Micrometer twisted ribbon

If one leaves water and gold to organic solvents as a medium, the situation will change. Biopolymers and synthetic block polymers form ill-defined clusters, nanometer helices are replaced by micrometer twisted ribbons, and sheets immediately crystallize. In the case of micellar assemblies bilayer sheets prevail, showing a tendency to roll up and form bulky scrolls. 

The above gels of compound 25a and b do not form helical fibers that can be observed by SEM. However, several chiral gelators do selectively self-assemble into helicoidal fibers. For example, Escuder et al. have reported that (S,S)-26 gelated several organic solvents. SEM of the gel formed in benzene showed the presence of isolated right-handed twisted ribbons of several micrometers of... 

Figure 15. Schematic illustration of a chiral bilayer (A), with the molecules tilted with respect to the local layer normal. (The arrows indicate the direction of the molecular tilt, projected into the layer plane.) The favored twist between the chiral molecules leads the whole membrane to curve into (B), a wound ribbon, then fuse into (C), a cylindrical tube. The observed CD spectra come from the chiral molecular packing common to all three figures, not from the micrometer-scale helical structure in (B) and (C). Reproduced from ref. 171 (Schnur et al.. Science 1994,264,945) with permission of the American Association for the Advancement of Science.

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