Singlet Oxygen Quencher Research Articles

The Benefits and Risks of Certain Dietary Carotenoids that Exhibit both Anti- and Pro-Oxidative Mechanisms-A Comprehensive Review.

Carotenoid pigments, particularly β-carotene and lycopene, are consumed in human foodstuffs and play a vital role in maintaining health. β-carotene is known to quench singlet oxygen and can have strong antioxidant activity. As such, it was proposed that β-carotene might reduce the risk of cancer. Epidemiological studies found inverse relationships between cancer risk and β-carotene intake or blood levels. However, clinical trials failed to support those findings and β-carotene supplementation actually increased lung cancer incidence in male smokers. Early experimental animal studies found dietary β-carotene inhibited UV-induced skin cancers. Later studies found that β-carotene supplementation exacerbated UV-carcinogenic expression. The discrepancies of these results were related to the type of diet the animals consumed. Lycopene has been associated with reduced risk of lethal stage prostate cancer. Other carotenoids, e.g., lutein and zeaxanthin, play a vital role in visual health. Numerous studies of molecular mechanisms to explain the carotenoids’ mode of action have centered on singlet oxygen, as well as radical reactions. In cellular systems, singlet oxygen quenching by carotenoids has been reported but is more complex than in organic solvents. In dietary β-carotene supplement studies, damaging pro-oxidant reactivity can also arise. Reasons for this switch are likely due to the properties of the carotenoid radicals themselves. Understanding singlet oxygen reactions and the anti-/pro-oxidant roles of carotenoids are of importance to photosynthesis, vision and cancer.

Basic Investigations of Singlet Oxygen Detection Systems with ESR for the Measurement of Singlet Oxygen Quenching Activities.

Singlet oxygen (1O2) is highly oxidative and exerts strong cytotoxic effects. We tried to establish the best combination of a singlet oxygen generation system and a detection method with ESR, for measurement of the quenching activities of various substances. The photosensitizing reaction of rose bengal or thermal decomposition of 4-methyl-1,4-etheno-2,3-benzodioxin-1(4H)-propanoic acid (endoperoxide, EP) was used for the generation of 1O2, and a sterically hindered secondary amine, 2,2,6,6-tetramethyl-4-piperidone (TEMPD) or 2,2,6,6-tetramethyl-4-piperidinol (TEMP-OH), was used as the 1O2 detection probe. These secondary amines were oxidized by 1O2 to form stable nitroxide radicals, which were detectable by ESR. TEMPD was found to be readily oxidized by air, causing large background signals in comparison with TEMP-OH. The ESR signal obtained by the irradiation of rose bengal with visible light in the presence of TEMP-OH consisted of two kinds of nitroxide radical overlapping. In contrast, only a single nitroxide signal was observed when TEMP-OH was reacted with 1O2 generated from EP. Therefore, the best combination should be EP as the 1O2 generator and TEMP-OH as the detection probe. When using this combination, we found that the concentrations of some organic solvents such as dimethyl sulfoxide and acetonitrile should be kept constant for reliable quantification, because the concentrations of organic solvents affect the ESR signal intensity.

Riboflavin Plays a Pivotal Role in the UVA-Induced Cytotoxicity of Fibroblasts as a Key Molecule in the Production of H2O2 by UVA Radiation in Collaboration with Amino Acids and Vitamins.

To investigate environmental factors that contribute to ultraviolet A (UVA)-induced oxidative stress, which accelerates the senescence and toxicity of skin cells, we irradiated human fibroblasts cultured in commonly used essential media with UVA and evaluated their viability and production of reactive oxygen species. The viability of fibroblasts exposed to a single dose of 3.6 J/cm2 UVA was not reduced when cultured in Hanks balanced salt solution, but it was significantly decreased when cultured in Dulbecco’s modified Eagle’s medium (DMEM), which contains various amino acids and vitamins. Furthermore, cell viability was not reduced when fibroblasts were cultured in DMEM and treated with a hydrogen peroxide (H2O2) scavenger such as glutathione or catalase added after UVA irradiation. In addition, we confirmed that the production of H2O2 was dramatically increased by UVA photosensitization when riboflavin (R) coexisted with amino acids such as tryptophan (T), and found that R with folic acid (F) produced high levels of H2O2 after UVA irradiation. Furthermore, we noticed that R and F or R and T have different photosensitization mechanisms since NaN3, which is a singlet oxygen quencher, suppressed only R and T photosensitization. Lastly, we examined the effects of antioxidants (L-ascorbic acid, trolox, L-cysteine, and L-histidine), which are singlet oxygen or superoxide or H2O2 scavengers, on R and F or on R and T photosensitization, and found that 1 mM ascorbic acid, Trolox, and L-histidine were strongly photosensitized with R, and produced significant levels of H2O2 during UVA exposure. However, 1 mM L-cysteine dramatically suppressed H2O2 production by UVA photosensitization. These data suggest that a low concentration of R-derived photosensitization is elicited by different mechanisms depending on the coexisting vitamins and amino acids, and regulates cellular oxidative stress by producing H2O2 during UVA exposure.

In-Vivo Optical Monitoring of the Efficacy of Epidermal Growth Factor Receptor Targeted Photodynamic Therapy: The Effect of Fluence Rate.

Targeted photodynamic therapy (PDT) has the potential to improve the therapeutic effect of PDT due to significantly better tumor responses and less normal tissue damage. Here we investigated if the efficacy of epidermal growth factor receptor (EGFR) targeted PDT using cetuximab-IRDye700DX is fluence rate dependent. Cell survival after treatment with different fluence rates was investigated in three cell lines. Singlet oxygen formation was investigated using the singlet oxygen quencher sodium azide and singlet oxygen sensor green (SOSG). The long-term response (to 90 days) of solid OSC-19-luc2-cGFP tumors in mice was determined after illumination with 20, 50, or 150 mW·cm−2. Reflectance and fluorescence spectroscopy were used to monitor therapy. Singlet oxygen was formed during illumination as shown by the increase in SOSG fluorescence and the decreased response in the presence of sodium azide. Significantly more cell death and more cures were observed after reducing the fluence rate from 150 mW·cm−2 to 20 mW·cm−2 both in-vitro and in-vivo. Photobleaching of IRDye700DX increased with lower fluence rates and correlated with efficacy. The response in EGFR targeted PDT is strongly dependent on fluence rate used. The effectiveness of targeted PDT is, like PDT, dependent on the generation of singlet oxygen and thus the availability of intracellular oxygen.

Kinetic Study of Singlet-Oxygen Quenching and Aroxyl-Radical Scavenging Activities of Vitamin E Homologs and Fatty Acids Present in Vegetable Oils.

Recently, singlet-oxygen (1O2) quenching and aroxyl-radical (ArO·) scavenging rates (kQ and kS, respectively) of eight vegetable oils were measured in the ethanol/chloroform/D2O solution. Furthermore, the kQ and kS values and concentrations of four tocopherols and four tocotrienols contained in the vegetable oils were measured. In this study, the concentrations of nine fatty acids (including stearic, oleic, linoleic, and linolenic acids) comprising the above-mentioned eight vegetable oils were determined by gas chromatography. The kQ and kS values for ethyl stearate, ethyl oleate, ethyl linoleate, methyl linolenate, and glyceryl trioleate in the ethanol/chloroform/D2O solution were measured by UV-vis spectrophotometry. Based on the results obtained for the above-mentioned fatty acid esters, the kQ and kS values were estimated for nine fatty acids. Furthermore, comparisons of kQ values observed for the vegetable oils with the sum of the product {∑kQAO-i [AO-i]} of the kQAO-i values obtained for each antioxidant-i (AO-i) and the concentrations ([AO-i]) of AO-i (i.e., four tocopherols (& four tocotrienols) and nine fatty acids) contained in vegetable oils were performed. Based on the results, a detailed comparison of the contributions of the tocopherols (and tocotrienols) and the fatty acids to the 1O2-quenching rate constants (kQ) was performed. This indicated that both the tocopherols (and tocotrienols) and the fatty acids contribute to the 1O2- quenching. A similar comparison was conducted for the ArO· -scavenging rate constants (kS). The results suggested that only the tocopherols (and tocotrienols) contained in the oils contributed to the ArO· -scavenging, with negligible contribution from the fatty acids.

Acetyl zingerone: An efficacious multifunctional ingredient for continued protection against ongoing DNA damage in melanocytes after sun exposure ends

ObjectiveRecent research has shown that significant levels of cyclobutane pyrimidine dimers (CPDs) in DNA continue to form in melanocytes for several hours in the dark after exposure to ultraviolet radiation (UVR) ends. We document the utility of a new multifunctional ingredient, 3‐(4‐hydroxy, 3‐methoxybenzyl)‐pentane‐2,4‐dione (INCI acetyl zingerone (AZ)), to protect melanocytes against CPD formation after UVR exposure ends.MethodsThe use of AZ as an intervention to reduce CPD formation after irradiation was assessed in vitro by comparing kinetic profiles of CPD formation for several hours after irradiation in cells that were untreated or treated with AZ immediately after irradiation. Multifunctional performance of AZ as an antioxidant, quencher and scavenger was established using industry‐standard in vitro chemical assays, and then, its efficacy in a more biological assay was confirmed by its in vitro ability to reduce intracellular levels of reactive oxygen species (ROS) in keratinocytes exposed to UVA radiation. Molecular photostability was assessed in solution during exposure to solar‐simulated UVR and compared with the conventional antioxidant α‐tocopherol.ResultsEven when added immediately after irradiation, AZ significantly inhibited ongoing formation of CPDs in melanocytes after exposure to UVA. Incubation with AZ before irradiation decreased intracellular levels of UVA‐induced ROS formation in keratinocytes. Compared with α‐tocopherol, the molecular structure of AZ endows it with significantly better photostability and efficacy to neutralize free radicals (∙OH, ∙OOH), physically quench singlet oxygen (1O2) and scavenge peroxynitrite (ONOO−).ConclusionThese results designate AZ as a new type of multifunctional ingredient with strong potential to extend photoprotection of traditional sunscreens and daily skincare products over the first few hours after sun exposure ends.

Modulatory effect of Ficus carica on oxidative stress and hematological changes induced by gamma-radiation in male albino rats

The fig, Ficus carica L. (Moraceae), is a rich source of polysaccharides that possessed anti-tumour and anti-oxidant properties. The present study aimed to evaluate the ability of F. carica to protect against radiation-induced changes in certain biochemical and hematological parameters. This was achieved by measuring different hematological parameters, antioxidant enzyme activities, and lipid peroxidation; histological examination of liver and kidney was also performed. Rats used in this study were divided into four groups of 10 each- group 1: control, group 2: F. carica, group 3: irradiated rats, and group 4: F. carica pretreated irradiated rats. Ficus carica extract was prepared in water in a 1:3 w:v ratio and administered by gavage for three consecutive weeks before whole body gamma irradiation with 8 Gy (single dose). Five rats were sacrificed from each group at 24 and 72 h after radiation exposure. Irradiation resulted in marked reduction in white blood cell (WBC), platelets (PLT), lymphocyte, and neutrophil counts, whereas no significant changes were observed in red blood cells (RBCs) count, mean corpuscular volume (MCV), haemoglobin (Hb) concentration, mean corpuscular Hb (MCH), red cell distribution width (RDW), hematocrit (HCT) mean corpuscular Hb concentration (MCHC) and mean PLT volume (MPV). Radiation treatment increased thiobarbituric acid-reactive substances (TBARS) levels, catalase and superoxide dismutase (SOD) activities, and caused hepatic and renal damage. Oral administration of F. carica before irradiation significantly increased WBC, PLT, lymphocytes and neutrophils counts, along with a decrease in TBARS levels, and catalase and SOD activities in serum, liver, and kidney. These results suggested that consumption of F. carica a natural product with antioxidant capacity and capability to quench singlet oxygen could help mitigate cellular damage caused by whole-body irradiation-induced free radicals.

Novel Antioxidative Activity of Astaxanthin and Its Synergistic Effect with Vitamin E.

Astaxanthin (Asx) is known to be a potent quencher of singlet oxygen and an efficient scavenger of superoxide anion. However, the scavenging activity of Asx toward the hydroxyl radical was currently unclear because the high lipophilicity of Asx prevents analysis of such activity in water. Liposomes containing Asx (Asx-lipo) were previously shown to be dispersed in water. Analysis of the hydroxyl radical scavenging activity of Asx-lipo demonstrated a dose-dependence in water, with the effect of Asx being more potent than the vitamin E α-tocopherol (α-T). Furthermore, liposomes co-encapsulating Asx and vitamin E derivatives, namely tocotrienols (T3), showed a synergistic elimination effect on singlet oxygen and hydroxyl radical, although the antioxidative activity of liposomes co-encapsulating Asx and α-T was lower than the calculated additive value of each independent activity. A calculation of the most stable structure of Asx in the presence of α-T or T3, suggested that only T3 was able to hydrogen bond with Asx, and the Asx polyene chain partially interacting with the α-T3 triene chain, which could explain the synergistic effect between Asx and T3, but not Asx and α-T. This review introduces the hydroxyl radical scavenging activity of Asx, and its synergistic effect with T3.

Symmetrical phthalocyanine bearing four triptycene moieties: Synthesis, photophysical and singlet oxygen generation

Novel metal-free (7) and zinc(II) (8) phthalocyanine derivatives bearing four substituted triptycene moieties were synthesized and fully characterized by various spectroscopic methods including 1H-NMR, 13C-NMR, mass, FT-IR and UV-vis. Photophysical and photochemical properties such as electronic absorption, fluorescence emission, fluorescence lifetimes and singlet oxygen generation were investigated in toluene. The UV-vis spectra of 7 and 8 exhibited absorption bands in the visible region. The fluorescence lifetimes of 7 and 8 phthalocyanines were found to be 6.2 and 3.6 ns, respectively. The ability of the examined zinc(II) (8) and metal-free (7) to produce the singlet oxygen has been determined by both chemical and direct methods. While the chemical method 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen quencher was used in the first method, the direct determination has been done by recording the weak emission band of the singlet oxygen in the near-infrared region (1270 nm). From the direct process, the quantum yields of the singlet oxygen were found to be 0.28 (for 7) and 0.60 (for 8) and similar values were also obtained by the chemical method. The fluorescence quenching behavior of the studied phthalocyanine compounds (8 and 7) by electron-accepting 1,4 benzoquinone (BQ) was also studied in toluene. The powerful nanosecond laser flash photolysis technique was also employed to record the transient absorption spectra of the long-lived triplet states of the investigated compounds.

Cover Picture: Conditional Singlet Oxygen Generation through a Bioorthogonal DNA‐targeted Tetrazine Reaction (Angew. Chem. Int. Ed. 37/2019)

Tetrazine can act as an effective singlet oxygen quencher of halogenated BODIPY photosensitizers. In their Communication on page 12868 ff., O. Vázquez and co-workers report bioorthogonal, activatable probes that allow both organelle-specific localization and conditional singlet oxygen production simultaneously. These compounds open new avenues to combat the current limitations of photodynamic therapy. Cover design: Prof. M. Eugenio Vázquez.

Mutual Conservation of Redox Mediator and Singlet Oxygen Quencher in Lithium–Oxygen Batteries

Li–O2 batteries are plagued by side reactions that cause poor rechargeability and efficiency. These reactions were recently revealed to be predominantly caused by singlet oxygen, which can be neutralized by chemical traps or physical quenchers. However, traps are irreversibly consumed and thus only active for a limited time, and so far identified quenchers lack oxidative stability to be suitable for typically required recharge potentials. Thus, reducing the charge potential within the stability limit of the quencher and/or finding more stable quenchers is required. Here, we show that dimethylphenazine as a redox mediator decreases the charge potential well within the stability limit of the quencher 1,4-diazabicyclo[2.2.2]octane. The quencher can thus mitigate the parasitic reactions without being oxidatively decomposed. At the same time the quencher protects the redox mediator from singlet oxygen attack. The mutual conservation of the redox mediator and the quencher is rational for stable and effective Li...

Lycopene improves methotrexate-induced functional alterations of the Madin-Darby kidney cells in a concentration-dependent manner.

Lycopene is one of the most potent antioxidants among carotenoids due to its ability to quench singlet oxygen and react with free radicals to reduce DNA damage. Methotrexate is widely used in the treatment of several types of cancers and autoimmune diseases. One of the most common side effects of a high-dose of methotrexate is kidney injury. In this study, we evaluated effects of lycopene on the Madin-Darby canine kidney cells (MDCK) treated with methotrexate through the estimation of their mitochondrial and lysosomal functions ((4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide reduction assay and neutral red uptake assay) and changes in cell oxidative status (determination of advanced oxidized proteins concentrations and reduced glutathione levels) and lysosomal enzymes activity (β-N-acetyl glucosaminidase activity). Results of our study showed that lycopene applied in high concentration caused significant impairment of the MDCK function leading to cell death. Contrarily, in relatively low concentrations lycopene moderately ameliorated methotrexate-induced MDCK cell death estimated by both biochemical and microscopic analyses. It also prevented a significant decline in the MDCK cell lysosomal function estimated by neutral red accumulation ability and activity of the lysosomal enzyme β-N-acetyl glucosaminidase.

Lycopene – a bioactive carotenoid offering multiple health benefits: a review

SummaryLycopene is a natural red tomato pigment whose presence in the diet is beneficial to human health. It is believed to modify the course of chronic conditions, including neoplastic diseases. Clinical research results confirm its protective effects on the cardiovascular system. It lowers the risk of myocardial infarction, reduces blood pressure and prevents LDL cholesterol oxidation. High blood lycopene concentrations are also associated with lower risks of developing prostate, lung, uterine and breast cancer. Lycopene does not only inhibit proliferation of neoplastic cells, but it also induces their apoptosis and prevents metastasis. The health effects attributed to this compound are mostly derived from its antioxidant properties. It is a strong singlet oxygen quencher, and it thwarts lipid oxidation. Experimental and clinical studies have also confirmed lycopene's positive effects on the skeletal system and on neurodegenerative diseases, including Alzheimer's and Parkinson's.

Carbon-Carbon Double Bond and Resorcinol in Resveratrol and Its Analogues: What Is the Characteristic Structure in Quenching Singlet Oxygen?

Stilbenes, particularly resveratrol and resveratrol dimers, could effectively quench singlet oxygen (1O2). It was reported that both resorcinol and carbon-carbon double bond quenching 1O2 can participate in the mechanism. However, it is still not clear which structure plays a dominant role in quenching 1O2. To investigate the characteristic structure in the mechanism of quenching 1O2, the resveratrol, pterostilbene and piceatannol quenching 1O2 abilities were compared by UHPLC-QTOF-MS2 and UHPLC-QQQ-MS2. Results showed that catechol, carbon-carbon double bond and resorcinol participated in the quenching of 1O2. Catechol ring plays a leading role in the mechanism, and the contribution of the structures in quenching 1O2 activity are as follows: catechol ring > carbon-carbon double bond > resorcinol ring, which is supported by the calculation of energy. Our findings will contribute to the future screening of stilbenes with higher activity, and those stilbenes may have great therapeutic potential in 1O2-mediated diseases.

Synergistic Effect in Zinc Phthalocyanine—Nanoporous Gold Hybrid Materials for Enhanced Photocatalytic Oxidations

Nanoporous gold (npAu) supports were prepared as disks and powders by corrosion of Au-Ag alloys. The npAu materials have pore sizes in the range of 40 nm as shown by scanning electron microscopy (SEM). The surface was modified by a self-assembled monolayer (SAM) with an azidohexylthioate and then functionalized by a zinc (II) phthalocyanine (ZnPc) derivative using “click chemistry”. By atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) the content of zinc was determined and the amount of immobilized ZnPc on npAu was calculated. Energy-dispersive X-ray (EDX) spectroscopy gave information about the spatial distribution of the ZnPc throughout the whole porous structure. NpAu and ZnPc are both absorbing light in the visible region, therefore, the heterogeneous hybrid systems were studied as photocatalysts for photooxidations using molecular oxygen. By irradiation of the hybrid system, singlet oxygen is formed, which was quantified using the photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a selective singlet oxygen quencher. The illuminated surface area of the npAu-ZnPc hybrid system and the coverage of the ZnPc were optimized. The synergistic effect between the plasmon resonance of npAu and the photosensitizer ZnPc was shown by selective irradiation and excitation of only the phthalocyanine, the plasmon resonance of the npAu support and both absorption bands simultaneously, resulting in an enhanced photooxidation activity by nearly an order of magnitude.

Quenching of singlet oxygen by extract of peels of the fruit of syzygium cumini

Recent research has shown the importance of plant extracts as powerful antioxidants owing to the presence of chemically active components such as polyphenols, anthocyanins, flavonoids, among others. This synergy of the components becomes a possible alternative to the use of antioxidants of synthetic origin. In this study, Syzygium cumini fruit peel was used to determine the antioxidant activity against singlet oxygen. The extract showed appreciable amounts of phenolic groups (about 8.55 AGE mg/g fruit weight). HPLC-DAD characterization showed at least 3 anthocyanins of higher relative abundance (malvidin 3,5-diglucoside, delphinidin 3,5-diglucoside and petunidin 3,5-diglucoside). The percentage of quenching of singlet oxygen was determined at different concentrations of the ethanolic extract, finding a value of 60% at a concentration of 0.39 mg/mL.

To perform phytochemical screening and study the antioxidant potential of isolated compound from Hemidesmus indicus

“Anantmul” is an important and widely used medicinal plant. The study aimed to determine the physicochemical composition, bioactive compounds and antioxidant activity of Hemidesmus indicus (Asclepiadaceae). The roots of the plant were collected and sequentially extracted using petroleum ether, ethyl acetate, and methanol. The preliminary phytochemical screening of extracts was carried out and found to be a good source of bioactive compounds. Biological activities of flavonoid and phenolic compounds have been discovered in several latest studies. Further phytochemical isolation was carried out, and Lupeol was isolated. Phenols are shown to be multifunctional antioxidants which will perform as singlet oxygen quenchers. Lupeol was evaluated for in-vitro antioxidant activity. It showed a correlation with antioxidant activity by DPPH (IC50 = 0.52, P 6 0.05) and H2O2 (IC50 = 0.43, P 6 0.05). The results show promising perspectives for the exploitation and use of anantmul rhizome as a constituent of anti-aging as well as anticancer diet.
 Keywords: Anantmul, Lupeol, Antioxidant, DPPH

Quenchers Protect BChl850 from Action of Singlet Oxygen in the Membranes of a Sulfur Photosynthetic Bacterium Allochromatium vinosum Strain MSU

The effect of singlet oxygen was studied in the system of Allochromatium (Alc.) vinosum MSU membranes, rose bengal, and light (547−600nm) with and without a quencher. In the system without a quencher, bleaching of the BChl850 band of the LH2 light-harvesting complex was observed and an absorption peak emerged at 698 nm, which belonged to the oxidized product, 3-acetyl-chlorophyll. The efficiency of five quenchers of singlet oxygen for neutralization of the effect of singlet oxygen on bacteriochlorophyll in the light-harvesting complexes of the membranes Alc. vinosum MSU was studied: sodium ascorbate, histidine, imidazole, trolox, and sodium azide. All of them, with the exception of sodium azide, neutralized successively the effect of singlet oxygen.

Antioxidant role on the protection of melanocytes against visible light-induced photodamage

Visible light can induce the generation of singlet oxygen and can cause oxidative stress, especially in melanocytes due to melanin photosensitization. Currently, there is no organic UV-filter that provide visible light protection. Previous studies showed that some antioxidants, such as apigenin (API), chrysin (CRI) and beta-carotene (BTC) besides neutralizing radical chain reactions can also quench singlet oxygen via physical or chemical quenching and exhibit potential for use in photoprotection. Therefore, the aim of this study is to evaluate the efficacy of API, CRI and BTC on the protection against cell death induced by melanin photosensitization and understand the underlying mechanisms that are involved in the protection. Precise protocols of melanogenesis and quantification of singlet oxygen generation were developed. Viability of B16-F10 cells with melanin basal levels and after melanogenesis induction was evaluated after visible light exposure in the presence and absence of API, CRI and BTC. Results showed that API and BTC protected cells from photoinduced cell death API exhibiting superior photoprotective effect. We noticed that the efficiency of cell protection and the rate of singlet oxygen suppression are not well correlated, at least for the studied series of antioxidants, indicating that the anti-radical capacity should be playing a major role in protecting cells against the damage induced by melanin photosensitization. In terms of sun care strategies, both API and BTC offer protection against visible light-induced damages and may be effective topical antioxidants to be added to sunscreens.

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

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).