This paper presents an overview of recent work on the binding interactions between a series of 4,4'-bipyridinium (viologen) derivatives and the hosts cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7), which give rise to stable 'wheel-on-an-axle' inclusion complexes (pseudorotaxanes) in aqueous solution. The carboxylic acid termini on the pseudorotaxane axle can be used as handles to control-via proton transfer reactions -the relative position of the CB wheel along the axle. We also report on a different type of pseudorotaxane in which the reversible oxidation of the axle's ferrocenyl end groups leads to controlled displacement of the C137 wheel.