A MODEL FOR CRYSTALLINE ORDER WITHIN HELICAL AND TUBULAR STRUCTURES OF CHIRAL BILAYERS

Some theories have suggested that packing interactions like those found in cholesteric liquid crystals may stabilize the cylindrical curvature of a chiral lipid bilayer. A crystalline bilayer modeled after this interaction is indicated to involve highly anisotropic packing interactions, in which the curvature-stabilizing interaction occurs along a single crystallographic direction. This corresponds to a principal packing interaction that is directed along a helical curve through the cylindrical bilayer, and suggests that the bilayer may be modeled as a parallel array of helical chains of molecules assembled side-by-side to produce a contiguous bilayer with cylindrical curvature. The stability of long-range order in such a quasi-one-dimensional system is, however, subject to serious limitations, which becomes critical to the formation of a single crystal bilayer composed of helical chains. The significance of the packing interactions transverse to the helical chains becomes paramount to the relative stability of this crystalline state for a cylindrical bilayer, and may therefore be a discriminating factor in the relatively rare appearance of chiral lipid bilayers in helical and tubular forms.