NMR and UV–VIS Investigation of water-soluble fullerene-60–γ-cyclodextrin complex

Abstract

Fullerene-60 can be made water-soluble by forming an inclusion complex with γ-cyclodextrin (γ-CD). The complex between C₆₀ and γ-CD is selectively formed; neither β- or α-CD, nor C₇₀ takes part in complex formation. The UV–VIS and ¹³C NMR spectra of C₆₀ in the complex are almost identical to those of C₆₀ in organic solvents. The ¹H NMR spectrum of the host, γ-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 γ-CD and C₆₀ are believed to exist in water. On heating in water, the complexes are transformed into water-soluble aggregates containing several fullerenes and γ-CD molecules. On addition of excess γ-CD to this solution and further heating, the initial complexes, monomeric in C₆₀, are reformed.