Conformation and structure of bis­(glycyl-L-aspartic acid) oxalate 0.4-hydrate

The title bis­(glycyl-L-aspartic acid) oxalate complex {systematic name: bis­[2-(2-ammonio­acetamido)butane­dioic acid] oxalate 0.4-hydrate}, 2C₆H₁₁N₂O₅⁺·C₂O₄²⁻·4H₂O, crystallizes in a triclinic space group with the planar peptide unit in a trans conformation. The asymmetric unit consists of two glycyl-L-aspartic acid mol­ecules with positively charged amino groups and neutral carboxyl groups, and an oxalate dianion. The twist around the C—Cα bond indicates that both the peptide mol­ecules adopt extended conformations, while the twist around the N—Cα bond shows that one has a folded and the other a semi-extended state. The present complex can be described as an inclusion compound with the dipeptide mol­ecule as the host and the oxalate anion as the guest. The usual head-to-tail sequence of aggregation is not observed in this complex, as is also the case with the glycyl-L-aspartic acid dihydrate mol­ecule. The study of aggregation and inter­action patterns in binary systems is the first step towards understanding more complex phenomena. This further leads to results that are of general interest in bimolecular aggregation.