Nungruethai Yoswathananont, Kazunori Nakano*, Kazuki Sada, and Mikiji Miyata
Department of Material and Life Science, Graduate School of Engineering, Osaka University. 2-1 Yamadaoka, Suita, Osaka. 565-0871, JAPAN and *Nagoya Municipal Industrial Research Institute, Atsuta-ku, Nagoya 456-0058, JAPAN
Tel: +81-6-6879-7405 Fax: +81-6-6879-7404
E-mail: nun@ap.chem.eng.osaka-u.ac.jp
Inclusion compounds of cholic acid (CA) and its derivatives have been systematically investigated. Substitution of a carboxylic acid group by other functional groups at the steroidal side chain gives a wide variety of CA derivatives. For example, CA derivatives with amide and ester side chains are called cholamide (CAM) and methyl cholate (MC), respectively. Their inclusion crystals have been obtained by recrystallization from various organic compounds. It was found that CAM included various alcoholic guests, while CA did only limited alcohols. X-ray diffraction studies made clear that CAM forms a similar bilayer structure to CA, indicating that both the hosts form the robust motif. In the case of MC, only small polar guests such as alcohols and nitriles are found to be included. This result indicates that the number of hydrogen bond donor at the side chains play an important role for the inclusion abilities of bile acids. Moreover, we demonstrate that PCcavity, volume ratio of guest molecules to the host cavities, is a useful parameter for estimating the steric size fit between host cavities and guest molecules as well as prediction of isomerization of the host framework and/or change of the host-guest ratios.