Acta Cryst. (2003). E59, o955-o958  [ doi:10.1107/S1600536803012686 ]

L-Histidinium hemihydrochloride tartrate tartaric acid dihydrate

K. Rajagopal, R. V. Krishnakumar, M. Subha Nandhini and S. Natarajan

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-HO, N-HO and O-HCl hydrogen bonds, in addition to van der Waals interactions. Water molecules are also found to mediate O-HO 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.

Online 17 June 2003

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