THE MOLECULAR NECKLACE - A ROTAXANE CONTAINING MANY THREADED ALPHA-CYCLODEXTRINS

THE importance of non-covalent interactions in biological systems motivates much of the current interest in supramolecular assemblies 1. A classic example of a supermolecule is provided by the rotaxanes 2-5, in which a molecular 'rotor' is threaded by a linear 'axle'. Previous examples have included cyclic crown ethers threaded by polymers 6, paraquat-hydroquinone complexes 7 and cyclodextrin complexes 8,9. We found recently that alpha-cyclodextrin will form high yields of a crystalline complex with polyethylene glycol (PEG), and suggested that the PEG penetrates the 'beaker-like' tunnel of the cyclodextrin 10,11. We report here the preparation of a compound in which several cyclodextrins are threaded on a single PEG chain and are trapped by capping the chain with bulky end groups. This brings a step closer the 'molecular abacus' proposed by Stoddart and coworkers 7. We call this supramolecular assembly a 'molecular necklace'.