  A homologous series of two-station [2]rotaxanes incorporating amino-acid
units in the molecular thread has been developed. The degenerate [2]rotaxanes
exhibit amino-acid specific shuttling rates between two fumaric stations
related to the steric factor associated to the amino-acid side chain, as
demonstrated by variable-temperature 1H NMR spectroscopy and exchange
spectroscopy (EXSY). This allows tuning of the macrocycle shuttling rate over 4
orders of magnitude, which further has a relatively small solvent dependency.
