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Polymorphism of l ‐Tryptophan
Author(s) -
Al Rahal Okba,
Hughes Colan E.,
Williams P. Andrew,
Logsdail Andrew J.,
DiskinPosner Yael,
Harris Kenneth D. M.
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201908247
Subject(s) - hydrogen bond , polymorphism (computer science) , steric effects , crystallization , crystallography , tryptophan , chemistry , side chain , gas phase , amino acid , stereochemistry , molecule , organic chemistry , polymer , biochemistry , genotype , gene
A new polymorph of l ‐tryptophan was prepared through 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 l 2‐ l 2 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.