Host–guest complexation between cucurbit[7]uril and doxepin induced supramolecular assembly

Abstract

The supramolecular complexation of doxepin (DOX) with cucurbit[7]uril (CB7) was investigated in aqueous solution. The results indicated the formation of a host–guest complex, as verified by complexation-induced chemical shifts in the NMR experiments and supported by quantum-chemical calculations, in which the alkylammonium tail of DOX was found to be encapsulated inside the CB7 cavity, while the tricyclic moiety remained exposed to bulk water. Isothermal titration calorimetry and dye-displacement experiments provided a moderate binding affinity (10⁴ M⁻¹). Interestingly, the partial encapsulation of DOX by the CB7 macrocycle led to the development of a supramolecular assembly at a low millimolar concentration, as verified by NMR and dynamic light scattering (DLS) measurements, which showed homogeneous size distributions with an average diameter of 1700 nm.