title: Binding modes of cucurbit[6]uril and cucurbit[7]uril with a tetracationic bis(viologen) guest.
abstract: Binding behaviors of two cucurbit[n]urils (CB[n]) hosts with the [CH3bpy(CH2)6bpyCH3]4+ (bpy = 4,4'-bipyridinium) guest were investigated by 1H NMR and MALDI-TOF-MS experiments. While the CB[6] and CB[7] form [2]pseudorotaxanes with the host located over the hexamethylene chain of the guest, only the CB[7] forms a [3]pseudorotaxane with both host molecules residing over the bipyridinium groups. The initial CB[7] host vacates the inclusion of the hexamethylene chain as a result of the electrostatic and steric repulsions that would arise in simultaneous binding of adjacent aliphatic and aromatic portions of the guest.
authors.affiliation: Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Lina
authors.initials: L
authors.lastname: Yuan
authors.forename: Ruibing
authors.initials: R
authors.lastname: Wang
authors.forename: Donal H
authors.initials: DH
authors.lastname: Macartney