Direct detection of superoxide anion generated in C60-photosensitized oxidation of NADH and an analogue by molecular oxygen

Visible-light irradiation of poly(vinylpyrrolidone) (PVP)-solubilized C60 in water in the presence of NADH (dihydronicotinamide adenine dinucleotide) and molecular oxygen (O2) results in formation of superoxide anion (O2˙−). Formation of O2˙− having a characteristic g‖ value of 2.18 was evidenced by the direct observation with use of a low-temperature EPR technique at 77 K. Photoinduced O2˙− formation was also observed for an N-methyl-2-pyrrolidone (NMP) solution of C60 and 1-benzyl-1,4-dihydronicotinamide (BNAH) in the presence of O2, whereas C60 radical anion (C60˙−) was formed in the absence of O2 under otherwise the same experimental conditions. These results suggest that C602− formed in the photoinduced electron-transfer reduction of C60 by BNAH acts as an electron donor to O2 to give O2˙− in NMP.