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

Abstract

The host molecule cucurbit[7]uril forms very stable host-guest complexes (1:1 and 2:1) and [2]pseudorotaxanes with α,ω-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.