Fullerene γ-Cyclodextrin Complexes
The fullerenes, C60 and C70, can form inclusion complexes with .gamma.-cyclodextrin as the host. The complexes are formed by refluxing a water solution of .gamma.-cyclodextrin with a few mg of either C60 and C70 added. To form a complex, the .gamma.-cyclodextrin must be in a large excess. Due to the water solubility of .gamma.-cyclodextrin, the complexes are also water soluble.
When the .gamma.-cyclodextrin/C60 solution is cooled after the reflux a precipitate forms. This precipitate can again be soluble in water by careful warming. The precipitate contains much less uncomplexed .gamma.-cyclodextrin than the solution of the complex and can therefor be analyzed by NMR and FAB/LSIMS-MS spectroscopy. From FAB/LSIMS the complex is believed to consist of two g-cyclodextrins and one C60, i.e. a 2:1 complex. The NMR investigation confirms the predictions that the C60 has small overall ring-current magnetic susceptibility. If a water solution of the precipitate is heated, it is transformed to aggregates containing several fullerenes and .gamma.-cyclodextrins. The size of the aggregates depends on the amount of uncomplexed .gamma.-cyclodextrins in the precipitate. The original 2:1 complex can be recovered by adding more .gamma.-cyclodextrin to the aggregate solution. Unfortunately, the C70 complex does not form a precipitate which prevent analyzes by NMR and MS spectroscopy.