Formation of host-guest and sandwich complexes by a β-cyclodextrin derivative

A unimer with two host binding sites of beta-cyclodextrin and two guest binding sites (two p-tert-butylphenyl moities) has been synthesized. The host and guest residues are linked through an EDTA bridge. Static and dynamic light scattering measurements evidence the formation of supramolecular entities in aqueous solution with a low degree of polymerization (< 10). The formation of dendrimer-like structures is demonstrated by TEM measurements. From NMR experiments it is concluded that the p-tert-butylphenyl group is located at three different environments. Two of these sites correspond to the typical locations of a guest in equilibrium with a host, i.e., inside the host cavity and in the bulk solution. The third location corresponds to a p-tert-butylphenyl group sandwiched between the outer surface of at least two cyclodextrin residues and the bridge of the unimer, forming an external complex.