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 modi cations of L-alanyl-L-tyrosyl-l-alanine with water, C(15)H(21)N(3)O(5)(.)2.63H(2)O [(I), at 9 K], and ethanol, (C15H21N3O5C2H5O)-C-. [(II), at 20 K], solvent molecules in the crystal lattice show that the overall conformations of both modi cations 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 modi cations 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.