Pearls on a string: a Z' = 7 structure for glycyl-L-valine.

Acta crystallographica. Section C, Crystal structure communications (2007-01-09)
Carl Henrik Görbitz, Silja Agustsdottir, Francesca Bleken

The title peptide, C7H14N2O3, crystallizes with seven independent molecules in the asymmetric unit. All have essentially the same overall conformation, but some flexibility is exhibited by the glycine residue. It appears that the high Z' value, observed only three times before for an organic compound, permits formation of shorter hydrogen bonds in one of the two head-to-tail chains involving the N-terminal amino groups and the C-terminal carboxylate groups than found in a hypothetical model structure of glycyl-L-valine with Z' = 1, and that it furthermore alleviates strain associated with an eclipsed orientation of the amino group.