L-Leu-L-val center dot 3/4H(2)O: A hexagonal crystal structure with Z=24

L-Leu-L-Val crystallizes in the hexagonal space group P6(2) with four peptide molecules and three solvent water molecules in the asymmetric unit. It is the first linear peptide to have Z=24. The structure was solved with direct methods and refined to a final R-factor 0.048 and R(W)=0.039 using 5311 unique reflections (I>3.0 sigma I) collected at 120 K. Cell parameters: a=29.212(16), c=11.723(9) Angstrom. The four dipeptides have different conformations and form a complex three-dimensional hydrogen-bond network in the crystal with a unique packing pattern unlike all those found for other structures of linear peptides. The most salient feature is the aggregation of side chains into two different types of hydrophobic columns parallel to the hexagonal axis.