Electron Paramagnetic Resonance Spin Trapping Research Articles

The Interaction of Myeloperoxidase with the Industrial Contaminant 6-PPD: A Potential Pathway for Reactive Metabolites.

6-PPD (N-[1,3-dimethylbutyl]-N'-phenyl-p-phenylenediamine) is an industrial antioxidant reported to be an environmental contaminant. It was found to be highly toxic to coho salmon and potentially other aquatic organisms. The toxicity of 6-PPD in humans, however, remains unknown. The neutrophil enzyme myeloperoxidase (MPO) is known to catalyze xenobiotic metabolism; therefore, its role in 6-PPD cytotoxicity was investigated using the MPO-rich HL-60 cell line. UV-visible spectroscopy and liquid chromatography-mass spectrometry (LC/MS) were performed to investigate the MPO-mediated oxidation of 6-PPD and identify possible metabolites in the absence and presence of glutathione (GSH). 6-PPD's cytotoxicity, effect on mitochondrial membrane potential (MMP), and GSH-depleting ability in HL-60 cells were assessed. Electron paramagnetic resonance (EPR) was used to determine GSH radical formation using DMPO, and mitochondrial-derived superoxide was assessed with the mito-TEMPO-H probe. Evaluation of the 6-PPD-induced cellular injury pathways was performed by preincubating an antioxidant and an MPO inhibitor with HL-60 cells. UV-vis analysis of MPO-catalyzed oxidation of 6-PPD demonstrated changes in the 6-PPD spectrum, whereas the addition of GSH altered the spectrum, indicating possible GSH conjugate formation. LC/MS showed the formation of multiple products, including GSH-6-PPD conjugates and a GSH conjugate to a 4-hydroxydiphenylamine (a known 6-PPD degradant), which could potentially induce cytotoxicity. 6-PPD demonstrated concentration-dependent cytotoxicity, and cellular GSH levels were decreased by 6-PPD. Similarly, the level of MMP decreased, suggesting mitochondrial depolarization. Furthermore, the EPR spin probe for mitochondrial superoxide showed a positive relationship with 6-PPD concentration, and EPR spin-trapping demonstrated 6-PPD concentration-dependent GSH radical signal intensity using MPO/H2O2. The GSH precursor, NAC, demonstrated partial cytoprotection against 6-PPD; however, the MPO inhibitor PF-1355 surprisingly showed no significant cytoprotective effect. Our results suggest that MPO could be a potential catalyst for 6-PPD toxicity in humans. However, MPO inhibition did not significantly affect cellular viability, suggesting an MPO-independent toxicity pathway. These findings warrant a deeper investigation to determine 6-PPD mammalian toxicity pathways.

A complex and dynamic redox network regulates oxygen reduction at photosystem I in Arabidopsis.

Thiol-dependent redox regulation of enzyme activities plays a central role in regulating photosynthesis. Beside the regulation of metabolic pathways, alternative electron transport is subjected to thiol-dependent regulation. We investigated the regulation of O2 reduction at photosystem I. The level of O2 reduction in leaves and isolated thylakoid membranes depends on the photoperiod in which plants are grown. We used a set of Arabidopsis (Arabidopsis thaliana) mutant plants affected in the stromal, membrane and lumenal thiol network to study the redox protein partners involved in regulating O2 reduction. Light-dependent O2 reduction was determined in leaves and in thylakoids of plants grown in short day and long day conditions using a spin-trapping electron paramagnetic resonance (EPR) assay. In wild type samples from short day conditions, reactive oxygen species (ROS) generation was double that of samples from long day conditions, while this difference was abolished in several redoxin mutants. An in vitro reconstitution assay showed that thioredoxin m, NADPH-dependent reductase C and NADPH are required for high O2 reduction levels in thylakoids from plants grown in long day conditions. Using isolated photosystem I, we also showed that reduction of a photosystem I protein is responsible for the increase in O2 reduction. Furthermore, differences in the membrane localization of m-type thioredoxins and 2-Cys peroxiredoxin were detected between thylakoids of short day and long day plants. Overall, we propose a model of redox regulation of O2 reduction according to the reduction power of the stroma and the ability of different thiol-containing proteins to form a network of redox interactions.

Efficient generation of 1O2 by activating peroxymonosulfate on graphitic carbon nanoribbons for water remediation

Few-layer graphitic carbon nanoribbons (GCN) with rich defective sites were prepared by pyrolysis at 800 oC in N2 of in situ-chelated Fe-polyaniline complexes synthesized via one-pot homogeneous Fenton-like oxidative polymerization of an acidic aniline solution. A minimal amount of iron (0.47 wt%) made a pivotal role in the nanoribbon growth and graphitization of GCN, and deposited highly dispersed iron species on GCN without post-synthesis acid leaching, which greatly simplified the synthesis procedure of GCN with improved yield. GCN exhibited high activity and stability for catalytic degradation of organic pollutants with peroxymonosulfate (PMS) mainly via non-radical pathways. The influences of various operating parameters on the catalytic performance of GCN were investigated. Scavenging tests, spin-trapping electron paramagnetic resonance spectra, electrochemical analyses, and theoretical calculations unveiled that 1O2 was the main reactive oxygen species generated from synergistic activation of PMS on GCN while GCN-mediated electron transfer made a minor contribution to organic degradation.

A dual-functional α-diketone-based disulfide monomer for visible LED photopolymerization: Mitigating volumetric shrinkage and triggering polymerization

A α-diketone-based disulfide monomer (OHS), which serves the function of both volumetric shrinkage decreases and photopolymerization initiation under the irradiation of 405 light-emitting diode (LED) was designed and synthesized. The photochemical and photoinitiating performances were study by ultraviolet–visible spectrophotometer, electron spin resonance spin trapping (ESR-ST) experiments and real-time infrared spectrometer (FTIR). Despite OHS exhibits weak absorption at approximately 405 nm, OHS can effectively produce aromatic sulfur radicals to induce photopolymerization of itself and the bisphenol A glycerolate dimethacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) photopolymerizable system under 405 nm LED exposure. With increasing OHS addition, the final double bond conversion and maximum polymerization rate of the Bis-GMA/TEGDMA system improved, reaching up to 86.0% and 2.33% s-1, respectively. Importantly, OHS significantly reduces the volumetric shrinkage ratio of the Bis-GMA/TEGDMA photopolymerizable system, with the volumetric shrinkage ratio (5.01%) of the system containing 5% OHS declining by almost 50% compared to that (8.51%) of the control system without OHS. This reduction is attributed to reversible characteristic of the disulphide bonds and intermolecular hydrogen bondings. Furthermore, OHS has little influence on the gelation ratio, thermostability, and frictional resistance of the cured film.

Facile construction of copper-doped metal organic framework as a novel visible light-responsive photocatalyst for contaminant degradation

ABSTRACT Metal–organic frameworks (MOFs) with photocatalytic activity have garnered significant attentions in environmental remediation. Herein, copper-doped zeolitic imidazolate framework-7 (Cu-doped ZIF-7) was synthesized rapidly and easily using a microwave-assisted technique. Various analytical and spectroscopic methods were employed to access the framework, morphology, light absorption, photo-electrochemical and photocatalytic performance of the synthesized materials. Compared to ZIF-7, Cu/ZIF-7 (molar ratio of Cu2+ to Zn2+ is 1:1) demonstrates superior visible light absorption ability, narrower band gap, enhanced charge separation capability, and reduced electron–hole recombination performance. Under visible light irradiation, Cu/ZIF-7 serves as a Fenton-like catalyst and demonstrates exceptional activity for contaminant degradation, while virgin ZIF-7 remains inactive. With the addition of 9.8 mmol H2O2 and exposure to visible light for 30 min, 10 mg of Cu/ZIF-7 can completely decompose RhB solution (10 mg/L, 50 mL). The synergistic effect of the Cu/ZIF-7/H2O2/visible light system is attributed to visible light photocatalysis and Fenton-like reactions. Cu/ZIF-7 demonstrates excellent catalytic performance stability, with only a slight decrease in degradation efficiency from an initial 97.0% to 95.4% over four cycles. Additionally, spin-trapping ESR measurements and active species trapping experiments revealed that h+ and ·OH occupied a significant position for Rhodamine B (RhB) degradation. Degradation intermediate products of Rhodamine B have been identified using UPLC-MS, and the degradation pathways have been proposed and discussed. This work offers a facile and efficient technique for developing MOF-based visible light photocatalysts for water purification.

Mechanisms Associated with Superoxide Radical Scavenging Reactions Involving Phenolic Compounds Deduced Based on the Correlation between Oxidation Peak Potentials and Second-Order Rate Constants Determined Using Flow-Injection Spin-Trapping EPR Methods.

Flow-injection spin-trapping electron paramagnetic resonance (FI-EPR) methods that involve the use of 5,5-dimethyl-pyrroline-N-oxide (DMPO) as a spin-trapping reagent have been developed for the kinetic study of the O2•- radical scavenging reactions occurring in the presence of various plant-derived and synthetic phenolic antioxidants (Aox), such as flavonoid, pyrogallol, catechol, hydroquinone, resorcinol, and phenol derivatives in aqueous media (pH 7.4 at 25 °C). The systematically estimated second-order rate constants (ks) of these phenolic compounds span a wide range (from 4.5 × 10 to 1.0 × 106 M-1 s-1). The semilogarithm plots presenting the relationship between ks values and oxidation peak potential (Ep) values of phenolic Aox are divided into three groups (A1, A2, and B). The ks-Ep plots of phenolic Aox bearing two or three OH moieties, such as pyrogallol, catechol, and hydroquinone derivatives, belonged to Groups A1 and A2. These molecules are potent O2•- radical scavengers with ks values above 3.8 × 104 (M-1 s-1). The ks-Ep plots of all phenol and resorcinol derivatives, and a few catechol and hydroquinone derivatives containing carboxyl groups adjacent to the OH groups, were categorized into the group poor scavengers (ks < 1.6 × 103 M-1 s-1). The ks values of each group correlated negatively with Ep values, supporting the hypothesis that the O2•- radical scavenging reaction proceeds via one-electron and two-proton processes. The processes were accompanied by the production of hydrogen peroxide at pH 7.4. Furthermore, the correlation between the plots of ks and the OH proton dissociation constant (pKa•) of the intermediate aroxyl radicals (ks-pKa• plots) revealed that the second proton transfer process could potentially be the rate-determining step of the O2•- radical scavenging reaction of phenolic compounds. The ks-Ep plots provide practical information to predict the O2•- radical scavenging activity of plant-derived phenolic compounds based on those molecular structures.

Aryl structural effect on the photoinitiation abilities of aryl glycine derivatives for polymerization upon exposure to blue light

AbstractThe design and development of photoinitiating systems applicable to visible light delivered from light‐emitting diodes (LEDs) have attracted increasing attention owing to the wide application of photopolymerization. In this study, four aryl glycine derivatives are designed and synthesized, and their applicability as visible light‐sensitive photoinitiators is thoroughly investigated. Specifically, the photoinitiation mechanism of these aryl glycine derivatives, when combined with iodonium salt, is investigated using steady‐state photolysis, fluorescence, and electron paramagnetic resonance spin trapping techniques. It is revealed that radicals can be generated from aryl glycine derivatives/iodonium salt combinations upon exposure to blue LEDs (410 and 445 nm) to induce free radical photopolymerization (FRP) of (meth)acrylates. Additionally, besides FRP, a photobase generator based on one of the investigated aryl glycine derivatives is synthesized and demonstrates the capability to initiate epoxy‐thiol polymerization under light irradiation. The remarkable photolatent characteristics demonstrate the significant potential in broadening the application of aryl glycine derivatives in controlled photopolymerization processes.

Eosin Y derivatives for visible light-mediated free-radical polymerization: Applications in 3D-photoprinting and bacterial photodynamic inactivation

This study reports the design and the subsequent use of mono-allylated (EY-MA) and di-allylated (EY-DA) derivatives of eosin Y (EY) as highly efficient visible light-sensitive photosensitizers (PS) of bio-based H-donor molecules (cysteamine (Cys) or N-acetyl-L-cysteine (NAC)) and an electron donor (N-methyldiethanolamine, MDEA) for free-radical and thiol-acrylate polymerizations of a biobased monomer derived from soybean oil (SOA) upon exposure to visible light. High final acrylate conversions for SOA polymerization (up to 80 %) evidence the efficient photoinitiating properties of the eosin derivatives systems under irradiation with light emitting diodes (LEDs) centred at 405, 455 and 505 nm, and outperform those obtained with EY and other common photosensitizers such as camphorquinone or benzophenone. As described by fluorescence and phosphorescence analyses, laser flash photolysis (LFP) and electron paramagnetic resonance spin-trapping (EPR-ST) experiments, EY-MA and EY-DA can react via a proton/proton-coupled electron transfer reaction with Cys (or NAC) and MDEA respectively. The efficient singlet oxygen generation of the EY-MA-based materials upon exposure to visible light leads to excellent antibacterial properties, against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). A 3-log decrease of E. coli adhesion on the surface of the materials is observed and 100 % adhesion inhibition of S. aureus is also demonstrated. The co-polymerization of the eosin-derived PS with the polymer matrix ensures sustainable antibacterial properties against both bacteria strains upon visible light exposure as it prevents their leakage out of the polymer network. Finally, finely complex 3D structures are successfully obtained by a 3D-photoprinting technology with the investigated EY-MA-based formulation using LED@405 nm.

EPR Spin-Trapping for Monitoring Temporal Dynamics of Singlet Oxygen during Photoprotection in Photosynthesis.

A central goal of photoprotective energy dissipation processes is the regulation of singlet oxygen (1O2*) and reactive oxygen species in the photosynthetic apparatus. Despite the involvement of 1O2* in photodamage and cell signaling, few studies directly correlate 1O2* formation to nonphotochemical quenching (NPQ) or lack thereof. Here, we combine spin-trapping electron paramagnetic resonance (EPR) and time-resolved fluorescence spectroscopies to track in real time the involvement of 1O2* during photoprotection in plant thylakoid membranes. The EPR spin-trapping method for detection of 1O2* was first optimized for photosensitization in dye-based chemical systems and then used to establish methods for monitoring the temporal dynamics of 1O2* in chlorophyll-containing photosynthetic membranes. We find that the apparent 1O2* concentration in membranes changes throughout a 1 h period of continuous illumination. During an initial response to high light intensity, the concentration of 1O2* decreased in parallel with a decrease in the chlorophyll fluorescence lifetime via NPQ. Treatment of membranes with nigericin, an uncoupler of the transmembrane proton gradient, delayed the activation of NPQ and the associated quenching of 1O2* during high light. Upon saturation of NPQ, the concentration of 1O2* increased in both untreated and nigericin-treated membranes, reflecting the utility of excess energy dissipation in mitigating photooxidative stress in the short term (i.e., the initial ∼10 min of high light).

Photocatalytic Degradation of Tetracycline Hydrochloride Based on the Structure-Property Exploration of BiOCl.

The correlation between structure and properties in the photodegradation reaction of bismuth oxychloride (BiOCl) was explored in this work. Three BiOCl samples with different sizes, morphological structures, and defects were prepared through a hydrothermal method with experimental manipulation. Their structural properties were comprehensively characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron spin resonance, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and photoluminescence. Taking the photodegradation of tetracycline hydrochloride (TC-HCl) as the probe reaction, we found that high activity could be achieved by decreasing their crystal size and thickness, introducing proper defects in the structure, and assembling the nanosheets to get microball structure. Combined with radical-scavenge experiments and electron spin resonance (ESR) spin-trap spectra, we conclude that ̇O2- was the dominant reactive oxygen species for the degradation reaction. The degradation detailed pathway of TC-HCl was further analyzed using liquid chromatography-mass spectrometry. This work explores the structure-property correlation of BiOCl and provides strategies for the rational design of active photocatalysts for water remediation.

Ultrafast Sunlight-Induced Polymerization: Unveiling 2-Phenylnaphtho[2,3-d]Thiazole-4,9-dione as a Unique Scaffold for High-Speed and Precision 3D Printing.

A series of 15 dyes based on the 2-phenylnaphtho[2,3-d]thiazole-4,9-dione scaffold and 1 compound based on the 2,3-diphenyl-1,2,3,4-tetrahydrobenzo[g]quinoxaline-5,10-dione scaffold are studied as photoinitiators. These compounds are used in two- and three-component high-performance photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and polyethylene glycol diacrylate (PEGDA) under sunlight. Remarkably, the conversion of TMPTA can reach ≈60% within 20s, while PEGDA attains a 96% conversion within 90s. To delve into the intricate chemical mechanisms governing the polymerization, an array of analytical techniques is employed. Specifically, UV-vis absorption and fluorescence spectroscopy, steady-state photolysis, stability experiments, fluorescence quenching experiments, cyclic voltammetry, and electron spin resonance spin trapping (ESR-ST) experiments, collectively contribute to a comprehensive understanding of the photochemical mechanisms. Photoinitiation capacities of these systems are determined using real-time Fourier transformed infrared spectroscopy (RT-FTIR). Of particular interest is the revelation that, owing to the superior initiation ability of these dyes, high-resolution 3D patterns can be manufactured by direct laser write (DLW) technology and 3D printing. This underscores the efficient initiation of free radical polymerization processes by the newly developed dyes under both artificial and natural light sources, presenting an avenue for energy-saving, and environmentally friendly polymerization conditions.

Nickel-doped microtubular CeVO4 inspired by wood powder structure for visible light photocatalytic degradation of methylene blue and bacterial inactivation

In this study, inspired by natural wood powder structure, nickel-doped microtubular cerium vanadate (Ni/T-CeVO4) was obtained using wood powder as a biological template. Photocatalytic experiments under visible light revealed that Ni/T-CeVO4-3wt possessed the highest photocatalytic activity, with a degradation efficiency of up to 99 % for methylene blue. The enhanced photocatalytic performance was not only attributed to the microtubule wood powder structure assigned the composite a larger specific surface area but also the nickel doping narrowed the band gap of the composites while introducing more oxygen vacancies. The rapidly generated current in transient photocurrent responses and small arc radius in electrochemical impedance spectra further indicated the higher photogenerated carrier separation and smaller photogenerated electron transfer resistance within the composite. ESR spin-trapping tests proved that O2− and OH dominated the photocatalytic process. Furthermore, owing to its unique structural characteristics, the composite showed excellent photocatalytic antibacterial activity against Staphylococcus aureus and Escherichia coli. The present study provides a theoretical basis for developing efficient dual-effect photocatalysts using visible light to remove organic dyes and pathogenic bacteria from the water environment.

Vascular protein disulfide isomerase A1 mediates endothelial dysfunction induced by angiotensin II in mice.

Protein disulfide isomerases (PDIs) are involved in platelet aggregation and intravascular thrombosis, but their role in regulating endothelial function is unclear. Here, we characterized the involvement of vascular PDIA1 in angiotensin II (Ang II)-induced endothelial dysfunction in mice. Endothelial dysfunction was induced in C57BL/6JCmd male mice via Ang II subcutaneous infusion, and PDIA1 was inhibited with bepristat. Endothelial function was assessed invivo with magnetic resonance imaging and exvivo with a myography, while arterial stiffness was measured as pulse wave velocity. Nitric oxide (NO) bioavailability was measured in the aorta (spin-trapping electron paramagnetic resonance) and plasma (NO2 - and NO3 - levels). Oxidative stress, eNOS uncoupling (DHE-based aorta staining), and thrombin activity (thrombin-antithrombin complex; calibrated automated thrombography) were evaluated. The inhibition of PDIA1 by bepristat in Ang II-treated mice prevented the impairment of NO-dependent vasodilation in the aorta as evidenced by the response to acetylcholine invivo, increased systemic NO bioavailability and the aortic NO production, and decreased vascular stiffness. Bepristat's effect on NO-dependent function was recapitulated exvivo in Ang II-induced endothelial dysfunction in isolated aorta. Furthermore, bepristat diminished the Ang II-induced eNOS uncoupling and overproduction of ROS without affecting thrombin activity. In Ang II-treated mice, the inhibition of PDIA1 normalized the NO-ROS balance, prevented endothelial eNOS uncoupling, and, thereby, improved vascular function. These results indicate the importance of vascular PDIA1 in regulating endothelial function, but further studies are needed to elucidate the details of the mechanisms involved.

Preparation of core-shell structure Ag@TiO2 plasma photocatalysts and reduction of Cr(VI): Size dependent and LSPR effect

The poor light absorption and low carrier separation efficiency of Titanium dioxide (TiO2) limit its further application. The introduction of plasma metal Ag have the potential to solve these drawbacks owing to its plasma resonance effect. Thus core-shell structure Ag@TiO2 plasma photocatalysts was prepared by using facile reduction method in this work. More specifically, Ag@TiO2 composite catalysts with different Ag loading amounts were prepared in the presence of surfactant PVP. Ag@TiO2 demonstrates excellent light absorption performance and photoelectric separation efficiency compared with pure TiO2. As a result, it displays excellent performance of Cr(VI) reduction under visible light. The optimal composite catalysts Ag@TiO2–5P achieves exceptional visible-light-driven photocatalytic Cr(VI) reduction efficiency of 0.01416 min−1 that is 2.29 times greater than pure TiO2. To investigate the role of PVP, we also synthesized Ag@TiO2-5 without PVP. The experimental results show that although Ag@TiO2-5 Cr(VI) reduction performance is superior to pure TiO2, it significantly decreases compared with Ag@TiO2–5P. The results of TEM and optoelectronic testing show that agglomeration of Ag particles leads to a decrease in the photoelectric separation efficiency of Ag@TiO2-5. The smaller Ag particles provide more active sites and demonstrating a stronger overall local surface plasmon resonance (LSPR) effect. DMPO spin-trapping ESR spectra testing indicates that ∙O2− and ∙OH are the main reactive species. This research provides a potential strategy to prepare Ag-based plasma photocatalysts for environment protection.

Designing step-scheme AgI decorated Ta2O5-x heterojunctions for boosted photodegradation of organic pollutants

Step-scheme (S-scheme) AgI decorated Ta2O5-x heterojunctions have been designed and synthesized via a combination of solvothermal and chemical deposition methods for enhanced visible-light harvesting and high-performance photocatalysis. The AgI nanoparticles showed great influences on the visible-light absorption and charge separation between AgI and Ta2O5-x microspheres. The experimental results indicated that the as-prepare AgI/Ta2O5-x composites achieved enhanced photocatalytic performance towards tetracycline degradation under visible light, and the AgI/Ta2O5-x-11 sample displayed the highest photocatalytic performance and the maximum rate constant of approximately 0.09483 min−1, which was 7.22 times that of Ta2O5-x microspheres and 2.56 times that of AgI, respectively. The highly enhanced photocatalytic performance was mainly attributed to the construction of S-scheme heterostructure and formation of oxygen vacancies in Ta2O5-x microspheres. In addition, the trapping experimental and DMPO spin-trapping ESR spectra confirmed the ⸱O2− and ⸱OH species as the main radicals during tetracycline degradation. Current work indicates an S-scheme tantalum-based composites for high-performance environmental photocatalysis.

Fine-tuning metal nodes accessibility of metal-organic frameworks for boosting net photocatalytic H2O2 production

Coordination unsaturated metal nodes in metal-organic frameworks (MOFs) work as photocatalytic active sites in H2O2 production, but over-exposed metal nodes also act as decomposing sites towards the photogenerated H2O2, resulting in low net yield. Herein, fine-tuning of metal nodes accessibility in MOFs was applied for boosting net photocatalytic H2O2 production. The accessibility of the nodes was fine-tuning through varying the feeding amount of benzoic acid (BA) during synthesis, treated MOFs with HCl, re-installed with variable BA, etc. The correlation between nodes accessibility and H2O2 production was systematically investigated, which demonstrates that the NH2-UiO-66-XBA with higher compensated BA possessing large steric effect at nodes would hinder the decomposition of photogenerated H2O2, thus promoting the net H2O2 yield. As a contrary, NH2-UiO-66-HCl without BA showed a distinctive decomposition rate of H2O2, resulting in a low net H2O2 production yield. The re-installed NH2-UiO-66-ReBA10 with compensated BA showed a recovered H2O2 production yield. A combination of O2 sorption isothermals, PL spectra, ESR spin-trap plots, and Koutecky-Levich plots disclosed that O2 was enriched by the framework and then reduced at the metal nodes mainly through two-electron pathway, especially for highly compensated MOFs. This strategy had been applied to other MOFs for boosting the H2O2 production like NU-1401 and PCN-222. This work reveals the fine-tuning of metal nodes accessibility in MOFs is an effective way for boosting H2O2 production.

Study on the photoinitiation mechanism of carbazole-based oxime esters (OXEs) as novel photoinitiators for free radical photopolymerization under near UV/visible-light irradiation exposure and the application of 3D printing

In this work, twenty-two oxime esters bearing different functional groups and based on carbazole as the chromophore were designed and synthesized as Type I photoinitiators. Interestingly, all structures mentioned in this work have never been reported before (even for their synthesis). These oxime esters were found to have good light absorption properties in the UV–visible range, and especially at 405 nm which is a reference wavelength in photopolymerization. Noticeably, several structures showed better photoinitiation abilities than the benchmark photoinitiator i.e. diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), evidencing the interest of these structures. In order to investigate the photoinitiation mechanism of the two series of oxime esters differing by the position of the photocleavable groups, electronic absorption spectra were determined by molecular modeling and density functional theory calculations. Photopolymerization abilities of the different oxime esters and release of CO2 during the polymerization experiments were determined by Real-Time Fourier Transformed Infrared (RT-FTIR). Active free radicals were characterized by mean of Electron Spin Resonance Spin Trapping (ESR-ST) experiments. On the basis of these different complementary experiments, chemical mechanisms occurring during photopolymerization could be proposed. Experimental results showed that the decarboxylation reaction occurring subsequent to the photocleavage of oxime esters had a beneficial effect on the photoinitiation ability. Finally, 3D printed objects were successfully obtained by using oxime esters exhibiting the best photoinitiating abilities.

Visible-light-driven quantitative photooxidation of anthracene to anthraquinone under mild conditions

This paper discloses a mild and atom-economic photo-oxidation protocol for visible-light-driven quantitative oxidation of anthracene (AN) to anthraquinone (AQ), which can obtain excellent AN conversion (∼100%) and AQ yield (99.2%) without any catalysts and additives under 10 h of visible light illumination. In addition, the protocol also works well with other chemical molecules that have a similar structure. In this protocol, AN is directly oxidized from AN to AQ without the observation of the intermediate anthrone (AO). Based on a series of control tests, as well as free radical quenching and electron paramagnetic resonance (EPR) spin trapping studies, it can be inferred that the process of photo-oxygenation in AN is most likely initiated by its photo-excited state, denoted as AN*. This photo-excited state has the ability to activate molecular oxygen (O2) by an electron transfer mechanism, resulting in the formation of a superoxide free radical (O2•-). Following this, the process of photo-oxidation is progressively controlled by the oxygenated product AQ, which acts as an active photo-catalyst. AQ is derived from the oxidation of AN by O2•- and its presence accelerates the process of photo-oxidation due to its rapid accumulation. Furthermore, the yield of AQ can be improved by enhancing the light intensity of the light source, timely separating the yellow solid oxidation product AQ formed during the reaction, and pre-adding the oxidation product AQ to the protocol as an active photocatalyst.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)–H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h−1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h−1) and BiMo (482 μmol g-1h−1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin–trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94–98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)–H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Triggering “signal-on” photoelectrochemical responses by heterojunction transition for selective detection of copper(II) based on Pd/MoS2@g-C3N4 nanocomposites

Controlling the concentration of copper(II) in aquatic systems is of importance for human health. Numerous traditional technologies to detect Cu2+ may encounter with limitations, such as high signal background and complicated operation. Herein, a highly selective photoelectrochemical (PEC) sensor is proposed for the “signal-on” detection of Cu2+ employing g-C3N4 nanosheets with MoS2 and Pd quantum dots deposited (Pd/MoS2@g-C3N4). Pd/MoS2@g-C3N4 could present the enhanced photocurrents of specific responses to Cu2+ under light irradiation. MoS2 quantum dots on the sensor are agglomerated into MoS2 bulk during sensing Cu2+, forming an efficient Z-scheme heterojunction. The heterojunction transition induced photoelectrons transferring from the bulk MoS2 to g-C3N4, resulting in “signal-on” PEC responses. Such Z-scheme heterojunction has conquered the traditional heterojunction towards “signal-on” mechanism, that was further verified by band structure measurements and DMPO spin trapping ESR analysis. Photocurrent intensities increased gradually with the addition of incremental Cu2+ concentrations, achieving a detection limit of 0.21 μM and a broad linear interval range from 1 μM to 1 mM with high selectivity and stability. This work may open a new door towards the in situ construction of g–C3N4–based Z-scheme heterojunctions for the signal-on PEC sensing platform, providing wide applications in environmental monitoring and food safety.