SYNTHESIS OF A TUBULAR POLYMER FROM THREADED CYCLODEXTRINS

MUCH attention has been focused recently on the design and fabrication of large-scale molecular structures1. Carbon nanotubes formed by an arc-discharge method2,3 have attracted particular attention. These tubes range from about 1 to 30 nanometres in diameter and a micrometre or so in length. To construct smaller tubes, direct chemical synthesis may be a more convenient approach. The cyclic oligomers of glucose known as cyclodextrins (CDs) would seem to be ideal candidates for the components of a molecular tube: they contain cylindrical cavities about 0.7 nm deep, with diameters of 0.45 nm, 0.7 nm and 0.85 nm for alpha-CD, beta-CD and gamma-CD respectively4. Lehn has recently reported the use of 'bouquet molecules' built from beta-CD with long side chains as artificial ion channels5. We have previously prepared rotaxane super-molecules in which CDs are threaded on a polymer chain, and we6 and others7,8, have reported polyrotaxanes with many threaded CDs. Here we report the crosslinking of adjacent CD units in a polyrotaxane to create a molecular tube. By removing the bulky ends of the polymer thread, the tube can be unthreaded and can act as a host for reversible binding of small molecules.