چکیده (انگلیسی):

The purpose of this study was to elucidate the formation of crystal hydrates of niclosamide and to delineate the effect of relative humidity on the crystal forms obtained from acetone and ethyl acetate. Recrystallization of niclosamide was per-formed in the presence and absence of moisture. Two hy-drates and their corresponding anhydrates were isolated. The hydrates obtained by the process of recrystallization from acetone (Form I) and that obtained from ethyl acetate (Form II) were classified based on differences in their dehydration profile, crystal structure, shape, and morphology. Crystals obtained in the absence of moisture were unstable, and when exposed to the laboratory atmosphere transformed to their corresponding hydrates. Differential scanning calo-rimetry thermograms indicate that Form I changes to an an-hydrate at temperatures below 100°C, while Form II dehy-drates in a stepwise manner above 140°C. This finding was further confirmed by thermogravimetric analysis. Dehydra-tion of Form II was accompanied by a loss of structural in-tegrity, demonstrating that water molecules play an impor-tant role in maintaining its crystal structure. Form I, Form II, and the anhydrate of Form II showed no significant moisture sorption over the entire range of relative humidity. Although the anhydrate of Form I did not show any moisture uptake at low humidity, it converted to the monohydrate at elevated relative humidity (>95%). All forms could be interconverted depending on the solvent and humidity conditions.