Effect of Encapsulating Agents on　Dispersion Status and　Photochemical Reactivity of C_(60) in the Aqueous Phase

摘要

This study demonstrates that the degree of C_(60) 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 C_(60). The degree of C_(60) clustering was quantitatively analyzed using ultraviolet-visible spectral characteristics. The dispersion status played a critical role in determining the photochemical reactivity of C_(60), 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, C_(60) 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 C_(60). This study suggests that the photochemical reactivity of C_(60) 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 C_(60).