Abstract
Glycine is the simplest and most polymorphic amino acid, with five phases having been structurally characterized at atmospheric or high pressure. A sixth form, the elusive ζ phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure ∊ phase transformed to the γ form on decompression. However, its structure has remained unsolved. We now report the structure of the ζ phase, which was trapped at 100 K enabling neutron powder diffraction data to be obtained. The structure was solved using the results of a crystal structure prediction procedure based on fullyab initioenergy calculations combined with a genetic algorithm for searching phase space. We show that the fate of ζ-glycine depends on its thermal history: although at room temperature it transforms back to the γ phase, warming the sample from 100 K to room temperature yielded β-glycine, the least stable of the known ambient-pressure polymorphs.
Funder
Science and Technology Facilities Council/ISIS
Engineering and Physical Sciences Research Council
SISSA, CINECA and PRACE
H2020 European Research Council
Publisher
International Union of Crystallography (IUCr)
Subject
Condensed Matter Physics,General Materials Science,Biochemistry,General Chemistry
Cited by
23 articles.
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