The general design criteria and synthesis of four new peptide-based solid-state tubular array structures are described. Peptide nanotubes, which are extended tubular β-sheet-like structures, are constructed by the self-assembly of flat, ring-shaped peptide subunits made up of alternating d- and l-amino acid residues. Peptide self-assembly is directed by the formation of an extensive network of intersubunit hydrogen bonds. In the crystal structures, nanotubes are stabilized by intertubular hydrophobic packing interactions. Peptide nanotubes exhibit good mechanical and thermal stabilities in water and are stable for long periods of times in most common organic solvents including DMF and DMSO. The remarkable stability of peptide nanotubes can be attributed to the highly cooperative nature of the noncovalent interactions throughout the crystal lattice. Nanotube structures were characterized by cryoelectron microscopy, electron diffraction, Fourier-transform infrared spectroscopy, and crystal structure modelin...