Binding behaviors of para-dicyclohexanocucurbituril and meta-tricyclohexanocucurbituril with dialkyl viologens
The binding behaviours of para-dicyclohexanocucurbituril (Cy2Q) and meta-tricyclohexanocucurbituril (Cy3Q) with a series of dialkyl viologens (MV2+, EV2+, PV2+, BV2+, FV2+ and HV2+) have been investigated by various methods. In the aqueous solution, 1H NMR spectra suggest that the alkyl chains are more favourably encapsulated into the hydrophobic cavities of both hosts than the aromatic rings. Cyclic voltammograms (CV) curves show that the Cy2Q or Cy3Q bind the charged viologens more strongly than the reduced viologens. Isothermal titration calorimetry (ITC) data reveal that the binding processes of both hosts with viologens are enthalpic driven. In the solid state, the PV2+, BV2+ guests and two Cy3Q hosts generated dumbbell-shaped structures, with two Cy3Q hosts residing over two terminal alkyl chains of the guests.
Binding behaviors of para-dicyclohexanocucurbituril and meta-tricyclohexanocucurbituril with six dialkyl viologens were investigated by various tools, indicating that the driving forces of the formation of the host−guest inclusion complexes result from the cooperativity of the hydrophobic effect, ion−dipole interaction and van der Waals interaction.