Single-crystal investigation of L-tryptophan with Z′ = 16

Abstract

A complex, disorder-free structure in the space group P1 has been established for L-tryptophan, for which no crystal structure has previously been available. The 16 molecules in the asymmetric unit can be divided into two groups of eight; one where the side chains have gauche orientations and one with trans orientations. Molecules within each group have almost identical molecular geometries. The unit-cell parameters mimic a hexagonal cell, but deviations from 90° for the cell angles α = 84.421 (4) and β = 87.694 (4)° give a small tilt that rules out hexagonal symmetry. The hydrogen-bonding pattern resembles that found in the crystal structure of the racemic structure of DL-tryptophan, but a lower density combined with longer hydrogen bonds and inter-aromatic interactions show that the enantiomeric structure is less efficiently packed.