Involvement Of 1O2 Research Articles

Activation of peroxymonosulfate via mediated electron transfer mechanism on single-atom Fe catalyst for effective organic pollutants removal

Cheap and abundant Fe based catalysts in advanced oxidation progresses (AOPs) usually exhibit radicals or high-valent Fe species (HV-Fe) dominated activation mechanism. In this contribution, the atomically dispersed Fe on g-C3N4 (SAFe-CN) was fabricated for peroxymonosulfate (PMS) activation to degrade o-phenylphenol (OPP). OPP removal was not impeded by common radical scavengers, indicating the absence of SO4•− and •OH. The involvement of 1O2 and HV–Fe was excluded and the mediated electron transfer was finally identified as the dominated mechanism. Atomically dispersed Fe sites in SAFe-CN were verified as active sites for reacting with OO bond of PMS and ulteriorly electron shuttling in pollutants degradation. A water treatment filter was fabricated using SAFe-CN and it remained 100% of OPP removal after 100 h of operation. These results provide new insights into the mechanism of mediated electron transfer as well as potential application of non-radical dominated process at device level.

Contribution of dissolved organic matter to the photolysis of methylmercury in estuarine water

The photodemethylation (PD) is a dominant degradation process of methylmercury (MeHg) in sunlit surface seawater, leading to the decreased bioaccumulation of MeHg in pelagic organisms. This study investigated the PD rate constant of MeHg in artificial estuarine water under UV-A irradiation, with the addition of various types of dissolved organic matter (DOM) to understand the PD pathway. In the PD simulation with ~180 μmol C L−1 of DOM, microbial fulvic acid showed a higher rate constant (k = 0.16 m2 E−1) than that of terrestrial humic acid (k = 0.11 m2 E−1) and fulvic acid (k = 0.12 m2 E−1). Adding sodium azide and isopropyl alcohol decreased the PD rate constant by 44–74% in the presence of humic and fulvic acids, implying the considerable involvement of 1O2 and ∙OH. On the contrary, the direct PD of MeHg-Cl was a major process in the presence of non-thiol aromatic ligands with the rate constant ranging from 0.033 to 0.036 m2 E−1. When glutathione was added to the artificial estuarine water, the rate constant increased to 0.15 m2 E−1 with MeHg-glutathione as a major MeHg species, implying that as the HgC bond is weakened by the formation of MeHg-thiol complex, the PD rate constant is increased. It is noteworthy that the addition of thiosalicylic acid to simulated estuarine water produced an exceptionally high rate constant (k = 4.1 m2 E−1); however, such a high value was not obtained from natural coastal water (k = 0.15–0.18 m2 E−1). The results suggest that the ordinary contents of DOM in estuarine water are likely to increase the PD rate of MeHg via the production of 1O2 and ∙OH, and the formation of MeHg-aliphatic thiol complexes facilitating intramolecular charge transfer.

Effect of Reactive Species Photogenerated by the Ultraviolet Irradiation of TiO2 on the Peroxidation of Linoleic Acid

This article shows that hydroxyl radicals adsorbed on the surface of TiO2 (Ti-•OH groups) account for about 70–100% of the photocatalytic peroxidation of linoleic acid under UVB irradiation, which results into malondialdehyde production. The experimental data are silent concerning the involvement of 1O2 in the process, although an upper limit of 30% can be hypothesized, while an involvement of surface-bound holes into the lipoperoxidation process can be excluded.

Singlet oxygen quantum yields (Φd) in water using beetroot extract and an array of LEDs

It is proposed a simple and inexpensive strategy to determine singlet oxygen (¹O2) quantum yields (ΦΔ) of photosensitizers (PS) in water using beetroot extract containing betacyanin (Bc) and a set of light emitting diodes (LEDs) for excitation. Bc, a cationic natural dye, was obtained by flash chromatography purification from the red beet extract (Beta vulgaris) and employed as a convenient probe for ¹O2 detection. Solutions of Bc and PS were illuminated with an array of LEDs adapted in the cuvette compartment of a commercial spectrophotometer, and the decrease in Bc absorbance was followed as a function of time. Bc photobleaching decreased in de-aerated solution and increased in D2O, indicating the involvement of ¹O2. The observed photobleaching rate constant (k obs) was proportional to the LED intensity, concentration and ΦΔ of the PS. By keeping the light source constant we could estimate the overlap integral (R) between the LED emission and PS absorbance for different PS concentrations. The slope of R versus k obs is the value of the photobleaching rate constant (k), which was shown to be proportional to ΦΔ. Values of ΦΔ obtained by this method were compared with those obtained by measuring NIR (near infrared) emission for a series phenothiazine dyes.

Involvement of Singlet Oxygen in Cytochrome P450-Dependent Substrate Oxidations

Cytochrome P450 (P450)-dependent p-hydroxylation of aniline and o-deethylation of 7-ethoxycoumarin were examined in rat liver microsomes in the presence of radical scavengers. The addition of β-carotene, a quencher of singlet oxygen species (1O2), suppressed the aniline hydroxylation, while the addition of sodium azide (NaN3) (1O2 quencher) enhanced the reaction. No other reactive oxygen scavengers or chelating agents such as superoxide dismutase, catalase, dimethylsulfoxide, or deferoxamine altered the reaction. In contrast, the microsomal o-deethylation of 7-ethoxycoumarin was suppressed by the addition of NaN3. 1O2 was detectable during the reaction of microsomes and NADPH by ESR spin-trapping when 2,2,6,6-tetramethyl-4-piperidone (TMPD) was used as a spin trap, and the 1O2 was quenched by the additions of β-carotene, NaN3, aniline, and 7-ethoxycoumarin. The enhancement effect of NaN3 in the hydroxylation of aniline appeared to be due to the conformational change of P450 protein, which in turn enhances the binding of aniline to P450 in terms of the spectral dissociation constant (Ks). In contrast, 1O2 appeared to be active in the o-deethylation of 7-ethoxycoumarin. On the basis of the results, the involvement of 1O2 in P450-dependent substrate oxygenations is proposed.

Oxidation of Hypotaurine to Taurine with Photochemically Generated Singlet Oxygen: The Effect of Azide

Hypotaurine is oxidized to taurine by singlet oxygen (1O2) generated with methylene blue used as a photosensitizer. The oxidation rate increases in the presence of deuterium oxide as expected for the involvement of1O2. Addition of the1O2quencher azide also produced an activating effect in contrast with the expected inhibition. Azidyl radicals produced by the oxidation of azide by the horseradish peroxidase/hydrogen peroxide system stimulate the oxidation of the added hypotaurine. It is concluded that azide competes with hypotaurine for1O2generating the azidyl radical which is a strong one-electron oxidant transfer of the radical to hypotaurine. The hypotaurine radical is then converted into taurine, possibly through the disulfone intermediate. Formation of the sulfonic hydroperoxide is the possible intermediate in the absence of azide. The finding that the azidyl radical efficiently oxidizes hypotaurine to its metabolic product taurine raises the expectation of hypotaurine being a valuable scavenger of endogenous and exogenous radicals.

Selective para hydroxylation of phenol and aniline by singlet molecular oxygen.

Phenol reacts with singlet oxygen (1O2) generated in aqueous solution (H2O or D2O) by (a) the exposure of methylene blue to light or (b) the thermal dissociation of the endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate to lead selectively to hydroquinone as the primary product. The other isomers of phenol hydroxylation, catechol and resorcinol, were not observed. In agreement with the involvement of 1O2 as the reactive species in the hydroxylation, in D2O the yield of hydroquinone is 7 times that in H2O, and the 1O2 quenchers azide and the thiols, glutathione and dithiothreitol, suppress the production of hydroquinone. In contrast, the hydroxyl radical scavengers, tert-butyl alcohol, propanol, or sodium formate, are without effect. In a follow-up reaction, hydroquinone is converted into benzoquinone. Reaction of 1O2 with aniline leads to the selective formation of 4-hydroxyaniline as the initial product. This is further converted to hydroquinone with formation of ammonia (deamination), and then to benzoquinone. On the basis of these results, the selective para hydroxylation of phenol or aniline may be used as an indicator for the involvement of singlet oxygen as compared to .OH radical- or cytochrome P450-mediated reactions.

Evidence for the Generation of Singlet Molecular Oxygen during Dopa and Dopamine Peroxidation

Participation of singlet molecular oxygen (1O2) in peroxidation of dopa and dopamine was studied by measurements of chemiluminescence spectra, the influence of solvents with various lifetime of O2 (1 delta g) and O2 (1 delta g)-quenchers on quantum yield of chemiluminescence. A decrease of absorption and fluorescence intensities of 1,3-diphenylizobenzofuran (DPBF) was also studied in the presence of dopa and dopamine oxidized with alkaline H2O2 as a criterion for the involvement of 1O2.

On the Involvement of Singlet Oxygen in the Biosynthesis of Oxygenation Products of the Furocoumarin Imperatorine

The role of singlet oxygen (1O2) in the photo-oxidation of the furocoumarin im peratorine was investigated in vitro. Irradiation with visible light and sensitization with methylene blue yielded the imperatorine oxidation product isogosferol and the corresponding ketone as main products. The involvement of 1O2 was dem onstrated by studying the rate of oxidation under conditions that affect the lifetime of 1O2. Com pared to a range of other furocoumarins, im peratorine appeared to be moderately active as a 1O2 generator. The extent of 1O2 production correlated with the skin sensitizing activity. Upon irradiation of im peratorine itself with UVA light (360 nm) no isogosferol formation is observed, probably as a consequence of its photochemical instability. Irradiation with visible light (λ > 400 nm) of a chlorophyll chromophore containing sensitizer in the presence of imperatorine, yielded isogosferol and the corresponding ketone product. This dem onstrates that in the formation of 1O2 oxidation products of imperatorine in plants naturally occuring sensitizers e.g. chlorophyll and visible light are involved, rather than 1O2 produced by im peratorine or other furocoumarins and UVA light. The protective effect on the chlorophyll sensitized im peratorine oxidation by the 1O2- and chlorophyll triplet quencher β-carotene was demonstrated in a lipophilic solvent.

MESODIPHENYLHELIANTHRENE—THE MOST REACTIVE SINGLET OXYGEN ACCEPTOR

Abstract— The self‐sensitized photooxidation of mesodiphenylhelianthrene in various solvents has been investigated. The involvement of 1O2 as the reactive intermediate in the formation of the endoperoxide has been demonstrated by the quenching of the photooxidation by the efficient 1O2‐quencher β‐carotene. The rate constant for the addition of 1O2 to mesodiphenylhelianthrene has been determined to be kR≅ 1010M‐1 s‐1, which is the highest value hitherto known in the literature. The probability factor p, which describes the concentration independent part of the overall quantum yield, has been measured to be p=0.17.

The Vitamin‐B12‐derived Co(III)‐Complex ‘Pyrocobester’ as Photosensitizer and as Substrate in Reactions Involving ‘Singlet Oxygen’

AbstractThe vitamin‐B12 derivative ‘pyrocobester’ (1) acts as photosensitizer in its light‐induced oxygenation which involves ‘singlet oxygen’ (1O2) and which gives ‘5,6‐dioxosecopyrocobester’ (2) cleanly. The identity of the photosensitizer is deduced from a match of the ‘photochemical action spectrum’ of the photooxygenation with the UV/VIS absorption spectrum of 1. The involvement of 1O2 in this reaction is established on the basis of solvent and solvent H/D isotope effects, of quenching studies with β‐carotene and of competition experiments with 9,10‐dimethylanthracene. Also, decomposition of the thermal 1O2‐source 1,4‐dimethylnaphthalene‐1,4‐endoperoxide in a solution of 1 induces a clean oxygenation of 1 to 2 in the dark as well.

RIBOFLAVIN‐PHOTOSENSITIZED OXIDATIVE DEGRADATION OF A VARIETY OF LIGNIN MODEL COMPOUNDS

AbstractOxidation of several lignin model compounds with alkylated paraphenolic groups by photosensitizing riboflavin (RF). rose bengal (RB) and methylene blue (MB) was examined. Photosensitizing RF cleaved l–(3‘‐4’‐diethoxyphenyl)‐1.3 dihydroxy‐2‐(4‐methoxyphenyl)propane (I). 4‐ethoxy‐3‐methoxyphenylglycerol‐(3‐guaiacyl ether (II) and l‐(4‘‐ethoxy‐3’‐methoxyphenyI)‐1,3 dihydroxypropane (IV) at their respective Cα‐Cβ bonds. Riboflavin also oxidized 3.4‐diethoxy‐benzaldehyde (VI) to the corresponding acid, and hydroxylated the conjugated olefin l‐(4‘‐ethoxy‐3’‐methoxyphenyl)1.2 propene (III) to yield the initial product IV. In contrast, MB and RB hydroxylated III but had no effect on I, II, IV or VI under identical conditions. This suggested RF effected transformations via a hydrogen radical abstraction (Type I) rather than a 1O2 mediated reaction.To confirm this, the effects of deuterium oxide (D:0) and oxygen pressure on the photosensitizing dye reactions were examined. The effect of D20 on tryptophan (Trp) oxidation and hydroxylation of III by MB and RB was significant, indicating involvement of 1O2. D2O had no significant effect on cleavage of the diarylpropane (I) and the olefin (III) by RF, indicating these reactions did not proceed by a Type II mechanism. While O2 pressure effect on Trp oxidation by MB was insignificant, it had a large negative effect on cleavage of I by RF. These results, coupled with the relatively slow oxidation rate of Trp by RF. indicate that photosensitizing RF produces 1O2 inefficiently and is not effecting oxidation of these lignin model compounds via a Type II mechanism.

PHOTOOXIDATION OF 8‐METHOXYPSORALEN WITH SINGLET OXYGEN*

Abstract— The in vitro photooxidation of 8‐methoxypsoralen (8‐MOP) with singlet oxygen is studied. Irradiation of 8‐MOP(295–400 or320–400 nm) in the presence of oxygen for 72 h results in the formation of a product (1.4%) which is identified as 6‐formyl‐7‐hydroxy‐8‐methoxycoumarin by aid of IR, NMR, MS and co‐chromatography with an authentic sample. A study of this reaction in the presence of l,4‐diazobicyclo(2,2,2)octane, a singlet oxygen scavenger, indicates the involvement of 1O2 in the formation of this compound. In addition to this, formation of a novel dimer of 8‐MOP is reported.

The involvement of 1O2 in the inactivation of mixed function oxidase and peroxidation of membrane lipids during the photosensitized oxidation of liver microsomes.

Abstract— Dye sensitized photooxidation of rat liver microsomes results in inactivation of mixed function oxidase and peroxidation of the membrane lipids. Both the flavoenzyme NADPH: cytochrome P450 reductase and cytochrome P450 components of the mixed function oxidase were inactivated. Singlet oxygen was responsible for these effects as the inactivation was markedly enhanced if the microsomes were in D2O buffer during the irradiation. Singlet oxygen quenchers or traps also protected the microsomes against enzyme inactivation and lipid peroxidation. Antioxidants, whilst preventing the lipid peroxidation, did not protect cytochrome P450 from inactivation which suggests that lipid peroxidation was not responsible for cytochrome P450 inactivation.