Structure and conformation of linear peptides XIII. Structure of l‐phenylalanyl‐glycyl‐glycine

Abstract
The crystal structure of a tripeptide, L=phenylalanyl-glycyl-glycine (C13H17N3O4), molecular weight = 279.3, has been determined. The crystals are orthorhombic, space group P212121, with a = 5462(1), A, b = 15.285(5), c = 16.056(4), Z = 4, and P (calc) = 1.384 g.cntdot.cm-3. The final R-index is 0.052 for 866 reflections with sin.theta./.lambda. .ltoreq. 0.55 A-1 and I > 1.sigma.. The molecule exists as a zwitterion, with the N-terminus protonated and the C-terminus in an ionized form. Both the peptide units are in the trans configuration and planar, though one of them shows significant deviations from planarity (