Polymorphism of L-Tryptophan: data

A new polymorph of L‑tryptophan has been prepared by crystallization from the gas phase, with structure determination carried out directly from powder XRD data augmented by periodic DFT-D calculations. The new polymorph (denoted β) and the previously reported polymorph (denoted α) are both based on alternating hydrophilic and hydrophobic layers, but with substantially different hydrogen-bonding arrangements. The β polymorph exhibits the energetically favourable L2-L2 hydrogen-bonding arrangement, which is unprecedented for amino acids with aromatic side-chains; the specific molecular conformations adopted in the β polymorph facilitate this hydrogen-bonding scheme while avoiding steric conflict of the side-chains.

Data presented is the powder XRD on the new polymorph over a range of temperatures, NMR data on the new polymorph and results from DFT-D calculations of the stabilities of the two forms.

Researhc results based upon these data are published at https://doi.org/10.1002/anie.201908247