The quinolone antibiotic premafloxacin crystallizes in at least five solid modifications, including three anhydrous phases (Forms I-III), a hydrate, and a methanolate. The anhydrous phases were studied by optical microscopy, X-ray powder diffraction, HPLC, hot-stage microscopy, dynamic moisture sorption gravimetry, differential scanning calorimetry, thermal gravimetry, and solution and isothermal calorimetry. Dry samples of Form I converted to Form II and ultimately to Form III through a sequence of melts and recrystallizations. Form III was stable to its melting temperature near 200 degrees C. Humidified samples of Form I converted directly to Form III via a moisture-mediated solid-state phase transformation at temperatures as low as 40 degrees C. The calorimetric and solubility data confirmed that Form III was lower in free energy and enthalpy than Form I at room temperature. Our investigation revealed that Form I was not crystallized directly from solution. Rather, Form I was the product of facile solid-state desolvation of the methanol solvate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.