A wide range of applications has been suggested for peptide-based nanotubes, which first attracted considerable interest as model systems for membrane channels and pores. The intriguing and unprecedented observation of nanotube formation by supramolecular self-assembly of the four dipeptides L-Leu-L-Leu, L-Leu-L-Phe, L-Phe-L-Leu and L-Phe-L-Phe is described here. These simple compounds crystallize with hydrogen-bonded head-to-tail chains in the shape of helices with four to six peptide molecules per turn. The resulting structures have chiral hydrophilic channels with a van der Waals' diameter up to 10 A.

Alzheimer's beta-amyloid diphenylalanine motif has previously been shown to self-assemble into discrete and extraordinary stiff nanotubes; these nanotubes were initially thought to be distinct from the single crystal structure of diphenylalanine, but it is now shown that the X-ray powder diffraction pattern of the nanotubes is identical to the simulated pattern for the single crystal structure, affording a new foundation for understanding and rationalizing the properties of this remarkable organic material.

In the last few years dipeptides with two hydrophobic residues (hydrophobic dipeptides) have emerged as an unexpected source of stable microporous organic materials. Supramolecular self-assembly of the rather small building blocks is dictated by stringent demands on the hydrogen-bond formation by the peptide main chains and the aggregation of hydrophobic entities in the side chains. A systematic survey of structures derived from single-crystal X-ray diffraction studies has revealed the existence of two large classes of structures, differing in the dimensionality of the hydrogen-bonding patterns in the crystals and the nature of the channels. The present review summarizes the structural properties of the microporous dipeptides and discusses their potential applications.

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