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-m-xylyl-4,4'-bipyridinium and cucurbit[7]uril (CB7) was studied at pH = 4.5 in water. The stability constants of the mono- and bis-CB7 adducts were determined at 25 degrees C by UV-vis spectroscopy. Stopped-flow kinetic experiments were performed to measure the formation and dissociation rate constants of the monoadduct: k(1), = (6.01 +/- 0.03) x 10(6) M-1 s(-1) and k(-1) = 52.7 +/- 0.4 s(-1), respectively. Possible mechanisms of complexation are discussed in view of the kinetic results.