Photochemical generation of nitric oxide from 6-nitrobenzo[a]pyrene

Photolabile 6-nitrobenzo[a]pyrene (6-nitroBaP) released nitric oxide (NO) under visible-light irradiation. The generation of NO and the concomitant formation of the 6-oxyBaP radical were confirmed by ESR. BaP quinones were also detected as further oxidized products of the 6-oxyBaP radical. No such photodegradation was observed with other nitrated BaPs, such as 1-nitroBaP and 3-nitroBaP. DNA-strand breakage, caused by photoexcited 6-nitroBaP, was closely related to its NO-releasing activity. MO calculations of nitrated BaP suggest that the perpendicular conformation of the nitro substituent to the aromatic ring is important for the release of NO with light. These findings may be useful for the development of a new type of NO donor.