Template-directed supramolecular assembly of a new type of nanoporous peptide-based material

Dipeptides with two hydrophobic residues are known to often form crystals with hydrophobic or hydrophilic channels. One of the exceptions is Leu-Ile, which has been previously shown to crystallize as a nonporous 0.75 hydrate in the hexagonal space group P6(1) with Z' = 4. We have now found that in the presence of D-Leu, a second pseudopolymorph of the dipeptide is formed. The crystal structure has hydrophilic, water-filled channels with an irregular cross section of approximately 5.5 x 3.5 A and constitutes the first example of a crystal packing arrangement where the direction of the channels is perpendicular to the direction of hydrophobic stacking of side chains rather than parallel as in all other porous peptide-based materials.