TOPOLOGICAL AND NONTOPOLOGICAL REARRANGEMENT IN CRYSTAL-LATTICE OF CHOLIC-ACID INCLUSION COMPLEX-INDUCED BY GUEST EXCHANGE

This article describes single-crystal to single-crystal transformations in the crystal lattice of the multimolecular inclusion complex of cholic acid (CA). These transformations are induced by the guest-exchange method, i.e., soaking the crystals of CA complex in liquid guest. In the present study, 2-, 3-, and 4-fluorobenzyl alcohol (2-, 3-, and 4-FBzOH, respectively) and water were used as guest molecules. The guest exchange from 2- to 4-FBzOH retained essentially both the amphiphilic bilayered structure and space group P2(1) of the starting complex. Similarly, the exchange from 3- to 4-FBzOH retained the bilayered structure and space group P2(1); in CA-3-FBzOH, the guest molecules in the channel are not related by 2(1) symmetry; if the crystals are soaked in 4-FBzOH, exchange of guests takes place, associated with the appearance of 2(1) symmetry between the guest molecules. The exchange from 3-FBzOH to water caused a drastic structural change accompanied by space group change from P2(1) to P6(5)22. The exchange from 2-FBzOH to water afforded two types of CA-H2O structure: one has space group P6(5)22 and the other has the bilayered structure with space group P2(1). In contrast to CA-2- and -3-FBzOH, the crystal of CA-4-FBzOH did not undergo any transformation. Several transformations accompany the conspicuous change in the hydrogen bond network which plays an;important role in constructing the crystal lattice. Such phenomena indicate the crystal flexibility of the CA inclusion complex.