Cucurbit[7]uril host-guest and pseudorotaxane complexes with alpha,omega-bis(pyridinium)alkane dications

The host molecule cucurbit[7]uril forms very stable host-guest complexes ( 1: 1 and 2: 1) and [2]pseudorotaxanes with alpha,omega-bis( pyridinium) alkane dications in aqueous solution. With the dications containing pyridinium, 2- and 3-picolinium, and 4-dimethylaminopyridinium end groups and a hexyl chain, [2] pseudorotaxanes are formed with one equivalent of CB[7] positioned over the central chain. A second equivalent of CB[7] encapsulating one of the end groups results in the translocation of the first CB[7] to the other end group. For the dications with these end groups, the 2: 1 host-guest complexes exhibit stability constants which are considerably smaller than the 1: 1 values as the result of steric and electronic repulsions between the two CB[7] hosts.