Mechanisms of photochemistry and reactive oxygen production by fullerene suspensions in water

Buckminsterfullerene (C-60) is a known photosensitizer that produces. reactive oxygen species (ROS) in the presence of light; however, its properties in aqueous environments are still not well understood or modeled. In this study, production of both singlet oxygen and superoxide by UV photosensitization of colloidal aggregates of C-60 in water was measured by two distinct methods: electron paramagnetic resonance (EPR) with a spin trapping compound, and spectrophotometric detection of the reduced form of the tetrazolium compound XTT. Both sing let oxygen and superoxide were generated by fullerol suspensions while neither was detected in the aqu/nC(60) suspensions. A mechanistic framework for photosensitization that takes into account differences in C-60 aggregate structure in water is proposed to explain these results. While theory developed for single molecules suggests that alterations to the C-60 cage should reduce the quantum yield for the triplet state and associated ROS production, the failure to detect ROS production by aqu/nC(60) is explained in part by a more dense aggregate structure compared with the hydroxylated C-60.