NMR AND UV-VIS INVESTIGATION OF WATER-SOLUBLE FULLERENE-60-GAMMA-CYCLODEXTRIN COMPLEX

Fullerene-60 can be made water-soluble by forming an inclusion complex with gamma-cyclodextrin (gamma-CD). The complex between C-60 and gamma-CD is selectively formed; neither beta- or alpha-CD, nor C-70 takes part in complex formation. The UV-VIS and C-13 NMR spectra of C-60 in the complex are almost identical to those of C-60 in organic solvents. The H-1 NMR spectrum of the host, gamma-CD, in the complex has been identified. Only small differences to the spectrum of the free host are observed; this is interpreted as being due mainly to a conformational change to a more conical structure in the host. Both 2:1 and 1:1 complexes between gamma-CD and C-60 are believed to exist in water. On heating in water. the complexes are transformed into water-soluble aggregates containing several fullerenes and gamma-CD molecules. On addition of excess gamma-CD to this solution and further heating, the initial complexes, monomeric in C-60, are reformed.