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Supramolecular gelation as the first stage in Ostwald’s rule.

Andrews, Jessica L. and Pearson, Emma and Yufit, Dmitry S. and Steed, Jonathan W. and Edkins, Katharina (2018) 'Supramolecular gelation as the first stage in Ostwald’s rule.', Crystal growth & design., 18 (12). pp. 7690-7700.

Abstract

Ostwald’s rule of stages describes the observation that a metastable polymorph of a particular compound will crystallise before the thermodynamically stable form under the same conditions. Whilst traditionally applied to crystalline systems, there have been recent examples in which non-crystalline supramolecular assemblies transform according to this rule. In this work we report the highly selective organogelation behaviour of a mono-iodinated 2,4,5-triphenylimidazole (lophine) derivative (I-TPI). The gel emerges as a kinetically trapped intermediate, prior to the crystallisation of a series of increasingly stable methanol solvates. As such, we describe the supramolecular gel as a pre-crystalline phase, representing the first of Ostwald’s stages for this system. Similar behaviour can be observed when the gel is used as a medium for pharmaceutical crystallisation of diatrizoic acid (DTA). In this case, two solid forms are produced, both containing molecules of DTA, I-TPI and methanol in different stoichiometries, and once again crystallising in sequence according to Ostwald’s rule. These results demonstrate that supramolecular gelation may be considered the first stage in the stepwise crystallisation of a gelator, as governed by Ostwald’s rule, and that this behaviour also applies to multi-component systems, facilitating the production of metastable pharmaceutical solid forms.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1021/acs.cgd.8b01539
Publisher statement:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal growth & design copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.cgd.8b01539
Date accepted:08 November 2018
Date deposited:13 November 2018
Date of first online publication:08 November 2018
Date first made open access:08 November 2019

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