Kinetics of Formation of the Host–Guest Complex of a Viologen with Cucurbit[7]uril

Host–guest complexation between the dicationic viologen 1-tri(ethylene glycol)-1′-methyl-<i>m</i>-xylyl-4,4′-bipyridinium and cucurbit[7]uril (<b>CB7</b>) was studied at pH = 4.5 in water. The stability constants of the mono- and bis-<b>CB7</b> adducts were determined at 25 °C by UV–vis spectroscopy. Stopped-flow kinetic experiments were performed to measure the formation and dissociation rate constants of the monoadduct: <i>k</i>₁ = (6.01 ± 0.03) × 10⁶ M^–1s^–1 and <i>k</i>_–1 = 52.7 ± 0.4 s^–1, respectively. Possible mechanisms of complexation are discussed in view of the kinetic results