An amino derivative of -cyclodextrin [6-(6-aminehexanamide)-6-deoxy)--cyclodextrin (6-CD)] was synthesized, and the formation of an intramolecular inclusion complex was studied by NMR techniques. The deprotonation/protonation of the amino group stimulates an in/out movement of the pendant group toward/ from the cyclodextrin cavity, the protonated species lying outside the hydrophobic cyclodextrin cavity but the unprotonated one residing inside and outside the cavity. The protonation of the amino group is a fast exchange rate NMR time-scale process, but the chain movement is a slow one. The equilibrium constants of both processes were determined from 1 H NMR experiments and the kinetic constants for the slow process were determined from exchange spectroscopy (EXSY) experiments.

A head-to-head dimer of cholic acid linked at C3 carbon atoms by a urea bridge was synthesized and the crystal structure was studied. The crystal belongs to the monoclinic crystal system, space group I 2 . The packing shows a bilayer structure with alternating hydrophobic and hydrophilic layers. The horizontal and vertical planes of the two cholic residues are almost parallel to each other, the vertical ones being perpendicular to the bilayers. The hydrogen bond network is two-dimensional as it does not propagate in the direction perpendicular to the bilayers. It is noteworthy that the nitrogen atoms of the urea bridge do not participate in that network. The carbonyl urea group and only one of the ester of the two side chains form hydrogen bonds with two other dimers through the steroid hydroxy O7-H and O12-H groups. This means that each dimer forms eight hydrogen bonds but only four are different.