Participation Of Singlet Oxygen Research Articles

Unraveling the generation mechanism of singlet oxygen in Bi2WxMo1-xO6 solid solution and roles in photocatalytic degradation of gaseous toluene under visible-light irradiation

Photocatalytic degradation volatile organic compounds (VOCs) represent an appealing strategy since the inexhaustible solar energy and facile reaction condition. In this work, a flower-like microsphere Bi2WxMo1-xO6 solid solution photocatalysts with abundant oxygen vacancies (OVs) were prepared via HTAB-assisted hydrothermal method. The mole ratio of W and Mo atoms were regulated by adjusting the stoichiometric ratio of their precursor. The optimized Bi2W0.25Mo0.75O6 presented outstanding photocatalytic performance with 96.8% of toluene degradation rate after 180 min of irradiation under visible light (>420 nm), which was 13.76 times higher than that of pure Bi2MoO6 and 10.32 times higher than that of pure Bi2WO6, respectively. The enhanced photocatalytic activity of Bi2W0.25Mo0.75O6 was attributed to the optimized band structure and efficient separation efficiency of carriers as well as the participation of singlet oxygen (1O2) radicals. Free radical trap experiments and electron spin resonance investigations revealed that 1O2, hydroxyl radical, and holes were the predominated reactive oxygen species (ROSs) in toluene degradation. Meanwhile, the generation of 1O2 was related to abundant OVs of Bi2W0.25Mo0.75O6 solid solution. This work suggested that solid solution with abundant OVs was an effective photocatalyst to improve the VOCs degradation activity under visible-light irradiation.

Formation of long-lived reactive species of blood serum proteins induced by low-intensity irradiation of helium-neon laser and their involvement in the generation of reactive oxygen species

It was demonstrated that low-intensity radiation of helium-neon (He-Ne) laser at 632.8nm, which leads to the transition of oxygen to a singlet state, causes the formation of reactive oxygen species (ROS) – hydrogen peroxide, hydroxyl and superoxide (hydroperoxide) radicals – in aqueous solutions. The oxygen effect – dependence of hydrogen peroxide formation on the concentration of molecular oxygen – was shown, and the participation of singlet oxygen, hydroxyl radicals and superoxide (hydroperoxide) radicals in this process was testified. Laser radiation-induced ROS in solutions of blood serum proteins, bovine serum albumin and bovine gamma-globulin, cause the formation of long-lived reactive protein species (LRPS) with a half-life of about 4h. The generation of LRPS caused by laser irradiation results in prolonged several-hour generation of ROS – hydrogen peroxide, hydroxyl and superoxide radicals. As affected by LRPS, coupled radical reactions lead to conversion of dissolved molecular oxygen to hydrogen peroxide. Irradiation with light sources away from the oxygen absorption band is not attended by formation of ROS and LRPS. A consideration is provided for the possible molecular mechanisms of ROS formation under the influence of He-Ne laser irradiation, the role of proteins in their generation and the biological significance of these processes.

Abstract 5396: Nanoparticles loaded with indium (III) phthalocyanine are more effective in promoting cell proliferation inhibition on MCF-7 breast cancer cells when compared to free InPc

Abstract Background: Indium (III) phthalocyanine (InPc) was encapsulated into nanoparticles (NP) of PEGylated poly (D,L-lactide-co-glycolide) (PLGA-PEG) to improve the photobiological activity of the photosensitizer. The efficacy of NP loaded with InPc and their cellular uptake was investigated with MCF-7 cells, and compared with the free InPc. Methods: NP were prepared by the method of emulsion/evaporation. The emulsion was washed and centrifuged and lyophilized. The lyophilized particles were characterized via scanning electron microscopy. The evaluation of the cell suspensions viability incubated with InPc free and encapsulated and subsequently irradiated with a 665 nm laser diode was performed at different concentrations of InPc (1.8-7.5 mol/L), incubation times (1-2h) and laser power (10-100mW) by MTT assay. The internalization of the InPc free and encapsulated cells was assessed via confocal microscopy. Measurement of absorbance spectra and fluorescence of free and encapsulated InPc were monitored during irradiation assessment photodegradation to the photosensitizer. The generation of singlet oxygen was monitored by electron paramagnetic resonance spectroscopy. Findings: The influence of photosensitizer (PS) concentration (1.8-7.5 mol/L), incubation time (1-2h), and laser power (10-100mW) were studied on the photodynamic effect caused by the encapsulated and the free InPc. NP with a size distribution ranging from 61 to 243 and with InPc entrapment efficiency of 72±6% were used in the experiments. Only the photodynamic effect of encapsulated InPc was dependent on PS concentration and laser power. The InPc loaded NP were more efficient in reducing MCF-7 cell viability than the free PS. For a light dose of 7.5 J/cm2 and laser power of 100 mW, the effectiveness of encapsulated InPc to reduce the viability was 34±3 % while for free InPc was 60±7 %. Confocal microscopy showed that InPc-loaded NP, as well as free InPc, were found throughout the cytosol. The NP aggregates and the aggregates of free PS were found in the cell periphery and outside of the cell. The NP aggregates were generated due to the particles concentration used in the experiment because of the small loading of the InPc while the low solubility of InPc caused the formation of aggregates of free PS in the culture medium. The participation of singlet oxygen in the photocytotoxic effect of InPc-loaded NP was corroborated by electron paramagnetic resonance experiments, and the encapsulation of photosensitizers reduced the photobleaching of InPc. Interpretation: The InPc encapsulated was more effective in reducing the MCF-7 viability compared to InPc free due to increased internalization of InPc encapsulated in tumor cells due to the aggregate state of the InPc free hampering the generation of singlet oxygen. Note: This abstract was not presented at the meeting. Citation Format: Carlos Augusto Zanoni Souto, Klesia Pirola Madeira, Leticia Rangel, André Romero da Silva. Nanoparticles loaded with indium (III) phthalocyanine are more effective in promoting cell proliferation inhibition on MCF-7 breast cancer cells when compared to free InPc. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5396. doi:10.1158/1538-7445.AM2014-5396

Improved photodynamic action of nanoparticles loaded with indium (III) phthalocyanine on MCF-7 breast cancer cells

Indium (III) phthalocyanine (InPc) was encapsulated into nanoparticles of PEGylated poly(d,l-lactide-co-glycolide) (PLGA-PEG) to improve the photobiological activity of the photosensitizer. The efficacy of nanoparticles loaded with InPc and their cellular uptake was investigated with MCF-7 breast tumor cells, and compared with the free InPc. The influence of photosensitizer (PS) concentration (1.8–7.5 μmol/L), incubation time (1–2 h), and laser power (10–100 mW) were studied on the photodynamic effect caused by the encapsulated and the free InPc. Nanoparticles with a size distribution ranging from 61 to 243 nm and with InPc entrapment efficiency of 72 ± 6 % were used in the experiments. Only the photodynamic effect of encapsulated InPc was dependent on PS concentration and laser power. The InPc-loaded nanoparticles were more efficient in reducing MCF-7 cell viability than the free PS. For a light dose of 7.5 J/cm2 and laser power of 100 mW, the effectiveness of encapsulated InPc to reduce the viability was 34 ± 3 % while for free InPc was 60 ± 7 %. Confocal microscopy showed that InPc-loaded nanoparticles, as well as free InPc, were found throughout the cytosol. However, the nanoparticle aggregates and the aggregates of free PS were found in the cell periphery and outside of the cell. The nanoparticles aggregates were generated due to the particles concentration used in the experiment because of the small loading of the InPc while the low solubility of InPc caused the formation of aggregates of free PS in the culture medium. The participation of singlet oxygen in the photocytotoxic effect of InPc-loaded nanoparticles was corroborated by electron paramagnetic resonance experiments, and the encapsulation of photosensitizers reduced the photobleaching of InPc.

Photochemical Degradation of the Plant Growth Regulator 2‐(1‐Naphthyl) acetamide in Aqueous Solution Upon UV Irradiation

The photochemical degradation of 2-(1-naphthyl) acetamide (NAD) in aqueous solution using simulated sunlight excitation as well as UV light within the 254-300 nm range was investigated to obtain an insight into the transformation mechanism that could occur under environmental conditions. Several photoproducts were identified using HPLC/MS/MS techniques. The degradation quantum yield was found to be independent of the excitation wavelength, but showed a dependence of oxygen concentration. This increased by a factor of approximately 3 from aerated to oxygen-free solutions. There is a clear involvement of both triplet and singlet excited states in NAD photoreactivity. The participation of singlet oxygen as a significant route in NAD degradation was ruled out by comparison with the behavior using Rose Bengal as a photosensitizer. A mechanistic pathway implying hydroxylation process through NAD radical cation species as well as an oxidation reaction by molecular oxygen is proposed. The photochemical behavior of NAD appears to mainly involve the aromatic moieties without any participation of the amide side chain. Toxicity tests clearly show that the generated primary photoproducts are responsible for a significant increase in the toxicity. However, upon prolonged irradiation this toxicity tends to decrease.

Singlet oxygen in the heterogeneous catalytic oxidation of benzene

The partial oxidation of benzene on vanadium and molybdenum oxides and the participation of singlet oxygen in this reaction were studied. A correlation between the activity of the catalysts in the partial oxidation of benzene and their ability to generate singlet oxygen was observed. The character of the initiation of oxidative benzene transformations under the action of molecular singlet oxygen was analyzed.

Photooxidation of Acyclovir with Thermally Generated Triplet Excited Ketones. A Comparison with Type I and II Photosensitizers

The antiviral drug acyclovir (Ac, 1) was treated with triplet excited ketones, which have been generated in thermal decomposition of 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane (HTMD), in the dark. Three major oxidation products were detected by means of spectroscopic measurements. The products were (2-hydroxyethoxy) methyl spiroiminodihydantoin (2), (2-hydroxyethoxy) methyl (amino)-2-imino-1,2-dihydroimidazole-5-one (3), and 2,2-diamino-4-[(2-hydroxyethoxy) methyl) amino)-5-[2H]-oxazolone (4). Equal amounts of type I and type II photooxidation products were found, as could be established by comparison with predominant type I (riboflavin) and type II (rose bengal) photosensitizers. The concentration and time profiles for the HTMD-induced oxidation of Ac were also determined. The participation of singlet oxygen in HTMD-induced oxidation was confirmed by the substantial D(2)O effect in the formation of spiroiminodihydantoin (2).

P-nitrobenzamide substituted phosphorus(V) porphyrins: synthesis and interactions with DNA

Four new phosphorus(V) porphyrins were designed and synthesized. The compounds were diaxially substituted with 4-nitrobenzamide. The axial ligands were attached to the P(V) center of the porphyrins through methylene linkers of different lengths. DNA titrations showed the expected porphyrin binding. When exposed to 532 nm laser light, which corresponds to the porphyrin Q band, the photosensitizers induced DNA nicking. Inhibition of the nicking by sodium azide suggested participation of singlet oxygen in the process. Photoexcitation with 305 nm laser light, which corresponds to absorption of 4-nitrobenzamide, also resulted in DNA damage. Due to the lack of electronic communication between the axial ligands and the porphyrin, the desired pathway of DNA cleavage was chosen by selecting a proper wavelength of the light used for photoexcitation. The activities of the porphyrins in photoinduced DNA nicking were very similar in both experiments: irradiation with 305 and 532 nm light, and were inversely correlated with the length of the linkers.

Production of singlet oxygen in a non-self-sustained discharge

The production of O2(a1Δg) singlet oxygen in non-self-sustained discharges in pure oxygen and mixtures of oxygen with noble gases (Ar or He) was studied experimentally. It is shown that the energy efficiency of O2(a1Δg production can be optimized with respect to the reduced electric field E/N. It is shown that the optimal E/N values correspond to electron temperatures of 1.2–1.4 eV. At these E/N values, a decrease in the oxygen percentage in the mixture leads to an increase in the excitation rate of singlet oxygen because of the increase in the specific energy deposition per O2 molecule. The onset of discharge instabilities not only greatly reduces the energy efficiency of singlet oxygen production but also makes it impossible to achieve high energy deposition in a non-self-sustained discharge. A model of a non-self-sustained discharge in pure oxygen is developed. It is shown that good agreement between the experimental and computed results for a discharge in oxygen over a wide range of reduced electric fields can be achieved only by taking into account the ion component of the discharge current. The cross section for the electron-impact excitation of O2(a1Δg and the kinetic scheme of the discharge processes with the participation of singlet oxygen are verified by comparing the experimental and computed data on the energy efficiency of the production of O2(a1Δg and the dynamics of its concentration. It is shown that, in the dynamics of O2(a1Δg molecules in the discharge afterglow, an important role is played by their deexcitation in a three-body reaction with the participation of O(3P) atoms. At high energy depositions in a non-self-sustained discharge, this reaction can reduce the maximal attainable concentration of singlet oxygen. The effect of a hydrogen additive to an Ar: O2 mixture is analyzed based on the results obtained using the model developed. It is shown that, for actual electron beam current densities, a significant energy deposition in a non-self-sustained discharge in the mixtures under study can be achieved due to the high rate of electron detachment from negative ions. In this case, however, significant heating of the mixture can lead to a rapid quenching of O2(a1Δg molecules by atomic hydrogen.

Participation of singlet oxygen in ultraviolet-a-induced lipid peroxidation in mouse skin and its inhibition by dietary β-carotene: an ex vivo study

Dietary β-carotene acts as a photoprotective agent in the skin, but the exact mechanism of protection is unknown. This ex vivo study is focused on determining the mechanism of action of β-carotene against UV-A-induced skin damage by characterizing peroxidized phosphatidylcholine (PC) and β-carotene oxidation products. BALB/c mice were fed with basal or a β-carotene-supplemented diet, and homogenates from their dorsal skin were prepared after 3 weeks for UV-A irradiation. Analyses revealed that the degree of lipid peroxidation in the β-carotene group was significantly lower than that in the controls. The isomeric composition of hydroperoxy fatty acids, constituting peroxidized PC, was determined by thin-layer chromatography-blotting followed by gas chromatography/mass spectrometry (MS)/selected ion monitoring analysis. The 9- and 10-isomers of peroxidized PC, resulting from the reaction of singlet molecular oxygen ( 1O 2) with oleic acid, were elevated in the UV-A-exposed control group compared to the experimental group. Similar results were obtained from methylene-blue-sensitized photooxidation of mouse skin lipids in vitro. Liquid chromatography/MS analysis of the homogenates confirmed the formation of β-carotene 5,8-endoperoxide, a specific marker for the 1O 2 reaction. These results indicate that dietary β-carotene accumulates in the skin and acts as a protective agent against UV-A-induced oxidative damage, by quenching the 1O 2.

Enhancement of Riboflavin-Mediated Photo-Oxidation of Glucose-6-P Dehydrogenase by Urocanic Acid

We have investigated the riboflavin (RF)-sensitized inactivation of glucose 6-phosphate dehydrogenase (G6PD) in the presence and absence of trans-urocanic acid (UCA). The inactivation of the enzyme results from its direct oxidation by the excited triplet RF in a Type-I-photosensitized reaction whose efficiency increases at low oxygen concentration. The addition of histidine to the system produced no change in the inactivation rate, discarding the participation of singlet oxygen in the reaction. On the other hand, the presence of UCA results in its bleaching, with a significant enhancement of RF-mediated inactivation of G6PD. Both the consumption of UCA and G6PD are faster at low oxygen concentrations. UCA also produced a decrease in the sensitizer photodecomposition yield. These results indicate that the enhancement of the RF-mediated G6PD inactivation observed in the presence of UCA is not a singlet oxygen-mediated process. It is proposed that UCA consumption and its effect on G6PD inactivation are due to a complex reaction sequence initiated by a direct oxidation of UCA by the excited sensitizer triplet. The oxidation of the semireduced flavin gives rise to reactive oxygen species (ROS) responsible for the increased rate of the process. This is supported by the protection afforded by several additives with ROS removal capacity: benzoate, superoxide dismutase and catalase.

Photoprotector capacity of lichen metabolites assessed through the inhibition of the 8-methoxypsoralen photobinding to protein

Lichens produce a diversity of phenolic compounds, some of which efficiently absorb ultraviolet radiation, 8-Methoxypsoralen (8-MOP), commonly used in the treatment of psoriasis, binds irreversibly to proteins in the presence of ultraviolet radiation by a mechanism that is not well established. In this paper we demonstrate the photoprotector capacity of three phenolic compounds — pannarin, l'-chloropannarin and atranorin — through the inhibition of 8-MOP-human serum albumin (HSA) photobinding. The method measures the UV-filtering capacity of lichen compounds by means of a double-tube compartment (thus, solubility and interaction with the reaction medium is avoided). Photobinding was determined by measuring the radioactivity of mixtures containing 8-(methyl- 3H) MOP and HSA irradiated at 360 and 310 nm in the presence of increasing concentrations of lichen phenolics. Pannarin, l'-chloropannarin and atranorin at a concentration of 10 mM and irradiated at 360 nm, inhibited photobinding to HSA by 40.4%, 31.7% and 20.1% respectively. Pannarin (10 mM) irradiated at 310 nm inhibited the photobinding by 35.2%. The participation of singlet oxygen and hydroxyl radicals was demonstrated in the photoreaction process.

Reaction of singlet oxygen with 2'-deoxyguanosine and DNA. Isolation and characterization of the main oxidation products.

The reaction of singlet molecular oxygen with 2'-deoxyguanosine and DNA was studied. Emphasis was placed on the identification and characterization of the main methylene blue mediated type II (singlet oxygen) oxidation products of 2'-deoxyguanosine and its corresponding 3',5'-di-O-acetylated derivative. Two major oxidation products of 2'-deoxyguanosine were isolated and characterized by mass spectrometry analysis and extensive 1H and 13C NMR measurements as the two 4R* and 4S* diastereomers of 4,8-dihydro-4-hydroxy-8-oxo-2'-deoxyguanosine. The addition of 1O2 was also found to occur to the base moiety of the corresponding 3',5'-di-O-acetylated derivative. Methylene blue mediated photosensitization of 2'-deoxyguanosine led also to the production of 7,8-dihydro-8-oxo-2'-deoxyguanosine, but in a relatively lower yield with respect to the two above diastereomers. The participation of singlet oxygen in the mechanism of formation of these oxidation products was confirmed. A reasonable mechanism involving the transient formation of an unstable endoperoxide produced through a Diels-Alder 1,4-cycloaddition of singlet oxygen to the purine ring is suggested. Quantitative analysis allowed us to demonstrate that the two diastereomers of 4,8-dihydro-4-hydroxy-8-oxo-2'-deoxyguanosine are the main singlet oxygen oxidation products of the guanine moiety within nucleosides, whereas 7,8-dihydro-8-oxoguanine was found to be the major 1O2 oxidation product of guanine in double-stranded DNA.

Diterpenes from the aerial part of Salvia columbariae

The new diterpenes 11,12-di- O-methylrosmanol and 11,12-di- O-methylcarnosol, together with the known compounds carnosic acid, carnosol, rosmanol, epirosmanol, isorosmanol, salvicanol and rosmadial were isolated from the aerial part of Salvia columbariae. The structures of the new diterpenes were established from their spectral data and by chemical correlations. The co-occurence of all these compounds in a single species provides further support of our previously postulated biogenetic pathway to highly oxidized abietatriene compounds involving enzymatic dehydrogenation processes and the participation of singlet oxygen.

Ascorbate-assisted, phthalocyanine-sensitized photohaemolysis of human erythrocytes.

The rate of photohaemolysis of human red blood cells sensitized by chloroaluminium phthalocyanine sulphonate is increased by ascorbate, with or without added FeCl3. Stimulation of haemolysis by ascorbate without addition of metal salt, and in the presence of a strong chelator such as desferrioxamine, is an unexpected phenomenon. Lysis rate and ascorbate concentration were directly related, suggesting that ascorbate acts as a reactant and not as a catalyst. The process also requires oxygen; azide and D2O tests indicate some participation of singlet oxygen, although to a lesser extent than in the photosensitized haemolysis in the absence of ascorbate. Kinetic considerations suggest a reaction path initiated by excited sensitizer and ascorbate, parallel to the singlet oxygen-mediated process. Because of the ubiquitous presence of ascorbate in human tissues in concentrations comparable to those of dissolved oxygen, it is quite possible that in photodynamic therapy a fraction of the photodynamic damage proceeds via a Type I, ascorbate-assisted, mechanism.

ChemInform Abstract: The Participation of Singlet Oxygen in Dye‐Sensitized Photooxidation Reaction of Catecholamines.

AbstractThe photooxidation of catecholamines (adrenaline, noradrenaline, and dopamine) sensitized by methylene blue, rose bengal, and fluoresceine proceed via aminochromes and an indolic pathway.

The Participation of Singlet Oxygen in Dye-Sensitized Photooxidation Reaction of Catecholamines

The Participation of Singlet Oxygen in Dye-Sensitized Photooxidation Reaction of Catecholamines

ChemInform Abstract: Dye‐sensitized Photo‐oxygenation of sym‐Diphenylthiourea.

AbstractThe participation of singlet oxygen in the title reaction has been confirmed by using scavengers which decreäse the yield considerably (yield not given).

Mechanisms of photodynamic inactivation of acridine orange-sensitized transfer RNA : Participation of singlet oxygen and base damage leading to inactivation.

The photodynamic inactivation of acridine orange (AO)-sensitized tRNA was investigated with respect to the type of photochemical pathways and the base damage leading to the inactivation. The diagnostic tests for singlet oxygen (1O2), namely the enhancement effect of deuterium oxide (D2O) and the inhibition effect by sodium azide, indicated that 1O2 was involved as the reactive intermediate in the photoinactivation (the Type II mechanism). Furthermore, the D2O effect was more pronounced at high ionic strength and under low dye to RNA ratio conditions, indicating that monomerically bound AO acts exclusively through the Type II mechanism. With respect to base damage, the present studies show that guanine is destroyed and tRNA-AO occurs as a photoadduct. The formation of photoadduct was enhanced under N2, and little affected by D2O, excluding the possibility that the photoadduct is responsible for the photoinactivation. Conversely, effects of D2O and azide on the photoinactivation, in conjunction with the predominance of the Type II mechanism in the known cases of guanine destruction by AO-photosensitization, indicate that the destruction of guanine by 1O2 is the most probable critical damage in the photodynamic inactivation of tRNA.

Participation of singlet oxygen in photodegradation of air-saturated solutions of coumarin dyes

Solutions of coumarin dyes are used to generate stimulated emission in the blue-green region of the spectrum [i]. During irradiation of the active medium by flash pump lamps, the dye becomes degraded~ and this leads to a decrease in the generation energy. The photolysis ofcoumarin dyes has been studied by several authors [2-6]. At present, the photodimerization reaction of coumarins in solutions [2] and photoreduction in deoxygenated ethanol [3] are known, and the opening of the pyrone ring of coumarins by the action of irradiation is suggested in some papers [4, 5]. Dealkylation products of amino groups and oxidation products of the methyl group were isolated as the photolysis products of 7-diethylamino-4methylcoumarin. It was shown that it is oxidation of the methyl group that determines deterioration in the generational characteristics of the laser, since the photoproducts formed absorb emission in the generation region, while the role of the remaining processes is inappreciable [6]. The oxidation mechanism was not studied. To clarify the oxidation mechanism of the photooxidation of coumarin dyes serving as laser media, we studied the regularities of their photolysis in air-saturated solutions.