L-Isoleucyl-L-serine 0.33-hydrate, L-phenylalanyl-L-serine and L-methionyl-L-serine 0.34-hydrate.

The structures of the title dipeptides, C9H18N2O4.0.33H2O, C12H16N2O4 and C8H16N2O4S.0.34H2O, complete a series of investigations focused on L-Xaa-L-serine peptides, where Xaa is a hydrophobic residue. All three structures are divided into hydrophilic and hydrophobic layers. The hydrophilic layers are thin for L-phenylalanyl-L-serine, rendered possible by an unusual peptide conformation, and thick for L-isoleucyl-L-serine and L-methionyl-L-serine, which include cocrystallized water molecules on the twofold axes.