Contribution Of Singlet Oxygen Research Articles

Improving the non-free radical activated peroxymonosulfate capability of sludge biochar through sacrificial template method: Efficacy and mechanism evaluation

Improving the non-free radical activation ability of persulfate has great significance for the degradation of persistent contaminant in complex water environments. Here, special nitrogen-doped sludge-based catalysts for peroxymonosulfate (PMS) activation were developed through sacrificial template method by employing polymer surfactant (PS) as template agent. The PS usage and acid etching significantly improved the catalyst’s non-radical activation performance for PMS, the contribution of singlet oxygen (1O2) and electron transfer pathway (ETP) to bisphenol A (BPA) removal could be well matched to 72.31 % and 27.69 % in NCF-1/PMS system, respectively. Such non-radical activation characteristic ensures that NCF-1/PMS systems exhibit super oxidation ability of BPA (Kobs = 0.3714 min−1) and strong anti-interference ability to environmental matrixes via simultaneously enhancing both 1O2 and ETP. The critical roles of graphitic N and as-formed Si-O-C sites in activating PMS were revealed through electrochemical analysis, in-situ characterization technology and theoretical calculations. Density functional theory calculations confirmed that the PS addition and desilication process reduced the adsorption energy of the NCF-1 for PMS, and achieved lower energy barrier to cleave the O–H bond of NCF-1/PMS complex, significantly achieving the surge in the major active species of 1O2. This study provides novel regulatory strategies to modulate the non-radical path for persistent pollutant treatment.

Efficient fenton-like catalysis enabled by single cobalt atoms anchored on expanded graphite: Remarkable intrinsic activity of Co-N4 sites and the enhanced mass transfer facilitated by gradient mesopore structure

The single-atom catalysts derived from traditional Zeolitic Imidazolate Framework (ZIF) materials are exclusively characterized by a micropore structure, which severely hampers both the mass transfer efficiency and the accessibility of metal sites during catalysis. Herein, by utilizing mesoporous expanded graphite (EG) and ZIF-67 as precursors, a novel single-atom cobalt catalyst anchored on three-dimensional porous carbon materials (ZIF-67-x@EG) has been developed. Experiments demonstrate that introducing cobalt atoms in the formed bulges of EG increases carrier concentration and significantly enhances carrier mobility. The resulting ZIF-67-1@EG catalyst exhibits remarkable efficiency in degrading levofloxacin (LEVO concentration = 48 mg/L), with a degradation rate constant (0.078 min−1) 3.25 times higher than EG@N (0.024 min−1). The Co amounts in all ZIF-67-x@EG catalysts positively correlated with the reaction rate constant (R2 = 0.995). The ZIF-67-1@EG, with a small amount of cobalt loading (2.29 at%), exhibited an exceptionally high turnover frequency (TOF) value for LEVO (0.49 min−1). The degradation process involves an electron transfer pathway (ETP) and the contribution of singlet oxygen (1O2). The toxicity of the intermediates was characterized by quantitative structure-activity relationship (QSAR) prognostication, and the toxicity was reduced post-reaction. PMS/Co-N4 (-0.37 eV) and PMS/pyridinic N (-0.39 eV) configurations exhibit lower adsorption energies than PMS/pyrrolic N (-0.32 eV) structure, indicating that PMS primarily binds to these sites in the ZIF-67-1@EG/PMS system.

Promoted peroxydisulfate activation by nitrogen-doped carbon embedding iron on a nickel foam cathode: Performance, mechanism and relationship between C[dbnd]O and 1O2 generation

Nitrogen doped carbon embedding iron on a nickel foam (xN-C@Fe/NF) cathode was prepared and used to activate peroxydisulfate (PDS) for organic pollutant degradation. Benefiting from N doping-induced CO content increasing, which possessed good electron-withdrawing properties from Fe and the cathode, the optimum 3 NC@Fe/NF cathode displayed superior model organic pollutant (sulfamethoxazole, SMX) removal efficiency. Specifically, almost 100 % SMX removal efficiency was achieved within 15 min. It was found that the contribution of singlet oxygen (1O2) to SMX degradation gradually became more important with increasing N doping. On the basis of the semiquantitative and quantitative structure–activity relationship and density functional theory (DFT) calculation, it is conclusively identified that CO in the NC@Fe/NF tuned by the doped pyrrolic N and graphitic N are the core catalytic active sites for PDS activation, which was further evidenced by the high linear correlation (R2 of 0.983) between CO content and 1O2 yield. Furthermore, the 3 NC@Fe/NF cathode displayed attractive practical application prospect because of its wide pH applicability, good anti-interference ability, stable catalytic performance and universal adaptability for multiple organics removal. This study not only established a high-efficiency method for green remediation of actual polluted water but also developed valuable insight for discriminating the catalytic active sites of the cathode for PDS activation.

Novel Three-Dimensional Electrochemical Reactor with P and N-Codoped Activated Carbon for Water Decontamination: High Efficiency and Contribution of Singlet Oxygen

Novel Three-Dimensional Electrochemical Reactor with P and N-Codoped Activated Carbon for Water Decontamination: High Efficiency and Contribution of Singlet Oxygen

Tetrakis(N-methyl-p-pyridinio)porphyrin and its zinc complex can photosensitize damage of human serum albumin through electron transfer and singlet oxygen generation

The photosensitized protein-damaging activity of water-soluble freebase tetrakis([Formula: see text]-methyl-[Formula: see text]-pyridinio)porphyrin (H2TMPyP), and its zinc complex (ZnTMPyP) was investigated using human serum albumin (HSA) as a target protein. These porphyrins bound to HSA and caused photosensitized oxidation of the tryptophan residue. The protein damage was enhanced in deuterium oxide and inhibited by sodium azide, a physical quencher of singlet oxygen, suggesting the contribution of singlet oxygen. However, an excess amount of sodium azide could not completely inhibit protein damage. These findings suggest the partial contribution of another mechanism to the protein damage, possibly the electron transfer mechanism. The Gibbs free energy of the electron transfer mechanism showed that electron transfer-mediated tryptophan oxidation by photoexcited H2TMPyP is more advantageous than that by ZnTMPyP. Actually, the quantum yield of protein damage through electron transfer by H2TMPyP was larger than that by ZnTMPyP. In addition, this study demonstrated that the association between porphyrin and protein plays an important role in photosensitized protein damage.

Photo-induced DNA cleavage and cytotoxicity of a ruthenium(II) arene anticancer complex

We report DNA cleavage by ruthenium(II) arene anticancer complex [(η6-p-terp)RuII(en)Cl]+ (p-terp=para-terphenyl, en=1,2-diaminoethane, complex 1) after its photoactivation by UVA and visible light, and the toxic effects of photoactivated 1 in cancer cells. It was shown in our previous work (T. Bugarcic et al., J. Med. Chem. 51 (2008) 5310–5319) that this complex exhibits promising toxic effects in several human tumor cell lines and concomitantly its DNA binding mode involves combined intercalative and monofunctional (coordination) binding modes. We demonstrate in the present work that when photoactivated by UVA or visible light, 1 efficiently photocleaves DNA, also in hypoxic media. Studies of the mechanism underlying DNA cleavage by photoactivated 1 reveal that the photocleavage reaction does not involve generation of reactive oxygen species (ROS), although contribution of singlet oxygen (1O2) to the DNA photocleavage process cannot be entirely excluded. Notably, the mechanism of DNA photocleavage by 1 appears to involve a direct modification of mainly those guanine residues to which 1 is coordinatively bound. As some tumors are oxygen-deficient and cytotoxic effects of photoactivated ruthenium compounds containing {Ru(η6-arene)}2+ do not require the presence of oxygen, this class of ruthenium complexes may be considered potential candidate agents for improved photodynamic anticancer chemotherapy.

Examination of Protein-Damaging Activity of Phosphorus(V) Porphyrin Photosensitizer for Photodynamic Therapy

For the fundamental study of photodynamic therapy, protein-damaging activity of the water-soluble phosphorus(V) porphyrin (DDP(V)TPP) was examined. Absorption spectrum measurement demonstrated the binding interaction between DDP(V)TPP and human serum albumin, a water-soluble protein. Photo-irradiated DDP(V)TPP damaged the amino acid residue of human serum albumin, resulting in the decrease of fluorescence intensity from the tryptophan residue of human serum albumin. Protein damage photosensitized by DDP(V)TPP was inhibited by the addition of sodium azide and enhanced in deuterium oxide, indicating the contribution of singlet oxygen. However, sodium azide could not completely inhibit the damage of human serum albumin, suggesting that the electron transfer mechanism contributes to protein damage as does singlet oxygen generation. Isolated tryptophan was also damaged by a photosensitization of DDP(V)TPP in solution, whereas DDP(V)TPP did not induce photodamage to tyrosine and phenylalanine. Using the application of a fluorometry of hydrogen peroxide, the deactivation of catalase photosensitized by DDP(V)TPP was demonstrated.

Photochemical fate of atorvastatin (lipitor) in simulated natural waters

Cholesterol-lowering statin drugs are among the most frequently prescribed for reducing human blood cholesterol and they have been detected as contaminants in natural waters. In this study the photochemical behavior of atorvastatin (lipitor) was investigated at two different concentrations of 35.8 μM (20 mg L−1) and 35.8 nM (20 μg L−1) using a solar simulator and a UV reactor. Photochemical fate in natural waters can be described in most cases by the sum of the loss due to hydrolysis, direct photolysis, and, reaction with hydroxyl radical (OH), singlet oxygen (1O2) (or O2 (1D)), and excited state dissolved organic matter (DOM). The absolute bimolecular reaction rate constant with OH was measured, using pulsed radiolysis, (1.19 ± 0.04) × 1010 M−1 s−1. The reaction rate constant of 1O2 was determined to be (3.1 ± 0.2) × 108 M−1 s−1. Under the experimental conditions used, at high atorvastatin concentration (35.8 μM) the contribution of singlet oxygen (1O2) to the photodegradation of atorvastatin in natural waters was higher than that of hydroxyl radical, and accounted for up to 23% of the loss in aqueous solutions. Whereas, at a concentration of 35.8 nM, 1O2 (and OH) both played a minor role in the removal of this compound. Lastly, it also appears that atorvastatin reacts with 3DOM* contributing to its loss in simulated natural waters.

Indirect Photodegradation of Dissolved Free Amino Acids: The Contribution of Singlet Oxygen and the Differential Reactivity of DOM from Various Sources

The role of photochemically generated singlet oxygen (1O2) in the DOM-sensitized degradation of eighteen dissolved free amino acids was investigated. The fraction of total sensitized degradation due to reaction with 1O2 was determined through a kinetic analysis based on a measured reaction rate constant for each amino acid coupled with measured 1O2 concentrations and was confirmed through quenching experiments. Only four of the eighteen free amino acid residues examined were found to be photolabile under environmentally relevant conditions: histidine, methionine, tyrosine, and tryptophan. The fraction of Suwannee River Humic Acid (SRHA)-sensitized degradation due to reaction with 1O2 ranged from an upper value of 110 +/- 10% for histidine to 8 +/- 1% for tryptophan, with 26 +/- 3% contribution for methionine and 33 +/- 4% for tyrosine. In addition to degradation through reaction with 1O2, other reactive intermediates involved in the SRHA-photosensitized degradation of these amino acids were identified. Methionine was thought to be additionally degraded through reaction with H2O2 and triplet excited-state DOM, and 67% of tyrosine's indirect photodegradation was assigned to an oxygen-dependent type I photooxidation reaction. The majority of tryptophan indirect degradation was due to reaction with 3DOM. Photodegradation experiments with various DOM sources including Pony Lake (Antarctica) fulvic acid and a synthetic estuarine sample, as well as Minnesota freshwater samples (lakes Itasca, Superior, Josephine, and the St Louis River), demonstrated distinct reactivity patterns, indicating that DOM's 1O2-generation efficiency is not strongly coupled to its ability to promote other photooxidation pathways. These four amino acids highlightthe differential photoreactivity of DOM from various sources.

Coexposure to benzo[ a]pyrene and UVA induces phosphorylation of histone H2AX

Phosphorylation of histone H2AX (termed γ-H2AX) was recently identified as an early event after induction of DNA double strand breaks (DSBs). We have previously shown that coexposure to benzo[ a]pyrene (BaP), a wide-spread environmental carcinogen, and ultraviolet A (UVA), a major component of solar UV radiation, induced DSBs in mammalian cells. In the present study, we examined whether coexposure to BaP and UVA generates γ-H2AX in CHO-K1 cells. Single treatment with BaP (10 −9–10 −7 M) or UVA (∼2.4 J/cm 2) did not result in γ-H2AX, however, coexposure drastically induced foci of γ-H2AX in a dose-dependent manner. γ-H2AX could be detected even at very low concentration of BaP (10 −9 M) plus UVA (0.6 J/cm 2), which did not change cell survival rates. NaN 3 effectively inhibited the formation of γ-H2AX induced by coexposure, indicating the contribution of singlet oxygen. This is the first evidence that coexposure to BaP and UVA induced DSBs, involving γ-H2AX.

Aqueous photodegradation of fenthion by ultraviolet B irradiation: contribution of singlet oxygen in photodegradation and photochemical hydrolysis

The objective of this study was to evaluate the photodegradation of the organophosphorus pesticide fenthion in the environment from a human health effect viewpoint. The major photodegradation products of fenthion in an aqueous solution under UVB irradiation (280–320 nm radiation) were identified as fenthion sulfoxide, 3-methyl-4-methylthiophenol (MMTP), dimethyl phosphorothioate and 3-methyl-4-methylsulfinylphenol (MMSP). MMTP, dimethyl phosphorothioate and MMSP were discovered as novel photodegradation products of fenthion. Kinetic analysis of these products showed the formation of MMTP and dimethyl phosphorothioate by the photochemical hydrolysis of fenthion, which was accelerated under alkaline conditions. The former was further oxidized to MMSP. Fenthion sulfoxide was directly produced by the oxidative reaction of fenthion. Contribution of dissolved oxygen in this photooxidation was observed by replacing the air with nitrogen gas in the reaction system, which prevented oxidative formation of fenthion sulfoxide from fenthion and MMSP from MMTP. These oxidative compounds were also formed from fenthion in the presence of singlet oxygen ( 1O 2) generated by the visible light irradiation of rose bengal solution, while 1O 2 scavengers, l-histidine and sodium azide (NaN 3) inhibited this reaction. The aqueous photolysis mechanisms of fenthion were proposed from a kinetic photolysis experiment study as follows: there were two kinds of UVB photodegradation pathways of fenthion, one being photochemical hydrolysis of the phosphorus- O-phenyl ester to form MMTP and dimethyl phosphorothioate, and the other oxygenation triggered by 1O 2 and producing fenthion sulfoxide and MMSP. Therefore, the steady photodegradation products of fenthion in the water environment may be fenthion sulfoxide and MMSP.

Quenching of reactive oxidative species by probucol and comparison with other antioxidants

One-electron oxidation of the antiatherogenic and antiatherosclerotic drug probucol has been studied in relation to its activity as an antioxidant. Oxidation by triplet excited states of duroquinone and benzophenone, and by the inorganic radicals Br 2 and N 3 ·−, lead to the formation of a transient absorption at 500 nm. This was identified by time-resolved resonance Raman spectroscopy as the phenoxyl radical from probucol, formed by hydrogen atom or electron plus proton loss from one of the phenolic groups of probucol. The reactivity of probucol with triplet duroquinone and triplet benzophenone, and as a quencher of singlet oxygen, was compared with the reactivities of other antioxidants (α-tocopherol, palmitoyl ascorbic acid, dihydrolipoic acid and N-acetyl cysteine). In quenching of the triplet states the reactivity of probucol was comparable with that of a-tocopherol, whereas as a quencher of singlet oxygen probucol ( k < 10 6 M −1 s −1) was less effective than α-tocopherol ( k < 2.0 × 10 8 M −1s −1 ) by more than two orders of magnitude. This difference in reactivity may allow the contribution of singlet oxygen towards oxidative stress to be quantified separately.

Bilirubin chemiluminescence induced by the attack of active oxygen species.

Ultraweak chemiluminescence (CL) from bilirubin occurs in the presence of triplet oxygen and is stimulated by the addition of aldehydes. Active oxygen species also enhance bilirubin CL, in the absence of aldehydes. An inhibitory effect of active oxygen scavengers on the CL indicated that active oxygens generated from the decomposition of added hydrogen peroxide or from the xanthine-xanthine oxidase reaction contributed to the CL from bilirubin molecules. However, the contribution of singlet oxygen to the CL disappeared in the presence of formaldehyde. This suggested that the scission of tetrapyrrole bonds via a dioxetane intermediate or the production of triplet carbonyls from the oxidation of aldehydes by singlet oxygen was not involved in the CL, at least in the presence of formaldehyde. The spectrum of CL induced by the generation of active oxygen was the same as that from the aldehyde-enhanced CL reaction. We propose that the formation of a hydroperoxide (and/or hydroxide) bilirubin intermediate, but not a dioxetane, may be involved in the excitation of bilirubin molecules for CL.

Characteristics of mutagenesis by glyoxal in Salmonella typhimurium: contribution of singlet oxygen

The characteristics of mutagenesis by glyoxal in Salmonella tester strains TA100 and TA104, and particularly a possible role of active oxygen species, were investigated. Glyoxal was converted into a non-mutagenic chemical with glutathione (GSH) by glyoxalase I, and the mutagenic activity was enhanced by the depletion of intracellular GSH. Glyoxal caused the reduction of nitro blie tetrazolium, which was suppressed by the addition of 2,5-diphenylfuran, superoxide dismutase (SOD) and catalase (CAT), scavengers of singlet oxygen ( 1O 2), superoxide radical ( O 2 ̇ − ) and hydrogen peroxide (H 2O 2), respectively. However, only the 1O 2 scavenger almost completely suppressed the mutagenic activity of glyoxal. Mutagenicity assays using strains pretreated with N, N-diethydithiocarbamate of a SOD inhibitor and strains with low levels of SOD and CAT indicated that the mutagenesis by glyoxal was independent of intracellular levels of SOD and CAT, though glyoxal itself repressed them. Therefore, all the results suggest that 1O 2 formed from glyoxal is related to its mutagenesis, but that neither O 2 ̇ − nor H 2O 2 is intracellularly predominantly related to it. The action of glyoxal against SOD and CAT, and the formation of glyoxal adducts with amino acids as their components are also discussed.

Contribution of singlet oxygen to the accelerated decolorizing of dye mixtures

Binary mixtures of dispersed dyes, which during irradiation with polychromatic light give an effect of accelerated decolorization, were studied. Quantum yields of the formation of singlet oxygen by individual dyes were estimated during irradiation of solutions in ethyl acetate with light of 435 and 546 nm as well as quantum yields of the reaction of dyes with singlet oxygen. It was found that the contribution of the reaction of dyes with singlet oxygen to the effects of accelerated decolorization were vanishingly small. The quantum yield of the photodestruction of dyes in a mixture was 10−3-10−5 and the quantum yield of reaction with singlet oxygen was less than 10−6. It was concluded that accelerated decolorization of the systems studied is not determined by reaction with singlet oxygen.

Mechanism of the photofading of Dye. Contribution of singlet oxygen in the catalytic fading of anthraquinone dye mixtures

AbstractThe mechanism of the catalytic fading of some dyes has been investigated. The relative fading of quinophthalone in solution increases when C.I. Disperse Red 15 was added. The mechanism of catalytic fading proceeds via the singlet oxygen mechanism, since this phenomenon is suppressed by adding singlet oxygen quencher as DABCO or nickel dimethyldithiocarbamate (NMC). However, when quinophthalone mixed with C.I. Disperse Blue 14 was irradiated under the same conditions (λ &gt; 520 nm), no catalytic fading occurred. Competitive photo‐oxidation experiments for these dyes with NMC, giving evidence for intermediacy of singlet oxygen by the self‐sensitised process, were carried out. The relative rate constants for reactions in solution were examined to predict the possibility of the catalytic fading in these dye mixtures.