Organic Intercalation Material: Reversible Change in Interlayer Distances by Guest Release and Insertion in Sandwich‐Type Inclusion Crystals of Cholic Acid

Abstract

Cholic acid (CA) forms inclusion crystals that have a sandwich-type lamellar structure constructed by the alternative stacking of host bilayers and guest layers. Five disubstituted benzenes, o-toluidine, m-fluoroaniline, o-chlorotoluene, o-bromotoluene, and indene, are accommodated in the two-dimensional void space between the host bilayers at 1:2 host-guest stoichiometries. Thermal gravimetric analysis of the inclusion crystals revealed that all the guest molecules, except o-toluidine, are released in two separate steps, indicating the formation of intermediate crystals after the first guest release. Adequate heat treatment of the four inclusion crystals induces release of half or three quarters of the guest molecules. X-ray diffraction patterns of the intermediate crystals revealed that the crystals have a bilayer structure the same as those of the common CA inclusion crystals. They have one-dimensional cavities, in which the guest molecules are included at a 1:1 or 2:1 host-guest stoichiometry. These facts indicate that the host bilayers move 1.6-4.5 A perpendicular to the layer direction by desorption of the guest molecules. Furthermore, a reverse structural change is also achieved by absorption of the guest molecules to regenerate the starting sandwich-type inclusion crystals. This reversible change in the host bilayer by the guest sorption and desorption is a novel example of organic intercalation materials.

Supramolecular Chirality in Crystalline Assemblies of Bile Acids and Their Derivatives; Three-Axial, Tilt, Helical, and Bundle Chirality

“…The assembly modes are host-inherent in some cases but guest-dependent in the other cases. These results brought about the idea that the steroidal molecules are located in an intermediate among small molecules and biopolymers from various viewpoints of host-guest, inclusion, recognition, polymorphism [67][68][69][70][71][72], dynamics [17,[73][74][75][76][77], polymerization [78][79][80][81][82][83], separation [3,84,85], and so on, as shown schematically in Figure 5.…”

Cholic acid as host for long linear molecules: a series of co-crystals with n-alkylammonia

“…1). 12,13 In-between the bilayers long hydrophobic alkyl chains of n-alkylammonia molecules are inserted. The NH 3 + polar heads of n-alkylammonia molecules are immersed into the hydrophilic interior of the CA bilayers to form hydrogen bonds with the OH groups of CA and with the water molecules.…”

Selective guest retention in thermal guest-release process in sandwich-type inclusion crystal of cholic acid

“…3a and 3b show the sandwich-type structures of CA$G1 and CA$G2 crystals, respectively, which were already reported. 15 These two crystals have the following structural features; (i) the two crystals consist of alternative stacking of host and guest layers, and the host layer is maintained by host-host cyclic hydrogen bond networks; (ii) the guest molecules are included in 2D cavities of two non-equivalent sites, A and B. Only the guest molecule at the site A in CA$G1 forms a host-guest hydrogen bond network, while in the two crystals CH/p interactions are observed between the guests at site A and B; (iii) the two crystals have different side chain conformations of the host molecules: trans-type in CA$G1 and gauche-type in CA$G2.…”

“…13,14 Interestingly, several guests, such as m-fluoroaniline (G1) and indene (G2), force CA to employ sandwich-type crystal structures with two-dimensional (2D) cavities. 15 The present paper describes that the 2D cavities enabled us to observe novel guest selectivities in the following two cases: (i) competitive incorporation during recrystallization of CA from a liquid mixture of G1 and G2; (ii) competitive guestrelease from the ternary inclusion crystal of CA with G1 and G2.…”