L-Histidinium hemihydrochloride tartrate tartaric acid dihydrate

Abstract

In the title compound, C6H10N3O2+·C4H5O6−·0.5HCl·C4H6O6·2H2O, histidine exists, in the zwitterionic form, as a cation with a protonated amino group, a protonated ring N atom and a deprotonated carboxyl­ic acid group. The tartaric acid mol­ecules exist as a semi-tartrate anion and a neutral tartaric acid mol­ecule. The chloride ion sits on a special position. The structure is stabilized by a number of O—H⋯O, N—H⋯O and O—H⋯Cl hydrogen bonds, in addition to van der Waals interactions. Water mol­ecules are also found to mediate O—H⋯O hydrogen-bonded interactions among amino acid and tartaric acid mol­ecules. In the crystal structure, the histidinium cation exists in an open conformation I, which is sterically the most favourable; the imidazole group is trans to the carboxyl group and gauche to the amino N atom.