Electron Paramagnetic Resonance Spin Trapping Research Articles

Benzo[A]Pyrene and Benzo[E]Pyrene: Photoreactivity and Phototoxicity toward Human Keratinocytes.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds derived mostly from the incomplete combustion of fossil fuels and biomass. Human skin can absorb PAHs and the uptake increases with their molar mass and lipophilicity. Benzopyrene is high molecular weight PAH frequently appearing in ambient pollution. It exists in two isomeric forms: benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP), which exhibit different biological activity. Although certain properties of benzopyrenes suggested photoreactivity of the compounds, no direct measurements were previously conducted to characterize their photochemical activity. In this study, quantum yield and action spectra of singlet oxygen photogeneration by BaP and BeP were measured by time-resolved near-infrared phosphorescence, and the ability of both compounds to photogenerate superoxide anion was assessed by electron paramagnetic resonance (EPR) spin-trapping. The measurements revealed high efficiency of benzopyrenes to photogenerate singlet oxygen and their ability to photogenerate superoxide anion. Using HaCaT cells as single-layer skin model, we demonstrated concentration-dependent and light-dependent cytotoxicity of BaP and BeP. The compounds induced damage to the cell mitochondria and elevated the levels of intracellular reactive oxygen species.

(Invited) Operando EPR Study on Radicals in Anion-Exchange Membrane Fuel Cells

In the rapidly developing modern society, there is an urgent need for the wide-ranging availability of advanced and eco-friendly energy sources. One of the possible alternatives is the application of anion exchange membrane fuel cells (AEMFCs) with a catalyst reducing dioxygen efficiently. These promising devices can revolutionize the energy sector since they practically produce no pollution. However, to make them more widely used, several obstacles must be overcome. As a result, vast-ranging investigations focus on improving the properties of conductive polymer membranes [1] and catalysts for the oxygen reduction reaction (ORR) [2]. The durability of the membrane electrode assembly (MEA) is one of the critical requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). Despite significant impacts of nucleophilic degradation on ion-exchange capability and the anionic conductivity of investigated membranes, it is believed to affect only cationic sites of membrane polymers and thus cannot explain the reported loss in the mechanical strength of degraded AEMs. Such a phenomenon might be related to polymer backbone degradation caused by free radicals. This was widely described in the literature in the case of fuel cells using proton-conducting membranes [3] but barely mentioned for AEMFCs [4]. Since the oxidative degradation of hydrocarbon polymers is very well known, we aimed to comprehensively investigate the formation of the short-lived species generated during the operation of AEMFCs as well as stable radicals present in the polymer membranes.We investigated the LDPE-base membranes with Pt black, Pd black, PdAg, and Ag as the ORR catalysts, whereas for HOR the Pt black, Pd black, and NiFe catalysts were used. The in-situ measurements are performed with a micro-AEMFC inserted into a resonator of an electron paramagnetic resonance (EPR) spectrometer, which enables separate monitoring of radicals formed on the anode and cathode sides. The creation of radicals was monitored by the EPR spin trapping technique. In Figure 1 the EPR spectra of DMPO spin adducts trapped during operation of micro-fuel cell placed in EPR spectrometer cavity are presented. In this experiment, the LDPE-base membrane with platinum catalysts on both sides was used. The main detected adducts during the operation of the micro-AEMFC were DMPO-OOH and DMPO-OH on the cathode side and DMPO-H on the anode side. Additionally, we clearly show the formation and presence of stable radicals in AEMs during and after long-term AEMFC operation [5]. Preliminary results suggest that the creation of the short-living radicals during AEMFCs operation is independent of the used membrane. However, the applied catalysts determine the number of detected radicals. The EPR investigations indicate that, in addition to the known chemical degradation mechanisms of the cationic ammonium groups of the membrane, oxidative degradation, including radical reactions, has to be taken into account when the stability of an anion conductive polymer for AEMFCs is investigated. The formation of stable radicals in AEMs was proven for the first time in this study. All short-living radicals formed during the AEMFC operation were fully identified. The presence of radicals in the AEM after AEMFC testing indicates that reactive oxygen species may play a very important role in the degradation mechanism of the anion conducting polymers. Results from this study shed light on the understanding of radical formation and presence in the membranes during AEMFC tests, which in turn may help to solve the challenge of anion exchange membrane stability. Acknowledgments. This work was supported by the Polish National Science Centre (NCN) project OPUS-14, No. 2017/27/B/ST5/01004.

Highly active Cs2SnCl6/C3N4 heterojunction photocatalysts operating via interfacial charge transfer mechanism

In this study, a novel lead-free perovskite heterojunction Cs2SnCl6/C3N4 composite was constructed and applied for photocatalytic NO purification. After design optimization, the Cs2SnCl6/C3N4 heterojunction exhibit excellent and stable photocatalytic NO purification ability under visible-light irradiation, which is significantly better than pristine Cs2SnCl6 and C3N4. Combined in-situ DRIFTS and electron spin resonance spin-trapping, the mechanism of Cs2SnCl6/C3N4 photocatalytic NO removal was revealed. Under visible-light irradiation, the photo-generated electrons on the conduction band of C3N4 would spontaneously migrate to the CB of Cs2SnCl6, leaving holes (h+) on the valence band of C3N4, contributing to efficiently segregated charge carriers and improved photocatalytic NO purification. Density functional theory calculations also revealed the directional electron transfer at the C3N4 and Cs2SnCl6 interface, in which the charge was migrated from C3N4 to Cs2SnCl6 induced by the internal electric field. This research sheds fresh light on the fabrication of Cs2SnCl6/C3N4 heterojunctions as well as its effective interfacial charge separation.

Multifunctional Ag/AgCl/ZnTiO3 structures as highly efficient photocatalysts for the removal of nitrophenols, CO2 photoreduction, biomedical waste treatment, and bacteria inactivation

Over the past few decades, biological hazards and organic pollution have become major environmental concerns. Photocatalysis has been found to be effective in minimizing the negative impacts of these issues in air and water. Lozenge shape Ag/AgCl/ZnTiO3 photocatalysts were fabricated by a facile two-step synthesis method, including hydrothermal and coprecipitation. The physicochemical characteristics and morphological properties of the structures were comprehensively described taking advantage of a multi-technique approach. The prepared photocatalysts offered excellent nitrophenol mineralization (>90%) after 90 min of visible light irradiation. Based on the spin-trapping ESR technique, •O2̅– was recognized as the eminent reactive species during the photocatalytic process. Interestingly, the plasmonic Ag/AgCl/ZnTiO3 photocatalyst presented promising CO2 to CO/CH4 conversion with a production rate of 95.0/18.5 μmol.g−1.h−1 under visible light irradiation, which is about 1.6 times higher than that of ZnTiO3, implying the synergetic effects due to Ag/AgCl in the ternary construction. In addition to the investigation of antibacterial activity, the prepared photocatalysts were successfully applied to treat the hazardous biological waste bearing U87-MG cancer cells under visible light for the first time. Several as-related analytical techniques were served to demonstrate the activity and interaction pathways. This work may hone a new insight into designing highly efficacious ternary photocatalytic materials.

Characterization of radicals in polysorbate 80 using electron paramagnetic resonance (EPR) spectroscopy and spin trapping

Polysorbates are an important class of nonionic surfactants that are widely used to stabilize biopharmaceuticals. The degradation of polysorbate 20 and 80 and the related particle formation in biologics are heavily discussed in the pharmaceutical community. Although a lot of experimental effort was spent in the detailed study of potential degradation pathways, the underlying mechanisms are only sparsely understood. Besides enzymatic hydrolysis, another proposed mechanism is associated with radical-induced (auto)oxidation of polysorbates. To characterize the types and the origin of the involved radicals and their propagation in bulk material as well as in diluted polysorbate 80 solutions, we applied electron paramagnetic resonance (EPR) spectroscopy using a spin trapping approach. The prerequisite for a meaningful experiment using spin traps is an understanding of the trapping rate, which is an interplay of (i) the presence of the spin trap at the scene of action, (ii) the specific reactivity of the selected spin trap with a certain radical as well as (iii) the stability of the formed spin adducts (a slow decay rate). We discuss whether and to which extent these criteria are fulfilled regarding the identification of different radical classes that might be involved in polysorbate oxidative degradation processes. The ratio of different radicals for different scenarios was determined for various polysorbate 80 quality grades in bulk material and in aqueous solution, showing differences in the ratio of present radicals. Possible correlations between the radical content and product parameters such as the quality grade, the manufacturing date, the manufacturer, the initial peroxide content according to the certificate of analysis of polysorbate 80 are discussed.

Photocatalytic degradation of GenX in water using a new adsorptive photocatalyst

GenX, the ammonium salt of hexafluoropropylene oxide dimer acid, has been used as a replacement for perfluorooctanoic acid. Due to its widespread uses, GenX has been detected in waters around the world amid growing concerns about its persistence and adverse health effects. As relevant regulations are rapidly evolving, new technologies are needed to cost-effectively remove and degrade GenX. In this study, we developed an adsorptive photocatalyst by depositing a small amount (3 wt.%) of bismuth (Bi) onto activated-carbon supported titanate nanotubes, Bi/TNTs@AC, and tested the material for adsorption and subsequent solid-phase photodegradation of GenX. Bi/TNTs@AC at 1 g/L was able to adsorb GenX (100 µg/L, pH 7.0) within 1 h, and then degrade 70.0% and mineralize 42.7% of pre-sorbed GenX under UV (254 nm) in 4 h. The efficient degradation also regenerated the material, allowing for repeated uses without chemical regeneration. Material characterizations revealed that the active components of Bi/TNTs@AC included activated carbon, anatase, and Bi nanoparticles with a metallic Bi core and an amorphous Bi2O3 shell. Electron paramagnetic resonance spin-trapping, UV-vis diffuse reflectance spectrometry, and photoluminescence analyses indicated the superior photoactivity of Bi/TNTs@AC was attributed to enhanced light harvesting and generation of charge carriers due to the UV-induced surface plasmon resonance effect, which was enabled by the metallic Bi nanoparticles. •OH radicals and photogenerated holes (h+) were responsible for degradation of GenX. Based on the analysis of degradation byproducts and density functional theory calculations, photocatalytic degradation of GenX started with cleavage of the carboxyl group and/or ether group by •OH, h+, and/or eaq−, and the resulting intermediates were transformed into shorter-chain fluorochemicals following the stepwise defluorination mechanism. Bi/TNTs@AC holds the potential for more cost-effective degradation of GenX and other per- and polyfluorinated alkyl substances.

Neutrophil Myeloperoxidase-Mediated N-Demethylation of Quetiapine Leads to N-Desalkylquetiapine, a Pharmacologically Active Cytochrome P450 Metabolite

The atypical antipsychotic drugs, quetiapine and clozapine, are associated with idiosyncratic drug reactions (such as agranulocytosis or neutropenia) that are thought to involve reactive metabolites. Neutrophil myeloperoxidase (MPO) metabolism of quetiapine is not well-studied, but is metabolized by cytochrome P450. Based on structural similarity to clozapine, we hypothesized that quetiapine can be metabolized by MPO and that there is overlap between cytochrome P450 and MPO metabolism of quetiapine. The interaction of quetiapine and clozapine with MPO and MPO chlorination activity was studied using UV-vis spectrophotometry. The metabolites were characterized using liquid chromatography-mass spectrometry (LC-MS), and electron paramagnetic resonance (EPR) spectroscopy was used for detecting drug-catalyzed glutathione oxidation. In the presence of quetiapine, MPO compound II accumulated for about 7.5 min, whereas in the presence of clozapine, MPO compound II was not observed as it was rapidly reduced back to the resting state. Increasing quetiapine concentrations resulted in a decrease in MPO chlorination activity, while the opposite result was found in the case of clozapine. UV-vis spectral studies showed no change when quetiapine was oxidized in the absence and presence of chloride anion (Cl-, to catalyze chlorination reactions). Significant changes, however, were observed in the same assay with clozapine, where Cl- appeared to hinder the rate of clozapine metabolism. The MPO-catalyzed hydroxylated and dealkylated metabolites of quetiapine and hydroxylated metabolites of clozapine were observed from the LC-MS analyses, particularly when Cl- was included in the reaction. In addition, hydroxylated, dealkylated, and a proposed sulfoxide metabolite of quetiapine were also observed in the reaction catalyzed by human microsomes/NADPH. Lastly, compared to quetiapine, clozapine metabolism by MPO/H2O2 and glutathione produced more glutathionyl radicals using EPR spin trapping. In conclusion, MPO/H2O2/Cl- was shown to metabolize quetiapine to S-oxidation and P450-like dealkylation products, and quetiapine metabolites were generally less reactive than clozapine.

Improved performance of photosynthetic H2O2 and photodegradation by K-, P-, O-, and S-co-doped g-C3N4 with enhanced charge transfer ability under visible light

Elemental doping can modulate the electronic and molecular structure of g-C3N4 to improve its photocatalytic properties. In this study, potassium (K), phosphorus (P), oxygen (O), and sulfur (S) were doped into the g-C3N4 photocatalyst (K, P, O, S/g-C3N4), and the four-element doped photocatalyst was successfully prepared. UV–vis diffuse reflection spectroscopy, photoluminescence, and transient photocurrent revealed that the co-doping of g-C3N4 with K, P, O and S broadens the visible response and accelerates the transfer of photogenerated charges. Under visible light irradiation, the H2O2 concentration produced with K, P, O, S/g-C3N4 was 12.85 times higher than that with g-C3N4. Moreover, tetracycline (TC) can be effectively degraded by the photocatalyst in surface water. The degradation pathway of TC and the molecular structures of 12 intermediates were analyzed by liquid chromatography-mass spectrometry. The superoxide radical (·O2−) trapping-electron spin resonance (ESR) technique confirmed that ·O2− is the main active species in the system. Therefore, the four-element doping strategy adopted in this research proved the feasibility of increasing the amount of H2O2 produced and degrading the antibiotics in natural water under visible light.

In Situ EPR Spin Trapping and Competition Kinetics Demonstrate Temperature-Dependent Mechanisms of Synergistic Radical Production by Ultrasonically Activated Persulfate.

Ultrasound coupled with activated persulfate can synergistically degrade aqueous organic contaminants. Here, in situ electron paramagnetic resonance spin trapping was used to compare radicals produced by ultrasonically activated persulfate (US-PS) and its individual technologies, ultrasound alone (US) and heat-activated persulfate (PS), with respect to temperature. Radicals were trapped using 5,5-dimethyl-1-pyrroline-N-oxide, DMPO, to form detectable nitroxide adducts. Using initial rates of radical adduct formation, and compared to US and PS, US-PS at 40 and 50 °C resulted in the largest synergistic production of radicals. Radicals generated from US were reasonably consistent from 40 to 70 °C, indicating that temperature had little effect on cavitational bubble collapse over this range. However, synergy indexes calculated from initial rates showed that ultrasonic activation of persulfate at the bubble interface changes with temperature. From these results, we speculate that higher temperatures enhance persulfate uptake into cavitation bubbles via nanodroplet injection. DMPO-OH was the predominant adduct detected for all conditions. However, competition modeling and spin trapping in the presence of nitrobenzene and atrazine probes showed that SO4•- predominated. Therefore, the DMPO-OH signal is derived from SO4•- trapping with subsequent DMPO-SO4- hydrolysis to DMPO-OH. Spin trapping is effective in quantifying total radical adduct formation but limited in measuring primary radical speciation in this case.

True oxygen reduction capacity during photosynthetic electron transfer in thylakoids and intact leaves.

Reactive oxygen species (ROS) are generated in electron transport processes of living organisms in oxygenic environments. Chloroplasts are plant bioenergetics hubs where imbalances between photosynthetic inputs and outputs drive ROS generation upon changing environmental conditions. Plants have harnessed various site-specific thylakoid membrane ROS products into environmental sensory signals. Our current understanding of ROS production in thylakoids suggests that oxygen (O2) reduction takes place at numerous components of the photosynthetic electron transfer chain (PETC). To refine models of site-specific O2 reduction capacity of various PETC components in isolated thylakoids of Arabidopsis thaliana, we quantified the stoichiometry of oxygen production and consumption reactions associated with hydrogen peroxide (H2O2) accumulation using membrane inlet mass spectrometry and specific inhibitors. Combined with P700 spectroscopy and electron paramagnetic resonance spin trapping, we demonstrate that electron flow to photosystem I (PSI) is essential for H2O2 accumulation during the photosynthetic linear electron transport process. Further leaf disc measurements provided clues that H2O2 from PETC has a potential of increasing mitochondrial respiration and CO2 release. Based on gas exchange analyses in control, site-specific inhibitor-, methyl viologen-, and catalase-treated thylakoids, we provide compelling evidence of no contribution of plastoquinone pool or cytochrome b6f to chloroplastic H2O2 accumulation. The putative production of H2O2 in any PETC location other than PSI is rapidly quenched and therefore cannot function in H2O2 translocation to another cellular location or in signaling.

On the effect of zeolite acid property and reaction pathway in Pd–catalyzed hydrogenation of furfural to cyclopentanone

Aqueous phase hydrogenative rearrangement of furfural (FAL) to cyclopentanone (CPO) via furfuryl alcohol (FOL) has been studied over Pd catalysts supported on H–ZSM–5 zeolites. Pd states, zeolite properties and reaction condition parameters were optimized, affording 98% selectivity and 120 h−1 specific reaction rate over 2% Pd/H–ZSM–5(25) catalyst at 160 °C and 3 MPa H2. For hydrogenation of FAL–to–FOL, the activity was related to the Si/Al ratio and acid property of zeolite supports. For hydrogenative rearrangement of FOL–to–CPO, pure H–ZSM–5 zeolite could catalyze single–step conversion with relatively low reaction rate, whereas the presence of Pd sites could achieve multi–step transformation with remarkably increased rate, highlighting Pd–zeolite acid sites synergy. Proton and furanylmethoxy–relevant intermediates were captured with spin trapping electron paramagnetic resonance experiments, and 4–hydroxy–2–cyclopentenone and 2–cyclopentenone were also identified as key intermediates in tandem reaction pathway to produce CPO.

Accelerated photocatalytic degradation of tetracycline hydrochloride over CuAl2O4/g-C3N4 p-n heterojunctions under visible light irradiation

The as-prepared CuAl 2 O 4 /g-C 3 N 4 hybrid systems by decorating p -type CuAl 2 O 4 nanoplates on the surface of n -type g-C 3 N 4 nanosheets exhibit enhanced photocatalytic activity for the degradation of tetracycline hydrochloride because of speedy charge separation driving by p-n heterojunctions. • CuAl 2 O 4 nanoplates assembled on g-C 3 N 4 nanosheets yield many p - n heterojunctions. • CuAl 2 O 4 /g-C 3 N 4 achieved 90% tetracycline hydrochloride photodegradation in 1 h. • Improved photocatalytic activity attributed to rapid charge separation and transfer. In current study, the CuAl 2 O 4 /g-C 3 N 4 p-n heterojunctions were synthesized by a self-assembly route in isopropanol, in which a tight loading structure achieved by immobilizing the p -type CuAl 2 O 4 nanoplates on the n -type g-C 3 N 4 nanosheets was established and verified by morphological and microstructural observations. The catalytic activity of the resultant p-n heterojunctions was examined for the photodegradation of tetracycline hydrochloride (TCH) under illumination of visible light. The results indicate that the p-n heterojunctions containing 10 wt% CuAl 2 O 4 (10 wt% CuAl 2 O 4 /g-C 3 N 4 ) showed the maximum activity and high structural stability although after multiple cycles. Photocatalytic experiments with the addition of trapping agents and spin-trapping electron paramagnetic resonance (EPR) analysis clearly revealed that the photocatalytic TCH degradation in these p-n heterojunctions mainly proceeds via superoxide radicals ( O 2 − ) and photogenerated holes (h + ). The significant enhancement of photocatalytic activity is attributed to the construction of abundant p-n heterojunctions, which effectively accelerate the separation of charge pairs, and thereby improve the catalytic activity towards TCH photodegradation.

Structural, optical and photocatalytic properties of magnetic recoverable Mn0.6Zn0.4Fe2O4@Zn0.9Mn0.1O heterojunction prepared from waste Mn–Zn batteries

Green, simple and high value-adding technology is crucial for realizing waste batteries recycling. In this work, the magnetically recyclable Mn0.6Zn0.4Fe2O4@Zn0.9Mn0.1O (MZFO@ZMO) heterojunctions are prepared from waste Mn–Zn batteries via a green bioleaching and sample co-precipitation method. The as-prepared catalysts with different Zn0.9Mn0.1O weight percentage (25%, 50% and 75%) have been comprehensively characterized in structure, optics, photoelectrochemistry and photocatalytic activity. Characterization results indicate that MZFO@ZMO heterojunctions with the core-shell structure, demonstrates excellent absorption intensity in the visible light region, outperforming that of individual ZnO and Zn0.9Mn0.1O. Especially, the staggered bandgap alignment of Mn0.6Zn0.4Fe2O4 and Zn0.9Mn0.1O greatly enhances electron transfer and charge separation in the binary heterojunction system. The optimized MZFO@50%-ZMO shows the highest photodegradation performance toward methylene blue (MB) under the visible light irradiation, with a 99.7% of photodegradation efficiency of 20 mg L−1 of MB within 90 min, and its reactive kinetic constants is about 7.2, 10.8 and 21.7 times higher than that of Zn0.9Mn0.1O, P25 TiO2 and Mn0.6Zn0.4Fe2O4, respectively. The MB photocatalytic mechanism is investigated in the scavenger and 5,5-dimethylpyrroline-N-oxide (DMPO) spin-trapping electron spin resonance (ESR) experiments, and h+ and *O2− are identified as the major active species for MB degradation. In addition, MZFO@50%-ZMO also exhibits a good reusability and high magnetic separation properties after six successive cycles. This new material indicates the advantages of low costs, simple reuse and great potential in application.

Caffeine degradation using peroxydisulfate and peroxymonosulfate in the presence of Mn2O3. Efficiency, reactive species formation and application in sewage treatment plant water

The crucial role of manganese(III) species in the oxidative and catalytic reactivity of manganese oxides have been widely reported. However, the direct activation of radical precursors by Mn(III) oxides is still a matter of discussion. In this work, the ability of Mn(III)-bearing oxide (Mn2O3) for activation of peroxydisulfate (PS) and peroxymonosulfate (PMS) was evaluated and compared using caffeine (CAF) as a model pollutant. Complete CAF removal was achieved with 5 mM of PS or PMS after 8 h of reaction time, whereas 48% of mineralization was obtained after 70 h of reaction when PMS was used as oxidant. Electron paramagnetic resonance spin trapping (EPR) and radical scavenging experiments showed that the sulfate radical (SO4•–) was the dominant radical in the Mn2O3/PMS system. In comparison, a non-radical mechanism such as Mn2O3 surface-activated PS promoted the removal of CAF in the system of Mn2O3/PS. Liquid chromatography coupled to mass spectrometry analyses enabled the detection of main degradation products and the proposition of the CAF degradation pathways. Investigations in the real sewage treatment plant water showed that the decrease of CAF removal observed in wastewater as compared to pure water can be alleviated by increasing the Mn2O3 dosage. These findings highlight the great ability of Mn-species in PS or PMS activation in different water matrices, which have important implications for the development of novel wastewater treatment technologies.

Chirally modified cobalt-vanadate grafted on battery waste derived layered reduced graphene oxide for enantioselective photooxidation of 2-naphthol: Asymmetric induction through non-covalent interaction

The cobalt oxide-vanadium oxide (Co3O4-V2O5) combined with reduced graphene oxide (rGO) having band gap of ∼ 3.3 eV appeared as a suitable photocatalyst for selective oxidation of 2-naphthol to BINOL. C2-symmetric BINOL was achieved with good yield using hydrogen peroxide as the oxidant under UV-light irradiation. The same catalyst was chirally modified with cinchonidine and a newly synthesized chiral Schiff base ligand having a sigma-hole center. The strong interaction of the chiral modifiers with the cobalt-vanadium oxide was truly evident from various spectroscopic studies and DFT calculations. The chirally modified mixed metal oxide transformed the oxidative CC coupling reaction with high enantioselectivity. High enantiomeric excess upto 92 % of R-BINOL was obtained in acetonitrile solvent and hydrogen peroxide as the oxidant. A significant achievement was the formation of S-BINOL in the case of the cinchonidine modified catalyst and R-BINOL with the Schiff base ligand anchored chiral catalyst. The UV-light induced catalytic reaction was found to involve hydroxyl radical as the active reactive species. The spin trapping ESR and fluorescence experiment provided relevant evidence for the formation of such species through photodecomposition of hydrogen peroxide on the catalyst surface. The chiral induction to the resultant product was found to induce through supramolecular interaction like OH…π, H…Br interaction. The presence of sigma hole center was believed to play significant role in naphtholate ion recognition during the catalytic cycle.

Liquid-Phase Cyclohexene Oxidation with O2 over Spray-Flame-Synthesized La1-x Srx CoO3 Perovskite Nanoparticles.

La1−x Sr x CoO3 (x=0, 0.1, 0.2, 0.3, 0.4) nanoparticles were prepared by spray‐flame synthesis and applied in the liquid‐phase oxidation of cyclohexene with molecular O2 as oxidant under mild conditions. The catalysts were systematically characterized by state‐of‐the‐art techniques. With increasing Sr content, the concentration of surface oxygen vacancy defects increases, which is beneficial for cyclohexene oxidation, but the surface concentration of less active Co2+ was also increased. However, Co2+ cations have a superior activity towards peroxide decomposition, which also plays an important role in cyclohexene oxidation. A Sr doping of 20 at. % was found to be the optimum in terms of activity and product selectivity. The catalyst also showed excellent reusability over three catalytic runs; this can be attributed to its highly stable particle size and morphology. Kinetic investigations revealed first‐order reaction kinetics for temperatures between 60 and 100 °C and an apparent activation energy of 68 kJ mol−1 for cyclohexene oxidation. Moreover, the reaction was not affected by the applied O2 pressure in the range from 10 to 20 bar. In situ attenuated total reflection infrared spectroscopy was used to monitor the conversion of cyclohexene and the formation of reaction products including the key intermediate cyclohex‐2‐ene‐1‐hydroperoxide; spin trap electron paramagnetic resonance spectroscopy provided strong evidence for a radical reaction pathway by identifying the cyclohexenyl alkoxyl radical.

Metastatic Colorectal Cancer: Redox Metabolism and Malignancy

Investigating the tumor microenvironment has a direct impact on the understanding of the mechanisms which regulate cancer progression and treatment. Tumor cells undergoing profound changes in their own intrinsic metabolism affect the microenvironment. Colorectal cancer (CRC) is the third most common cancer with the predominant metastases (Mts) into the liver. Mts in liver tissues (LT), adjacent to Mts (AMT) and remote tissues (RMT, taken at the distance of 5 cm from Mts) from 25 patients with metachronous liver Mts after the liver resection as well as blood and urine were studied by electron paramagnetic resonance (EPR) including the spin-trapping EPR for the detection and quantification of the activity of N2 iron-sulfur proteins, levels of NO-N2 complexes, labile iron pool (LIP), lactoferrin (Lf), superoxide and NO radicals. Activity of metalloproteinase MMP-2 and MMP-9 were determined. In adjacent and remote LT low activity of N2 in mitochondrial electron transport chain (EPR signal with g=1.94), loss of functions of detoxification system (cytochrome P450, g=2.25), appearance and growth of NO-N2 complexes (g=2.007) are obtained. Intensive EPR signals from LIP (g=2.2-2.4) and Lf (g=4.3) are registered. Superoxide generation rates were of up to 6 times higher than in the reference LT tissues and blood (p<0.001). NO levels are of 1.7 times higher for the AMT compared to RMT (p<0.05) while being 15 times higher for blood comparing to the reference species (p<0.001). Activity of MMP-2 and MMP-9 was registered both in AMT and RMT and is in 1.7 times higher in ALT (p<0.05). The obtained results can be used to estimate the functional state of organs and tissues with distant metastases, the risk of recurrence, to correct the antitumor therapeutic procedures.

S-scheme assisted Cu2O/ZnO flower-shaped heterojunction catalyst for breakthrough hydrogen evolution by water splitting

Zinc and copper are considered as excellent metals for oxidation and reducibility, respectively. This study aims to obtain a redox-coupled composite semiconductor, wherein oxides of Zn and Cu were obtained and junctioned, for application as a photocatalyst in hydrogen production. To create a large number of activated sites on the catalyst's surface, the morphologies of the catalysts were controlled and several angular parts were formed. During the junction process, Cu2O and ZnO particles were controlled in cubic and starfish shapes, respectively, and the structure of the junctioned Cu2O/ZnO composite was similar to that of a chrysanthemum flower. Kubelka–Munk and Mott–Schottky plots demonstrated that ZnO and Cu2O have band gaps of 3.2 and 1.9 eV, respectively, and they are n- and p-type semiconductors, respectively. The TRPL and IMVS, as well as the photocurrent density and IMPS, confirmed that the recombination between electrons and holes in the junctioned Cu2O/ZnO particles was very slow, and effective charge separation was achieved. As a result, the amount of hydrogen generated from the junction catalyst was significantly higher than that generated from the single catalysts. In particular, the accumulated amount of evolved hydrogen after 10 h in the 2Cu2O/1ZnO junction catalyst was 2089.5 μmol. Results obtained from spin-trapping ESR experiments suggest that the charge-transfer mechanism in the redox-coupled 2Cu2O/1ZnO junction catalyst follows the S-scheme with a stronger reducing power.

Insulin signaling alters antioxidant capacity in the diabetic heart

Diabetic cardiomyopathy is associated with an increase in oxidative stress. However, antioxidant therapy has shown a limited capacity to mitigate disease pathology. The molecular mechanisms responsible for the modulation of reactive oxygen species (ROS) production and clearance must be better defined. The objective of this study was to determine how insulin affects superoxide radical (O2•–) levels. O2•– production was evaluated in adult cardiomyocytes isolated from control and Akita (type 1 diabetic) mice by spin-trapping electron paramagnetic resonance spectroscopy. We found that the basal rates of O2•– production were comparable in control and Akita cardiomyocytes. However, culturing cardiomyocytes without insulin resulted in a significant increase in O2•– production only in the Akita group. In contrast, O2•– production was unaffected by high glucose and/or fatty acid supplementation. The increase in O2•– was due in part to a decrease in superoxide dismutase (SOD) activity. The PI3K inhibitor, LY294002, decreased Akita SOD activity when insulin was present, indicating that the modulation of antioxidant activity is through insulin signaling. The effect of insulin on mitochondrial O2•– production was evaluated in Akita mice that underwent a 1-week treatment of insulin. Mitochondria isolated from insulin-treated Akita mice produced less O2•– than vehicle-treated diabetic mice. Quantitative proteomics was performed on whole heart homogenates to determine how insulin affects antioxidant protein expression. Of 29 antioxidant enzymes quantified, thioredoxin 1 was the only one that was significantly enhanced by insulin treatment. In vitro analysis of thioredoxin 1 revealed a previously undescribed capacity of the enzyme to directly scavenge O2•–. These findings demonstrate that insulin has a role in mitigating cardiac oxidative stress in diabetes via regulation of endogenous antioxidant activity.

Development of Nonheme {FeNO}7 Complexes Based on the Pyrococcus furiosus Rubredoxin for Red-Light-Controllable Nitric Oxide Release

Nitric oxide (NO) is an essential biological messenger, contributing a significant role in a diverse range of physiological processes. The light-controllable NO releasers are of great interest because of their potential as agents for NO-related research and therapeutics. Herein, we developed a pair of red-light-controllable NO releasers, pfRd-C9A-{FeNO}7 and pfRd-C42A-{FeNO}7 (pfRd = Pyrococcus furiosus rubredoxin), by constructing a nonheme {FeNO}7 center within the redesigned iron-sulfur protein scaffolds. While shown to be both air and thermally stable, these complexes are highly sensitive to red-light irradiation with temporal precision, which was confirmed by electron paramagnetic resonance spin trapping and Griess assay. The temporally controlled NO release from these complexes was also demonstrated in DNA cleavage assay. Overall, this study demonstrates that such a protein-based nonheme iron nitrosyl system could be a viable chemical tool for precise NO administration.