Spin Trapping Agent Research Articles

New insights into the singlet oxygen-independent formation of TEMPO signals in electron paramagnetic resonance analysis

Electron paramagnetic resonance (EPR) is currently the most commonly used technique for measurement of singlet oxygen (1O2) in advanced oxidation processes. However, the characteristic EPR signal associated with 1O2 (2,2,6,6-tetramethylpiperidine-N-oxide radical, TEMPO) can be generated via alternative pathways not involving 1O2, leading to misinterpreted results. In this study, in-situ EPR analysis was used to re-examine the interaction between peroxymonosulfate (PMS), a common oxidant, and 2,2,6,6-tetramethyl-4-piperidinol (TEMP), the spin-trapping agent of 1O2. It was found that TEMPO could be generated in TEMP/PMS system over a broad pH range (3.0–11.0). The pathway for TEMPO formation was the direct oxidation of TEMP by PMS, and 1O2 was not involved. Furthermore, the intensity of TEMPO (ITEMPO) followed a reverse parabolic pattern as the [TEMP]/[PMS] ratios changed across all pH values. Kinetic analysis unveiled three distinct patterns (continuous linear increase; linear increase followed by a lower rate of increase; increase followed by reaching a plateau) in ITEMPO. Finally, an electron transfer mechanism was proposed for the conversion of TEMP to TEMPO by PMS. The results from this study are expected to advance the understanding of 1O2-independent formation of TEMPO in TEMP/PMS and to mitigate the interference during the detection of 1O2 by EPR.

ZnO nanostructures grown from spent batteries: Ambient catalytic aspects and novel mechanistic insights

The present work includes a facile and economic microwave assisted hydrothermal synthesis of Zinc Oxide (ZnO), Diethylene Triamine Pentaacetic Acid (DTPA) stabilized Zinc Oxide (ZD) and DTPA stabilized Silver doped Zinc Oxide (ZAD) nanostructures using Zn from spent alkaline batteries. The synthesised nanostructures were well characterised using electronic, vibrational and X-Ray spectroscopic techniques as well as thermal and microscopic techniques revealing the successful stabilisation of DTPA in ZD and doping of Ag in ZAD. The Fourier Transform Infrared Spectroscopy (FTIR) spectra showed peaks characteristic to the presence of ZnO in the fingerprint region and those to the presence of DTPA. The X-Ray Diffraction Spectroscopy (XRD) pattern of ZnO, ZD and ZAD indicated the hexagonal wurtzite structure of ZnO and face centred cubic metallic Ag in ZAD. The Transmission Electron Microscopy (TEM) images revealed rod shaped morphology for ZnO and spherical morphologies for ZD and ZAD. The nanostructures proved to be efficient catalysts to achieve 100 % degradation of Malachite Green, Crystal Violet and Reactive Blue-21 and their binary mixtures under ambient conditions in presence of Hydrogen peroxide (H2O2). ZAD exhibited relatively rapid degradation with rate constants 0.754 min−1, 0.187 min−1 and 0.0150 min−1 for MG, CV, and RB-21 respectively as well as 99 % reduction in Chemical Oxygen Demand (COD) value of the dye solutions. Scavenging studies and Electron Paramagnetic Resonance (EPR) studies using different spin trapping agents revealed the involvement of singlet oxygen species, hydroxyl radicals (OH.) and superoxide radicals (O2.-) in the degradation process. This work aligns with Sustainable Development Goals 6, 12 and 13.

Degradation processes in polyolefins with phenolic stabilizers subjected to ionizing or non-ionizing radiation

We investigated degradation processes in polymer plaques made of polyolefin (HDPE or UHMWPE or COC) prepared by melt-mixing with or without phenolic stabilizer (natural α-tocopherol or synthetic Irganox®1010) and spin trapping agent (TTBNB; 2,4,6-Tri‑tert-butylnitrosobenzene). The degradation was initiated either by low-energy, non-ionizing radiation (wavelengths corresponding to terrestrial range of solar UV radiation) or high-energy, ionizing radiation (electrons accelerated at 1.5 MeV). The motivation for the study was our recent finding that some phenolic stabilizers exhibited a surprising pro-oxidant activity in polyolefins subjected to non-ionizing radiation. Consequently, we asked if the phenolic stabilizers in polyolefins behave in the same way during long-term, low-energy, non-ionizing UV irradiation and after short-term, high-energy, ionizing e-beam irradiation. All samples were characterized thoroughly by means of electron spin resonance (ESR; the information about radiation-induced radicals), infrared microspectroscopy (IR; the detection of oxidation products and structural changes), instrumented microindentation (MHI; local mechanical properties) and light and electron microscopy (LM and SEM; surface morphology). The results proved that (i) the degradation processes in polyolefins subjected to non-ionizing or ionizing radiation were different, (ii) the phenolic stabilizers exhibited mostly their expected antioxidant activity, while pro-oxidant activity was detected only for specific conditions and/or systems subjected to non-ionizing radiation, and (iii) the selected spin trapping agent, TTBNB, was stable enough to survive standard sample preparation by melt-mixing and catch short-living unstable radicals.

Identification and quantification of electron-generated atomic hydrogen through in-situ electron spin resonance and density functional theory

Electro-generated atomic hydrogen (H*) plays a crucial role in the electrochemical reduction process, serving as the key species that mediates the electrocatalytic hydrogenation reduction of stubborn contaminants in wastewater treatment. However, precisely identifying and quantifying transient atomic H* presents a significant challenge due to its limited lifespan and its existence solely within the boundary layer at the electrode/solution interface. Herein, we developed the electrodeposition of palladium nanoparticles onto carbon cloth and assessed its effectiveness as a cathode for generating and stabilizing atomic H*. The environmental application of atomic H* was validated through the dechlorination of 2, 4-dichlorophenol wastewater and the reduction of antimonite wastewater. Additionally, the identification of atomic H* was verified by electrochemical measurements, high-resolution mass spectra, and density functional theory. Moreover, introducing an excess of a spin trapping agent (5,5-dimethyl-1-pyrroline-N-oxide) and fast in-situ spin trapping facilitated creating favorable conditions for efficient trapping of atomic H* and subsequent electron spin resonance (ESR) spectroscopy quantification analysis. Subsequently, the quantification of atomic H* was achieved by double integration of the ESR signal of spin adduct and comparison with the external standard agent (4-hydroxy-2,2,6,6-tetramethyl-1-piperidine 1-oxyl). This study introduces a novel method for in-situ spin trapping and quantification of atomic H*, facilitating the advancement of electrochemical reduction technology and its application in wastewater treatment.

Unusual singlet oxygen-dependent hydroxyl radical production by a unique ruthenium-polypyridyl-hydroxamate complex under visible light irradiation

A novel ˙OH-generating system mediated by Ru complexes under visible light irradiation was discovered, which were found to be not only dependent on the well-known spin-trapping agent DMPO, but also on 1O2 and the presence of H-donating agents

Boosted photocatalytic H2 production over p-n S-scheme heterojunction of 0D Ni3V2O8 quantum dots decorated on ultra-thin 2D g-C3N4 nanosheets

Novel 0D Ni3V2O8 quantum dots (QDs) were decorated on the ultra-thin 2D g-C3N4 nanosheet (UCN) using a hydrothermal approach. The embedded Ni3V2O8 QDs play a dual role by trapping charge carriers, promoting electron-hole separation, and forming a p-n S-scheme heterojunction, improving the redox potential of the electrons and holes for surface reactions. HR-TEM analysis confirmed that Ni3V2O8 QDs with a size varying between 3 to 5 nm have intimate contact with the UCN surface. XPS and ESR spin-trapping agents experiment confirmed the formation of S-scheme heterojunctions between Ni3V2O8 QDs and UCN. Photocurrent and PL spectra indicated the synthesized heterostructures have high charge carrier transportation and lower recombination rates. The optimum Ni3V2O8 QDs/UCN heterostructure showed the highest photocatalytic hydrogen evolution activity, about 14 times higher than that of pristine UCN. This remarkable improvement in activity can be ascribed to the synergy effect of the S-scheme charge pathway mechanism and the improved light absorption facilitated by the Ni3V2O8 quantum dots. As a result, these factors effectively accelerate the migration and transportation of photoinduced charge carriers, offering increased active sites for the H2 generation process. This study emphasizes the importance of a well-designed interfacial heterojunction to achieve enhanced photocatalytic performance.

Unravelling the Mechanistic Understanding of Metal Nanoparticle-Induced Reactive Oxygen Species Formation: Insights from a Cu Nanoparticle Study.

Humans can be exposed to engineered and nonintentionally formed metal and metal oxide nanoparticles (Me NPs) in occupational settings, in public transportation areas, or by means of contact with different consumer products. A critical factor in the toxic potency of Me NPs is their ability to induce oxidative stress. It is thus essential to assess the potential reactive oxygen species (ROS) formation properties of Me NPs. A common way to assess the relative extent of ROS formation in vitro is to use fluorescence spectroscopy with the DCFH-DA (2',7'-dichlorofluorescein diacetate) probe, with and without HRP (horseradish peroxidase). However, this method does not provide any information about specific ROS species or reaction mechanisms. This study investigated the possibility of using complementary techniques to obtain more specific information about formed ROS species, both the type and reaction mechanisms. Cu NPs in PBS (phosphate buffered saline) were chosen as a test system to have the simplest (least interference from other components) aqueous solution with a physiologically relevant pH. ROS formation was assessed using fluorescence by means of the DCFH-DA method (information on relative amounts of oxygen radicals without selectivity), the Ghormley's triiodide method using UV-vis spectrophotometry (concentrations of H2O2), and electron paramagnetic resonance with DMPO as the spin-trap agent (information on specific oxygen radicals). This approach elucidates that Cu NPs undergo ROS-generating corrosion reactions, which previously have not been assessed in situ. In the presence of H2O2, and based on the type of oxygen radical formed, it was concluded that released copper participates in Haber-Weiss and/or Fenton reactions rather than in Fenton-like reactions. The new combination of techniques used to determine ROS induced by Me NPs provides a way forward to gain a mechanistic understanding of Me NP-induced ROS formation, which is important for gaining crucial insight into their ability to induce oxidative stress.

Application of Fe0.66Cu0.33@Al(OH)3 catalyst from fluidized-bed crystallizer by-product for RB5 azo dye treatment using visible light-assisted photo-Fenton technology

This study aims to explore the reusability of wastewater treatment by-product for photo-Fenton process to treat an organic pollutant model. The optimal condition, reactive oxygen species (ROS), and kinetic approach in photo-Fenton process was discussed. The Metal oxide crystal pellets from are a by-product of the Fluidized-Bed Crystallization (FBC) process and can be used as a catalyst in the Photo-Fenton process. Electroplating wastewater containing iron and copper was treated via the FBC process using granulated Al(OH)3 as carrier seeds. The binary oxide of FeOOH and Cu2O on the Al(OH)3 surface (Fe0.66Cu0.33@Al(OH)3) was identified as the FBC by-product after characterization using FTIR and XPS analysis.In the photo-Fenton process, visible light from a fluorescence lamp with a wavelength of 400–610 nm was chosen as an irradiation source. Oxalic acid was added as chelating agent to form photosensitive iron oxalate species and hydrogen peroxide was applied as oxidant to generate active radical to decolorize and mineralize RB5 synthesized solution (100 mg/L). The operating conditions including the oxalic acid to pollutant ratio ([OA]0/[RB5]0) of 4.5–13.0, reaction pH (pHr) of 3–7 and initial to theoretical hydrogen peroxide molar ratio [H2O2]0/[ H2O2]theoretical of 35%–120% were optimized. Under the optimal conditions, pHr = 5.0; [H2O2]0/[RB5]0 at 75% stoichiometric and [OA]0/[RB5]0 = 9, the RB5 is almost completely decolorized after 210 min of operation and the mineralization efficiency is 58%. The contribution of •OH, O2•-, and O21 to the Photo-Fenton system was determined using ESR analysis with the addition of DMPO and TEMP as spin trap agents. The kinetic analysis reveals the observed rate constants kRB5, kOA and kR from fitting are 0.0120, 0.0054 and 0.0001 M−1s−1, respectively.

Research on the reaction path of chlorobenzene oxidation by electrochemical-sodium persulfate system

Chlorobenzene (CB) is an important organic chemical material that is volatile and difficult to degrade, and has received much attention because of its strong ozone generation potential. An electrochemical-sodium peroxydisulfate (PDS) system was constructed and the oxidation reaction path of chlorobenzene in this system was analyzed. The effects of current density, PDS concentration, initial pH, CB blow-off gas ratio and temperature on the oxidation and mineralization rate of chlorobenzene in the system were investigated respectively. At a current density of 168 A/m2, a PDS concentration of 0.5 mol/L, an initial pH of 10, a CB blow-off gas ratio of 20% and a reaction temperature of 60 °C, the CB conversion and mineralization rates were able to reach more than 90%. The results of electron paramagnetic resonance (EPR) experiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidone hydrochloride (TEMP) as spin trapping agents indicate the presence of ⦁OH, · SO4− and 1O2 in the system. The signal of ·O2− was also captured after the quenching of ⦁OH, which further indicates the presence of 1O2. And the results of active substance quenching experiments showed that the active species that mainly contributed to the oxidation of chlorobenzene included ⦁OH, · SO4− and 1O2, and their contributions to the oxidation of chlorobenzene were 25.0%, 31.7% and 22.2%, respectively. The Liquid Chromatograph Mass Spectrometer (LC-MS) characterization results showed that the formation of chlorophenol and hydroquinone and their ring-opening reactions were the most critical processes in the oxidative decomposition of chlorobenzene, and the reaction pathways for the oxidation of chlorobenzene by ⦁OH, · SO4− and 1O2 were proposed by these characterization results.

Capture and Stabilization of the Hydroxyl Radical in a Uranyl Peroxide Cluster.

Here we describe the synthesis and characterization of a new uranyl peroxide cluster (UPC), U60 Ox30 *, which captures and stabilizes oxygen-based free radicals for more than one week. These radical species were first detected with a nitroblue tetrazolium colorimetric assay and U60 Ox30 * was characterized by single crystal X-ray diffraction as well as infrared (IR), Raman, UV-Vis-NIR, and electron paramagnetic resonance (EPR) spectroscopies. Identification of the free radicals present in U60 Ox30 * was done via room temperature solid and solution state X-band EPR studies using spin trapping methods. The spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was definitive for identifying the free radicals in U60 Ox30 *, which are hydroxyl radicals (⋅OH) that are stable for up to ten days that also persist upon addition of the metalloenzymes catalase and superoxide dismutase. Addition of the spin trapping agent α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) further confirmed the radicals were oxygen based, and deuteration experiments showed that the origin of the free radicals was from the decomposition of H2 O2 in water. These results demonstrate that highly oxidizing species such as the ⋅OH radical can be stabilized in UPCs, which alters our understanding of the role of free radicals present in spent nuclear fuel.

Photoenhanced Radical Formation in Aqueous Mixtures of Levoglucosan and Benzoquinone: Implications to Photochemical Aging of Biomass-Burning Organic Aerosols.

The photochemical aging of biomass-burning organic aerosols (BBOAs) by exposure to sunlight changes the chemical composition over its atmospheric lifetime, affecting the toxicological and climate-relevant properties of BBOA particles. This study used electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping agent, 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), high-resolution mass spectrometry, and kinetic modeling to study the photosensitized formation of reactive oxygen species (ROS) and free radicals in mixtures of benzoquinone and levoglucosan, known BBOA tracer molecules. EPR analysis of irradiated benzoquinone solutions showed dominant formation of hydroxyl radicals (•OH), which are known products of reaction of triplet-state benzoquinone with water, also yielding semiquinone radicals. In addition, hydrogen radicals (H•) were also observed, which were not detected in previous studies. They were most likely generated by photochemical decomposition of semiquinone radicals. The irradiation of mixtures of benzoquinone and levoglucosan led to substantial formation of carbon- and oxygen-centered organic radicals, which became prominent in mixtures with a higher fraction of levoglucosan. High-resolution mass spectrometry permitted direct observation of BMPO-radical adducts and demonstrated the formation of •OH, semiquinone radicals, and organic radicals derived from oxidation of benzoquinone and levoglucosan. Mass spectrometry also detected superoxide radical adducts (BMPO-OOH) that did not appear in the EPR spectra. Kinetic modeling of the processes in the irradiated mixtures successfully reproduced the time evolution of the observed formation of the BMPO adducts of •OH and H• observed with EPR. The model was then applied to describe photochemical processes that would occur in mixtures of benzoquinone and levoglucosan in the absence of BMPO, predicting the generation of HO2• due to the reaction of H• with dissolved oxygen. These results imply that photoirradiation of aerosols containing photosensitizers induces ROS formation and secondary radical chemistry to drive photochemical aging of BBOA in the atmosphere.

An unprecedented free radical mechanism for the formation of DNA adducts by the carcinogenic N-sulfonated metabolite of aristolochic acids

The carcinogenicity of aristolochic acids (AAs) has been attributed mainly to the formation of stable DNA-aristolactam (DNA-AL) adducts by its reactive N-sulfonated metabolite N-sulfonatooxyaristolactam (N–OSO3--AL). The most accepted mechanism for such DNA-AL adduct formation is via the postulated but never unequivocally-confirmed aristolactam nitrenium ion. Here we found that both sulfate radical and two ALI-derived radicals (N-centered and C-centered spin isomers) were produced by N–OSO3--ALI, which were detected and unequivocally identified by complementary applications of ESR spin-trapping, HPLC-MS coupled with deuterium-exchange methods. Both the formation of the three radical species and DNA-ALI adducts can be significantly inhibited (up to 90%) by several well-known antioxidants, typical radical scavengers, and spin-trapping agents. Taken together, we propose that N–OSO3--ALI decomposes mainly via a new N–O bond homolysis rather than the previously proposed heterolysis pathway, yielding reactive sulfate and ALI-derived radicals, which are together and in concert responsible for forming DNA-ALI adducts. This study presents strong and direct evidence for the production of free radical intermediates during N–OSO3--ALI decomposition, providing an unprecedented free radical perspective and conceptual breakthrough, which can better explain and understand the molecular mechanism for the formation of DNA-AA adducts, the carcinogenicity of AAs and their potential prevention.

Low-temperature persulfate activation by powdered activated carbon for simultaneous destruction of perfluorinated carboxylic acids and 1,4-dioxane.

Carbonaceous materials have emerged as a method of persulfate activation for remediation. In this study, persulfate activation using powdered activated carbon (PAC) was demonstrated at temperatures relevant to groundwater (5-25°C). At room temperature, increasing doses of PAC (1-20gL-1) led to increased persulfate activation (3.06×10-6s-1 to 2.10×10-4 with 1 and 20gL-1 PAC). Activation slowed at lower temperatures (5 and 11°C); however, substantial (>70 %) persulfate activation was achieved. PAC characterization showed that persulfate is activated at the surface of the PAC, as indicated by an increase in the PAC C:O ratio. Similarly, electron paramagnetic resonance (EPR) spectroscopy studies with a spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide (DMPO)) and 2,2,6,6-tetramethylpiperidine (TEMP) revealed that singlet oxygen was not the main oxidizing species in the reaction. DMPO was oxidized to form 5,5-dimethylpyrrolidone-2(2)-oxyl-(1) (DMPOX), which forms in the presence of strong oxidizers, such as sulfate radicals. The persulfate/PAC system is demonstrated to simultaneously degrade both perfluorooctanoic acid (PFOA) and 1,4-dioxane at room temperature and 11°C. With a 20gL-1 PAC and 75mM persulfate, 80 % and 70 % of the PFOA and 1,4-dioxane, respectively, degraded within 6h at room temperature. At 11°C, the same PAC and persulfate doses led to 57% dioxane degradation and 54 % PFOA degradation within 6h. Coupling PAC with persulfate offers an effective, low-cost treatment for simultaneous destruction of 1,4-dioxane and PFOA.

Revealing the Unexplored Mechanism of Photochemical Oxaziridine Conversion Process of 2H‐imidazole 1‐oxides

The photochemistry of 2H-imidazole-1-oxides has been explored using the two well-known spin-trapping agents, TMIO and DMPIO as the representative systems of this cyclic nitrone category. Computational studies have revealed that the photo-excitation of these compounds involve a strongly allowed S0→S2 transition which is subsequently followed by S2/S1 and S0/S1 conical intersections to form the photo-product oxaziridine. The authors declare no conflict of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

In vivo Detection of Macromolecule Free Radicals in Mouse Sepsis-Associated Encephalopathy Using a New MRI and Immunospin Trapping Strategy.

IntroductionFree radicals in oxidative stress are known to play a pathogenic role in sepsis. A major clinical challenge associated with sepsis is sepsis-associated encephalopathy (SAE). The rapid increase of free radicals in the brain promotes SAE progression. Here, macromolecule free radicals in the mouse brain were uniquely detected by immunospin trapping (IST) and magnetic resonance imaging (MRI).MethodsThe new strategy uses spin trapping agent DEPMPO-biotin to capture macromolecule free radicals in lesions and form biotin-DEPMPO-radical adducts. Then, a targeting MRI probe, avidin-BSA@Gd-ESIO, was used to detect the radical adducts through the highly specific binding of avidin and biotin. The avidin-BSA@Gd-ESIO probe was synthesized and systematically characterized. The detection capability of the new strategy was evaluated in vitro and in vivo using a confocal microscope and a 7T MRI, respectively.ResultsIn reactive oxygen species (ROS)–induced microglial cells, the accumulation of the avidin-BSA@Gd-ESIO probe in the DEPMPO-biotin-treated group was significantly higher than that of control groups. In vivo MRI T1 signal intensities were significantly higher within the hippocampus, striatum, and medial cortex of the brain in mice with a mild or severe degree of sepsis compared with the sham control group. Histological analysis validated that the distribution of the avidin-BSA@Gd-ESIO probe in brain tissue slices was consistent with the MRI images. The fluorescence signals of ROS and avidin-BSA@Gd-ESIO probe were overlapped and visualized using immunofluorescent staining. By evaluating the T1 signal changes over time in different areas of the brain, we estimated the optimal MRI detection time to be 30 minutes after the probe administration.DiscussionThis method can be applied specifically to assess the level of macromolecular free radicals in vivo in a simple and stable manner, providing a pathway for a more comprehensive understanding of the role of free radicals in SAE.

Therapeutic Potential of Small Molecules Targeting Oxidative Stress in the Treatment of Chronic Obstructive Pulmonary Disease (COPD): A Comprehensive Review.

Chronic obstructive pulmonary disease (COPD) is an increasing and major global health problem. COPD is also the third leading cause of death worldwide. Oxidative stress (OS) takes place when various reactive species and free radicals swamp the availability of antioxidants. Reactive nitrogen species, reactive oxygen species (ROS), and their counterpart antioxidants are important for host defense and physiological signaling pathways, and the development and progression of inflammation. During the disturbance of their normal steady states, imbalances between antioxidants and oxidants might induce pathological mechanisms that can further result in many non-respiratory and respiratory diseases including COPD. ROS might be either endogenously produced in response to various infectious pathogens including fungi, viruses, or bacteria, or exogenously generated from several inhaled particulate or gaseous agents including some occupational dust, cigarette smoke (CS), and air pollutants. Therefore, targeting systemic and local OS with therapeutic agents such as small molecules that can increase endogenous antioxidants or regulate the redox/antioxidants system can be an effective approach in treating COPD. Various thiol-based antioxidants including fudosteine, erdosteine, carbocysteine, and N-acetyl-L-cysteine have the capacity to increase thiol content in the lungs. Many synthetic molecules including inhibitors/blockers of protein carbonylation and lipid peroxidation, catalytic antioxidants including superoxide dismutase mimetics, and spin trapping agents can effectively modulate CS-induced OS and its resulting cellular alterations. Several clinical and pre-clinical studies have demonstrated that these antioxidants have the capacity to decrease OS and affect the expressions of several pro-inflammatory genes and genes that are involved with redox and glutathione biosynthesis. In this article, we have summarized the role of OS in COPD pathogenesis. Furthermore, we have particularly focused on the therapeutic potential of numerous chemicals, particularly antioxidants in the treatment of COPD.

Semi-quantitative probing of reactive oxygen species in persulfate-based heterogeneous catalytic oxidation systems for elucidating the reaction mechanism

Persulfate-based heterogeneous catalytic oxidation systems have attracted increasing interests in water pollution control field. Sulfate/hydroxyl radical, singlet oxygen, and catalyst-mediated electron transfer are commonly recognized to be responsible for the organic pollutant removal. However, reliable quantitative methods for detecting reactive oxygen species (ROS) are still lacking to clarify their contribution to the reaction mechanism. In this work, a soluble probe, 9,10-Anthracenediyl-bis (methylene)-dimalonic acid, which is sensitive to both sulfate/hydroxyl radical and singlet oxygen, was developed to semi-quantify the ROS in persulfate-based catalytic oxidation systems. The detection results reveal the predominant catalyst-mediated electron transfer mechanism, rather than the ROS mechanism, and its universality in several representative heterogeneous catalytic systems (i.e., FeMnO, CNT, Mn3O4, and biochar catalyzing peroxymonosulfate and peroxydisulfate for organic pollutant degradation). Compared with the electron paramagnetic resonance detection with DMPO and TEMP as spin-trapping agents and quenching effects of ROS by alcohol, furfuryl alcohol, and L-histidine, such a semi-quantitative detection method exhibits simplicity and improved reliability in mechanism elucidation. This semi-quantitative method plays a vital role in clarifying the reaction mechanism in persulfate-based heterogeneous catalytic oxidation systems, which might open a door for the optimization and regulation of catalytic oxidation water purification technology.

Photocatalytic Selective Degradation of Catechol and Resorcinol on the TiO2 with Exposed {001} Facets: Roles of Two Types of Hydroxyl Radicals

Photocatalytic studies on contaminant degradation in water suspension generally suggest that the degradation reaction mainly takes place on the surface of the photocatalysts rather than in the water phase. The mechanism of selective degradation is often difficult to distinguish concerning the contribution of adsorption and radical selectivity. This study is thus designed to investigate the roles of two types of hydroxyl radicals, adsorbed hydroxyl radical (·OHa) and free hydroxyl radical (·OHf), on the selective degradation of catechol (CT) and resorcinol (RE). CT and RE are significantly different in adsorption on a TiO2 photocatalyst with a highly exposed {001} facet. CT can be selectively degraded by TiO2 and was highly correlated with adsorption. Free radical quenching experiment results showed that the degradation of CT can be identified as the combined effect of both ·OHa and ·OHf, while the degradation of RE was mainly due to the ·OHf. Electron paramagnetic resonance coupled with spin trapping agents was used to detect the relative concentration of hydroxyl radicals in all the photocatalytic degradation processes. After a series analysis, we proposed that the mechanism of selective degradation mainly depends on the concentration of ·OHf for the pollutant molecules with weak adsorption on the catalyst surface.

Oxidative cleavage of polyunsaturated fatty acid chains via dioxygenation/pseudoperoxidation by 15-lipoxygenase

Aberrant progression of one-electron reduction of fatty acid hydroperoxides in cells is thought to be responsible for cell death, such as ferroptosis caused by reactive carbonyl compounds and hydrocarbon radicals generated through the cleavage of C-C bonds of fatty acid alkoxyl radicals belonging to oxygen-centered radicals. In the present study, we investigated the mechanism underlying the oxidative cleavage of polyunsaturated fatty acid chains by 15-lipoxygenase under anaerobic conditions using soybean 15-lipoxygenase as a model enzyme. The apparent reaction rate constant of lipoxygenase(Fe2+) with 13-hydroperoxyoctadecadienoic acid (13-HpODE) was approximately 7.3 times higher than that with 9-HpODE. The production of 13-oxo-tridecadienoic acid (13-OTA) in this reaction was remarkably inhibited in the presence of a five-membered nitroxyl radical, 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl (CmΔP), which is a specific spin-trapping agent for carbon-centered radicals. The trapped adduct appeared to be a CmΔP adduct with a linoleate epoxyallyl radical, which was derived from the linoleate alkoxyl radical through intramolecular rearrangement at the reaction site on the enzyme. Furthermore, 13-OTA production in the α-linolenate hydroperoxide/lipoxygenase(Fe2+) system was six times higher than that in the linoleate hydroperoxide/lipoxygenase(Fe2+) system. Based on these facts, we hypothesized that under anaerobic conditions, the fatty acid epoxyallyl radical at the reaction site on the enzyme spontaneously degrades into reactive carbonyl compounds and hydrocarbon radicals through the cleavage of C-C bonds. In conclusion, radical scavengers against carbon-centered radicals should inhibit the lipoxygenase-inducing cell death through preventing the cleavage of C-C bond of fatty acid epoxyallyl radicals.

Analysis of glutathione mediated S-(de)nitrosylation in complex biological matrices by immuno-spin trapping and identification of two novel substrates

The intracellular concentration of reduced glutathione (GSH) lies in the range of 1–10 mM, thereby indisputably making it the most abundant intracellular thiol. Such a copious amount of GSH makes it the most potent and robust cellular antioxidant that plays a crucial role in cellular defence against redox stress. The role of GSH as a denitrosylating agent is well established; in this study, we demonstrate GSH mediated denitrosylation of HepG2 cell-derived protein nitrosothiols (PSNOs), by a unique spin-trapping mechanism, using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trapping agent, followed by a western blot analysis. We also report our findings of two, hitherto unidentified substrates of GSH mediated S-denitrosylation, namely S-nitrosoglutaredoxin 1 (Grx1-SNO) and S-nitrosylated R1 subunit of ribonucleotide reductase (R1-SNO).