Binding behaviors of para-dicyclohexanocucurbit[6]uril and meta-tricyclohexanocucurbit[6]uril with dialkyl viologens

Abstract

The binding behaviours of para-dicyclohexanocucurbit[6]uril (Cy2Q[6]) and meta-tricyclohexanocucurbit[6]uril (Cy3Q[6]) 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[6] or Cy3Q[6] 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[6] hosts generated dumbbell-shaped structures, with two Cy3Q[6] hosts residing over two terminal alkyl chains of the guests.