Suppressing Effect of 2-Nitrobenzaldehyde on Singlet Oxygen Generation, Fatty Acid Photooxidation, and Dye-Sensitizer Degradation.

Günther Knör,Atena Vaziri Sereshk,Clemens Schwarzinger,Mahdi Hajimohammadi

doi:10.3390/antiox7120194

Abstract

2-Nitrobenzaldehyde was found to efficiently block singlet oxygen generation in a series of different test samples upon exposure to UV and visible light under aerobic conditions. The effect of quenching singlet oxygen formation was monitored in the presence of 1, 4-diazabicyclo [2.2.2] octane (DABCO) acting as a well-known singlet oxygen scavenger. A comparison of different nitrobenzaldehyde isomers with other highly effective synthetic antioxidants used in the food industry such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ) revealed that the protection of materials from singlet oxygen decreases in the order of 2-nitrobenzaldehyde > DABCO > TBHQ > 3-nitrobenzaldehyde > BHA > 4-nitrobenzaldehyde > BHT. Upon addition of 2-nitrobenzaldehyde, the oxidation of fatty acids and the degradation of photosensitizers was found to be considerably diminished, which indicates that the presence of 2-nitrobenzaldehyde has a significant protective influence by restricting the singlet oxygen generation and photodegradation of dyes. Moreover, the compound turned out to display its highly suppressing effects on typical singlet oxygen-dependent reactions, such as fatty acid photooxidation and dye photosensitizer degradation, in a rather broad spectral region covering wavelengths from 300 nm (UV-B) to 575 nm (close to the maximum of ambient solar radiation).

Highlights

In its electronic ground state (3 Σg − ), molecular oxygen is characterized as a triplet diradical species carrying two unpaired electrons of parallel spin
A suitable chemical probe is usually applied to selectively trap singlet oxygen and enable its quantification based on absorption measurements
The generation of singlet oxygen induced by photoexcited methylene blue (MB) was evidenced by chemical trapping of 1 O2 with anthracene

Summary

Introduction

In its electronic ground state (3 Σg − ), molecular oxygen is characterized as a triplet diradical species carrying two unpaired electrons of parallel spin. These valence electrons may get paired together with opposite spin to generate a singlet oxygen molecule in the 1 ∆g excited state [1]. The electrophilic character of singlet oxygen may cause damage to lipids, amino acids, nucleic acids, and many other biological targets [2]. Singlet oxygen can be generated in biological tissues and food systems, especially in the presence of endogenous photosensitizers such as riboflavin and chlorophylls [3,4,5]. Singlet oxygen attacks unsaturated fatty acids and produces lipid hydroperoxides as primary products of fatty acids [6]. Exposure to UV radiation causes DNA damage and protein oxidation and induces the synthesis of matrix metalloproteinases [7]

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Conclusion