Crystal structures of Z–Gly–Aib–O−·0.5Ca2+·H2O and Z–Gly–Aib–OH

Abstract

Both deprotonated and neutral achiral title dipeptides assume similar structures of two conformations, which are related by a unit-cell inversion centre. Two molecules of both conformations of the metal-free neutral dipeptide are linked by two hydrogen bonds, while two molecules of both conformations of the ionized form coordinate a calcium ion in calcium(II) bis[2-(2-{[(benzyloxy)carbonyl]amino}acetamido)-2-methylpropanoate] monohydrate, 0.5Ca2+·C14H17N2O5 −·0.5H2O, which lies on an inversion centre and forms a distorted octahedral complex with the metal ion. These CaII complexes are connected in the crystal via hydrogen bonds in the b- and c-axis directions, whereas in the a-axis direction, they stack via apolar contacts. In the metal-free crystal, namely 2-(2-{[(benzyloxy)carbonyl]amino}acetamido)-2-methylpropanoic acid, C14H18N2O5, molecules are hydrogen bonded in the a- and c-axis directions, and stack in the b–axis direction via apolar contacts.