Energetic aspects of diclofenac acid in crystal modifications and in solutions—mechanism of solvation, partitioning and distribution

✍ Scribed by German L. Perlovich; Artem O. Surov; Lars Kr. Hansen; Annette Bauer-Brandl

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 265 KB
• Volume: 96
• Category: Article
• ISSN: 0022-3549
• DOI: 10.1002/jps.20936

✦ Synopsis

Temperature dependency of saturated vapor pressure and heat capacity for the diclofenac acid (Form II) were measured and thermodynamic functions of sublimation calculated (DG 298 sub ¼ 49.3 kJ Á mol À1 ; DH 298 sub ¼ 115.6 AE 1.3 kJ Á mol À1 ; DS 298 sub

). Crystal polymorphic Forms I (P2 1 /c) and II (C2/c) of diclofenac acid have been prepared and characterized by X-ray diffraction experiments. The difference between crystal lattice energies of the two forms were obtained by solution calorimetry: DDH sol (I ! II) ¼ 1.6 AE 0.4 kJ Á mol À1 . Temperature dependencies of the solubility in buffers with pH 2.0 and 7.4, n-octanol and n-hexane were measured. The thermodynamic functions of solubility, solvation, and transfer processes were deduced. Specific and non-specific solvation terms were distinguished using the transfer from the ''inert'' n-hexane to the other solvents. The transfer of diclofenac acid molecules from the buffers to n-octanol (partitioning and distribution) is an entropy driven process. ß 2007