Self-Assembling Organic Nanotubes from Enantiopure Cyclo-N,N′-Linked Oligoureas: Design, Synthesis, and Crystal Structure

Square‐shaped hydrogen‐bonded polar nanotubes are formed when the C4‐symmetrical all‐S cyclotetraurea bearing side chains of alanine self‐assembles in the solid state (see picture). The four urea fragments in the macrocyle present an all‐trans planar conformation with an unidirectional alignment of all the carbonyl groups. The anisotropy is further maintained in the crystal as neighboring tubes are all arranged in the same direction.