Electron Paramagnetic Resonance Spin Trapping Research Articles

Efficient Oxidative Removal of Organic Pollutants by Ordered Mesoporous Carbon-Supported Cobalt Phthalocyanine

Ordered mesoporous carbon (OMC) materials have received attention for use as supports in highly efficient catalytic systems because of their excellent properties. We used epoxy compound 2,3-epoxypropyl trimethylammonium chloride (EPTAC) to modify cobalt tetraaminophthalocyanine (CoTAPc) and obtained a novel catalyst (OMC-CoTAPc-EPTAC) based on OMC-bonded CoTAPc-EPTAC that could oxidize Acid Red 1 (AR1) dyes by hydrogen peroxide (H2O2) activation under neutral conditions. OMC enhanced the catalytic performance of OMC-CoTAPc-EPTAC, which resulted in the combined high catalytic activity and high stability. Because of its large surface area and tunable pore texture, OMC has high substrate accessibility, and the modification of the catalyst with EPTAC could promote adsorption of the target substrate into OMC, which achieved the aim of in situ catalytic oxidation with enrichment of the target substrate and improved the catalytic efficiency significantly. Electron paramagnetic resonance spin-trap experiments confirmed that the OMC-CoTAPc-EPTAC/H2O2system had a nonradical catalytic mechanism, and the high-valent cobalt-oxo intermediates and generated holes were speculated to act as dominant oxidation species for the catalytic degradation of AR1. These results demonstrated a new strategy for the elimination of low-concentration organic pollutants.

Electrolysis of trichloromethylated organic compounds under aerobic conditions catalyzed by the B12 model complex for ester and amide formation.

The electrolysis of benzotrichloride at -0.9 V vs. Ag/AgCl in the presence of the B12 model complex, heptamethyl cobyrinate perchlorate, in ethanol under aerobic conditions using an undivided cell equipped with a platinum mesh cathode and a zinc plate anode produced ethylbenzoate in 56% yield with 92% selectivity. The corresponding esters were obtained when the electrolysis was carried out in various alcohols such as methanol, n-propanol, and i-propanol. Benzoyl chloride was detected by GC-MS during the electrolysis as an intermediate for the ester formation. When the electrolysis was carried out under anaerobic conditions, partially dechlorinated products, 1,1,2,2-tetrachloro-1,2-diphenylethane and 1,2-dichlorostilibenes (E and Z forms), were obtained instead of an ester. ESR spin-trapping experiments using 5,5,-dimethylpyrroline N-oxide (DMPO) revealed that the corresponding oxygen-centered radical and carbon-centered radical were steadily generated during the electrolyses under aerobic and anaerobic conditions, respectively. Applications of the aerobic electrolysis to various organic halides, such as substituted benzotrichlorides, are described. Furthermore, the formation of amides with moderate yields by the aerobic electrolysis of benzotrichloride catalyzed by the B12 model complex in the presence of amines in acetonitrile is reported.

Effect of platinum nanoparticles on cell death induced by ultrasound in human lymphoma U937 cells

In this study, we report on the potential use of platinum nanoparticles (Pt-NPs), a superoxide dismutase (SOD)/catalase mimetic antioxidant, in combination with 1MHz ultrasound (US) at an intensity of 0.4W/cm2, 10% duty factor, 100Hz PRF, for 2min. Apoptosis induction was assessed by DNA fragmentation assay, cell cycle analysis and Annexin V-FITC/PI staining. Cell killing was confirmed by cell counting and microscopic examination. The mitochondrial and Ca2+-dependent pathways were investigated. Caspase-8 expression and autophagy-related proteins were detected by spectrophotometry and western blot analysis, respectively. Intracellular reactive oxygen species (ROS) elevation was detected by flow cytometry, while extracellular free radical formation was assessed by electron paramagnetic resonance spin trapping spectrometry. The results showed that Pt-NPs exerted differential effects depending on their internalization. Pt-NPs functioned as potent free radical scavengers when added immediately before sonication while pre-treatment with Pt-NPs suppressed the induction of apoptosis as well as autophagy (AP), and resulted in enhanced cell killing. Dead cells displayed the features of pyknosis. The exact mode of cell death is still unclear. In conclusion, the results indicate that US-induced AP may contribute to cell survival post sonication. To our knowledge this is the first study to discuss autophagy as a pro-survival pathway in the context of US. The combination of Pt-NPs and US might be effective in cancer eradication.

Sulfite oxidase activity of cytochrome c: Role of hydrogen peroxide

In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe3+cyt c) in the absence and presence of H2O2. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe3+cyt c, and H2O2. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO3-) was obtained. The amount of DMPO-SO3- formed from the oxidation of sulfite by the Fe3+cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO3- formed by the peroxidase activity of Fe3+cyt c also increased with sulfite and H2O2 concentration. From these results, we propose a mechanism in which the Fe3+cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe3+cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

In Vivo Immuno-Spin Trapping: Imaging the Footprints of Oxidative Stress.

A plethora of disease processes are associated with elevated reactive species formation and allied reactions with biomolecules that alter cell signaling, induce overt damage, and promote dysfunction of tissues. Unfortunately, effective detection of reactive species in tissues is wrought with issues that significantly limit capacity for validating species identity, establishing accurate concentrations, and identifying anatomic sites of production. These shortcomings reveal the pressing need for new approaches to more precisely assess reactive species generation in vivo. Herein, we describe an in vivo immuno-spin trapping method for indirectly assessing oxidant levels by detecting free radicals resulting from reaction of oxidants with biomolecules to form stable, immunologically detectable nitrone-biomolecular adducts. This process couples the reactivity and sensitivity of an electron paramagnetic resonance spin trap with the resolution of confocal imaging to visualize the extent of cell and tissue oxidation and anatomic sites of production by detecting resultant free radical formation.

Mass-Controlled Direct Synthesis of Graphene-like Carbon Nitride Nanosheets with Exceptional High Visible Light Activity. Less is Better.

In the present work, it is very surprising to find that the precursors mass, a long overlooked factor for synthesis of 2D g-C3N4, exerts unexpected impact on g-C3N4 fabrication. The nanoarchitecture and photocatalytic capability of g-C3N4 can be well-tailored only by altering the precursors mass. As thiourea mass decreases, thin g-C3N4 nanosheets with higher surface area, elevated conduction band position and enhanced photocatalytic capability was triumphantly achieved. The optimized 2D g-C3N4 (CN-2T) exhibited exceptional high photocatalytic performance with a NO removal ratio of 48.3%, superior to that of BiOBr (21.3%), (BiO)2CO3 (18.6%) and Au/(BiO)2CO3 (33.8%). The excellent activity of CN-2T can be ascribed to the co-contribution of enlarged surface areas, strengthened electron-hole separation efficiency, enhanced electrons reduction capability and prolonged charge carriers lifetime. The DMPO ESR-spin trapping and hole trapping results demonstrate that the superoxide radicals (•O2−) and photogenerated holes are the main reactive species, while hydroxyl radicals (•OH) play a minor role in photocatalysis reaction. By monitoring the reaction intermediate and active species, the reaction mechanism for photocatalytic oxidation of NO by g-C3N4 was proposed. This strategy is novel and facile, which could stimulate numerous attentions in development of high-performance g-C3N4 based functional nanomaterials.

Spin trapping studies of essential oils in lipid systems

Abstract In the present work, we report the results of a spin trapping ESR study of four essential oils widely used for skin care products such as creams and bath salts. The studied essential oils are Rosmarini aetheroleum (rosemary), Menthae piperitae aetheroleum (mint), Lavandulae aetheroleum (lavender), and Thymi aetheroleum (thyme). Fenton reaction in the presence of ethanol was used to generate free radicals. The N-tert-butyl-α-phenylnitrone (PBN) was used as a spin trap. In the Fenton reaction, the rosemary oil had the lowest effect on radical adduct formation as compared to the reference Fenton system. Since essential oils are known to be lipid soluble, we also conducted studies of essential oils in Fenton reaction in the presence of lipids. Two model lipids were used, namely 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The obtained results suggested that in the presence of DOPC lipids, the •OH and PBN/•CHCH3(OH) radicals are formed in both phases, that is, water and lipids, and all the studied essential oils affected the Fenton reaction in a similar way. Whereas, in the DPPC system, the additional type of PBN/X (aN = 16.1 G, aH = 2.9 G) radical adduct was generated. DFT calculations of hyperfine splittings were performed at B3LYP/6-311+G(d,p)/EPR-II level of theory for the set of c-centered PBN adducts in order to identify PBN/X radical.

Pleiotropic Effects of Levofloxacin, Fluoroquinolone Antibiotics, against Influenza Virus-Induced Lung Injury.

Reactive oxygen species (ROS) and nitric oxide (NO) are major pathogenic molecules produced during viral lung infections, including influenza. While fluoroquinolones are widely used as antimicrobial agents for treating a variety of bacterial infections, including secondary infections associated with the influenza virus, it has been reported that they also function as anti-oxidants against ROS and as a NO regulator. Therefore, we hypothesized that levofloxacin (LVFX), one of the most frequently used fluoroquinolone derivatives, may attenuate pulmonary injuries associated with influenza virus infections by inhibiting the production of ROS species such as hydroxyl radicals and neutrophil-derived NO that is produced during an influenza viral infection. The therapeutic impact of LVFX was examined in a PR8 (H1N1) influenza virus-induced lung injury mouse model. ESR spin-trapping experiments indicated that LVFX showed scavenging activity against neutrophil-derived hydroxyl radicals. LVFX markedly improved the survival rate of mice that were infected with the influenza virus in a dose-dependent manner. In addition, the LVFX treatment resulted in a dose-dependent decrease in the level of 8-hydroxy-2’-deoxyguanosine (a marker of oxidative stress) and nitrotyrosine (a nitrative marker) in the lungs of virus-infected mice, and the nitrite/nitrate ratio (NO metabolites) and IFN-γ in BALF. These results indicate that LVFX may be of substantial benefit in the treatment of various acute inflammatory disorders such as influenza virus-induced pneumonia, by inhibiting inflammatory cell responses and suppressing the overproduction of NO in the lungs.

Metal-independent decomposition of organic hydroperoxides by the halogenated quinoid carcinogens and the potential biological implications

Abstract: Halogenated quinones are a class of carcinogenic intermediates and newly identified chlorination disinfection byproducts in drinking water. Organic hydroperoxides (ROOH) can be produced both by free radical reactions and enzymatic oxidation of polyunsaturated fatty acids. ROOH have been shown to undergo transition metal-catalyzed decomposition to alkoxyl radicals, which may initiate lipid peroxidation or further decompose to the reactive α, β-unsaturated aldehydes. However, it is not clear whether halogenated quinones react in a similar fashion with ROOH to produce alkoxyl radicals independent of transition metals. By complementary applications of ESR spin-trapping, HPLC/high resolution mass spectrometric and other analytical methods, we found that 2,5-dichloro- 1,4-benzoquinone (DCBQ) could markedly enhance the decomposition of a model ROOH tert -butylhydroperoxide, leading to the formation of t -butoxyl radicals independent of transition metals. Based on the above findings, we detected and identified, for the first time, an unprecedented carbon-centered quinone ketoxy radical, which is the spin isomer of the proposed oxygen-centered quinone enoxy radical. Then we extended our study to the more physiologically relevant endogenous lipid hydroperoxide 13-hydroperoxy-9,11-octadecadienoic acid, and found that DCBQ could also markedly enhance its decomposition to produce the reactive lipid alkyl radicals and the genotoxic 4-hydroxy-2-nonenal (HNE). Analogous results were observed with other halogenated quinones. In summary, these findings demonstrated that halogenated quinoid carcinogens can enhance the decomposition of ROOH and formation of reactive alkoxyl, quinone ketoxy, lipid alkyl radicals and genotoxic HNE via a novel metal-independent nucleophilic substitution coupled with homolytic decomposition mechanism, which may partly explain their potential genotoxicity and carcinogenicity.

Tea extracts protect normal lymphocytes but not leukemia cells from UV radiation-induced ROS production: An EPR spin trap study

Purpose: An ex vivo method for detection of free radicals and their neutralization by aqueous tea in human normal lymphocytes and MEC-1 leukemia cells under ultraviolet (UV) irradiation was investigated.Materials and methods: This method is based on the electron paramagnetic resonance (EPR) spectroscopy spin-trapping technique. 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide (BMPO) was used as the spin trap. Normal human lymphocytes and leukemia cells were exposed to UVB radiation (290–315 nm) at 47.7 and 159 mJ/cm2 and to UVA radiation (315–400 nm) at 53.7 J/cm2.Results: No significant radical production at 47.7 mJ/cm2 UVB dose in both cell lines was observed. In normal cells, free radical production was observed at 159 mJ/cm2 UVB and 53.7 J/cm2 UVA doses. However, both UV sources did not significantly produce free radicals in leukemia cells. A radical scavenging property of tea extracts (black, green, sage, rosehip) was observed in normal lymphocytes after both UVB and UVA exposure. In leukemia cells, the intensities of EPR signals produced in BMPO with tea extracts were found to be increased substantially after UVA exposure.Conclusion: These results showed that UV radiation induced free radical formation in normal human lymphocytes and indicated that tea extracts may be useful as photoprotective agents for them. On the other hand, tea extracts facilitated free radical production in leukemia cells.

ESR spin trapping of radicals in methanol solution irradiated by heavy ion beams. Dependence on specific energy and LET

Radicals produced by the heavy ion (He, C, Ne, Si, Ar, and Fe) irradiation of methanol were spin trapped with PBN. Three kinds of radicals, PBN-CH3O, PBN-CH2OH, and PBN-H, were observed similar to those by γ-irradiation. The relative radical yields, PBN-CH3O/PBN-CH2OH and (PBN-CH3O+PBN-CH2OH)/PBN-H, varied depending on the LET value, the specific energy and mass of ions.

Free radical generation induced by ultrasound in red wine and model wine: An EPR spin-trapping study

Direct evidence for the formation of 1-hydroxylethyl radicals by ultrasound in red wine and air-saturated model wine is presented in this paper. Free radicals are thought to be the key intermediates in the ultrasound processing of wine, but their nature has not been established yet. Electron paramagnetic resonance (EPR) spin trapping with 5,5-dimethyl-l-pyrrolin N-oxide (DMPO) was used for the detection of hydroxyl free radicals and 1-hydroxylethyl free radicals. Spin adducts of hydroxyl free radicals were detected in DMPO aqueous solution after sonication while 1-hydroxylethyl free radical adducts were observed in ultrasound-processed red wine and model wine. The latter radical arose from ethanol oxidation via the hydroxyl radical generated by ultrasound in water, thus providing the first direct evidence of the formation of 1-hydroxylethyl free radical in red wine exposed to ultrasound. Finally, the effects of ultrasound frequency, ultrasound power, temperature and ultrasound exposure time were assessed on the intensity of 1-hydroxylethyl radical spin adducts in model wine.

Quantitative Spin-trapping ESR Investigation of Alkoxyl Radical Derived from AAPH: Development of a Flow-injection Spin-trapping ESR System for the Oxygen Radical Absorbance Capacity Assay

A flow-injection electron spin resonance (ESR) system was developed for the quantitative detection of an alkoxyl radical (RO·, R = C(CH3)2–C(+NH2Cl−)NH2) derived from AAPH (2,2′-azobis(2,4-amidinopropane) dihydrochloride) by thermal decomposition. Optimal measurement conditions for the system were examined, and it was found that the control of the radical formation by quenching in an ice-water vessel should be effective to obtain the stable and accurate results. The system was applied for the estimation of the alkoxyl radical-elimination ability and the oxygen radical absorbance capacity values of selected biosubstances, such as Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), caffeic acid, 4-hydroxycinnamic acid, epinephrine, rutin, (+)-catechin, l-tryptophane, and d-mannitol. As the rate constant for the reaction between alkoxyl radical and substrate, k S, could not be unequivocally determined, the defined value, γ 50 = k S/k 1, (k 1, the rate constant for the reaction between alkoxyl radical and spin trap) was used as a reaction parameter of substrate for alkoxyl radical. The flow-injection electron spin resonance system using alkoxyl radical elimination gave valid γ 50 values for biosubstances, and the system should be a valuable method for the evaluation of the antioxidant ability.

Molecular mechanism of metal-independent decomposition of organic hydroperoxides by halogenated quinoid carcinogens and the potential biological implications.

Halogenated quinones (XQ) are a class of carcinogenic intermediates and newly identified chlorination disinfection byproducts in drinking water. Organic hydroperoxides (ROOH) can be produced both by free radical reactions and enzymatic oxidation of polyunsaturated fatty acids. ROOH have been shown to decompose to alkoxyl radicals via catalysis by transition metal ions, which may initiate lipid peroxidation or transform further to the reactive aldehydes. However, it is not clear whether XQ react with ROOH in a similar manner to generate alkoxyl radicals metal-independently. By complementary applications of ESR spin-trapping, HPLC/high resolution mass spectrometric and other analytical methods, we found that 2,5-dichloro-1,4-benzoquinone (DCBQ) could significantly enhance the decomposition of a model ROOH tert-butylhydroperoxide, resulting in the formation of t-butoxyl radicals independent of transition metals. On the basis of the above findings, we detected and identified, for the first time, an unprecedented C-centered quinone ketoxy radical. Then, we extended our study to the more physiologically relevant endogenous ROOH 13-hydroperoxy-9,11-octadecadienoic acid and found that DCBQ could also markedly enhance its decomposition to generate the reactive lipid alkyl radicals and the genotoxic 4-hydroxy-2-nonenal (HNE). Similar results were observed with other XQ. In summary, these findings demonstrated that XQ can facilitate ROOH decomposition to produce reactive alkoxyl, quinone ketoxy, lipid alkyl radicals, and genotoxic HNE via a novel metal-independent mechanism, which may explain partly their potential genotoxicity and carcinogenicity.

Generation of reactive oxygen species in thylakoids from senescing flag leaves of the barley varieties Lomerit and Carina

During senescence, production of reactive oxygen species increased in thylakoids. In two barley varieties, no difference in superoxide production was observed while singlet oxygen production increased only in one variety. During senescence, chlorophyll content decreased and photosynthetic electron transport was inhibited as shown for flag leaves collected from barley varieties Lomerit and Carina grown in the field. Spin trapping electron paramagnetic resonance (EPR) was used to investigate the production of reactive oxygen species in thylakoid membranes during senescence. EPR measurements were performed with specific spin traps to discriminate between singlet oxygen on one hand and reactive oxygen intermediates on the other hand. The results show that the generation of reactive oxygen intermediates increases in both varieties during senescence. Singlet oxygen increased only in the variety cv. Lomerit while it remained constant at a low level in the variety cv. Carina. Measurements in the presence of inhibitors of photosystem II and of the cytochrome b6f complex revealed that in senescing leaves reduction of oxygen at the acceptor side of photosystem I was the major, but not the only source of superoxide anions. This study shows that during senescence the production of individual reactive oxygen species varies in different barley varieties.

Application of a Flow-injection Spin-trapping ESR Method for Evaluating the Alkoxy Radical Elimination Capacity (AREC) of Selected Antioxidants

Abstract A flow-injection spin-trapping ESR system using DMPO (5,5-dimethyl-1-pyrroline N-oxide) was developed for quantitative detection of the alkoxy radicals (•OR, R = C(CH3)2-C(+NH2Cl−)NH2) formed by thermal decomposition of AAPH (2,2′-azobis(2,4-amidinopropane) dihydrochloride). This system was applied to estimate the alkoxy radical elimination capacity of selected antioxidants by using Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), as a standard.

New insights into how RGO influences the photocatalytic performance of BiOIO3/RGO nanocomposites under visible and UV irradiation

Reduced graphene oxide (RGO) has been demonstrated to be effective in enhancing the photocatalytic activity of various semiconductors. However, an important issue that has been overlooked is the role of RGO in UV-induced photocatalysis of RGO-based nanocomposites. In the present work, novel BiOIO3/RGO nanocomposites were prepared by a simple one-pot hydrothermal method, during which BiOIO3 nanoplates were formed in situ on RGO sheets resulting from partial reduction of RGO. The two components of the composite displayed intimate interfacial contact. The as-prepared BiOIO3/RGO nanocomposites exhibited highly enhanced visible photocatalytic activity, relative to that of pure BiOIO3, toward removal of NO from air. However, the BiOIO3/RGO nanocomposites showed only slightly increased photocatalytic activity, relative to pure, under UV irradiation. The limited enhancement of UV activity can be ascribed to the fact that BiOIO3 would be expected to compete with RGO with regard to absorption and utilization of UV light. Evidence shows that RGO can act as a semiconductor rather than a photosensitizer or electron reservoir in BiOIO3/RGO nano-composites. In addition, the active species responsible for photoactivity have been investigated by a DMPO spin-trapping electron spin resonance technique. Photo-generated holes were found to be the main active species inducing the photo-oxidation of NO under visible light, whereas holes and OH radicals are considered to be responsible for photo-activity under UV light. This work points to BiOIO3/RGO nano-composites as new and efficient visible light photocatalysts for environmental remediation applications, and also as a source of new insights into the pivotal role of RGO in photocatalysis of RGO-based nanocomposites under visible as well as UV light.

Artificial photosynthesis of C1-C3 hydrocarbons from water and CO2 on titanate nanotubes decorated with nanoparticle elemental copper and CdS quantum dots.

The conversion of CO2 and water into value-added fuels with visible light is difficult to achieve in inorganic photocatalytic systems. However, we synthesized a ternary catalyst, CdS/(Cu-TNTs), which is assembled on a core of sodium trititanate nanotubes (TNTs; NaxH2-xTi3O7) decorated with elemental copper deposits followed by an overcoat of CdS quantum dot deposits. This ternary photocatalyst is capable of catalyzing the conversion of CO2 and water into C1-C3 hydrocarbons (e.g., CH4, C2H6, C3H8, C2H4, C3H6) upon irradiation with visible light above 420 nm. With this composite photocatalyst, sacrificial electron donors are not required for the photoreduction of CO2. We have shown that water is the principal photoexcited-state electron donor, while CO2 bound to the composite surface serves as the corresponding electron acceptor. If the photochemical reaction is carried out under an atmosphere of 99.9% (13)CO2, then the product hydrocarbons are built upon a (13)C backbone. However, free molecular H2 is not observed over 5 h of visible light irradiation even though proton reduction in aqueous solution is thermodynamically favored over CO2 reduction. In terms of photocatalytic efficiency, the stoichiometric fraction of Na(+) in TNTs appears to be an important factor that influences the formation of the observed hydrocarbons. The coordination of CO2 to surface exchange sites on the ternary catalyst leads to the formation of surface-bound CO2 and related carbonate species. It appears that the bidentate binding of O═C═O to certain reactive surface sites reduces the energy barrier for conduction band electron transfer to CO2. The methyl radical (CH3(•)), an observed intermediate in the reaction, was positively identified using an ESR spin trapping probe molecule. The copper deposits on the surface of TNTs appear to play a major role in the transient trapping of methyl radical, which in turn self-reacts to produce ethane.

Pseudo flow-injection ESR technique combining spin-trapping and application to the evaluation of superoxide scavenging capacity of phenolic compound

Evaluation methods of superoxide scavenging capacity have been studied by many researchers. One of the methods is a spintrapping electron spin resonance (ESR) technique, in which 5,5-diemthyl-1-pyrroline 1-oxide (DMPO) was usually used as a spintrapping reagent. In previous reports, the evaluation method based on a competition reaction and spin-trapping ESR technique were proposed. However, a big key issue and unavoidable problem remained in this evaluation. This is the rapid decrease of DMPO-O2 adduct by the following chemical reactions. Therefore, the initial signal intensity of DMPO-O2 has to be estimated with an approximation from a decreasing curve. This approximation, however, includes at least a thirty-second time lag before starting an ESR measurement. So, the measurement of a shorter time lag is required to obtain a more accurate initial intensity of DMPO-O2 - adduct. In this study, the pseudo flow-injection ESR method using a peristaltic pump was adopted to inject the test solution directly into a quartz cell in ESR cavity. This method achieved a 10 times shorter time lag (ca. 3 seconds) compared with the previous method (ca. 30 seconds) using a hematocrit capillary. As a consequence, the initial signal intensity within 10 % error was obtained without any estimation. The second-order rate constants of the reaction between various phenolic compounds and superoxide were obtained as one of the applications of this method.

Efficacy of the Reactive Oxygen Species Generated by Immobilized TiO2in the Photocatalytic Degradation of Diclofenac

We report on the photodegradation of diclofenac (DCF) by hydrothermal anatase nanocrystals either free or immobilized in porous silica matrix (TS) in connection to the type and amount of reactive oxygen species (ROS), in order to have deeper insight into their role in the photocatalysis and to provide an effective tool to implement the DCF mineralization. TiO2and TS exhibit a remarkable efficiency in the DCF abatement, supporting that the utilization of anatase nanoparticles with the highly reactive{001},{010}, and{101}exposed surfaces can be an effective way for enhancing the photooxidation even of the persistent pollutants. Furthermore, the hydrothermal TiO2, when immobilized in silica matrix, preserves its functional properties, combining high photoactivity with an easy technical use and recovery of the catalyst. The catalysts performances have been related to the presence of OH•,O21, andO2-•species by electron paramagnetic resonance spin-trap technique. The results demonstrated that the ROS concentration increases with the increase of photoactivity and indicated a significant involvement ofO21in the DCF degradation. The efficacy of TiO2when immobilized on a silica matrix was associated with the high ROS life time and with the presence of singlet oxygen, which contributes to the complete photomineralization of DCF.