Physicochemical Studies of Medicinal Drug Polymorphism. I. Structural Studies of Bromodiethylacetylurea by Thermal and X-Ray Crystal Analyses

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Three crystalline forms of bromodiethylacetylurea (named α, β and γ) were characrerized by thermal analyses. The α→β→γ structural conversion was accompanied with endothermic change : the transition temperature and enthalpy change were 70.7-83.0℃, ΔH=0.71 (5) kcal/mol for the α→β transition and 83.0-96.5℃, ΔH=0.65 (4) kcal/mol for the β→γ transition, respectively. The γ-type crystal emerged only between 90 and 110℃. X-Ray analyses were performed for α- and β-type crystals. They have two molecules in the asymmetric unit (molecules A and B for α-type, molecules C and D for β-type). Conformational differences among these molecules were not significant, although the hydrogen bond networks characteristic of the two crystal types may be significant in relation to the bioavailabilities of this drug.

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