Detection of cocrystal formation based on binary phase diagrams using thermal analysis.
OBJECTIVE
Although a number of studies have reported that cocrystals can form by heating a physical mixture of two components, details surrounding heat-induced cocrystal formation remain unclear. Here, we attempted to clarify the thermal behavior of a physical mixture and cocrystal formation in reference to a binary phase diagram.


METHODS
Physical mixtures prepared using an agate mortar were heated at rates of 2, 5, 10, and 30 °C/min using differential scanning calorimetry (DSC). Some mixtures were further analyzed using X-ray DSC and polarization microscopy.


RESULTS
When a physical mixture consisting of two components which was capable of cocrystal formation was heated using DSC, an exothermic peak associated with cocrystal formation was detected immediately after an endothermic peak. In some combinations, several endothermic peaks were detected and associated with metastable eutectic melting, eutectic melting, and cocrystal melting. In contrast, when a physical mixture of two components which is incapable of cocrystal formation was heated using DSC, only a single endothermic peak associated with eutectic melting was detected.


CONCLUSIONS
These experimental observations demonstrated how the thermal events were attributed to phase transitions occurring in a binary mixture and clarified the relationship between exothermic peaks and cocrystal formation.
Analysis and Pharmacokinetics Research Labs, Astellas Pharma Inc, 21 Miyukigaoka, Tsukuba, Ibaraki 350-8585, Japan. hiroyuki.yamashita@astellas.com
Hiroyuki
H
Yamashita
Yutaka
Y
Hirakura
Masamichi
M
Yuda
Toshio
T
Teramura
Katsuhide
K
Terada
D002110:Caffeine / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002164:Camphor / Q000031:analogs & derivatives; D002220:Carbamazepine / Q000737:chemistry; D003460:Crystallization; D006361:Heating; D007213:Indomethacin / Q000737:chemistry; D009536:Niacinamide / Q000737:chemistry; D004364:Pharmaceutical Preparations / Q000737:chemistry*; D044367:Phase Transition; D010894:Piroxicam / Q000737:chemistry; D033362:Powder Diffraction; D020156:Salicylic Acid / Q000737:chemistry; D013806:Theophylline / Q000737:chemistry; D014961:X-Ray Diffraction
D004364:Pharmaceutical Preparations; D010894:Piroxicam; D009536:Niacinamide; D002220:Carbamazepine; D002110:Caffeine; D002164:Camphor; D013806:Theophylline; D020156:Salicylic Acid; D007213:Indomethacin