Redetermination of l-tryptophan hydro-bromide.

The redetermined crystal structure of the title compound, C(11)H(13)N(2)O(2) (+)·Br(-), is reported. Data collection at 100 K about three crystallographic axes resulted in a crystal structure with significantly higher precision in comparison to the two-dimensional data collected at 176 K [Takigawa et al. [(1966) Bull. Chem. Soc. Jpn, 39, 2369-2378]. The carboxyl group and indole ring system are planar, with maximum deviations of 0.002 (2) and 0.007 (2) Å, respectively, and make an angle of 70.17 (1)° with each other. The mol-ecules are arranged in double layers of carboxyl and amino groups parallel to the ab plane, stabilized by an extensive network of N-H⋯Br and O-H⋯Br hydrogen bonds. The polar layer is held together by a network of three N-H⋯Br hydrogen bonds and one O-H⋯Br hydrogen bond. In the non-polar layer, the indole rings are linked mainly by electrostatic N-H⋯C inter-actions between the polarized bond N-H (H is δ(+)) of the pyrrole unit and two of the ring C atoms (δ(-)) of the benzene rings of adjacent mol-ecules. The distances of these electrostatic inter-actions are 2.57 and 2.68 Å, respectively. C-H⋯O and C-H⋯π inter-actions are also present.