The molecular necklace: a rotaxane containing many threaded α-cyclodextrins

THE importance of non-covalent interactions in biological systems motivates much of the current interest in supramolecular assemblies1. A classic example of a supermolecule is provided by the rotaxanes2–5, in which a molecular 'rotor' is threaded by a linear 'axle'. Previous examples have included cyclic crown ethers threaded by polymers6, paraquat–hydroquinone complexes7 and cyclodextrin complexes8,9. We found recently that α-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 cyclodextrin10,11. 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 coworkers7. We call this supramolecular assembly a 'molecular necklace'.

[1]  D. Lawrence,et al.  Template-driven self-assembly of a porphyrin-containing supramolecular complex , 1990 .

[2]  Angel E. Kaifer,et al.  Novel class of asymmetric zwitterionic rotaxanes based on α-cyclodextrin , 1991 .

[3]  A. Zilkha,et al.  Synthesis of a catenane by a statistical double-stage method , 1976 .

[4]  D. Graiver,et al.  Studies on the formation of topological isomers by statistical methods , 1976 .

[5]  Jean-Marie Lehn,et al.  Perspectives in Supramolecular Chemistry—From Molecular Recognition towards Molecular Information Processing and Self‐Organization , 1990 .

[6]  R. Bergeron,et al.  Disposition requirements for binding in aqueous solution of polar substrates in the cyclohexaamylose cavity , 1977 .

[7]  H. Gibson,et al.  New polymer architectures: Polyrotaxanes , 1991 .

[8]  D. Lawrence,et al.  Self-Assembly of a Threaded Molecular Loop , 1990 .

[9]  Akira Harada,et al.  Complex formation between poly(ethylene glycol) and α-cyclodextrin , 1990 .

[10]  Christopher L. Brown,et al.  Molecular Trains: The Self‐Assembly and Dynamic Properties of Two New Catenaries , 1991 .

[11]  H. Ogino.  Relatively high-yield syntheses of rotaxanes. Syntheses and properties of compounds consisting of cyclodextrins threaded by .alpha.,.omega.-diaminoalkanes coordinated to cobalt(III) complexes , 1981 .

[12]  A. Harada,et al.  Complex formation between cyclodextrin and poly(propylene glycol) , 1990 .

[13]  H. Ogino,et al.  Synthesis and properties of rotaxane complexes. 2. Rotaxanes consisting of .alpha.-or .beta.-cyclodextrin threaded by (.mu.-.alpha.,.omega.-diaminoalkane)bis[chlorobis(ethylenediamine)cobalt(III)] complexes , 1984 .