Two modifications of l‐alanyl‐l‐tyrosyl‐l‐alanine with different solvent mol­ecules in the crystal lattice

The low‐temperature crystal and mol­ecular structure analyses of two modifications of l ‐alanyl‐l ‐tyrosyl‐l ‐alanine with water, C₁₅H₂₁N₃O₅·2.63H₂O (I), at 9 K], and ethanol, C₁₅H₂₁N₃O₅·C₂H₅O (II), at 20 K], solvent mol­ecules in the crystal lattice show that the overall conformations of both modifications of the title tripeptide are practically the same. Moreover, despite the presence of different solvent mol­ecules in the crystal lattice, the specific inter­molecular inter­actions characteristic for individual tripeptide mol­ecules of (I) and (II) are conserved. The crystal packing of the two modifications of Ala‐Tyr‐Ala differ from each other only in the solvent region. The tight arrangements of tripeptide mol­ecules seem to be responsible for similar displacement parameters for all non‐H atoms, despite the different distances from the mol­ecular centre of mass. Comparison of the displacement parameters between the room‐ and low‐temperature structures shows that an average U_eq value decrease of about 80% takes place at 9 K for (I)] and 20 K for (II)] with respect to room temperature.