Figure 4.

AFM images of helical porphyrin stacks drop-cast from (a) fresh and (b) refrigerated 33 μM MCH solutions of (S)-1. The width of the observed aggregates in micrographs of samples drop-cast from fresh solutions corresponds to the diameter of 1, obtained from molecular models (49 Å), indicating that the helices consist of a single fiber. Micrographs of the refrigerated samples show large aggregates with widths of 25 (green box, B) to 50 nm (red box, A). (c) Cartoon representation of the collapse of a single helical fiber to form a superhelix at high thermodynamic driving forces, which may further assemble to form double and triple helices.