UVA Photoirradiation of Nitro-Polycyclic Aromatic Hydrocarbons—Induction of Reactive Oxygen Species and Formation of Lipid Peroxides †

Abstract

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are a class of genotoxic environmental contaminants. We have long been interested in determining the mechanisms by which nitro-PAHs induce genotoxicity. Although the metabolic activation of nitro-PAHs leading to toxicological activities has been well studied, the photo-induced activation of nitro-PAHs has seldom been reported. In this paper, we report photo-induced lipid peroxidation by 19 nitro-PAHs. The results indicated that all but two of the nitro-PAHs can induce lipid peroxidation. Mechanistic studies suggest that lipid peroxidation by nitro-PAHs is mediated by free radicals generated in the reaction. There was no structural correlation between the nitro-PAHs and their ability to induce lipid peroxidation upon UVA irradiation, or between the HOMO-LUMO gap and the ability to cause lipid peroxidation. Most of the nitro-PAHs are less potent in terms of causing lipid peroxidation than their parent PAHs. The lack of correlation is attributed to the complex photophysics and photochemistry of the nitro-PAHs and the yield of reactive oxygen species (ROS) and other factors.

On the Primary Reaction Pathways in the Photochemistry of Nitro-Polycyclic Aromatic Hydrocarbons

“…Experiments aimed at measuring and quantifying the generation of singlet oxygen in the photochemistry of 2-nitronaphthalene and 2-methyl-1-nitronaphthalene are essential to evaluate their potential phototoxicity, as has been recently shown for other NPAHs [20]. A high yield of singlet oxygen has been reported for 1-nitronaphthalene in both acetonitrile and cyclohexane solutions [67].…”

“…Photochemical transformation is thought to be one of the main routes of natural removal of NPAHs in the environment [8,[16][17][18][19]. Importantly, NPAHs are frequently more toxic than their parent PAHs [8,20], and photochemical degradation of a number of NPAHs leads, in turn, to photoproducts, some of which are more toxic than their parent compounds [8,20,21]. However, the light-induced transformation mechanisms of NPAHs are still under debate and knowledge of their fates in the environment is of current interest [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39].…”

“…Consequently, development of laboratory models enabling accurate and quantitative measurements of these photochemical properties is essential for modeling the concentration and persistence of NPAHs in the environment and to understand their overall contribution to air quality [44][45][46]. Moreover, laboratory studies can facilitate the development of quantitative structure-activity relationships (QSARs), which connects photophysical and photochemical data to the physicochemical and structural properties of NPAHs [20,22,23,30,32,38,39,47]. In recent years, QSARs have been successfully developed [19,48,49], relating the toxicity, carcinogenicity, and mutagenicity of NPAHs with their physicochemical and structural properties.…”

Mechanism of Ultrafast Intersystem Crossing in 2‐Nitronaphthalene

“…Recently, NPAHs have gained great interest as they are widespread environmental pollutants with phototoxic effects, for example, promoting the formation of skin cancer 26. Among NPAHs, nitronaphthalene (NN) derivatives largely contribute to the overall ambient air toxicity 27.…”

Quenching of Charge Transfer in Nitrobenzene Induced by Vibrational Motion

“…Furthermore, nitrobenzene can be considered the smallest prototype of nitrated polycyclic aromatic hydrocarbons, a class of compounds that constitute an important type of widespread environmental pollutants with phototoxic effects, e.g., stimulating the formation of skin cancer. [22][23][24] Despite the large number of studies published until now, many features of the photophysics of nitrobenzene remain unclear. In particular, there is no consensus about the description of the charge-transfer (CT) character of the lowest-energy bright state of nitrobenzene obtained from different theoretical and experimental studies, indicating that the characterization of the excited states of this molecule is still a challenging task.…”