Flexible host frameworks with diverse cavities in inclusion crystals of bile acids and their derivatives

Abstract

We have systematically investigated structures and properties of inclusion crystals of bile acids and their derivatives. These steroidal compounds form diverse host frameworks having zero-, one- and two-dimensional cavities, causing various inclusion behaviors towards many organic compounds. The diverse host frameworks exhibit the following guest-dependent flexibility. First, the frameworks mainly depend on the included guests in size and shape. The size-dependence is quantitatively estimated by the parameter PCcavity, which is the volume ratio of a guest molecule to a host cavity. The resulting values of PCcavity lie in the range of 42-76%. Second, each of the host frameworks has its own range of the values. Some guests can employ two different frameworks with the boundary values, explaining formation of polymorphic crystals. Third, the host frameworks are selected by host-guest interactions through weak hydrogen bonds, such as NH/pi and CH/O. The weak hydrogen bonds play an important role for various selective inclusion processes. Fourth, the host frameworks are dynamically exchangeable, resulting in intercalation and polymerization in the cavities. These static and dynamic structures of the frameworks demonstrate great potential of crystalline organic inclusion compounds as functional materials.

Supramolecular Gels from Conjugates of Bile Acids and Amino Acids and Their Applications

“…It was observed that the steroidal ring systems, being rigid, have very similar conformations in all structures, whereas the conformations of the side chains were different. The conformation of the bile acid side chain can be described based on the combination of the dihedral angles C13–C17–C20–C22, C17–C20–C22–C23, C20–C22–C23–C24, and C22–C23–C24–N (Table , for assignments of the steroidal directions see Nakano et al and Miyata et al). When compared with other crystal structures, the side chain conformation of LC‐ L A‐OH ( 9 ) showed a nearly orthogonal turn (87° between the planes through C10–C13–C20 and C23–C24–C25) on the lipophilic back‐side of the steroidal skeleton (Figure ).…”

Biocompatible hydrogelators based on bile acid ethyl amides

“…[47][48][49] Another appealing solid-state property, which leads to remarkable lattice stabilization patterns, is their side chain modification. Modifications of side chains in bile acids have been extensively reviewed [50][51][52][53][54] and unarguably the conformations adopted by side-chains has represented wide range of applications in the field of crystal engineering, co-crystals, improved biological activity, and pharmaceutical applications. In the current study, inspired by the gelation properties, single crystals of N-ethylamide derivatives of lithocholic acid (1), deoxycholic acid (2) and cholic acid (3) were grown from acetonitrile by solvent evaporation to study the effect of inclusion of amide functionality to the hydrogen bonded bilayers.…”

Different crystal forms of a rich hydrogen bond acceptor compound resulting from alternative C–H⋯O and orthogonal CO⋯CO molecular interaction patterns

“…Cholic acid is a very effective inclusion host and also yields more than one crystal form. 25,26 This report explores the crystallisation behaviour of the simple tetraester 3 that also has a dish-shaped topology.…”