers, and the tendency of those bilayers to self-organize into lipid tubules as opposed to liposomes. A recent theory of tubule formation, proposed by P. G. de Gennes, suggests that if lipid bilayer molecular packing is like that of a smectic C* liquid crystal, effective charge separation could cause bilayer strips to curl into helices and tubules. The proposed work will test the structural assumption of this theory with regard to the crystallinity of tubules, and the theory's qualitative and quantitative predictions. Techniques to be used on known and potential tubule forming lipid systems include a) phase contrast and fluorescence microscopy to study morphology, helicity, and routes to tubule formation, and b) vibrational spectroscopy to determine packing, order, hydration, and orientation of molecules within tubules. The effects of ionic strength on formation, morphology, and stabilities of tubules and helices will test predictions from the theory. Data will be correlated with X-ray studies to develop a three-dimensional model of bilayer structure in tubules. This study continues one begun earlier by an expedited award. Lipids like those which are the principal structural elements of cell membranes spontaneously organize into membrane-like bilayers. The investigator was a co-discoverer of a new structure, lipid tubules, which can form spontaneously out of certain lipid bilayers. The tubules, only a few molecular layers thick, have a soda-straw structure. Study of the phenomenon should significantly advance our understanding of structural forces inside bilayers, including membrane structures in living cells. This work occurs at the interface between physical chemistry, biology, and engineering, though engineering applications of tubules are still speculative at this point. Lipid tubules have a unique combination of physical attributes: they are rigid and straight like crystals and graphite fibers, but are hollow, with extremely thin walls; they are also biocompatible like liposomes. There is no other known method to manufacture structures of their size, shape, and precision. It has already been demonstrated that they can be coated with metals. Potential applications are widespread, from obscuration, (by their interactions with electromagnetic radiation) through repair of demyelinated nerves to structural elements in ceramic composites.
