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

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 ? phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure ? phase transformed to the ? form on decompression. However, its structure has remained unsolved. We now report the structure of the ? 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 ?-glycine depends on its thermal history: although at room temperature it transforms back to the ? phase, warming the sample from 100?K to room temperature yielded ?-glycine, the least stable of the known ambient-pressure polymorphs.

SUBMITTER: Bull CL 

PROVIDER: S-EPMC5619850 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature