Effect of encapsulating agents on dispersion status and photochemical reactivity of C₆₀ in the aqueous phase

This study demonstrates that the degree of C₆₀ clustering in the aqueous phase is strongly dependent on the type and concentration of encapsulating agents, such as surfactant, polymer, and natural organic matter that interact with C₆₀. The degree of C₆₀ clustering was quantitatively analyzed using ultraviolet - visible spectral characteristics. The dispersion status played a critical role in determining the photochemical reactivity of C₆₀, in particular, its ability to mediate energy transfer and to produce singlet oxygen in the presence of oxygen. Consistent with findings in the organic phase, C₆₀ in the aqueous phase lost its intrinsic photochemical reactivity when they formed aggregates. Experiments performed using a laser flash photolysis suggested that the loss of reactivity resulted from a drastic decrease in lifetime of a key reaction intermediate, that is, triplet-state C₆₀. This study suggests that the photochemical reactivity of C₆₀ in the aqueous phase, which has been linked to oxidative damage in biological systems in earlier studies, is strongly dependent on the media environment surrounding C₆₀.