Guest-dependent conformations of side chains in cholic acid inclusion compounds

Abstract

An attractive role of a side chain of cholic acid is described. X-ray crystallographic studies made clear that the side chain employs guest-dependent conformations (called trans or gauche) in its channel-type inclusion compounds in contrast to that of deoxycholic acid. The flexibility of the side chain originates from a fact that the host molecules arrange in a tail-to-tail fashion to form cyclic hydrogen-bonding network. Guest molecules affect the network, leading to very sensitive infrared spectra to the guests. Molecular graphics study shows that there are two kinds of pockets in the channels. The conformational change is responsible for a change of shape of the pockets composed of the chains.