Self‑building molecular rings bring next‑generation drug delivery and smart materials closer‎

Rotaxanes are dumbbell-shaped mechanically interlocked molecules in which one or more ring-shaped molecules are threaded through a linear segment, known as the axle. To keep the ring from sliding off, two bulky groups, sometimes called stoppers, are added to the ends of the axle. Making a rotaxane has always been as challenging as its structure suggests.