Crystal structure of a tripeptide,L-alanyl-glycyl-glycine and its relevance to the poly(glycine)-II type of conformation

A tripeptide molecule, L -alanyl-glycyl-glycine, crystallizes in the form of a left-handed helix with (?,ψ) = ?83°, 170°. A pseudohexagonal packing arrangement and interchain hydrogen-bonded interactions are reminiscent of the model for the structure of poly(glycine)-II. Observations of certain intermolecular interactions appear to be relevant to the stereochemical assumptions incorporated in the models proposed for poly(glycine)-II and related polypeptides.