Fig. 2.

Dominant chemical interactions and the generation of intrinsic twist: a A Skeletal structural formula (left) and a ball-and-stick model (right) of C₁₂-β₁₂ in its bolaamphiphile-like configuration. The heads and chains are marked with blue and red respectively. At side A, the head contains two secondary amines, and at B, one primary and one secondary amine. b Hydrophobic interactions drive the assembly of C₁₂-β₁₂ into a ribbon, with hydrogen bonds forming along the x direction—the ribbons’ long axis. The domains within the orange circles are magnified in c, illustrating the hydrogen bonds (cyan lines) on sides A (secondary amines (2°)) and B (one secondary and one primary (1°) amines). This asymmetry leads to asymmetry between the two faces of the ribbon (the lysine are truncated in panels c–f, for clarity). d A top view (in the x-y plane) of two (S) left-handed head groups (side A). Close packing of the two heads directs the methylene group into the largest free volume. Right (orange arrow) zero (red arrow) and left (black arrow) optional twists are illustrated. e The same headgroups illustrated with the VdW radiuses. The chirality (in this case the difference in VdW radiuses) leads to a larger free space on the left (orange arrow) than on the right. f The conformation in e induces right-handed intrinsic twist along the x direction