Slow Intermolecular Complexation–Decomplexation Exchanges of Cyclodextrins in Fullerene and Its Derivative Complexes

Fullerenes (C₆₀ and C₇₀) and several functionalized C₆₀ derivatives can be encapsulated in two γ-cyclodextrins (γ-CDxs). Although intermolecular complexation–decomplexation exchange of γ-CDx is known to be very slow, the exchange rates have yet to be quantitatively measured. Herein, we determined that the pseudo-first-order association and dissociation rate constants for the γ-CDx₂•C₇₀ complex were 4.3 and 0.6 s⁻¹ at 23 °C, respectively. In contrast, the intermolecular exchange rates for the γ-CDx₂•C₆₀ and C₆₀ derivative complexes were slower than the time scale of exchange spectroscopy NMR experiments and the exchange rate constants were in the order of 10⁻⁴ s⁻¹. Furthermore, a γ-CDx₂•C₆₀ derivative complex was shown to have different intermolecular exchange rates for the two γ-CDxs depending on steric hindrance from the substituent on the C₆₀ derivative.