A type of compound that has a dumbbell-shaped molecule with a cyclic molecule around its axis. The dumbbell has a chain with large groups at each end, these being large enough to trap the ring. There is no formal chemical bonding between the dumbbell and the ring. Rotaxanes are examples of compounds with mechanical bonding. A number of natural peptide rotaxanes have been identified. Synthesis of new rotaxanes is a matter of interest because of their possible use as ‘molecular machines’ in nanotechnology (e.g. as molecular switches or information storage units).