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Issue 20, 2020
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Solution and calorimetric thermodynamic study of a new 1 : 1 sulfamethazine–3-methylsalicylic acid co-crystal

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Abstract

A new 1 : 1 co-crystal of sulfamethazine (API, SMT) and 3-methylsalicylic acid (coformer, 3mSA) has been synthesized and its crystal structure solved by single crystal X-ray diffraction (XRD). The co-crystal has been thoroughly characterized by powder XRD, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The pure co-crystal could be synthesized by solvent drop grinding, cooling crystallization and slurry conversion co-crystallization. Ternary phase diagrams have been constructed in methanol and acetonitrile at 30 °C. The co-crystal exhibits incongruent dissolution in both solvents. The thermodynamics of co-crystal formation have been estimated from solubility data and calorimetric data, respectively, showing that formation of the SMT–3mSA co-crystal from its solid components is spontaneous and entropy-driven. The co-crystal formation is associated with a 5% increase in molecular volume. A relationship between the size of the region where the co-crystal is the most stable solid phase and the relative solubility of the co-crystal components has been uncovered. The co-crystal region becomes smaller as the solubility ratio increases.

Graphical abstract: Solution and calorimetric thermodynamic study of a new 1 : 1 sulfamethazine–3-methylsalicylic acid co-crystal

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Article information


Submitted
02 Apr 2020
Accepted
03 May 2020
First published
04 May 2020

CrystEngComm, 2020,22, 3463-3473
Article type
Paper

Solution and calorimetric thermodynamic study of a new 1 : 1 sulfamethazine–3-methylsalicylic acid co-crystal

D. Ahuja, M. Svärd, M. Lusi and Å. C. Rasmuson, CrystEngComm, 2020, 22, 3463
DOI: 10.1039/D0CE00498G

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