Photochemical Generation of Nitric Oxide from 6-Nitrobenzo[a]pyrene

Abstract

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.

Environmental Carcinogenic Polycyclic Aromatic Hydrocarbons: Photochemistry and Phototoxicity

“…The DNA cleavage data clearly indicates a strong linkage between the photochemical reaction activity of the nitro-PAHs and their DNA photocleavage efficiency. This is possibly due to the nitro rearrangement reaction discussed above for nitro-PAHs with the nitro group perpendicular to the aromatic ring (56,89,90). Combining with the observation that PAHs that can easily convert to quinones are strong DNA photocleavers, DNA photocleavage by PAHs in general is closely related to their photochemical reaction rate, photochemical reactivity, and formation of reactive intermediates.…”

“…Photolysis of 6-nitro-B[a]P, another nitro-PAH with the nitro group peri to two hydrogen atoms, yields 1,6-, 3,6-, and 6,12-B[a]P-quinones and 6-hydroxy-B[a]P, also via the nitrite intermediate (82,83,(87)(88)(89) (Figure 11). The three quinones are the same as the photolysis products of B[a]P (66).…”

“…Thus nitric oxide is released into the solution by the photolysis of 6-nitro-B[a]P. The authors claim that the nitric oxide released can cause DNA single strand cleavage (89). Also, photolysis of 1-or 3-nitro-B[a]P does not result in the same intermediates, although their photoproducts have not been characterized.…”

“…Larger ring PAHs are relatively rare and their photoproducts can be more complex due to greater complexity of the rings. Photo-oxidation of some nitro (56,82,84,86,(88)(89)(90)146), amino (94)(95)(96)102), and hydroxy (71) PAHs also lead to quinones. In addition to quinones, hydroxy (53,65,67,93), carboxy (53), hydroxymethyl and formyl-PAHs for methyl substituted PAHs (70) are also detected among the photolysis products.…”

Photocontrol of NO, H₂S, and HNO Release in Biological Systems by Using Specific Caged Compounds

“…A key feature of this reaction seems to be the twisted conformation of the nitro group due to steric hindrance by hydrogen atoms at the peri-positions. 12) Although intense shorter-wavelength UV irradiation was reported to induce isomerization of simple nitrobenzenes, 13) Suzuki and colleagues in our group assumed that a twisted conformation induced by introduction of a bulky moiety, such as ortho-dimethyl groups, would facilitate the isomerization reaction. Therefore, we designed and developed compounds bearing a 2,6-dimethylnitrobenzene (DNB) moiety, in which the nitro group is considered to be twisted due to the presence of the two vicinal methyl groups at ortho-positions.…”