Electron Paramagnetic Resonance Spin Trapping Research Articles

EPR Method for ex vivo Detection of Reactive Oxygen Species in Tissue

Measurement of free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR) has been problematic. Here, a novel EPR spin trapping technique has been developed that places one or two large segments of porcine arterial tissue along with supernatant directly into a standard EPR spectrometer cavity at liquid nitrogen temperature. This approach is validated in porcine arterial tissues treated as controls in vivo. To investigate that this method has lower extraneous ROS generation than methods which slice tissue into thin slivers before assaying for reactive oxygen species (ROS), we take two sets of coronary arterial tissue from the same animal. In the first set, we excise one or two large segments of tissue, and in the second set we section the tissue into ten pieces. In both cases, tissue was harvested, placed in physiological saline solution with 190-mM PBN (N-tert-butyl-α-phenylnitrone) and incubated in the dark for 2 hours at physiological temperature while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at minus eighty degrees Celsius until EPR analysis. Although absorption of microwaves by an aqueous sample typically at room temperature limits the size of the sample; this method can accommodate as large as 20-mm3 tissue volume into the EPR cavity at liquid nitrogen temperature. In our experiments the tissue volumes were in a range of values between 2 mm3 and 5 mm3,and the EPR spectra were normalized with respect to tissue volume.

Metabolic activation of sulfur mustard leads to oxygen free radical formation

We recently published electron paramagnetic resonance (EPR) spin trapping results that demonstrated the enzymatic reduction of sulfur mustard sulfonium ions to carbon-based free radicals using an in vitro system containing sulfur mustard, cytochrome P450 reductase, NADPH, and the spin trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) in buffer (A.A. Brimfield et al., 2009, Toxicol. Appl. Pharmacol. 234:128–134). Carbon-based radicals have been shown to reduce molecular oxygen to form superoxide and, subsequently, peroxyl and hydroxyl radicals. In some cases, such as with the herbicide paraquat, a cyclic redox system results, leading to magnified oxygen free radical concentration and sustained tissue damage. Low mustard carbon radical concentrations recorded by EPR in our in vitro system, despite a robust (4.0mM) sulfur mustard starting concentration, led us to believe a similar oxygen reduction and redox cycling process might be involved with sulfur mustard. A comparison of the rate of mustard radical–POBN adduct formation in our in vitro system by EPR at atmospheric and reduced oxygen levels indicated a sixfold increase in 4-POBN adduct formation (0.5 to 3.0μM) at the reduced oxygen concentration. That result suggested competition between oxygen and POBN for the available carbon-based mustard radicals. In parallel experiments we found that the oxygen radical-specific spin trap 5-tert-butoxycarbonyl-5-methylpyrroline-N-oxide (BMPO) detected peroxyl and hydroxyl radicals directly when it was used in place of POBN in the in vitro system. Presumably these radicals originated from O2 reduced by carbon-based mustard radicals. We also showed that reactive oxygen species (ROS)–BMPO EPR signals were reduced or eliminated when mustard carbon radical production was impeded by systematically removing system components, indicating that carbon radicals were a necessary precursor to ROS production. ROS EPR signals were completely eliminated when superoxide dismutase and catalase were included in the complete in vitro enzymatic system, providing additional proof of oxygen radical participation. The redox cycling hypothesis was supported by density functional theory calculations and frontier molecular orbital analysis.

Photoinduced decarboxylation of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid

Photoinduced reactions of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid (SeQCA) were investigated in alkaline media (aqueous NaOH solutions) by electron paramagnetic resonance (EPR) spectroscopy, following the in situ formation of paramagnetic species. According to UV–Vis and nuclear magnetic resonance investigations, protonation (pH ≈ 11) and deprotonation (pH ≈ 13) of the imino hydrogen of the 4‐pyridone moiety has to be considered, reflected also in the different EPR spectra observed upon irradiation. Photoinduced generation of radicals was found only for carboxylate substituted SeQCA; other studied selenadiazoloquinolone derivatives, together with those substituted at the C(8) position (R = H, COOCH2CH3, COOCH3, COCH3 or CN), did not generate paramagnetic species during exposure. Consequently, photodecarboxylation was suggested as the decisive step, accompanied by the decomposition of the selenadiazole ring, resulting in the formation of ortho‐hydroxylate anions. EPR parameters elucidated from experimental EPR spectra obtained at pH ≈ 11 and pH ≈ 13 indicate the formation of oxygen‐centered radicals at the decarboxylated 4‐pyridone ring. EPR spin trapping experiments with nitromethane confirmed a very effective photoinduced electron transfer from all the selenadiazoloquinolones investigated. Copyright © 2011 John Wiley & Sons, Ltd.

Photolytic reaction mechanism and impacts of coexisting substances on photodegradation of bisphenol A by Bi 2WO 6 in water

Bi 2WO 6 displayed great photolytic degradation efficiency to bisphenol A (BPA) under simulated solar light irradiation but its reaction mechanism and the impacts of coexisting substances on the degradation remain unclear. In present study, the reaction mechanism was investigated using DMPO spin-trapping ESR spectra and experiments with scavengers of hydroxyl radicals ( OH) and holes. The results supported that hole oxidation mainly governed the photodegradation process. As a common humic substance in natural water, humic acid accelerated the degradation of BPA when its concentration was 1 mg/L, while the photodegradation was impeded with the increase of humic acid concentration in the range of 5–20 mg/L. Almost all anions, including NO 3 −, HCO 3 −, Cl −, SO 4 2− inhibited the degradation of BPA by Bi 2WO 6 and their inhibition effects followed the order of SO 4 2− > Cl − > HCO 3 − > NO 3 −. Cations of Na +, K +, Ca 2+ and Mg 2+ displayed slight suppressing effect on BPA degradation mainly due to the impact of Cl − coexisting in the solution. However, Cu 2+ hindered the BPA photodegradation heavily. Fe 3+ and H 2O 2 affected the photodegradation in a complicated way: they suppressed or promoted the photodegradation depending on their concentrations. This could be the result of competition between photolyitc hole generated by Bi 2WO 6 and OH produced by Fe 3+ or H 2O 2.

Efficient and Stable Photocatalytic Activity of CeVO<sub>4</sub>/TiO<sub>2</sub> Nanocrystalline Heterojunction under Visible Light Irradiation

A visible-light-driven CeVO4/TiO2 photocatalyst with nanostructured heterojunction has been successfully prepared by a simple coupled method. The catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and spin-trapping electron paramagnetic resonance (EPR). The visible light-induced photocatalytic activities were evaluated by decomposing benzene in gas phase. The result showed that the prepared catalyst exhibited efficient photocatalytic activities with high photochemical stability under visible light irradiation.

Evaluation of the Forrester–Hepburn Mechanism As an Artifact Source in ESR Spin-Trapping

Nitrone spin traps such as 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) are commonly used for free radical detection. Though proven examples are rare, artifact formation must be considered. For example, the Forrester-Hepburn mechanism yields the same radical adduct as that formed by genuine radical trapping. A hydroxylamine is formed by nucleophilic attack of the substrate on DMPO and subsequently oxidized to the respective nitroxide radical. One potential candidate for this artifact is the sulfur trioxide radical adduct (DMPO/(•)SO(3)(-)), as detected in spin-trapping experiments with horseradish peroxidase and sulfite. It has previously been shown by NMR experiments that the hydroxylamine intermediate does indeed form, but no direct proof for the ESR artifact has been provided. Here, we used isotopically labeled DMPO with horseradish peroxidase and ferricyanide to test for the Forrester-Hepburn artifact directly in a spin-trapping experiment. Besides sulfite, we investigated other nucleophiles such as cyanide, cysteine, and glutathione. Neither sulfite nor biological thiols produced detectable spin-trapping artifacts, but with cyanide the relatively weak signal originated entirely from the nucleophilic reaction. The hydroxylamine intermediate, which is more abundant with cyanide than with sulfite, was identified as cyano-hydroxylamine by means of 2D NMR experiments. Although our study found that spin trapping provided authentic free radical signals with most of the substrates, the occurrence of the Forrester-Hepburn mechanism artifact with cyanide emphasizes the importance of isotope measurements with nucleophile substrates.

Determination of reactive oxygen species generated by phorbol 12-myristate 13-acetate-stimulated oral polymorphonuclear cells from healthy human volunteers without any dental problems

Human oral polymorphonuclear cells (OPMNs) play an important role in the defence of oral cavity from bacteria by releasing reactive oxygen species (ROS). The purpose of the study is to determine ROS generated by OPMNs collected from healthy volunteers without any dental problems by applying a luminol analogue 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H)dione sodium salt-dependent chemiluminescence (CL) response in combination with radical and ROS scavengers. In the CL response induced by OPMNs primed with phorbol 12-myristate 13-acetate, 0.23M 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap, 12.5U/ml of super oxide dismutase (SOD) as a superoxide anion (O2−) scavenger, and 0.96M dimethyl sulfoxide (DMSO) as a hydroxyl radical (OH) scavenger inhibited the response by approximately 90%, 70%, and 60%, respectively. The inhibitory effects were obtained in a range of concentrations where viability of the OPMNs exposed to DMPO, SOD, and DMSO were more than 70%. Electron spin resonance-spin trapping analysis confirmed that at least O2− and OH were generated via primed OPMNs. Furthermore, the addition of both 12.5U/ml of SOD and 0.96M DMSO inhibited the CL response by more than 90%, which was in accordance with the inhibition rate obtained by the addition of DMPO. Therefore, it is suggested that around 90% of the CL response is induced by free radicals, and at least around 70% of the radicals are SOD-inhibitable, meaning that they are originally derived from O2−. In addition, some of the OH are generated independently of O2− because if all of the OH were formed through dismutation of O2−, only 70% of the CL response would be inhibited by the combination of SOD and DMSO as was inhibited by SOD alone.The present study suggests that OPMNs in health individuals have an ability to generate free radicals, which consist mainly of O2−, OH and possibly an intermediate ROS derived from O2− and OH.

Acyl-substituted ferrocenes as driers for solvent-borne alkyd paints

Ferrocenes bearing acyl substituents in the cyclopentadienyl rings [Fe(η 5-C 5H 4COR)(η 5-C 5H 5)] and [Fe(η 5-C 5H 4COR) 2] (R = CH 3, CF 3 and Ph) were examined as new driers for solvent-borne alkyd binder. All studied ferrocenes were found to be active catalysts for cross-linking reaction of the alkyd. These iron(II) compounds give solid polymeric films with hardness and drying time comparable to the commercial cobalt(II) drier. Acetyl- and benzoyl-substituted ferrocenes show an excellent synergic effect with the cobalt drier giving hard polymeric films within short drying time. The kinetics of the alkyd autoxidation was followed by FTIR spectroscopy. Spin-trapping ESR technique has proven the important role of the ferrocenium cation upon decomposition of hydroperoxides by ferrocene-based driers. The peroxy and alkoxy radicals, appearing in drying process, were resolved by the new spin trap methyl- N-mesityl nitrone.

Oxygen radical absorbance capacity (ORAC) of cyclodextrin-solubilized flavonoids, resveratrol and astaxanthin as measured with the ORAC-EPR method

Recently, we proposed an oxygen radical absorbance capacity method that directly quantifies the antioxidant’s scavenging capacity against free radicals and evaluated the radical scavenging abilities for water soluble antioxidant compounds. In this study, we determined the radical scavenging abilities of lipophilic antioxidants which were solubilized by cyclodextrin in water. Commonly employed fluorescence-based method measures the antioxidant’s protection capability for the fluorescent probe, while we directly quantify free-radical level using electron paramagnetic resonance spin trapping technique. In addition, the spin trapping-based method adopted controlled UV-photolysis of azo-initiator for free radical generation, but in fluorescence-based method, thermal decomposition of azo-initiator was utilized. We determined the radical scavenging abilities of seven well-known lipophilic antioxidants (five flavonoids, resveratrol and astaxanthin), using methylated β-cyclodextrin as a solubilizer. The results indicated that the agreement between spin trapping-based and fluorescence-based values was only fair partly because of a large variation in the previous fluorescence-based data. Typical radical scavenging abilities in trolox equivalent unit are: catechin 0.96; epicatechin 0.94; epigallocatechin gallate 1.3; kaempferol 0.37; myricetin 3.2; resveratrol 0.64; and astaxanthin 0.28, indicating that myricetin possesses the highest antioxidant capacity among the compounds tested. We sorted out the possible causes of the deviation between the two methods.

Ascorbic acid induced degradation of beta-glucan: Hydroxyl radicals as intermediates studied by spin trapping and electron spin resonance spectroscopy

Abstract The formation of hydroxyl radicals in beta-glucan solutions treated with ascorbic acid and iron(II) was demonstrated by ESR spin trapping based methods. Two different spin traps were tested, namely DMPO which is commonly used to detect hydroxyl radicals, and POBN often used to detect carbon centered radicals. The experiments performed showed that the presence of iron(II) with DMPO led to low DMPO–OH adduct stability and further to DMPO dimerization. The level of hydroxyl radicals formed during the beta-glucan radical mediated degradation was evaluated using two ESR spin trapping methods based on the use POBN together with either 2% (v/v) EtOH or DMSO. The addition of ascorbic acid together with iron(II) in beta-glucan solution led to an immediate maximal production of hydroxyl radicals while the presence of ascorbic acid alone led to a progressive production of radical. Further hydroxyl radicals were found to be formed when iron(II) was added alone in beta-glucan solutions. The viscosity loss observed in the three last mentioned beta-glucan solutions were found to relate with the formation of hydroxyl radicals. These data confirm the involvement of hydroxyl radical in the beta-glucan degradation.

Spin Trapping Studies of Amine-Stabilized Trialkylborane Free Radical Initiator Systems: Kinetics and Mechanism

The free radical initiation chemistry of highly reactive trialkylboranes (R3B, R = n-butyl), stabilized by complexation to amines (A–R3B), has been investigated using spin trapping methods and electron paramagnetic resonance spectroscopy. Protonation of A–R3B leads to release of R3B and its subsequent autooxidation in the presence of molecular oxygen. This reaction provides highly reactive alkyl and alkoxy radicals for initiation of α–olefin polymerization. Kinetic traces of the R3B autooxidation reaction were obtained by monitoring the relative concentrations of trapped radical species as a function of time for several different initial conditions (acid concentrations). Analysis of a representative kinetic run is discussed in terms of several proposed mechanisms from the literature.

Fragmentation of Perfluorinated Membranes Used in Fuel Cells: Detecting Very Early Events by Selective Encapsulation of Short-Lived Fragments in β-Cyclodextrin

The fragmentation of perfluorinated ionomeric membranes during fuel cell (FC) operation is studied in our laboratory by direct electron spin resonance (ESR) and by spin trapping ESR, and interpretation of the results is facilitated by the study of model compounds (MCs). The advantage of this approach is the ability to detect and identify "early events" in the fragmentation process, before the appearance of stable species that can be detected by NMR and other methods. We report a spin trapping ESR study of the fragmentation of Nafion, Aquivion, and 3M membranes in their water dispersions and of the corresponding model compounds in the presence of HO•, using 2-methyl-2-nitrosopropane (MNP) as a spin trap. Hydroxyl radicals were generated by UV irradiation of hydrogen peroxide. In the MCs the presence of both oxygen-centered radicals (OCRs) and carbon-centered radicals (CCRs) adducts as well as di-tert-butyl nitroxide radicals (DTBN, from spin trap decomposition) were detected. The presence of both OCR and CCR adducts is rationalized by the initial generation of OCRs with low stability and their transformation into the more stable CCRs. Addition of β-cyclodextrin (β-CD) led to a significant increase of the intensity of the MNP/OCR adducts and in one system also to the complete disappearance of the MNP/CCR adduct, results that we assign to the fast selective encapsulation of OCR adducts in the hydrophobic β-CD host. In the membrane dispersions the presence of oxygen-centered radical (OCR) adducts and DTBN radicals have been detected; this result is rationalized by the slower rate of transformation of OCR adducts to CCR adducts in the membrane systems.

Photodegradation of 4-chloronitrobenzene in the presence of aqueous titania suspensions in different gas atmospheres

The photocatalytic degradation of 4-chloronitrobenzene (4-CNB) was carried out using Degussa P25 TiO(2) as photocatalyst in three different gas atmospheres: nitrogen, oxygen, and ozone. The total organic carbon (TOC) and inorganic anions including chloride, nitrite, and nitrate anions were measured to monitor the mineralization processes, while the degradation of 4-CNB and the formation of intermediates were followed by liquid chromatography-mass spectrometry (LC/MS). Results showed that the photocatalytic efficiency followed the order of TiO(2)/UV/N(2) < TiO(2)/UV/O(2) < TiO(2)/UV/O(3), which was further proved by evaluating the reaction activities using electron paramagnetic resonance (EPR) spin trapping technique. Chlorine atom, nitro group and hydrogen atom of the benzene ring could be displaced by hydroxyl radical (•OH) leading to the formation of chloride, nitrite (III) anions and a variety of phenols, then the nitrite (III) anions were further oxidized to nitrate (V) anions. 4-Nitrophenol and 5-chloro-2-nitrophenol were identified and quantified in both of the TiO(2)/UV/N(2) and TiO(2)/UV/O(2) processes while no aromatic intermediates were monitored in the process of TiO(2)/UV/O(3).

Antioxidant activity of the halophyte Limonium tetragonum and its major active components

In this study, the antioxidant potentials of crude extracts and solvent-partitioned fractions of Limonium tetragonum were assessed by measuring their ability to scavenge intracellular reactive oxygen species (ROS) generated in HT-1080 cells. Following activity-oriented separation, four flavonol glycosides were isolated as active principles and their chemical structures were determined by 2 D NMR and by comparison with reported spectral data. The isolated compounds (1–4) were evaluated for their antioxidant capacity using three different activity tests; degree of occurrence of intracellular ROS, lipid peroxidation in HT-1080 cells and the extent of oxidative damage of genomic DNA purified from HT-1080 cells. All compounds exhibited significantly inhibited the generation of intracellular ROS and lipid peroxidation in HT-1080 cells, and significantly inhibited DNA oxidation. In addition, direct free radical scavenging effects of these compounds were investigated using the electron spin resonance (ESR) spin-trap technique.

Endothelial nitric oxide synthase enhancer reduces oxidative stress and restores endothelial function in db/db mice

Endothelial dysfunction is caused by reduced nitric oxide (NO) bioavailability and/or over-produced reactive oxygen species (ROS). The present study investigated a vascular benefit of AVE3085, an endothelial nitric oxide synthase (eNOS) enhancer, in preserving endothelial function in diabetic mice and the mechanisms involved. Male db/db and db/m(+) mice were orally administered AVE3085 for 7 days (10 mg kg(-1) day(-1)). Vascular reactivity of arteries was studied via myography under both isometric and isobaric conditions. ROS levels in aortas were determined using dihydroethidium fluorescence dye and electron paramagnetic resonance spin trapping. Chronic treatment with AVE3085 reduced blood pressure, enhanced endothelium-dependent relaxations (EDR) to acetylcholine in aortas, mesenteric, and renal arteries, lowered oxidative stress, and augmented the attenuated flow-dependent dilatation in mesenteric resistance arteries from db/db mice. Incubation of aortas from C57BL/6J mice in high glucose (30 mmol L(-1)) culture medium for 48 h impaired EDR and elevated ROS generation, and these effects were reversed by co-treatment with AVE3085 (1 µmol L(-1)). Benefits of AVE3085 were abolished by the transcription inhibitor actinomycin D, the NOS inhibitor N(G)-nitro-L-arginine methyl ester, and in eNOS(-/-) mice. NO production in primary endothelial cells from mouse aortas was detected with a NO-sensitive fluorescence dye. Protein expression was assayed by western blotting. Treatment with AVE3085 enhanced NO production in endothelial cells and eNOS expression in aortas. AVE3085 ameliorates endothelial dysfunction in db/db mice through increased NO bioavailability, which reduces oxidative stress in the vascular wall. Targeting eNOS and NO production may be a promising approach to combat diabetic vasculopathy.

Evaluation of the antioxidant activity of tetracycline antibiotics in vitro

Tetracyclines are the second most common antibiotic family in medicine usage. These antibiotics exhibit antioxidant potential; however, the exact mechanism remains unclear. The antiradical activity of the seven tetracyclines (TCs; tetracycline, chlortetracycline, oxytetracycline, doxocycline, methacycline, demeclocycline, minocycline) was determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH(•)) and hydroxyl radicals (HO(•)) generated in a Fenton reaction. Electron spin resonance (ESR), ESR spin-trapping, chemiluminescence and spectrophotometry techniques were applied. It was found that the TCs showed high DPPH antiradical activity in the range 26-96% at 2.5 mmol/L concentration. The second-order rate constants for the reaction between HO(•) and TCs were calculated, in the range (3.6-9.6) × 10(9) L/mol/s. The tetracycline compounds also exhibited a strong decrease in light emission (range 61-85% at concentration of 1 mmol/L). This study also showed that TCs promote the generation of singlet oxygen in the presence of H(2)O(2) and Fe(II)/Fe(III) ions. Our findings suggest direct scavenging activity of the examined tetracyclines towards free radicals, and may be relevant to therapeutic strategy.

4-Aminobenzoic acid hydrazide inhibition of microperoxidase-11: Catalytic inhibition by reactive metabolites

Inhibition of human peroxidase enzymes such as myeloperoxidase or eosinophil peroxidase represents a novel therapeutic area, for which there are no current clinical therapeutics. We utilized 4-aminobenzoic acid hydrazide which was reported to be a potent irreversible inhibitor of myeloperoxidase to gain insight into the role of reactive metabolites in catalytic inhibition. In order to carry out detailed studies, we used a model peroxidase, microperoxidase-11 (MP-11). We investigated the heme spectrum of MP-11 in the presence of 4-ABAH and found that heme bleaching occurred that was irreversible. This coincided with an absence of catalytic activity. The spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was able to significantly prevent inactivation of peroxidase activity, therefore, we performed ESR spin trapping studies and detected a carbonyl carbon-centered radical of 4-ABAH. In order to determine if the free radical metabolites became bound to MP-11, we performed high-resolution MALDI with elemental analysis to determine the change in elemental composition that occurred in these reactions. These masses were assigned to free radical metabolites of 4-ABAH and were not observed in reactions containing DMPO. We conclude that the 4-ABAH free radical metabolites which were bound to MP-11 were involved in the catalytic inhibition and were scavenged by DMPO.

Improved Photocatalytic Activity of WO3 through Clustered Fe2O3 for Organic Degradation in the Presence of H2O2

Photocatalytic degradation of organic substrates over WO(3) in an aerated aqueous suspension is very slow due to the difficulty of O(2) reduction by the conduction band electron on WO(3). In this work, we report on H(2)O(2) as an electron scavenger significantly accelerating the photodegradation of phenol and azo-dye X3B in water under UV or visible light. More importantly, an iron-containing WO(3) (FeW) synthesized through thermal decomposition of a ferrotungstenic acid displayed a much higher activity than pure WO(3) (HW) prepared in parallel. As the sintering temperature increased, both FeW and HW showed an exponential increase in activity. The maximum rate constant of phenol degradation obtained with FeW at 400 °C was about 2 times larger than that with HW at 600 °C. Sample characterization with electron paramagnetic resonance (EPR) spectroscopy and other techniques revealed that ferric species (0.3 wt % Fe(2)O(3)) were mainly present as clusters on the oxide surface at 120 °C and then they diffused toward the lattice sites of WO(3) at high temperature, which was detrimental to the photocatalytic reaction. 5,5-Dimethyl-1-pyrroline N-oxide spin-trapping EPR showed that the production of hydroxyl radicals was greatly enhanced upon the addition of H(2)O(2), the trend of which among different catalysts was the same as that of the rate of phenol degradation. The catalysts after excitation at 350 nm displayed a blue emission centered at 469 nm, the intensity of which varied with the catalyst activity nearly as expected. A possible mechanism for the improved photoactivity of WO(3) is proposed involving the electron transfer from WO(3) to Fe(2)O(3) and the reaction of the reduced oxide with H(2)O(2) to generate hydroxyl radicals.

Nanocomposite of Ag–AgBr–TiO2 as a photoactive and durable catalyst for degradation of volatile organic compounds in the gas phase

The nanocomposites of Ag–AgBr–TiO2 photocatalyst have been prepared by a simple deposition–precipitation method, which is used for the gas-phase degradation of volatile organic pollutants of aromatic benzene and non-aromatic acetone that are notorious volatile organic compounds (VOCs) present in indoor and outdoor air. A collection of joint techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet/visible diffuse reflectance spectra (UV/vis DRS) have been employed to determine the structure, morphology and optical properties of the as-prepared Ag–AgBr–TiO2 nanocomposite. The presence of surface Ag species existed as Ag (0) and Ag (I) in Ag–AgBr–TiO2 is confirmed by the analysis of X-ray photoelectron spectroscopy (XPS). The Fourier transformed infrared spectroscopy (FT-IR) analysis shows the enhanced chemical bonding of O–Ti and O–Ti–O after the deposition of AgBr and Ag species onto the surface of TiO2. It is found that the Ag–AgBr–TiO2 nanocomposite exhibits much higher photocatalytic activity and stability under both UV light and visible light irradiation as compared with that over commercial titania (Degussa P25) toward the gas-phase degradation of both aromatic benzene and non-aromatic acetone. The active radical species involved for degradation reactions over the Ag–AgBr–TiO2 photocatalyst have been investigated by the spin-trapping electron paramagnetic resonance (EPR) spectra and the OH-trapping photoluminescence (PL) spectra. Synergetic effects between Ag–AgBr and TiO2 have been observed and discussed for the gas-phase degradation of volatile organic compounds on the basis of joint results of characterization and photocatalytic activity.

Application of Flow-ESR Techniques for Mechanistic Study of Biological Radical Reactions: HPLC–ESR Spin-Trapping System for Post-Column Evaluation of the Superoxide Radical Scavenging Activity of Column Eluates

A new high-performance liquid chromatography (HPLC)–electron spin resonance (ESR) spin-trapping system for post-column on-line detection of the superoxide radical scavenging activity of column eluates was developed. A cyclic nitrone-type spin-trapping reagent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), was used for detection of the superoxide radical, which was produced by riboflavin-dependent photo-reduction of molecular oxygen in the presence of an electron donor. The reaction conditions were optimized by monitoring the ESR signal intensity of the spin-adduct of DMPO. HPLC–ESR chromatographs were recorded for the standard sample solution, which included three phenolic compounds, gallic acid (Gal), 4-hydroxycoumaric acid (Cou), and caffeic acid (Caf).