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 zeta phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure "phase transformed to the gamma form on decompression. However, its structure has remained unsolved. We now report the structure of the zeta 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 fully ab initio energy calculations combined with a genetic algorithm for searching phase space. We show that the fate of zeta-glycine depends on its thermal history: although at room temperature it transforms back to the gamma phase, warming the sample from 100 K to room temperature yielded beta-glycine, the least stable of the known ambient-pressure polymorphs.

zeta-Glycine: insight into the mechanism of a polymorphic phase transition / Bull, Craig L.; Flowitt-Hill, Giles; De Gironcoli, Stefano; Küçükbenli, Emine; Parsons, Simon; Pham, Cong Huy; Playford, Helen Y.; Tucker, Matthew G.. - In: IUCRJ. - ISSN 2052-2525. - 4:Pt 5(2017), pp. 569-574. [10.1107/S205225251701096X]

zeta-Glycine: insight into the mechanism of a polymorphic phase transition

De Gironcoli, Stefano;Küçükbenli, Emine;Pham, Cong Huy;
2017-01-01

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 zeta phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure "phase transformed to the gamma form on decompression. However, its structure has remained unsolved. We now report the structure of the zeta 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 fully ab initio energy calculations combined with a genetic algorithm for searching phase space. We show that the fate of zeta-glycine depends on its thermal history: although at room temperature it transforms back to the gamma phase, warming the sample from 100 K to room temperature yielded beta-glycine, the least stable of the known ambient-pressure polymorphs.
2017
4
Pt 5
569
574
http://journals.iucr.org/m/issues/2017/05/00/lq5008/index.html
Bull, Craig L.; Flowitt-Hill, Giles; De Gironcoli, Stefano; Küçükbenli, Emine; Parsons, Simon; Pham, Cong Huy; Playford, Helen Y.; Tucker, Matthew G.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/68929
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