Electron Paramagnetic Resonance Spin Trapping Research Articles

Tendency of lipid radical formation and volatiles in lose or vacuum-packed Brazil nuts stored at room temperature or under refrigeration

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.

Reactivity of redox sensitive paramagnetic nitroxyl contrast agents with reactive oxygen species.

The reactivity of nitroxyl free radicals, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (CmP), with reactive oxygen species (ROS) were compared as typical 6-membered and 5-membered ring nitroxyl compounds, respectively. The reactivity of the hydroxylamine forms of both these nitroxyl radicals (TEMPOL-H and CmP-H) was also assessed. Two free radical species of ROS, hydroxyl radical (•OH) and superoxide (O2•−), were subjected to a competing reaction. •OH was generated by UV irradiation from an aqueous H2O2 solution (H2O2-UV system), and O2•− was generated by a reaction between hypoxanthine and xanthine oxidase (HX-XO system). •OH and O2•− generated by the H2O2-UV and HX-XO systems, respectively, were measured by electron paramagnetic resonance (EPR) spin-trapping, and the amount of spin adducts generated by each system was adjusted to be equal. The time courses of the one-electron oxidation of TEMPOL, CmP, TEMPOL-H, and CmP-H in each ROS generation system were compared. A greater amount of TEMPOL was oxidized in the HX-XO system compared with the H2O2-UV system, whereas the reverse was observed for CmP. Although the hydroxylamine forms of the tested nitroxyl radicals were oxidized evenly in the H2O2-UV and HX-XO systems, the amount of oxidized CmP-H was approximately 3 times greater compared with TEMPOL-H.

Construction of novel CNT/LaVO4 nanostructures for efficient antibiotic photodegradation

It is an urgent matter to eliminate antibiotics in waste water, due to the rapid emergence of antibiotic resistance. The search for low cost, high activity and stable novel photocatalysts has attracted great interest. Herein, we demonstrated the rational construction of CNT/LaVO4 nanostructures for efficient antibiotic photodegradation by a one-step hydrothermal method. The phase structures, chemical compositions, morphologies, and optical properties of the prepared samples were investigated via various characterization techniques. The optimized CNT/LaVO4 nanostructures exhibited efficient photodegradation activity with remarkable stability. The 0.1% CNT/LaVO4 showed the highest tetracycline degradation rate, which is 2 times that of pure LaVO4. Photoluminescence (PL), transient photocurrent response and electrochemical impedance spectroscopy (EIS) together verified that this design successfully expedites the separation and transfer of photogenerated charge carriers. Subsequently, by the electron spin resonance (ESR) spin-trap technique, free radical trapping experiments and mass spectrometry analysis (MS), the active species, intermediate product, photodegradation pathway and reaction mechanism during the photocatalytic process were identified. The antibacterial results showed that the degrading products have lower toxicity. The CNT/LaVO4 composite is a potential photocatalyst for improving the water quality.

Dechlorination of triclosan by enhanced atomic hydrogen-mediated electrochemical reduction: Kinetics, mechanism, and toxicity assessment

Environmental-friendly and efficient technologies for the removal of halogenated organic compounds in water are highly desired. Triclosan (TCS) is a potential threat to the environment and human health, and is resistant to biodegradation. Here, a Pd/N-GR/Cu foam exhibits a much enhanced activity as the cathode for TCS degradation by electrochemical reduction. The dechlorination rate of Pd/N-GR/Cu foam is 5.50, 6.49, and 14.68 times higher than Pd/Cu, N-GR/Cu, and Cu foam, respectively. The leaching of Pd and Cu is inhibited due to the protection by cathodic currents and alkaline conditions. 2- and 1-chlorinated isomers are the main intermediates, and the final products are completely dechlorinated 2-phenoxyphenol with a small amount of further H radical addition product 6-phenoxycyclohex-3-enol. ESR spin trapping results indicate the coupling of Pd and N-GR promotes the production and utilization of atomic H*, and the contribution of atomic H* obeys the order of Pd/N-GR/Cu (68.5%) > Pd/Cu (56.6%) > N-GR/Cu (24.3%) > Cu (5.7%). The bacterial cytotoxicity and AhR activity of TCS solution after 60 min are decreased by 83.2% and 90.3%, respectively. The electrochemical reduction can be a promising option for supplementing the current technologies for TCS abatement in wastewater.

EDTA-Fe(III) Fenton-like oxidation for the degradation of malachite green

Industrial waste, urban sewage and aquaculture have led to severely increased grades of environment pollutants such as dyes, pesticides and fertilizer. The use of technologies for purifying contaminated waters can be difficult and toxic due to the anti-photolysis, anti-oxidation and anti-bio-oxidation characteristics of organic pollutants, and there is therefore a significant need for new approaches. Here, we report methods of Fenton oxidation and EDTA-Fe(III) Fenton-like oxidation which can be used to degrade malachite green (MG: a dye and antibiotic-like substance) from contaminated water. Compared with the degradation rate (59.34%) of the Fe(III)/H2O2 Fenton process, the EDTA-Fe(III) Fenton-like oxidation got a better degradation rate (92.7%) at neutral pH conditions. By conducting a series of parallel controlled experiments (changing parameters such as the reactant concentration, temperature, and pH), we report the relationships between the degradation effect and different parameters, and we fitted their pseudo first order kinetic curves. Furthermore, we repeated to adjustment of the concentrations of MG in solutions to test the cycle performance and catalytic activities of EDTA-Fe(III)/H2O2 system and it showed good repeatability in the first five rounds and all of them keep the degradation efficiencies greater than 80%. By conducting comparative spin-trapping electron paramagnetic resonance (EPR) experiments, we showed indirectly that the OH contributes to the degradation of MG. Additionally, the results of the EPR experiments showed that EDTA contributes to the generation of OH in the EDTA-Fe(III)/H2O2 Fenton-like system. By conducting total organic carbon (TOC) analysis experiments, we found that EDTA was also oxidized to some extent during the degradation of MG. In all, the findings of this work widen the range of the optimal pH values up to neutral condition for degradation of MG by use of EDTA-Fe(III) Fenton-like system. And this system could be used as one approach for the degradation of organic pollutants at neutral conditions and provide some initial information regarding EDTA-Fe(III) Fenton-like oxidations. It's significant for the expansion of the homogenous Fenton-like family and its application in the field of water treatment.

Peroxide-Free and Amine-Free Redox Free Radical Polymerization: Metal Acetylacetonates/Stable Carbonyl Compounds for Highly Efficient Synthesis of Composites

New peroxide-free, amine-free, and phosphine-free redox free radical polymerization (RFRP) initiating systems comprising remarkably stable (i) metal acetylacetonates (Mn(acac)3, Cu(acac)2) and (ii) carbonyl compounds bearing labile hydrogen in the α-position are presented for polymerization initiation under mild conditions (under air, at room temperature, nonpurified monomers). The systems proposed in this work are competitive or even outranked the well-known peroxide-based RFRP reference in several criteria: (i) toxicity, (ii) stability, (iii) surface curing, (iv) overall double-bond conversions, and (v) workability of the RFRP mixture (longer gel times are now possible). Radical initiating reactions are studied using many complementary experimental/theoretical techniques: optical pyrometry, thermal imaging, Raman confocal microscopy, electron spin resonance (ESR), ESR spin trapping (ESR-ST), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), density functional theory (DFT), simulations of bond dissociation energies (BDE), reaction enthalpies, and DFT simulations of seven unknown ESR-ST adducts. A full consistent picture of the chemical mechanisms involved in these new redox systems is provided.

Rectal Cancer: Redox State of Venous Blood and Tissues of Blood Vessels from Electron Paramagnetic Resonance and Its Correlation with the Five-Year Survival.

A role of pro- and antioxidants for reducing rectal cancer (RC) incidence in operative, preoperative, and postoperative treatments is still disputable and controversial. The redox state of venous blood and tissues of blood vessels of 60 patients with RC (T2-4N0-2M0G2) and 20 donors is studied by means of the conventional and spin-trapping electron paramagnetic resonance (EPR). The intensity of the signals from ceruloplasmin (CP), transferrin (TF), and labile iron pool (LIP) at temperature T = 77 K as well as superoxide generation rate and nitric oxide (NO) levels at T = 300 K is measured. The reduced CP and TF activity and decreased NO levels increased LIP levels and superoxide-generating rates are detected in blood species. Correlation analysis for the five-year survival rate as a function of the extracted values is done. The results show that the intensities of the corresponding EPR signals from the “native” and “trapped” paramagnetic centers can be potentially used for the understanding of the molecular mechanisms underlying the RC progression and treatment.

Vascular Nitric Oxide–Superoxide Balance and Thrombus Formation after Acute Exercise

An acute bout of strenuous exercise in humans results in transient impairment of nitric oxide (NO)-dependent function, but it remains unknown whether this phenomenon is associated with increased risk of thrombotic events after exercise. This study aimed to evaluate effects of a single bout of exhaustive running in mice on the balance of vascular NO/reactive oxygen species production, and on thrombogenicity. At different time points (0, 2, and 4 h) after exercise and in sedentary C57BL/6 mice, the production of NO and superoxide (O2) in aorta was measured by electron paramagnetic resonance spin trapping and by dihydroethidium/high-performance liquid chromatography-based method, respectively, whereas collagen-induced thrombus formation was analyzed in a microchip-based flow-chamber system (total thrombus-formation analysis system). We also measured pre- and postexercise plasma concentration of nitrite/nitrate and 6-keto-PGF1α. An acute bout of exhaustive running in mice resulted in decreased production of NO and increased production of O2 in aorta, with maximum changes 2 h after completion of exercise when compared with sedentary mice. However, platelet thrombus formation was not changed by exercise as evidenced by unaltered time to start of thrombus formation, capillary occlusion time, and total thrombogenicity (area under the flow pressure curve) as measured in a flow-chamber system. Strenuous exercise increased the plasma concentration of nitrite but did not affect nitrate and 6-keto-PGF1α concentrations. An acute bout of strenuous exercise in mice reduced NO and in parallel increased O2 production in aorta. This response was most pronounced 2 h after exercise. Surprisingly, the reduced NO and increased O2 production in mice after exercise did not result in increased platelet-dependent thrombogenicity. These results show that transient reduction in NO bioavailability does not modify thromboresistance in healthy mice after exercise.

Generation of hydroxyl radicals by Fe-polyphenol-activated CaO2 as a potential treatment for soil-borne diseases

An Fe-polyphenol catalyst was recently developed using anhydrous iron (III) chloride and coffee grounds as raw materials. The present study aims to test the application of this Fe-polyphenol catalyst with two hydrogen peroxide (H2O2) sources in soil as a new method for controlling the soil-borne disease caused by Ralstonia solanacearum and to test the hypothesis that hydroxyl radicals are involved in the catalytic process. Tomato cv. Momotaro was used as the test species. The results showed that powdered CaO2 (16% W/W) is a more effective H2O2 source for controlling bacterial wilt disease than liquid H2O2 (35% W/W) when applied with an Fe-polyphenol catalyst. An electron paramagnetic resonance spin trapping method using a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) assay and Fe-caffeic acid and Fe-chlorogenic acid complexes as models showed that these organometallic complexes react with the H2O2 released by CaO2, producing hydroxyl radicals in a manner that is consistent with the proposed catalytic process. The application of Fe-polyphenol with powdered CaO2 to soil could be a new environmentally friendly method for controlling soil-borne diseases.

Efficient photocatalytic removal of RhB using magnetic Fe3O4–SnO2 nanocomposites containing Sn2+ interstitial impurities

Fe3O4–SnO2 nanocomposites with SnO2 in the reduced form (without post-annealing) were prepared. X-ray diffraction, high resolution TEM microscopy, X-Ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy and magnetization measurements were used for sample characterizations. Additionally, nitrogen adsorption–desorption isotherms and surface area measurements (BET) were made for porosity and surface area determination. Depending on the amount of SnCl2 used in preparation, tetragonal tin oxide hydroxide Sn6O4(OH)4 or SnO secondary phases were also formed in various samples. XPS analysis shows the presence of surface Sn2+ states and as well as lack, or non-detectable, interstitial tin inside SnO2 nanocrystallites. The presence of Sn2+ surface states determines important changes of both magnetic and photocatalytic properties of samples. Thus Sn2+ surface states determine, on the one hand, an increased efficiency of photocatalytic processes and, on the other hand, a significant decrease of the saturation magnetization of Fe3O4 cores. Moreover, by using ESR spin trapping technique, the generation of reactive oxygen species (·OH, O2·−) resulted by light irradiation of samples was evidenced.

Facile Hydrothermal Synthesis of Z-Scheme Bi2Fe4O9/Bi2WO6 Heterojunction Photocatalyst with Enhanced Visible Light Photocatalytic Activity.

An efficient binary Bi2Fe4O9/Bi2WO6 Z-scheme heterojunction was fabricated through a facile hydrothermal route. The obtained Bi2Fe4O9/Bi2WO6 displays high catalytic activity for rhodamine B (RhB) photodegradation, and 100% of RhB was photodegraded by Bi2Fe4O9 (7%)/Bi2WO6 within 90 min, which is much better than that by pure Bi2Fe4O9 and Bi2WO6. The effective photoinduced carrier separation, the broadened photoabsorption range, high oxidation capacity of hole, and the high reduction power of electron are in charge of the elevated catalytic activity because of the formed Z-scheme system. In addition, the effects such as pollutant concentration, pH, inorganic anions, and water sources exerted on photocatalytic performance were also investigated, and the results suggest that Bi2Fe4O9/Bi2WO6 still possesses a high photocatalytic performance. The free-radical trapping experiments and electron spin resonance spin-trapping technology disclose that hole (h+), hydroxy radical (•OH), and superoxide radical (•O2-) are cardinal active radicals in the catalytic system. In terms of the above experimental analysis, a possible photodegradation mechanism of the as-fabricated photocatalyst is thoroughly elucidated. In addition, the possible RhB photodegradation pathway is also raised in the light of the analysis of liquid chromatography-mass/mass spectrometry. In addition, Bi2Fe4O9/Bi2WO6 composite does not display dramatic reduction of the catalytic performance after five recycles. Thus, this study reveals that the as-obtained Bi2Fe4O9/Bi2WO6 catalyst has a great prospect for the environmental purification.

P-390 - Oxidative stress mediated anti-leishmanial activity of endoperoxides represent a new therapeutic strategy in Leishmaniasis

Endoperoxides kill malaria parasites via cleavage of their endoperoxide bridge by heme or iron, leading to generation of cytotoxic oxygen-centered radicals. In view of the impaired anti-oxidant defense and high iron content of Leishmania parasites, the effectiveness of two endoperoxides, artemisinin and ascaridole was evaluated. Both demonstrated parasiticidal activity (in Leishmania donovani, LD and Leishmania tarentolae, LtP), along with lower cytotoxicity in macrophages. In LtP, carbon-centered radicals were identified in the presence of both endoperoxides by ESR spin-trapping and downstream formation of reactive oxygen species confirmed by flow cytometry. We explored whether leishmanial mitochondria are a target for this secondary oxygen radical formation. Both endoperoxides minimally impaired the electron transport chain, but impaired mitochondrial coupling upon prolonged exposure. Additionally, artemisinin depleted ATP levels, increased ATPase activity and enhanced Ca2+ release which collectively translated into a caspase-independent apoptotic-like cell death. Collectively, the endoperoxide-mediated radical formation was the initial step for their antileishmanial activity and represents a promising therapeutic strategy worthy of pharmacological consideration.

P-309 - Crosstalk between mitochondria and NOX2 in vitamin D3-induced differentiation in PLB-985 myeloid cells

To elucidate the role of reactive oxygen species (ROS) in immune enhancement, we focused on the redox signaling in vitamin D3-induced monocytic differentiation of leukemia cells. ROS generation in the cells was analyzed with ESR spin-trapping method. As a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used. Human myeloid PLB-985 cells were stimulated with 200 nM vitamin D3 and/or 100 nM phorbol 12-myristate 13-acetate. Immediately after vitamin D3-stimulation, ESR-spin trapping indicated the spectrum of DMPO-OH adduct. Flow cytometry showed the expression of CD11b/Mac1–alpha in the cells incubated with vitamin D3 for three days. Diphenyleneiodonium (NOX2 inhibitor:100 uM) and actinomycin A (mitochondrial electron transport chain complex III inhibitor:10 uM) have suppressed vitamin D3-induced the expression of CD11b and ROS generation. Our results indicate that vitamin D3-induced expression of CD11b have occurred through a close interaction between NOX2 and mitochondria.

P-227 - An unexpected double radical homolysis mechanism for the reactions between the pyridinium aldoxime nerve agent antidotes and polyhalogenated quinones under normal physiological conditions

We have recently shown that the pyridinium aldoximes, best-known as therapeutic antidotes for chemical warfare nerve-agents, could markedly detoxify the carcinogenic tetrachloro-1,4-benzoquinone (TCBQ) via an unusual double Beckmann fragmentation mechanism. However, it remains not clear why pralidoxime (2-PAM) cannot provide full protection against TCBQ-induced biological damage even when 2-PAM was in excess. Here we show, unexpectedly, that TCBQ can also activate pralidoxime to generate a reactive iminyl radical intermediate in two-consecutive steps, which was detected and unequivocally characterized by the complementary application of ESR spin-trapping, HPLC/MS and nitrogen-15 2-PAM isotope-labeling studies. The end product of iminyl radical was isolated and identified as its corresponding reactive and toxic aldehyde. We proposed that the reaction of 2-PAM and TCBQ might be via the following two competing mechanisms: double Beckmann fragmentation vs double radical homolysis. This study represents the first detection and identification of reactive iminyl radical intermediates produced under normal physiological conditions, which provides direct experimental evidence to explain the potential side-toxic effects induced by 2-PAM and other pyridinium aldoxime nerve-agent antidotes.

Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study.

X- and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.

Comparative study of oxidative status in blood of asthmatic patients

Bronchial asthma (BA) is a chronic inflammatory lungs disease, resulting in an airflow restriction, hyperactivity, and airway remodeling. The aim of present study is to investigate and compare the oxidative stress levels in blood of asthmatic patients differ in the disease control degree. In the current study were included 30 patients with bronchial asthma and 24 healthy volunteers. Patients were diagnosed with BA with allergic component longer than 1 year. For this purpose were explored the reactive oxygen species (ROS) and reactive nitrogen species (RNS), final products of lipids and proteins. Also, were studied the relationship between oxidative stress parameters and C-reactive protein (CRP) as a marker of inflammation degree. By using the electron paramagnetic resonance (EPR) spin trapping technique, ongoing the real-time oxidative processes were confirmed in blood samples isolated from asthmatic patients differing in the disease control degree. Moreover, positive correlation was found between the levels of studied oxidative stress (OS) biomarkers and CRP as a marker of inflammation degree. The oxidative processes in real time were demonstrated in BA patients. The correlation analysis results confirm the development and maintenance of inflammatory processes in respiratory tract is associated with the oxidative and nitrosative stress.

Improved photoelectric performance via fabricated heterojunction g-C3N4/TiO2/HNTs loaded photocatalysts for photodegradation of ciprofloxacin

An Intercalated heterostructural g-C3N4/TiO2/HNTs supported photocatalyst was successfully prepared via sol–gel and calcination methods. The introduction of HNTs and the g-C3N4-TiO2 heterojunction effectively enhanced the charge transfer and separation efficiency of photogenerated electron–hole pairs, which endued the g-C3N4/TiO2/HNTs hybrid material with an outstanding photoelectric performance and good stability. And an obviously enhanced photocatalytic activity was exhibited by photodegrading ciprofloxacin compared with pure TiO2. Furthermore, the main active species were detected through trapping experiment and ESR spin-trap technique with DMPO, which confirmed that the O2− and the h+ were the main active species in the photocatalytic system.

Phase transformation synthesis of a new Bi2SeO5 flower-like microsphere for efficiently photocatalytic degradation of organic pollutants

Orthorhombic Bi2SeO5 with a flower-like microsphere is synthesized by a phase transformation synthesis process for the first time. This new photocatalyst has a bandgap energy of 3.5 eV and its fermi level locates at −0.86 V vs NHE from the results of UV–vis DRS and Mott–Schottky plot. The effects of the calcination temperature and reaction time on the morphology, photoabsorption performance, photoelectric property and photocatalytic activity have been investigated in detail. The as-prepared Bi2SeO5 exhibits highly efficient photocatalytic activity in the decomposition of organic dyes and aromatic compound, such as rhodamine B, methyl orange and bisphenol A in aqueous solution under the simulative sunlight irradiation. The high photocatalytic activity of Bi2SeO5 may be attributed to the high crystallinity, the hierarchical structure and the high separation and mobility of the charge carrier. Notably, the effect of the surface area on the activity could be neglected. During the photocatalytic reaction process, Bi2SeO5 shows very high stabilities among the structure, surface chemical state and activity. Furthermore, the DMPO spin-trapping ESR spectra and the control experiments reveal that the O2− radicals and photoinduced holes play an important role in the photocatalytic degradation process. Finally, a probable photocatalytic mechanism of Bi2SeO5 has been proposed.

Gallic acid mediated oxidation of pentachlorophenol by the Fenton reaction under mild oxidative conditions

AbstractBACKGROUNDThe present study demonstrates the decomposition of pentachlorophenol (PCP) by the Fenton reaction in the presence of gallic acid (GA). Unlike other studies, catalytic Fe2+ concentrations were used with respect to PCP in an effort to evaluate an environmentally benign Fenton system, studying the effect of phenolic‐type compounds widely found in the environment. The effect of operating variables was evaluated.RESULTSAt initial reaction times or at low H2O2 and Fe concentrations, GA enhanced PCP removal. At high H2O2 and Fe concentrations GA enhanced PCP removal only at initial reaction times. GA was the determinant factor controlling activity acting both as a chelating agent and reducer of Fe3+. Electron paramagnetic resonance (EPR) spectroscopy was applied to shed light on mechanistic aspects, verifying the interaction of GA with Fe ions. GA accelerated significantly the Fe3+/Fe2+ redox cycling. This enhanced the formation of hydroxyl radicals (HO·) as confirmed by in situ EPR spin trap experiments. A reaction mechanism was proposed including the redox cycle of GA quinoide forms.CONCLUSIONThe operational variables of a GA modified Fenton system are provided and mechanistic steps are discussed including PCP degradation, GA/Fe interaction, Fe3+/Fe2+ redox cycling and HO· formation. GA concentration controls the catalytic degradation of PCP. © 2017 Society of Chemical Industry

Spin-Trapping Analysis and Characterization of Thermal Degradation of Thermoplastic Poly(ether–ester) Elastomer

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 con...