The Dissolution Properties and Physico-chemical Properties of Polymorphic Forms of (α-Bromoisovaleryl) urea

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The dissolution properties and physico-chemical properties of three polymorphic forms of (α-bromoisovaleryl) urea are reported. Form II transformed to form I repidly in water at 37℃, but this transition was delayed by 0.25% gelatin. The solubility of form II was 50% higher than that form I. The transition temperatures of form II to form I, and form III to form I were 70.2℃ and 11.4℃, respectively, as determined by measurements of dissolution rates and solubilities. The enthalpy values, ΔH_<sol> and ΔH_<diss>, of the polymorphs were calculated. The thermodynamic values of form II and form III for the conversion to form I were calculated from these values, i.e. heats of transition (ΔH_<trans>), differences of free energy at 37℃ (ΔG_T), differences of entropy at 37℃ (ΔS_T), and entropy changes at transition temperatures (ΔS_<trans>). The differences of free energy, which may affect the bioavaliabilities of polymorphs, and the ΔS_<trans> values were found to be fairly small.
公益社団法人日本薬学会の論文
1982-05-25