Mechanism of C60 photoreactivity in water:: Fate of triplet state and radical anion and production of reactive oxygen species

The mechanism involved with (1) energy and electron transfer by C-60 in the aqueous phase during UV irradiation and (2) subsequent production of reactive oxygen species (ROS) such as singlet oxygen and superoxide radical anion was investigated. Electron paramagnetic resonance (EPR) study showed that C-60 embedded in micelles of nonionic surfactant (Triton X 100) or anionic surfactant (sodium dodecylbenzenesulfonate) produced ROS, but aggregated C-60 did not, consistent with our earlier findings made using indicator chemicals. Nanosecond and ferntosecond laser flash photolysis showed that the aggregation of C-60 significantly accelerates the decay of excited triplet state C-60, which is a key intermediate for energy and electron transfer, thus blocking the pathway for ROS production. This finding suggests that C-60 clusters will not contribute to oxidative damage or redox reactions in natural environment and biological systems in the same way molecular C(6)0 in organic phase reportedly does. In contrast, C-60 embedded in surfactant micelles produces ROS and the evidence is presented for the formation Of C-60 radical anion as an intermediate.