Specific complexation of ursodeoxycholic acid with guest compounds induced by co-grinding

Ursodeoxycholic acid (UDCA) was ground with a variety of organic compounds using a vibrational mill. Only when either phenanthrene or anthrone was used did powder X-ray diffraction and thermal analysis data indicate that a specific interaction developed with UDCA in the ground mixture. From fluorescence and infrared spectroscopic data, inclusion complex formation with UDCA was suggested during the co-grinding process. The stoichiometry of the inclusion compounds of UDCA-phenanthrene/anthrone was evaluated as a 1:1 molar ratio. Interestingly, no complexes could be obtained by the coprecipitation method, which was conventionally applied for the preparation of inclusion complex of bile acids. Consequently, except when the co-grinding process was performed with either phenanthrene or anthrone, UDCA did not form an inclusion complex.