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A Simultaneous X-ray Diffraction-Differential Scanning Calorimetry Study into the Phase Transitions of Mefenamic Acid

Pang, Y; Buanz, A; Telford, R; Magdysyuk, O; Gaisford, S; Williams, G; (2019) A Simultaneous X-ray Diffraction-Differential Scanning Calorimetry Study into the Phase Transitions of Mefenamic Acid. Journal of Applied Crystallography , 52 (6) pp. 1264-1270. 10.1107/S1600576719012500. Green open access

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Abstract

In this study, the polymorphic transitions of mefenamic acid (MA) were studied by synchrotron X-ray powder diffraction combined with differential scanning calorimetry (XRD-DSC). The initial material was found to be phase-pure form I which, when heated, produces two endotherms that can be observed by DSC at 162.72 and 219.55°C. The former was found to correspond to a solid–solid enantiotropic transition from form I to a mixture of forms II and III. The latter is the melting point of form II. As form I is heated, significantly greater unit-cell expansion is seen in the a direction than in b and c, which can be explained by the stronger intermolecular interactions in the bc plane. Refinements of the reported MA structures against the patterns collected during heating revealed that at 175°C there exists a mixture of forms I, II and III, whereas only forms II and III remain at 205°C. However, reflections are observed at both temperatures which cannot be fitted with the known forms of MA. It is hypothesized that a new form of MA is produced upon heating. The stability of MA after the enantiotropic transition temperature is II > III > I, which differs from the previously reported II > I > III.

Type: Article
Title: A Simultaneous X-ray Diffraction-Differential Scanning Calorimetry Study into the Phase Transitions of Mefenamic Acid
Open access status: An open access version is available from UCL Discovery
DOI: 10.1107/S1600576719012500
Publisher version: https://doi.org/10.1107/S1600576719012500
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: synchrotron X-ray diffraction; differential scanning calorimetry; hyphenated techniques; mefenamic acid; polymorphic transitions; solid–solid transitions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > UCL School of Pharmacy
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > UCL School of Pharmacy > Pharmaceutics
URI: https://discovery.ucl.ac.uk/id/eprint/10082409
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