Structure of a 1:1 complex between L-Asp-L-Phe and L-His-Gly.

Both molecules occur in slightly folded conformations, characterized by phi 2 = -93.7 degrees in L-His-Gly and an unusual phi 2 = 60.2 degrees in L-Asp-L-Phe. The peptide linkage of L-His-Gly displays a substantial deviation from planarity with omega 1 = -163.5 degrees. The crystal packing is arranged in thick hydrophilic layers separated by hydrophobic sheets composed of L-Phe aromatic side chains. There are numerous hydrogen bonds, including an extremely short contact [O...N = 2.532 (6) A] between the ionized L-Asp and L-His side chains.