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Abstract The only general technique that allows the unambiguous detection of free radicals is electron spin resonance (ESR). However, ESR spin trapping has severe limitations especially in biological systems. The greatest limitation of ESR is poor sensitivity relative to the low steady-state concentration of free radical adducts, which in cells and in vivo is much lower than the best sensitivity of ESR. Limitations of ESR have led to an almost desperate search for alternatives to investigate free radicals in biological systems. Here we explore the use of the immuno-spin trapping technique, which combine the specificity of the spin trapping to the high sensitivity and universal use of immunological techniques. All of the immunological techniques based on antibody binding have become available for free radical detection in a wide variety of biological systems. Highlights • Immuno-spin trapping combines the specific detection of free radicals with the sensitivity of immunological techniques. • Detection of free radicals in subcellular compartments and in vivo is possible with immuno-spin trapping. • Immuno-spin trapping allows the rigorous free radical detection to all biomedical investigators. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Reported herein is a novel photoredox‐catalyzed approach for ether synthesis and it involves alkoxyl radicals generated from N‐alkoxypyridinium salts. A wide range of alkenes are smoothly difunctionalized in an anti‐Markovnikov fashion, affording various functionalized alkyl alkyl ethers. Notably, this mild process tolerates a number of functional groups and is efficiently carried out under both batch and flow conditions. Importantly, electron paramagnetic resonance (EPR) experiments by spin trapping were carried out to characterize the radical intermediates involved in this radical/cationic process. [ABSTRACT FROM AUTHOR]

The Brazil nut is an important product from the Amazonian region and its productive chain is an income source for local communities. The effect of combinations of packaging atmospheres (loose or vacuum-packed) and storage temperatures (4±1 °C or 24±2 °C) on the tendency of lipid radical formation and on volatiles was investigated for the first time in shelled Brazil nut kernels. It was observed that refrigeration, whether combined with lose packing or vacuum packing, was effective to reduce the tendency for lipid radical formation, as detected by spin-trapping electron spin resonance (ESR) spectroscopy, as well as peroxides, conjugated dienes and 3-octen-2-one. However, the combination of refrigeration with vacuum packing, even using low-density polyethylene (LDPE) pouches with a high oxygen transmission rate (OTR), also reduced the formation of hexanal, which is a major off-flavor volatile, and thus should be recommended for the storage of Brazil nut kernels for the studied period. [ABSTRACT FROM AUTHOR]

Computer modeling using a commercially available software package was used to explore the optimization of filling systems based on the relatively new concepts of avoiding entrainment of air bubbles and oxides by avoiding surface turbulence. The test casting was based on a pattern for a traditional top poured test bar, whose cross section was a tri-lobed clover-like shape. The study illustrates clearly that the detailed design of the filling system has a major influence on the conditions for defect generation during filling. Traditional steel casting systems using the widely popular assembly of preformed refractory tubes were found to behave poorly. Systems were demonstrated which were capable of delivering highly controlled filling behavior. The latest systems to be developed employed (1) a naturally pressurized filling system and (2) the use of filters placed flush on the top of the runner to act as bubble diverters, together with (3) terminal spin traps. These novel filling systems demonstrated excellent performance in simulation, in agreement with practical experience of the capability (of the trident gate in particular) to produce, for the first time in the history of casting, defect-free castings on a routine basis. [ABSTRACT FROM AUTHOR]

Formation of radical intermediates upon photocatalytic (UVA) glycerol transformation in aerated aqueous TiO 2 (P25) suspensions was followed by EPR spin trapping technique. Character and concentration of the spin-adducts generated by the addition of the radical species to 5,5-dimethyl-1-pyrroline N -oxide (DMPO) spin trap are significantly affected by the UVA radiation dose and by the initial composition of the photocatalytic system. The DMPO spin-adducts of hydroxyalkyl radicals R1 and R2 detected in the aerated aqueous P25 suspensions containing glycerol are compatible with the H-abstraction processes attributed to the interaction of physisorbed glycerol molecules with the trapped holes or to the reaction of free hydroxyl radicals with glycerol in solution. Addition of fluoride at various concentrations has no effect on the character and concentration of DMPO spin-adducts observed upon in situ UVA photoexcitation of photocatalytic system P25/DMPO/glycerol under given experimental conditions (pH > 7). [ABSTRACT FROM AUTHOR]

Abstract: Photoelectrocatalytic (PEC) system greatly improves the migration of photoexcited charges, retards the fast recombination of electron‐hole and increases the lifetime of photogenerated holes. In this article, we constructed a novel PEC system to degrade berberine chloride form (BCF). XRD patterns indicated aging time was an important condition for the crystal type of TiO2, and the best proportion of anatase/rutile was 80/20. The band gap energy of the TiO2 was 3.01 eV. We demonstrated that a synergistic effect existed between photocatalysis (PC) and electrocatalysis (EC). Besides, we discussed the influence of pH, current density, the amount of catalyst and initial BCF concentration on the degradation of BCF. Electron spin resonance (ESR) through spin trap 5, 5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) and the scavenging experiments suggested that the reactive oxygen species (ROS) were superoxide radicals ( O 2 · −), hydroxyl radicals (·OH) and sulfate radical ( SO 4 · −) in PEC system. Furthermore, we compared the two pathway of formation DMPO‐SO4 adducts and found that SO 4 · − was the most major oxidized species in degrading BCF. We proposed a plausible reaction mechanism. Intriguingly, even under lower current and weaker light conditions, the PEC process maintained its effectiveness, demonstrating the feasibility of the PEC approach. [ABSTRACT FROM AUTHOR]

Exogenous and endogenously produced sulfide derivatives, such as H 2 S/HS − /S 2− , polysulfides and products of the H 2 S/S-nitrosoglutathione interaction (S/GSNO), affect numerous biological processes in which superoxide anion (O 2 − ) and hydroxyl ( OH) radicals play an important role. Their cytoprotective-antioxidant and contrasting pro-oxidant-toxic effects have been reported. Therefore, the aim of our work was to contribute to resolving this apparent inconsistency by studying sulfide derivatives/free radical interactions and their consequent biological effects compared to the antioxidants glutathione (GSH) and Trolox. Using the electron paramagnetic resonance (EPR) spin trapping technique and O 2 − , we found that a polysulfide (Na 2 S 4 ) and S/GSNO were potent scavengers of O 2 − and cPTIO radicals compared to H 2 S (Na 2 S), GSH and Trolox, and S/GSNO scavenged the DEPMPO-OH radical. As detected by the EPR spectra of DEPMPO-OH, the formation of OH in physiological solution by S/GSNO was suggested. All the studied sulfide derivatives, but not Trolox or GSH, had a bell-shaped potency to decompose H 2 O 2 and produced OH in the following order: S/GSNO > Na 2 S 4 ≥ Na 2 S > GSH = Trolox = 0, but they scavenged OH at higher concentrations. In studies of the biological consequences of these sulfide derivatives/H 2 O 2 properties, we found the following: ( i ) S/GSNO alone and all sulfide derivatives in the presence of H 2 O 2 cleaved plasmid DNA; ( ii ) S/GSNO interfered with viral replication and consequently decreased the infectivity of viruses; ( iii ) the sulfide derivatives induced apoptosis in A2780 cells but inhibited apoptosis induced by H 2 O 2 ; and ( iv ) Na 2 S 4 modulated intracellular calcium in A87MG cells, which depended on the order of Na 2 S 4 /H 2 O 2 application. We suggest that the apparent inconsistency of the cytoprotective-antioxidant and contrasting pro-oxidant-toxic biological effects of sulfide derivatives results from their time- and concentration-dependent radical production/scavenging properties and their interactions with O 2 − , OH and H 2 O 2 . The results imply a direct involvement of sulfide derivatives in O 2 − and H 2 O 2 / OH free radical pathways modulating antioxidant/toxic biological processes. [ABSTRACT FROM AUTHOR]

- tert-butylmethanimine -oxide is a potent spin-trapping probe for biologically important radicals, and this nitrone undergoes complete regioselective cycloadditions to less electron-deficient monosubstituted olefins. In the present study, solvent effects on the cycloaddition of this nitrone to styrene have been theoretically studied in terms of the global properties of the reactants, electrophilic and nucleophilic Parr function analysis and the activation and reaction energies of located transition states and products. Formation energies of optimized radical adducts were computed to determine their stabilities in different solvents. The cycloaddition is predicted to be completely ortho regioselective which is in complete agreement with experiments and involved earlier C-C bond formation owing to the insufficient depopulation of -conjugated carbon atom in styrene and shows varying asymmetry indices in different solvents. Decrease in activation parameters and increase in stability of cycloadducts are predicted with decreasing solvent polarity. Aqueous media destabilize the radical adducts as predicted from the calculated formation energy, enthalpy and free energy of reaction. Hydroxyl as well as methyl radical adducts are predicted to be more stable than superoxide anion radical adducts. These predictions are in complete agreement with the experiments. [ABSTRACT FROM AUTHOR]

We investigated the thermal degradation of poly(butylene terephthalate)-co-poly(ethylene oxide) (PBT-co-PEO), a thermoplastic poly(ether-ester) elastomer (TPEE), through proton nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), gel permeation chromatography (GPC), and spin-trapping electron spin resonance (ESR) analysis to detect radical intermediates present during degradation. Three kinds of PBT-co-PEO with different component ratios of PBT/PEO were synthesized. The thermal degradation process of PBT-co-PEO was divided into four weight-loss stages. In the first stage from room temperature to 120 °C, we confirmed the production of two radical intermediates, O-°CH-CH2 and °CH2-, by the spin-trapping method. This suggested that the initial decomposition occurred at the OCH2-CH2O bond in the PEO units. Upon annealing at 120 °C, PBT-co-PEO showed a small degree of random degradation, while higher PBT contents induced gelation and the production of the characteristic oligomer PBT-PEO-PBT. The gelation was attributed to cross-linking between two O-°CH-CH2 moieties of PBT. In the second stage from 120 to 340 °C, a large thermo-oxidative degradation of the PEO segment occurred, accompanied by an increase in the radical amount of spin adducts. In the third stage, the thermo-oxidative degradation of PBT units was observed. The radical intermediates were thus shown to be a primary factor of the thermal degradation characteristics of TPEE. [ABSTRACT FROM AUTHOR]

The study highlights the preparation of novel Gum Arabic (GA) grafted polyacrylamide based silica nanocomposite using in-situ radial graft copolymerization method. The presence of radicals involved in synthesis of GA-g-PAM was detected using DMPO as a spin trapping agent by Electron paramagnetic resonance (EPR) analysis and the possible reaction pathway was proposed. The novel GA-g-PAM/SiO 2 nanocomposite was characterized by Elemental analyzer (CHNS/O), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Atomic force microscopy (AFM), Brunauer Emmett and Teller (BET) and zeta potential (ZP) to study the chemical, structural and textural properties of nanocomposite. The successful incorporation of silica in grafted copolymer matrix was confirmed by FTIR and XRD analysis. The results indicated that surface area increased significantly after formation of GA-g-PAM/SiO 2 compared to parental polymer (GA) matrix and 273.55 m 2 /g surface area was determined for GA-g-PAM/SiO 2 nanocomposite. The recovery of rare earth elements (REE) from aqueous solution was also investigated using GA-g-PAM/SiO 2 nanocomposite. The optimum conditions for REEs adsorption were determined from the batch adsorption experiments. The adsorption kinetics for REEs were well described by pseudo first order model. The adsorption equilibrium data fitted well with Langmuir isotherm except for Sc ions. The thermodynamic studies confirm that the adsorption is spontaneous and endothermic. Desorption studies affirmed the regenerative efficiency of loaded REEs up to three cycles. [ABSTRACT FROM AUTHOR]

Mesoporous Mn x Co 3 − x O 4 nanocages with high cobalt content, large surface area and high pore volume were synthesized through a self-assembly method. The as-prepared Mn x Co 3 − x O 4 nanocages displayed satisfactory catalytic activity toward peroxymonosulfate (PMS) and the metal ions leaching concentration could be negligible. Sulfate radical was identified as the predominant active species through radical quenching experiments and electron spin resonance spin-trapping technique. The kinetics of the oxidation process was of pseudo-first order. The increasing cobalt content in Mn x Co 3 − x O 4 NCs was in favor of enhancing the decomposition of PMS. Mn x Co 3 − x O 4 nanocages dosage, PMS concentration and reaction temperature put the promoting effect on the degradation, while initial CBZ concentration had the retarding impact. Mn x Co 3 − x O 4 nanocages could efficiently operate over a wide pH range of 5.0–8.0. Coexisting chloride ions exerted a dual role in the decomposition of PMS and this role was concentration-dependent. XPS analysis confirmed the reversible valence equilibrium between metal ions and the recovery of surface adsorbed oxygen, which ensured their sustainable catalytic activity even after five consecutive runs. Based on the main intermediates identified by liquid chromatography-tandem mass spectrometry, a possible pathway of CBZ oxidation was proposed. The potential risk resulting from the highly toxic intermediates can also be effectively controlled by Mn x Co 3 − x O 4 NCs activated PMS system. [ABSTRACT FROM AUTHOR]

Resveratrol (RSV) analogues have attracted much attention because of the expected health functions including antioxidant activities. We have carried out a quantitative determination of the scavenging abilities of six trans -RSV analogues against various reactive oxygen species and methyl radical (hydroxyl radical, superoxide, alkoxyl radical, peroxyl radical, methyl radical, and singlet oxygen). RSV analogues are in general more potent scavenger than the parent RSV. Furthermore, piceatannol (PIC) having two OH groups in the ortho position of resveratrol was found to show 11 times higher scavenging ability against peroxyl radical than parent resveratrol. With the aid of previous theoretical studies, the enhanced antioxidant ability was interpreted based on the effects of substituent that modifies the original resveratrol structure and function. [ABSTRACT FROM AUTHOR]

Effect of temperatures on thermal oxidation of palmitic acid was studied by the combination of EPR and GC–MS/MS. DMPO was used as the spin trap. The experimental spectrum was simulated with alkyl and alkoxyl spin adducts. Total amount of spins, a parameter to indicate radical concentrations, detected at 180 °C was nearly 10 times higher than that at 175 °C. Besides, total amounts of spins detected at 180 °C decreased rapidly because of the reaction between radical adducts and newly formed radicals. Signal intensities of alkyl radical adducts increased rapidly from 0.405 to 4.785 from 175 °C to 180 °C. Besides, more palmitic acid degraded to oxidized compounds from 175 °C to 180 °C than that of other temperature ranges. The C-C linkages between carbons 2 to 6 were easier to be oxidized at 180 °C. The results all implied that oxidation rates of palmitic acid samples increased rapidly from 175 °C to 180 °C. [ABSTRACT FROM AUTHOR]

The reduction of 5,10,15-triphenylcorrole (H3TPCor) with decamethylchromocene yields (Cp*2Cr+)(H+)(H2TPCorṖ2−)·C6H4Cl2 (1). It is accompanied by the deprotonation of H3TPCor and the formation of planar H2TPCorṖ2− radical dianions. Complex 1 manifests a band at about 750 nm observed in the solution spectra of H2TArylCorṖ2− and demonstrates an EPR signal attributed to the reduced corrole macrocycle. The magnetic moment of 1 of 4.10μB at 300 K indicates the contribution of Cp*2Cr+ (S = 3/2) and H2TPCorṖ2− (S = 1/2). These paramagnetic species alternate in the π-stacks providing rather effective antiferromagnetic coupling of spins at the Weiss temperature of −31 K. To distinguish the H2TPCṖ2− dianions from the deprotonated H2TPCor− anions, we also studied the {cryptand[2,2,2](Na+)}(H2TPCor−)·0.5C6H4Cl2 (2) salt with deprotonated corrole anions. In this case, a planar macrocycle was formed as well. However, the properties of H2TPCor− in 2 differ from those of H2TPCorṖ2− in 1. [ABSTRACT FROM AUTHOR]

A series of electron spin resonance (ESR) experiments is done to quantitatively measure the concentrations of aqueous ¹O2 and ·OH produced by a surface micro-discharge air plasma device. ¹O2 is tested to be existed in the plasma treated solution by using the spin trap of TEMP. However, the unexpected DMPOX spectrum is observed in measuring ·OH by the spin trap of 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO). With more chemical scavenger experiments, it is found that removal of aqueous ¹O2 leads to the disappearance of DMPOX in ESR. Therefore, the generation of DMPOX is directly related to the oxidation of DMPO by plasma-produced aqueous ¹O2. This oxidation process and interactions between DMPO and chemical scavengers used in experiments can all be well explained by a proposed reaction mechanism. The revelation of interactions between aqueous ¹O2 and the spin trap DMPO shows that the observation of spectra of DMPOX in the ESR measurement can be regarded as a marker of high concentrations of plasma-produced ¹O2 in liquid. These results also prove the existence of interactions between spin traps and non-targeted plasma-produced reactive species in ESR experiments. Also, these results have offered a better understanding of the use of spin traps such as DMPO in the plasma-induced highly oxidative aqueous environment. [ABSTRACT FROM AUTHOR]

The annual production of grape worldwide amounts to almost 70million tons and around 80% is used for winemaking. The two major wastes from winemaking process, pomace and lees account for 20 and 7% of the grapes, respectively. They have been expected as a valuable resource to be recycled because they are rich in polyphenols. Polyphenols possess prooxidatve activity as well as antioxidative one just like a two sides of a coin. A typical example of the prooxidative activity is antibacterial activity of catechins. The activity is exerted through oxidation of phenolic hydroxylmoiety coulpled with reduction of dissolved oxygen leading to hydrogen peroxide (H2O2) generation. In addition, once the oxidation of phenolic hydroxyl moiety is augmented by photoirradiation, highly reactive hydroxyl radical (.OH) is generated. Accordingly, there have been several reports showing that photoirardiation of polyphenols exerts bactericidal activity via .OH generation. This review focuses mainly on antimicrobial intervention by photoirradiation of grape pomace extract in relation to.OH generation analyzed by an electron spin resonance-spin trapping method. [ABSTRACT FROM AUTHOR]

Lignin and the quest for the origin of stable organic radicals in it have seen numerous developments. Although there have been various speculations over the years on the formation of these stable radicals, researchers have not been able to arrive at a solid, unequivocal hypothesis that applies to all treatments and types of lignin. The extreme complexity of lignin and its highly aromatic, cross-linked, branched, and rigid structure has made such efforts rather cumbersome. Since the early 1950s, researchers in this field have dedicated their efforts to the establishment of methods for the detection and determination of spin content, theoretical simulations, and reactions on model compounds and spin-trapping studies. Although a significant amount of published research is available on lignin or its model compounds and the reactive intermediates involved during various chemical treatments (pulping, bleaching, extractions, chemical modifications, etc.), the literature provides a limited view on the origin, nature, and stability of such radicals. Consequently, this review is focused on examining the origin of such species in lignin, factors affecting their presence, reactions involved in their formation, and methods for their detection. [ABSTRACT FROM AUTHOR]

We investigate the transfer of photoexcited charge carriers from GaP and GaNP nanowires to an electrolyte by bias-dependent photocurrent and electron paramagnetic resonance experiments using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap. The results of the latter show that hydroxyl radicals are created over the entire applied bias range from −1000mV to +1300mV by hole transfer. In contrast, the photocurrent changes from cathodic to anodic at the open circuit potential of the three-electrode setup with the nanowire sample acting as the working electrode. The experiments show that the photoelectrochemical response of GaNP nanowires is significantly stronger compared to that of the GaP nanowires. [ABSTRACT FROM AUTHOR]

The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H2O2 contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate, and chlorate with hydrogen peroxide in acidic medium at 60 °C is investigated by using the electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate, and chlorate in their reactions with hydrogen peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO3 and H2O2 is supposed to be the source of IO2 • radicals. The KBrO3 and H2O2 reaction did not produce any EPR signal, whereas the KClO3-H2O2 system was found to be a source of HO• radical. Moreover, KClO3 dissolved in sulfuric acid without hydrogen peroxide produced HO• radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO2 • and HOO• radicals, and ClO2 • and HO• radicals in the particular kinetic models of iodate-hydrogen peroxide and chlorate-hydrogen peroxide systems, as well as possible exclusion of BrO2 • radical from the kinetic scheme of the bromate-hydrogen peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen-containing species. [ABSTRACT FROM AUTHOR]

Forced degradation studies are an important tool for a systematic assessment of decomposition pathways and identification of reactive sites in active pharmaceutical ingredients (APIs). Two methodologies have been combined in order to provide a deeper understanding of singlet oxygen-related degradation pathways of APIs under light irradiation. First, we report that a “dark” singlet oxygen test enables the investigation of drug reactivity toward singlet oxygen independently of photolytic irradiation processes. Second, the photosensitizing properties of the API producing the singlet oxygen was proven and quantified by spin trapping and electron paramagnetic resonance analysis. A combination of these techniques is an interesting addition to the forced degradation portfolio as it can be used for (1) revealing unexpected degradation pathways of APIs due to singlet oxygen, (2) clarifying photolytic drug-drug interactions in fixed-dose combinations, and (3) synthesizing larger quantities of hardly accessible oxidative drug degradants. [ABSTRACT FROM AUTHOR]

Biogenic alkenes, which are among the most abundant volatile organic compounds in the atmosphere, are readily oxidized by ozone. Characterizing the reactivity and kinetics of the first-generation products of these reactions, carbonyl oxides (often named Criegee intermediates), is essential in defining the oxidation pathways of organic compounds in the atmosphere but is highly challenging due to the short lifetime of these zwitterions. Here, we report the development of a novel online method to quantify atmospherically relevant Criegee intermediates (CIs) in the gas phase by stabilization with spin traps and analysis with proton-transfer reaction mass spectrometry. Ozonolysis of α-pinene has been chosen as a proof-of-principle model system. To determine unambiguously the structure of the spin trap adducts with α-pinene CIs, the reaction was tested in solution, and reaction products were characterized with high-resolution mass spectrometry, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopy. DFT calculations show that addition of the Criegee intermediate to the DMPO spin trap, leading to the formation of a six-membered ring adduct, occurs through a very favorable pathway and that the product is significantly more stable than the reactants, supporting the experimental characterization. A flow tube set up has been used to generate spin trap adducts with α-pinene CIs in the gas phase. We demonstrate that spin trap adducts with α-pinene CIs also form in the gas phase and that they are stable enough to be detected with online mass spectrometry. This new technique offers for the first time a method to characterize highly reactive and atmospherically relevant radical intermediates in situ. [ABSTRACT FROM AUTHOR]

Ultrasound (US) was shown to activate persulfate (PS) providing an alternative activation method to base or heat as an in situ chemical oxidation (ISCO) method. The kinetics and mechanism of ultrasonic activation of PS were examined in aqueous solution using an in situ electron paramagnetic resonance (EPR) spin trapping technique and radical trapping with probe compounds. Using the spin trap, 5,5-dimethyl-1- pyrroline-N-oxide (DMPO), hydroxyl radical (•OH) and sulfate radical anion (SO4•-) were measured from ultrasonic activation of persulfate (US-PS). The yield of •OH was up to 1 order of magnitude greater than that of SO4•-. The comparatively high •OH yield was attributed to the hydrolysis of SO4•- in the warm interfacial region of cavitation bubbles formed from US. Using steady-state approximations, the dissociation rate of PS in cavitating bubble systems was determined to be 3 orders of magnitude greater than control experiments without sonication at ambient temperature. From calculations of the interfacial volume surrounding cavitation bubbles and using the Arrhenius equation, an effective mean temperature of 340 K at the bubble-water interface was estimated. Comparative studies using the probe compounds tert-butyl alcohol and nitrobenzene verified the bubble-water interface as the location for PS activation by high temperature with •OH contributing a minor role in activating PS to SO4•-. The mechanisms unveiled in this study provide a basis for optimizing US-PS as an ISCO technology. [ABSTRACT FROM AUTHOR]

Isotropic hyperfine coupling constants (HFCCs) of spin adducts of 5,5-dimethyl-1-pyrroline- N -oxide (DMPO) are calculated by DFT method with solvation effect. Geometries of ring conformers and rotational conformers of trapped radicals are optimized and their HFCCs are calculated. Boltzmann weighted average of HFCCs of low energy conformations shows very good agreement with the experimental value in benzene. Two or four water molecules hydrogen bonded to the spin adduct have to be explicitly incorporated in the case of water. The results show time-independent averaging of relevant conformers is a very practical method for calculation of HFCCs of DMPO spin adducts. [ABSTRACT FROM AUTHOR]

It is well established that the formation of radical species centered on various atoms is involved in the mechanism leading to the development of several diseases or to the appearance of deleterious effects of toxic molecules. The detection of free radical is possible using Electron Paramagnetic Resonance (EPR) spectroscopy and the spin trapping technique. The classical EPR spin-trapping technique can be considered as a “hypothesis-driven” approach because it requires an a priori assumption regarding the nature of the free radical in order to select the most appropriate spin-trap. We here describe a “data-driven” approach using EPR and a cocktail of spin-traps. The rationale for using this cocktail was that it would cover a wide range of biologically relevant free radicals and have a large range of hydrophilicity and lipophilicity in order to trap free radicals produced in different cellular compartments. As a proof-of-concept, we validated the ability of the system to measure a large variety of free radicals (O-, N-, C-, or S- centered) in well characterized conditions, and we illustrated the ability of the technique to unambiguously detect free radical production in cells exposed to chemicals known to be radical-mediated toxic agents. [ABSTRACT FROM AUTHOR]

Poly(butylene terephthalate) (PBT), and its oligomer, were doped with the spin-trapping reagent, 2-methyl-2-nitrosopropane (MNP), by a solution-casting method in order to detect the short-lived radical intermediates during thermal degradation. In the case of PBT, two types of spin adduct were observed by electron spin resonance (ESR) spectroscopy upon stepwise heating from room temperature to 200 °C and during annealing at 130 °C; the ESR spectrum exhibited an isotropic three-line signal, with a hyperfine coupling constant (hfcc) a N ≈ 0.8 mT, as well as an anisotropic component. These adducts were present on the order of 10-5 mol/L. The isotropic component was assigned to arise uniquely from the benzoyl radical, •CO-ϕ. The anisotropic component was carefully investigated by ESR spectroscopy and high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS), using low-molecular-weight model compounds such as n-butyl benzoate (BB), di-n-butyl terephthalate (DBT), and deuterated DBT (d-DBT). The newly observed ESR components, six lines for DBT and nine lines for d-DBT, were assigned to the α-carbon radicals, -O-•CH- and -O-•CD-, respectively. The existence of these spin adducts was also confirmed directly by MS analysis (as protonated ions). We conclude that the thermal degradation of PBT begins by hydrogen abstraction from the α-methylene group of PBT at low temperature (110 °C), with subsequent main chain decomposition through β-scission of the ester linkages. [ABSTRACT FROM AUTHOR]

The ability of nitrobenzoxadiazoles to induce the SOX-operon from a genetically engineered biosensor based on E. coli MG 1655 (pSoxS-lux) was confirmed by the fact of producing nitric oxide. The NO-donating properties of three nitrobenzoxadiazole derivatives bearing π-excessive carbo- and heterocycles were found by the ESR method using spin trapping. The yield of nitrogen(II) oxide was 17, 0.3, and 1.6%. Sodium sulfide accelerates the thiol-dependent transformation and increases the yield of nitric oxide to 27, 16, and 12%, respectively. [ABSTRACT FROM AUTHOR]

Paper degradation by iron gall ink is a challenging issue for the conservation of ancient manuscripts. It is usually attributed to both FeII catalyzed oxidation and acid catalyzed hydrolysis of cellulose, yet the dominant degradation pathway remains an open question. In this work, electron spin resonance spectroscopy (ESR) was used to identify radicals involved in cellulose degradation. Papers impregnated with iron salts were put in contact with an aqueous solution of DMPO (spin-trap) and analyzed by ESR. No DMPO–OHṖ adducts were detected while the addition of formate, an intermediary target molecule, led on the contrary to the detection of a significant amount of DMPO–CO2Ṗ− adducts. This reveals the predominant occurrence of reactive oxygen species (ROS) other than hydroxyl radicals (most likely superoxide or hydroperoxyl radicals). The production of DMPO–CO2Ṗ− adducts was found to be oxygen dependent and to originate mainly from ferrous ions lixiviated from the impregnated papers. At high iron loads (above 1 mmol L−1), it was shown that quantification of these adducts should be done with great care because of a competing formation of hydroxylamine that jeopardizes the ESR signal. Complementary TPA hydroxylation measurements performed by HPLC on ink and iron sulfate impregnated papers revealed some production of hydroxyl radicals but at a concentration several orders of magnitude below that of the ROS detected with formation of DMPO–CO2Ṗ− adducts. This HOṖ production was moreover not correlated with cellulose chain scissions, indicating that autooxidation by these radicals is not the main mechanism of cellulose depolymerisation in presence of iron gall ink. [ABSTRACT FROM AUTHOR]

Detection of superoxide produced by living cells has been an on-going challenge in biology for over forty years. Various methods have been proposed to address this issue, among which spin trapping with cyclic nitrones coupled to EPR spectroscopy, the gold standard for detection of radicals. This technique is based on the nucleophilic addition of superoxide to a diamagnetic cyclic nitrone, referred to as the spin trap, and the formation of a spin adduct, i.e. a persistent radical with a characteristic EPR spectrum. The first application of spin trapping to living cells dates back 1979. Since then, considerable improvements of the method have been achieved both in the structures of the spin traps, the EPR methodology, and the design of the experiments including appropriate controls. Here, we will concentrate on technical aspects of the spin trapping/EPR technique, delineating recent breakthroughs, inherent limitations, and potential artifacts. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy (also known as electron spin resonance, ESR, or electron magnetic resonance, EMR, spectroscopy) is often described as the “gold standard” for the detection and characterisation of radicals in chemical, biological and medical systems. The article reviews aspects of EPR spectroscopy and discusses how this methodology and related techniques can be used to obtain useful information from biological systems. Consideration is given to the direct detection of radicals, the use of spin traps and the detection of nitric oxide, and the advantages and pitfalls of various approaches. When used with care, this technique can provide a huge amount of valuable data on the presence of radicals, their identity and information on their concentration, structure, mobility and interactions. It is however a technique that has limitations, and the novice user needs to understand the various pitfalls and shortcomings of the method to avoid making significant errors. [ABSTRACT FROM AUTHOR]

Fenton reaction was used to produce hydroxyl radicals under conditions similar to AOPs with 5,5-dimethyl-1-pyrroline- N -oxide (DMPO) as a spin trap agent in electron paramagnetic resonance (EPR) analysis. A theoretical kinetics model was developed to determine conditions under which the spin-adduct DMPO-OH is not further oxidized by Fe 3+ and excessive radicals, so that hydroxyl radicals concentration could be accurately inferred. Experiments were designed based upon the model and H 2 O 2 and Fe 2+ concentrations were varied from 1 to 100 mM and from 0.1 to 10 mM, respectively, with a constant H 2 O 2 : Fe 2+ ratio of 10:1. Results confirmed that DMPO concentration should be at least 20 times higher than the concentration of H 2 O 2 and 200 times higher than iron concentration to produce stable DMPO-OH EPR signal. When DMPO: H 2 O 2 ratio varied from 1 to 10, DMPO-OH could generate intermediates and be further oxidized leading to the apparition of an additional triplet. This signal was attributed to a paramagnetic dimer: its structure and a formation mechanism were proposed. Finally, the utilization of sodium sulfite and catalase to terminate Fenton reaction was discussed. Catalase appeared to be compatible with DMPO. However, sodium sulfite should be avoided since it reacted with DMPO-OH to form DMPO-SO 3 . [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) is one of the few methods that allows for the unambiguous detection of nitric oxide (NO). However, the dithiocarbamate-iron spin traps employed with this method inhibit the activity of nitric oxide synthase and catalyze NO production from nitrite. These disadvantages limit EPR's application to biological NO detection. We present a liposome-encapsulated spin-trap (LEST) method for the capture and in situ detection of NO by EPR. The method shows a linear response for [NO]≥4 µM and can detect [NO]≥40 nM in a 500 µL sample (≥20 pmol). The kinetics of NO production can be followed in real time over minutes to hours. LEST does not inhibit the activity of inducible nitric oxide synthase or nitrate reductase and shows minimal abiotic NO production in the presence of nitrite and NADH. Nitrate reductase-like activity is detected in cell lysates of the coccolithophore Emiliania huxleyi and is elevated in virus-infected culture. This method shows particular promise for NO detection in cell lysates and crude preparations of NO-producing tissues. [ABSTRACT FROM AUTHOR]

Aprotic lithium-oxygen (Li-O2) batteries have attracted considerable attention in recent years owing to their outstanding theoretical energy density. A major challenge is their poor reversibility caused by degradation reactions, which mainly occur during battery charge and are still poorly understood. Herein, we show that singlet oxygen (1Δg) is formed upon Li2O2 oxidation at potentials above 3.5 V. Singlet oxygen was detected through a reaction with a spin trap to form a stable radical that was observed by time- and voltage-resolved in operando EPR spectroscopy in a purpose-built spectroelectrochemical cell. According to our estimate, a lower limit of approximately 0.5 % of the evolved oxygen is singlet oxygen. The occurrence of highly reactive singlet oxygen might be the long-overlooked missing link in the understanding of the electrolyte degradation and carbon corrosion reactions that occur during the charging of Li-O2 cells. [ABSTRACT FROM AUTHOR]

Sea cucumber Stichopus japonicus ( S. japonicus ) shows a strong ability of autolysis, which leads to severe deterioration in sea cucumber quality during processing and storage. In this study, to further characterize the mechanism of sea cucumber autolysis, hydroxyl radical production induced by ultraviolet A (UVA) irradiation was investigated. Homogenate from the body wall of S. japonicas was prepared and subjected to UVA irradiation at room temperature. Electron Spin Resonance (ESR) spectra of the treated samples were subsequently recorded. The results showed that hydroxyl radicals (OH ) became more abundant while the time of UVA treatment and the homogenate concentration were increased. Addition of superoxide dismutase (SOD), catalase, EDTA, desferal, NaN 3 and D 2 O to the homogenate samples led to different degrees of inhibition on OH production. Metal cations and pH also showed different effects on OH production. These results indicated that OH was produced in the homogenate with a possible pathway as follows: O 2 − → H 2 O 2 → OH , suggesting that OH might be a critical factor in UVA-induced S. japonicus autolysis. [ABSTRACT FROM AUTHOR]

Astaxanthin is a coloring agent which is used as a feed additive in aquaculture nutrition. Recently, potential health benefits of astaxanthin have been discussed which may be partly related to its free radical scavenging and antioxidant properties. Our electron spin resonance (ESR) and spin trapping data suggest that synthetic astaxanthin is a potent free radical scavenger in terms of diphenylpicryl-hydrazyl (DPPH) and galvinoxyl free radicals. Furthermore, astaxanthin dose-dependently quenched singlet oxygen as determined by photon counting. In addition to free radical scavenging and singlet oxygen quenching properties, astaxanthin induced the antioxidant enzyme paroxoanase-1, enhanced glutathione concentrations and prevented lipid peroxidation in cultured hepatocytes. Present results suggest that, beyond its coloring properties, synthetic astaxanthin exhibits free radical scavenging, singlet oxygen quenching, and antioxidant activities which could probably positively affect animal and human health. [ABSTRACT FROM AUTHOR]

Incontrast to metal centered 17 valence electron radicals, suchas [Mn(CO)5]•, ferroceniumions [Fe(C5H5)2]+(1+), [Fe(C5Me5)2]+(2+), [Fe(C5H5)(C5H4Et)]+(3+), [Fe(C5H5)(C5H4NHC(O)Me)]+(4+), and [Fe(C5H5)(C5H4NHC(S)Me)]+(5+) do not add to nitrosobenzene PhNO to givemetal-coordinated stable nitroxyl radicals. In the presence of thestrong and oxidatively stable phosphazene base tert-butylimino-tris(dimethylamino)phosphorane, the quite acidic ferroceniumions 1+–5+are deprotonated to give a pool of transientand persistent radicals with different deprotonation sites [1–Hx]•–[5–Hx]•. One rather persistent iron-centeredradical [4–HN]•, deprotonated at the nitrogen atom,has been detected by rapid-freeze EPR spectroscopy at 77 K. This iron-centeredradical [4–HN]•is also inert toward PhNO. The transientcarbon-centered radicals [1–Hx]•–[5–Hx]•appear to rapidly abstract hydrogen atoms fromthe adjacent base or the solvent to regenerate the corresponding ferrocenes 1–5. These transient radicals are onlypresent in trace amounts (<1%). However, some of the transientcarbon-centered radicals in the radical pool can be trapped by 1–1.2equiv of PhNO, even at room temperature. The corresponding resultingstable nitroxyl radicals [6]•–[10]•werestudied by EPR spectroscopy at room temperature and at 77 K. The hyperfinecoupling pattern to protons close to the spin center allows one toassign the site of PhNO attack in radicals [6]•–[10]•, namely, at the C5H5ring in [6]•, [9Cp]•, and [10Cp]•, at a methyl group in [7]•, and at the methylene group in [81]•. These studiesgive a deeper insight into the stability and reactivity of radicalsderived from ferrocene derivatives which might also be relevant forthe biological activity of high-potent antitumor and antimalaria ferrocene-baseddrugs and prodrugs such as ferrocifen or ferroquine. [ABSTRACT FROM AUTHOR]

The 17e− monoradical [Mn(CO)5] is widely recognized as an unstable organometallic transient and is known to dimerize rapidly with the formation of a MnMn single bond. As a result of this instability, isolable analogues of [Mn(CO)5] have remained elusive. Herein, we show that two sterically encumbering isocyanide ligands can destabilize the MnMn bond leading to the formation of the isolable, manganese(0) monoradical [Mn(CO)3(CNArDipp2)2] (ArDipp2=2,6-(2,6-( iPr)2C6H3)2C6H3). The persistence of [Mn(CO)3(CNArDipp2)2] has allowed for new insights into nitrosoarene spin-trapping studies of [Mn(CO)5]. [ABSTRACT FROM AUTHOR]

Spin trapping with cyclic nitrones coupled to electron spin resonance (ESR) is recognized as a specific method of detection of oxygen free radicals in biological systems, especially in culture cells. In this case, the detection is usually performed on cell suspensions, which is however unsuitable when adhesion influences free radical production. Here, we performed ESR detection of superoxide with four spin traps (5-diethoxyphosphoryl-5-methyl-1-pyrrolineN-oxide, DEPMPO; 5-diisopropoxyphosphoryl-5-methyl-1-pyrrolineN-oxide, DIPPMPO; (4R*, 5R*)-5-(diisopropyloxyphosphoryl)-5-methyl-4-[({[2-(triphenylphosphonio)ethyl]carbamoyl}oxy)methyl]pyrrolineN-oxide bromide, Mito-DIPPMPO; and 6-monodeoxy-6-mono-4-[(5-diisopropoxyphosphoryl-5-methyl-1-pyrroline-N-oxide)-ethylenecarbamoyl-(2,3-di-O-methyl) hexakis (2,3,6-tri-O-methyl)]-β-cyclodextrin, CD-DIPPMPO) directly on RAW 264.7 macrophages cultured on microscope coverslip glasses after phorbol 12-myristate 13-acetate (PMA) stimulation. Distinct ESR spectra were obtained with each spin trap using this method. CD-DIPPMPO, a recently published phosphorylated cyclic nitrone bearing a permethylated β-cyclodextrin moiety, was confirmed as the most specific spin trap of the superoxide radical, with exclusive detection of the superoxide adduct. ESR detection performed on cells attached to coverslips represents significant advances over other methods in terms of simplicity, speed, and measurement under near-physiological conditions. It thus opens the way for numerous applications, such as medium-throughput screening of antioxidants and reactive oxygen species (ROS)-modulating agents. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an intracellular milieu is discussed. [ABSTRACT FROM AUTHOR]

Extracellular or free hemoglobin (Hb) accumulates during hemolysis, tissue damage, and inflammation. Heme-triggered oxidative reactions can lead to diverse structural modifications of lipids and proteins, which contribute to the propagation of tissue damage. One important target of Hb׳s peroxidase reactivity is its own globin structure. Amino acid oxidation and crosslinking events destabilize the protein and ultimately cause accumulation of proinflammatory and cytotoxic Hb degradation products. The Hb scavenger haptoglobin (Hp) attenuates oxidation-induced Hb degradation. In this study we show that in the presence of hydrogen peroxide (H 2 O 2 ), Hb and the Hb:Hp complex share comparable peroxidative reactivity and free radical generation. While oxidation of both free Hb and Hb:Hp complex generates a common tyrosine-based free radical, the spin-trapping reaction with 5,5-dimethyl-1-pyrroline N -oxide (DMPO) yields dissimilar paramagnetic products in Hb and Hb:Hp, suggesting that radicals are differently redistributed within the complex before reacting with the spin trap. With LC-MS 2 mass spectrometry we assigned multiple known and novel DMPO adduct sites. Quantification of these adducts suggested that the Hb:Hp complex formation causes extensive delocalization of accessible free radicals with drastic reduction of the major tryptophan and cysteine modifications in the β-globin chain of the Hb:Hp complex, including decreased βCys93 DMPO adduction. In contrast, the quantitative changes in DMPO adduct formation on Hb:Hp complex formation were less pronounced in the Hb α-globin chain. In contrast to earlier speculations, we found no evidence that free Hb radicals are delocalized to the Hp chain of the complex. The observation that Hb:Hp complex formation alters free radical distribution in Hb may help to better understand the structural basis for Hp as an antioxidant protein. [ABSTRACT FROM AUTHOR]

The 31 P NMR-spectroscopy-based spin trap technique involving 5-diisopropoxy-phosphoryl-5-methyl-1-pyrroline- N -oxide (DIPPMPO) was used to achieve quantitative analyses of the radical species that are generated in different bleaching solutions. These solutions comprised a mixture of an ammonium salt and hydrogen peroxide. This spin trap-based approach was also applied, with modifications, to the study of bleaching systems of human hair. The obtained results clearly revealed the subtle differences in both the nature and the amounts of the radical species generated in different bleaching solutions, and when allowed to react on hair samples. Generally, the main species involved in the oxidation processes were superoxide and amino radicals. Their amounts, however, showed a significant variation upon the kind of bleaching system and nature of the hair, i.e. , virgin or dyed hair. [ABSTRACT FROM AUTHOR]

Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical (•O2-). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical (•OH) or exclusively hydroxyl radical. [ABSTRACT FROM AUTHOR]

Lunar dust toxicity has to be evaluated in view of future manned missions to the Moon. Previous studies on lunar specimens and simulated dusts have revealed an oxidant activity assigned to HO· release. However, the mechanisms behind the reactivity of lunar dust are still quite unclear at the molecular level. In the present study, a complementary set of tests-including terephthalate (TA) hydroxylation, free radical release as measured by means of the spin-trapping/electron paramagnetic resonance (EPR) technique, and cell-free lipoperoxidation-is proposed to investigate the reactions induced by the fine fraction of a lunar dust analogue (JSC-1A-vf) in biologically relevant experimental environments. Our study proved that JSC-1A-vf is able to hydroxylate TA also in anaerobic conditions, which indicates that molecular oxygen is not involved in such a reaction. Spin-trapping/EPR measures showed that the HO· radical is not the reactive intermediate involved in the oxidative potential of JSC-1A-vf. A surface reactivity implying a redox cycle of phosphate-complexed iron via a Fe(IV) state is proposed. The role of this iron species was investigated by assessing the reactivity of JSC-1A-vf toward hydrogen peroxide (Fenton-like activity), formate ions (homolytic rupture of C-H bond), and linoleic acid (cell-free lipoperoxidation). JSC-1A-vf was active in all tests, confirming that redox centers of transition metal ions on the surface of the dust may be responsible for dust reactivity and that the TA assay may be a useful field probe to monitor the surface oxidative potential of lunar dust. Key Words: Lunar dust-JSC-1A-vf lunar dust simulant-Free radicals-Terephthalate assay-Fenton activity-Lipid peroxidation. Astrobiology 15, 371-380. [ABSTRACT FROM AUTHOR]

Using the EPR spin trapping technique, we prove that simultaneous reactions take place in illuminated suspensions of TiO2 in aqueous carbonate solutions (pH ≈ 7). The adsorbed HCO3− is reduced to formate as directly made evident by the detection of formate radicals (ṖCO2−). In addition, the amount of OHṖ radicals from the photo-oxidation of water shows a linear dependence on the concentration of bicarbonate, indicating that electron scavenging by HCO3− increases the lifetime of holes. In a weakly alkaline medium, photo-oxidation of HCO3−/CO32− to ṖCO3− interferes with the oxidation of water. A comparative analysis of different TiO2 samples shows that formation of ṖCO2− is influenced by factors related to the nature of the surface, once expected surface area effects are accounted for. Modification of the TiO2 surface with noble metal nanoparticles does not have unequivocal benefits: the overall activity improves with Pd and Rh but not with Ru, which favours HCO3− photo-oxidation even at pH = 7. In general, identification of radical intermediates of oxidation and reduction reactions can provide useful mechanistic information that may be used in the development of photocatalytic systems for the reduction of CO2 also stored in the form of carbonates. [ABSTRACT FROM AUTHOR]

The article discusses several articles that has been published in previous issues of the periodical's sisters journals. Topics include "Two-dimensional covalent organic frameworks for carbon dioxide capture through channel-wall fictionalization" by N. Huang and others; "Improved sensitivity for imaging spin trapped hydroxyl radical at 250 megahertz by J. R. Biller and others; and "The role of metal halides in enhancing the dehydration of xylose to furfural" by K.R. Enslow and others.

CYPMPO (5-(2,2-dimethyl-1,3-propoxyl cyclophosphoryl)-5-methyl-1-pyrroline N-oxide) is a phosphorus containing spin trap that has been useful in aqueous media. Using a kinetic ESR spin trapping technique, we evaluated free radical trapping rate constants of two newly synthesized CYPMPO-type spin traps, including 2,2-dibutyl-substituted CYPMPO (DBCYP) and 5-phenylsubstituted CYPMPO (PhCYP). We investigated the spin trapping of five free radical species, i. e., superoxide, hydroxyl radical, alkoxyl radical, alkyl peroxyl radical and methyl radical. Other than superoxide, spin trapping rate constants of DBCYP and PhCYP are comparable to CYPMPO, ranging from 43.9% to 101% of CYPMPO's corresponding rate constants. However, PhCYP's spin-trapping rate constant against superoxide was 44% higher than that of CYPMPO. The results indicate that DBCYP and PhCYP may be the spin traps as useful as CYPMPO either in aqueous or non-aqueous medium. [ABSTRACT FROM AUTHOR]

The β-scission rate coefficient of tert-butyl radicals fragmenting off the intermediate resulting from their addition to tert-butyl dithiobenzoate-a reversible addition-fragmentation chain transfer (RAFT) agent-is estimated via the recently introduced electron spin resonance (ESR)-trapping methodology as a function of temperature. The newly introduced ESR-trapping methodology is critically evaluated and found to be reliable. At 20 °C, a fragmentation rate coefficient of close to 0.042 s−1 is observed, whereas the activation parameters for the fragmentation reaction-determined for the first time-read EA = 82 ± 13.3 kJ mol−1 and A = (1.4 ± 0.25) × 1013 s−1. The ESR spin-trapping methodology thus efficiently probes the stability of the RAFT adduct radical under conditions relevant for the pre-equilibrium of the RAFT process. It particularly indicates that stable RAFT adduct radicals are indeed formed in early stages of the RAFT poly­merization, at least when dithiobenzoates are employed as controlling agents as stipulated by the so-called slow fragmentation theory. By design of the methodology, the obtained fragmentation rate coefficients represent an upper limit. The ESR spin-trapping methodology is thus seen as a suitable tool for evaluating the fragmentation rate coefficients of a wide range of RAFT adduct radicals. [ABSTRACT FROM AUTHOR]

An overview is provided of the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review aims to demonstrate the considerable extent of scientific progress that has been made in this broad topic during the past few decades. Studies of catalytically active surfaces, including zeolites, are surveyed, and the detection of radical species, formed as intermediates in their reactions, using matrix isolation and spin-trapping techniques. Radical cation formation in zeolites is discussed, and the employment of muon spin rotation and relaxation techniques to study the mobility of labelled radicals in various porous and catalytic media. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, degradation of environmental pollutants, hydrocarbon conversions, fuel cells and sensor devices employing graphene. The review concludes with recent developments in the study of enzymes and their reactions, using ESR-based methods. [ABSTRACT FROM AUTHOR]

The organic bismuth compounds PhBi(OCCH=CHCH) and PhBi(OCEt) decompose under scattered light in the presence of spin traps (2-methyl-2-nitrosopropane and C-phenyl- N- tert-butylnitrone) in organic solvents (acetonitrile, benzene, toluene) to form adducts of phenyl radicals with the traps. [ABSTRACT FROM AUTHOR]

Using a competitive trapping method employing two different traps, the trapping rates of anionic radicals (CO2 - · and SO3 - ·), hydroxyl, and ethyl were quantified for various PBN- and DMPO-type traps. We have examined the characteristic effects of substituent and external pressure on the spin trapping of anionic radicals and compared with those of neutral radicals such as ethyl and hydroxyl radicals. In DMPO-type traps, the effects of substituent on trapping rates of two anionic radicals were small compared with that of C2H5 ·. In PBN-type traps, the large effects of substituent on trapping rates of CO2 - · and C2H5 · were observed. Further, the activation volumes determined from the pressure dependence experiments for competitive reactions show a difference in pressure behavior between the two trapping reactions, and enable us to speculate on the reaction mechanism of substituted PBN and DMPO traps for anionic radicals. [ABSTRACT FROM AUTHOR]