Understanding the single-crystal-to-single-crystal solid-state phase transition of dl-methionineElectronic supplementary information (ESI) available: CIF and CHECKCIF files of the SCXRD measurements of dl-MET at 338 and 420 K. Refinement parameters of the SCXRD measurements. Movie S1, thermal polarisation microscopy video of the solid-state phase transition in several single crystals of dl-MET, snapshots of which are shown in Fig. 7 (MP4). Movie S2, thermal polarisation microscopy video of the s
The solid-state phase transition between the low temperature β and the high temperature α forms of dl -methionine was characterised in detail using DSC, SCXRD, thermal stage polarisation microscopy and solid-state NMR. The thermodynamic transition point of the α ↔ β transition of dl -methionine was...
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Zusammenfassung: | The solid-state phase transition between the low temperature β and the high temperature α forms of
dl
-methionine was characterised in detail using DSC, SCXRD, thermal stage polarisation microscopy and solid-state NMR. The thermodynamic transition point of the α ↔ β transition of
dl
-methionine was determined to fall between 306 and 317 K. The transition is kinetically hindered, as is indicated by a large hysteresis. Moreover, the transition rate during cooling is significantly lower than during heating and there is a large temperature region of coexistence. The kinetic barriers involved are lower for single crystals than for powders.
dl
-Methionine crystals consist of 2D hydrogen-bonded bilayers interconnected by weak Van der Waals interactions. The crystals transform layer-wise, without complete delamination or deterioration, and with a transition front that propagates perpendicular to the layers and a relatively fast transition within one layer. The fast kinetics within the plane of the layers, combined with the faster kinetics in single crystals, indicate that cooperative motion could play a role in this single-crystal-to-single-crystal phase transition.
A multidisciplinary approach to understanding solid-state phase transitions in molecular crystals, using DSC, SCXRD, thermal stage polarisation microscopy and solid-state NMR. |
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ISSN: | 1466-8033 |
DOI: | 10.1039/c6ce02079h |