Bile acid derivatives inclusion compounds

Extensive systematic work over the past decade has established that bile acid derivatives have the ability to form crystalline inclusion compounds with various organic substances [1], The accumulated data tell us two notable things. One is that their inclusion behavior varies from one case to another. The other is that their crystals consist of host-inherent or guest-dependent assemblies with different molecular arrangements and hydrogen-bonding networks. These facts force us to direct our attention to separation engineering accompanied by crystallization and... 

In contrast to DCA, there were no detailed reports on the inclusion abilities of its related compounds. There are only a few descriptions of apocholic acid [5] (ACA, see later, in Figure 5) with a very similar bilayer structure to DCA. In 1986, Miyata and Miki et al. discovered lots of inclusion compounds of CA with the similar bilayer structures [6], On the other hand, it took a long time to determine the hexagonal crystal structures of CDCA inclusion compounds, and LCA exhibits no inclusion abilities as yet. In this way, it was confirmed that an increase or decrease of only one atom brings about completely different inclusion behaviors and crystal structures. This fascinating fact has given us adequate and continuous motivation to investigate the inclusion compounds of bile acid derivatives. 

We have researched the inclusion abilities of bile acid derivatives by using more than one hundred organic compounds as guest candidates. The inclusion phenomena vary from one case to another, indicating that subtle changes in molecular structures induce alteration in their molecular assemblies. In fact, X-ray diffraction studies prove that the steroidal hosts form various assemblies such as monolayers, bilayers, helical tubes, and so on, as shown in Figure 2. Therefore, systematic investigation of inclusion crystals of bile acid derivatives is expected to reveal a relationship between their molecular structures, assemblies and inclusion behavior. 

INCLUSION COMPOUNDS OF BILE ACID DERIVATIVES 3.1 Acid Derivatives... 

Table 3 Formation of the inclusion compounds of bile acid derivatives with their host-guest ratios. 

Inclusion crystals of bile acid derivatives can be obtained by direct recrystallization of host and liquid guests. When the guests do not have enough solubility for a host, the third component or the solvent were used. In the case of solid guests, solvents were used as well. The solvent should not form inclusion compounds with the host, and should not interact with host and guest compounds. 

Porous host substructures with parallel channels are typical of many inclusion compounds formed by bile acids and their derivatives (see Deoxycholic, Cholic, and Apocholic Acids). In this class of compounds, host molecules are always optically active, and the resulting host networks are chiral. The best known among them are inclusion compounds of deoxycholic acid (DCA) (also known as choleic acidsj. With most guests. DCA molecules assemble via hydrogen bonds into a coiTugated... 

INCLUSION COMPOUNDS OF BILE ACIDS AND THEIR DERIVATIVES... 

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