Coexistence of both histidine tautomers in the solid state and stabilisation of the unfavourable Nδ–H form by intramolecular hydrogen bonding: crystalline l-His-Gly hemihydrate

The crystal structure of L-His-Gly hemihydrate contains two independent peptide molecules which exhibit different histidine tautomers; the less favourable N(δ)–H form is stabilized by an intramolecular Nδ(n)–H···O(n + 1) hydrogen bond facilitated by a suitable molecular conformation.