Acta Crystallographica Section B

Structural Science

Volume 55, Part 1 (February 1999)

Acta Cryst. (1999). B55, 104-113 [doi:10.1107/S0108768198010192]

Symmetry, pseudosymmetry and packing disorder in the alcohol solvates of L-leucyl-L-valine

C. H. Görbitz and E. Torgersen

Abstract: The dipeptide L-Leu-L-Val can crystallize as a hydrate in the hexagonal space group P6₅ [Görbitz & Gundersen (1996). Acta Chem. Scand. 50, 537-543], but forms 1:1 solvates when methanol, ethanol and 2-propanol are used as precipitating agents. The structures of these complexes can be divided into hydrophobic and hydrophilic layers. The alcohol molecules are embedded in the hydrophobic layers, but with the hydroxyl groups as crucial parts of the hydrogen-bonding network. L-Leucyl-L-valine-methanol (1/1) crystallizes in the space group P2₁ with Z = 2. L-Leucyl-L-valine-ethanol (1/1) has very special systematic absences, and the structure could not be solved with direct methods. Unraveling the actual build-up of the crystal was an unusual process involving modeling with molecular graphics programs. The solution shows a structure which formally belongs to the space group P2₁, with four dipeptide molecules and four solvent molecules in the asymmetric unit (Z = 8). Additional non-crystallographic symmetry in three dimensions fixes all cell angles, including [beta] , to 90°. L-Leucyl-L-valine-2-propanol (1/1) is structurally closely related to the ethanol solvate, but owing to a rare type of packing disorder the length of the a axis is halved (Z = 4, P2₁2₁2₁). The hydrogen-bonding pattern is still the same as in the ethanol solvate, which means that the hydrogen-bond periodicity along the a axis in the 2-propanol solvate is two unit-cell lengths.

Online 1 February 1999


	Structure factor file (CIF format) (1883.3 kbytes) Contains datablock lvtest

	Structure factor file (CIF format) (593.9 kbytes) Contains datablock lvm2

	Structure factor file (CIF format) (611.8 kbytes) Contains datablock lv2ptest

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