Self-assembly of helical ribbons

The self assembly of helical ribbons is examined in a variety of multicompo nent enantiomerically pure systems that contain a bile salt or a nonionic d etergent, a phosphatidylcholine or a fatty acid, and a steroid analog of ch olesterol. In almost all systems, two different pitch types of helical ribb ons are observed: high pitch, with a pitch angle of 54 +/- 2 degrees, and l ow pitch, with a pitch angle of 11 +/- 2 degrees. Although the majority of these helices are right-handed, a small proportion of left-handed helices i s observed. Additionally, a third type of helical ribbon, with a pitch angl e in the range 30-47 degrees, is occasionally found. These experimental fin dings suggest that the helical ribbons are crystalline rather than liquid c rystal in nature and also suggest that molecular chirality may not be the d etermining factor in helix formation. The large yields of helices produced will permit a systematic investigation of their individual kinetic evolutio n and their elastic moduli.