Formation Of Reactive Intermediates Research Articles

Exploring the Reactivity of High Valent Iron Intermediates in Water

The exceptional reactivity observed in non‐heme iron enzymes can be attributed to their capability to access high‐valent iron oxygen species in their active site. Numerous inorganic model complexes have been reported to date, providing insights into the intricate structural and spectroscopic features of many iron‐containing enzymes and advancing our understanding of their enzymatic reaction pathways. While the reactivities of synthetic iron complexes have been evaluated using various oxidants, the investigation into the formation of reactive intermediates has primarily focused on acetonitrile. However, water, which serves as the medium in biological systems, has been less frequently employed in these studies. Motivated by this, we conducted a comprehensive study on the generation of key reactive species using various oxidants with a model complex, [(BnTPEN)Fe(II)(OTf)]+ (1) (where BnTPEN = N‐benzyl‐N,N,N‐tris(2‐pyridylmethyl)‐1,2‐diaminoethane) in water, which yielded important findings. In water, a quantitative yield of Fe(IV)=O species was achieved with the oxidant NaIO4. Additionally, we observed an equilibrium between side‐on Fe(III)‐OO and Fe(III)‐OOH, with the latter eventually converting to Fe(IV)=O. The insights gained from this study are likely to be relevant in the chemistry of other Fe(II) complexes with polypyridyl pentadentate ligands.

Novel Organosulfur Building Blocks for Heterocycle Synthesis

AbstractThe present article provides a personalized account of our recent work on the synthesis of substituted and fused five-membered heterocycles using various organosulfur building blocks, derived primarily through base-mediated condensation of active methylene compounds with (het)aryl/alkyl dithioesters, which have not been previously explored. We initially describe the ring-opening transformations of 4-[(methylthio)-(het)aryl-methylene]-2-phenyl-5-oxazolones, leading to the synthesis of functionalized oxazoles, thiazoles, and bisoxazoles. We then go on to focus on the synthesis of substituted benzothiophenes, indoles, and benzofurans, as well as their hetero-fused analogs. These compounds are synthesized via transition-metal-catalyzed intramolecular C–heteroatom (C–S, C–N, C–O) bond formation (via cross-coupling or C–H bond functionalization) of various reactive organosulfur intermediates, derived from base-mediated condensation of 2-bromo(het)arylacetonitriles, acetates, or desoxybenzoins or the corresponding 2-unsubstituted precursors. Finally, we highlight the synthetic applications of a new class of previously unexplored organosulfur building blocks, namely, unsymmetrically substituted 1,3-bis(het)aryl-1,3-monothioketones, derived via base-mediated condensation of ketones with (het)aryl/alkyl dithioesters, for the regioselective synthesis of substituted pyrazoles, isoxazoles, thiophenes, imidazoles, and benzothiophenes.1 Introduction2 4-[(Methylthio)-het(aryl)-methylene]-2-phenyl/2-(2-thienyl)-5-oxazolones: Versatile Templates for the Synthesis of Oxazoles, Thiazoles, and Bisoxazoles3 Synthesis of Benzothiophenes, Indoles, and Benzofurans via Transition-Metal-Catalyzed Intramolecular C–Heteroatom Bond Formation4 1,3-Bis(het)arylmonothio-1,3-diketones and 1,3-Bis(Het)aryl-3-(methylthio)-2-propenones: Versatile Intermediates for the Regioselective Synthesis of Five-Membered Heterocycles5 Conclusion

Post-Synthetically Treated ERI and SSZ-13 Zeolites Modified with Copper as Catalysts for NH3-SCR-DeNOx

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results in terms of NH3-SCR-DeNOx show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion did not vary for the different materials treated with NaOH or NaOH/HNO3. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH3-SCR-DeNOx was observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH3-SCR-DeNOx. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies show that besides the μ-η2,η2-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), copper nitrates (evidenced by in situ FT-IR spectroscopy) also act as reactive intermediates in these catalytic systems.

P-044 Increased CYP1A1 expression enhances sperm apoptosis in idiopathic infertile men

Abstract Study question How are the CYP1A1 and Caspase-9 genes expression and the relationship among the expression of these genes with sperm parameters in idiopathic infertile men? Summary answer The CYP1A1 and Caspase-9 gene expression showed a significant increase in patients in comparison with the healthy group. What is known already CYP1A1 (Cytochrome P450 Family 1 Subfamily A Member 1) plays a crucial role in xenobiotic metabolism induced by aryl hydrocarbon receptor (AHR). AHR, as a ligand-activated transcription factor is involved in exogenous ligand activation. CYP1A1 is one of the most essential enzymes in phase 1 of detoxification, metabolism, and bio-activation of carcinogens and is the most well-known target gene for AHR. Monooxygenase activity of CYP1A1 may lead to oxidative stress and the formation of reactive intermediates with destructive effects such as apoptosis in testicular germ cells. CYP1A1 may lead to apoptosis via Caspase-9 activation. Study design, size, duration In this study, we aimed to determine the CYP1A1 and Caspase-9 gene expression. Participants/materials, setting, methods The infertile idiopathic and healthy fertile men were selected and evaluated for sperm analysis and gene expression. The expression levels of CYP1A1 and Caspase-9 were also determined by real time PCR. Main results and the role of chance The sperm count, morphology and motility were significantly lower in patients compared to the control group (p < 0.05). The CYP1A1 and Caspase-9 gene expression showed a significant increase in patients in comparison with the healthy group (p < 0.05). Limitations, reasons for caution Further investigations of the effect of CYP1A1 and Caspase-9 expressions on infertility by using more infertile patients and also studying the effect of other important genes such as AHR can show us more accurate results. Wider implications of the findings Our results suggest that increased CYP1A1 and Caspase-9 expression could increase the rate of male infertility. In addition, the increase in Caspase-9 expression could lead to a reduced number of sperms and an increased infertility rate by increased apoptosis in the spermatogenic lineage. Trial registration number not applicable

Biodegradation of Pharmaceutical Pollutants Using Fungal Enzyme

Abstract: The potential of filamentous fungi and their enzymes are investigated for bioremediating pharmaceutical pollutants from wastewater thereby addressing the growing concern of emerging pollutants in water resources. Among the various microorganisms, the current abstract discusses the role of fungi in degrading antibiotics and persistent pharmaceutical compounds. These fungi allow the biodegradation via the formation of highly oxidative hydroxyl radicals. It summarizes the role of both intra (cytochrome P450) and extracellular (laccase) enzyme systems for the bioremediation of emerging clinical pollutants. It emphasizes the importance of both biosorption and biodegradation for effective pollutant removal by breaking down pharmaceuticals (e.g. antibiotics) and other hazardous compounds (e.g. endocrine-disrupting compounds, polycyclic aromatic hydrocarbons). Although the enzymes CYP450 are not directly engaged, their metabolic pathways execute mechanisms such as oxidation, the formation of reactive intermediates, and chemical modification, all of which result in the degradation of clinical pollutants. Amongst all enzyme systems in the case of laccase which oxidise a wide spectrum of substrates, converts them to free radicals. Additionally, the role of recombinant enzyme production and transgenic strains for pollutant degradation has also been elaborated. These considerations emphasise the need for ongoing research and biotechnological advancements to address the growing concern of pharmaceuticals and personal care product pollutants in water systems.

Acetate Assistance in Regioselective Hydroamination of Allenamides: A Combined Experimental and Density Functional Theory Study.

A key factor in the development of selective nucleophilic addition to allenamides is controlling the reactivity of electrophilic intermediates, which is generally achieved using an electrophilic activator via conjugated iminium intermediates. In this combined experimental and computational study, we show that a general and highly chemoselective hydroamination of allenamides can be accomplished using a combination of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and NaOAc. Experimental mechanistic studies revealed that HFIP mediates proton transfer to activate the allenamide, while the acetate additive significantly contributes to N-selective interception. This strategy enables a general hydroamination of allenamides without the use of metals. We demonstrated that various functionalized 1,3-diamines could be readily synthesized and diversified into value-added structural motifs. Detailed mechanistic investigations using the density functional theory revealed the role of NaOAc in the formation of reactive electrophilic intermediates, which ultimately governed the selective formation of 1,3-diamine products. Critically, calculations of the potential energy surface around the proton-transfer transition state revealed that two different reactive electrophilic intermediates were formed when NaOAc was added.

Formation of reactive intermediates in paddy water from different temperature zones for the promotion of abiotic ammonification

The paddy field is a hot area of biogeochemical process. The paddy water has a large capacity in photo-generation of reactive intermediates (RIs) due to abundant photosensitive dissolved organic matter (DOM), which is influenced by the spatial heterogeneity of paddy soils but rarely been explored. Our work presents the first investigation of the role of soil properties on photochemistry in paddy water. Soil organic matter (SOM), determined by the temperature, was the dominant factor for the photo-generation of RIs in paddy water of main rice producing areas. The RI concentrations generated with abundant SOM from cool regions are 0.05–8.71 times higher than those for the warm regions in China. The humic-like substance and aromatic-like compounds of DOM plays an essential role in RIs generation, which is abundant in paddy soils rich in SOM from Chinese cool regions. In addition, RIs can efficiently accelerate the photo-ammonification of urea and free amino acids by 15.2 %–164 %, leading to 0.13–0.17 mmol/L/d photo-produced ammonium after fertilization, which is preferentially absorbed by rice. The findings of this study will extend our knowledge of the geochemistry of global paddy field ecosystem. The potential role of RIs in nitrogen cycle should be highlighted in the agroecosystem.

Uncoupling of Cytochrome P450 2B6 and stimulation of reactive oxygen species production in pharmacogenomic alleles affected by interethnic variability

Cytochrome P450 mediated substrate metabolism is generally characterized by the formation of reactive intermediates. In vitro and in vivo reaction uncoupling, results in the accumulation and dissociation of reactive intermediates, leading to increased ROS formation. The susceptibility towards uncoupling and altered metabolic activity is partly modulated by pharmacogenomic alleles resulting in amino acid substitutions. A large variability in the prevalence of these alleles has been demonstrated in CYP2B6, with some being predominantly unique to African populations.The aim of this study is to characterize the uncoupling potential of recombinant CYP2B6*1, CYP2B6*6 and CYP2B6*34 metabolism of specific substrates.Therefore, functional effects of these alterations on enzyme activity were determined by quantification of bupropion, efavirenz and ketamine biotransformation using HPLC-MS/MS. Determination of H2O2 levels was performed by the AmplexRed/horseradish peroxidase assay.Our studies of the amino acid substitutions Q172H, K262R and R487S revealed an exclusive use of the peroxide shunt for the metabolism of bupropion and ketamine by CYP2B6*K262R. Ketamine was also identified as a trigger for the peroxide shunt in CYP2B6*1 and all variants. Concurrently, ketamine acted as an uncoupler for all enzymes. We further showed that the expressed CYP2B6*34 allele results in the highest H2O2 formation.We therefore conclude that the reaction uncoupling and peroxide shunt are directly linked and can be substrate specifically induced with K262R carriers being most likely to use the peroxide shunt and R487S carrier being most prone to reaction uncoupling. This elucidates the functional diversity of pharmacogenomics in drug metabolism and safety.

Bis(1-methylimidazol-2-yl) diselenide and its evaluation as a chemical radio-protector: role of kinetic rate constants for ROS scavenging and glutathione peroxidase like activity

Bis(1-methylimidazol-2-yl) diselenide (MeImSe), a derivative of selenoneine, has been examined for bimolecular rate constants for scavenging of various radiolytically and non-radiolytically generated reactive oxygen species (ROS). Further, its potential to show glutathione peroxidase (GPx)-like activity and to protect in vitro models of DNA and lipid against radiation induced strand breakage and lipid peroxidation, respectively were studied. The results confirmed that MeImSe scavenged all major short-lived (hydroxyl radical) and long-lived (peroxyl radical, carbonate radical, nitrogen dioxide radical, hypochlorite and hydrogen peroxide) oxidants involved in the radiation toxicity either directly or through GPx-like catalytic mechanism. The rate constants of MeImSe for these oxidants were found to be comparable to analogous sulfur and selenium-based compounds. The enzyme kinetics study established that MeImSe took part in the GPx cycle through the reductive pathway. Further, MeImSe inhibited the radiation induced DNA strand cleavage and lipid peroxidation with half maximal inhibitory concentration (IC50) of ∼ 60 μM and ∼100 μM, respectively. Interestingly, MeImSe treatment in the above concentration range (>100 μM) did not show any significant toxicity in normal human lung fibroblast (WI26) cells. The balance between efficacy and toxicity of MeImSe as a chemical radioprotector was attributed to the formation of less reactive intermediates during its oxidation/reduction reactions as evidenced from NMR studies. Highlights MeImSe, a derivative of selenoneine protects DNA and lipid from radiation damage MeImSe scavenges all major short- and long-lived oxidants involved in radiation toxicity Rate constants of MeImSe for ROS scavenging determined by pulse radiolysis technique First organoselenium compound reported to scavenge nitrogen dioxide radical MeImSe exhibits GPx-like activity through reductive pathway

Oral magnesium prevents acetaminophen-induced acute liver injury by modulating microbial metabolism

Acetaminophen overuse is a common cause of acute liver failure (ALF). During ALF, toxins are metabolized by enzymes such as CYP2E1 and transformed into reactive species, leading to oxidative damage and liver failure. Here, we found that oral magnesium (Mg) alleviated acetaminophen-induced ALF through metabolic changes in gut microbiota that inhibit CYP2E1. The gut microbiota from Mg-supplemented humans prevented acetaminophen-induced ALF in mice. Mg exposure modulated Bifidobacterium metabolism and enriched indole-3-carboxylic acid (I3C) levels. Formate C-acetyltransferase (pflB) was identified as a key Bifidobacterium enzyme involved in I3C generation. Accordingly, a Bifidobacterium pflB knockout showed diminished I3C generation and reduced the beneficial effects of Mg. Conversely, treatment with I3C or an engineered bacteria overexpressing Bifidobacterium pflB protected against ALF. Mechanistically, I3C bound and inactivated CYP2E1, thus suppressing formation of harmful reactive intermediates and diminishing hepatocyte oxidative damage. These findings highlight how interactions between Mg and gut microbiota may help combat ALF.

Amide-assisted synthesis of TS-1 zeolites with active Ti(OH2)2(OH)2(OSi)2 sites toward efficient oxidative desulfurization

Aiming to promote the activity of TS-1 zeolite in catalytic oxidative desulfurization (ODS), a general amide-assisted strategy was proposed to synthesize hierarchical TS-1 zeolite with rich and homogeneously distributed Ti(OH2)2(OH)2(OSi)2 species. Strong interactions between acrylamide (AM) and Si/Ti as well as self-polymerization of AM in synthetic gels change the zeolite formation process, thus to effectively construct Ti(OH2)2(OH)2(OSi)2, promote Ti evenly distribution and form micro-mesopore structure. The activity of Ti(OH2)2(OH)2(OSi)2 was evaluated by ODS of refractory sulfur-containing compounds. The advantages of Ti(OH2)2(OH)2(OSi)2 over TiO4 in substrate adsorption and reactive intermediate formation for ODS were further proved by theoretical calculations. By adjusting AM amount to optimize the Ti(OH2)2(OH)2(OSi)2 content and distribution, the obtained catalyst achieves 134.8 h-1 of turnover frequency and 100 % DBT removal at ten minutes, and maintains > 92 % removal after seven cycles at 333 K. This facile active-site construction strategy is promising to be extended to other heteroatom-containing zeolite catalysts.

A Tandem Reaction in the Synthesis of New 4,8‐Disubstituted‐pyrimido[5,4‐d]pyrimidine Derivatives

AbstractPyrimido[5,4‐d]pyrimidines are biologically important compounds with diverse activity depending on the substituent groups around the heterocycle. The 3,4‐dihydropyrimido[5,4‐d]pyrimidines are efficiently converted to the aromatic derivatives by Dimroth rearrangement promoted by reaction with piperidine, in a very slow process. Subsequently, the aromatic derivatives are converted to new 4,8‐disubstituted‐pyrimido[5,4‐d]pyrimidine derivatives by reaction with aldehydes in an acidic medium. The 4,8‐disubstituted‐pyrimido[5,4‐d]pyrimidines are also obtained much more efficiently by a tandem reaction between the 3,4‐dihydropyrimido[5,4‐d]pyrimidines, piperidine and a variety of aldehydes. The cascade reaction approach has a broad application since phenyl, haloaryl, alkoxy‐aryl, hydroxy‐aryl, and heteroaryl aldehydes are compatible with the reaction conditions. The reactions were studied by 1H NMR. These studies support the reaction mechanisms proposals. The tandem approach involves the formation of ionic reactive intermediates that allows explain this approach's efficiency.

Solution combusted ultrathin Co3O4/CoO heterophase electrocatalyst for solar‐energy driven bifunctional water electrolysis

AbstractPotential low‐cost solution combustion synthesis of cobalt oxide (SCSCO: Co3O4/CoO) by using sugar as a fuel for H2 and O2 generation. Co3O4/CoO heterophase provided multiple functional sites and abundant interfaces between the components owing to synergistic effect. The sufficient adsorption sites in SCSCO6 favoured the formation of reactive intermediates which leads to extraordinary OER and HER process. The SCSCO6 exhibits η of 271 mV (102 mV dec−1) for OER and 174 mV (73 mV dec−1) for HER to achieve 10 mA cm−2 (without iR correction). TOF of SCSCO6 (OER: 0.0624 s−1/IrO2‐ 0.0185 s−1; HER: 0.0282 s−1/Pt ‐ 0.0843 s−1) was found to be higher than IrO2 and near to Pt, respectively. The SCSCO6 displays durability of 130 h with potential loss of 3.2 % (OER) and 3.0 % (HER). The disordered oxidation states and high surface area of SCSCO6 (BET ‐ 99 m2 g−1: ECSA ‐ 151.27 m2/g) facilitates the bifunctional activity. The fabricated water electrolyzer consist of SCSCO6//SCSCO6 affords 10 mA cm−2 @1.64 V and exhibits high stability (>130 h: 4.1 % potential loss). The solar‐to‐hydrogen electrolyser (SCSCO6//SCSCO6) afforded non‐stop evolution of H2 and O2 @1.63 V which can be recommended for low‐cost, large‐scale hydrogen production.

Reactive intermediates formation and bioactivation pathways of spebrutinib revealed by LC-MS/MS: In vitro and in silico metabolic study

Spebrutinib is a new Bruton tyrosine kinase inhibitor developed by Avila Therapeutics and Celgene. Spebrutinib (SPB) is currently in phase Ib clinical trials for the treatment of lymphoma in the United States. Preliminary in-silico studies were first performed to predict susceptible sites of metabolism, reactivity pathways and structural alerts for toxicities by StarDrop WhichP450™ module, Xenosite web predictor tool and DEREK software; respectively. SPB metabolites and adducts were characterized in vitro from rat liver microsomes (RLM) using LC-MS/MS. Formation of reactive intermediates was investigated using potassium cyanide (KCN), glutathione (GSH) and methoxylamine as trapping nucleophiles for the unstable and reactive iminium, iminoquinone and aldehyde intermediates, respectively, with the aim to produce stable adducts that can be detected and characterized using mass spectrometry. Fourteen phase I metabolites, four cyanide adducts, six GSH adducts and three methoxylamine adducts of SPB were identified and characterized. The proposed metabolic pathways involved in generation of phase I metabolites of SPB are oxidation, hydroxylation, o-dealkylation, epoxidation, defluorination and reduction. Several in vitro reactive intermediates were identified and characterized, the formation of which can aid in explaining the adverse drug reactions of SPB. Several iminium, 2-iminopyrimidin-5(2H)-one and aldehyde intermediates of SPB were revealed. Acrylamide is identified as a structural alert for toxicity by DEREK report and was found to be involved in the formation of several glycidamide and aldehyde reactive intermediates.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17β-estradiol: Formation and contribution of reactive intermediates

In this study, humic acid (HA) enhanced 17β-estradiol (17β-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17β-E2 was increased from (14.414 ± 0.315) × 10−3 min−1 to (122.677 ± 1.729) × 10−3 min−1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2−) were the dominant RIs for 17β-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 >1O2 > •O2−> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17β-E2 during the sonophotocatalytic process.

Investigation of Fenebrutinib Metabolism and Bioactivation Using MS3 Methodology in Ion Trap LC/MS.

Fenebrutinib is an orally available Bruton tyrosine kinase inhibitor. It is currently in multiple phase III clinical trials for the management of B-cell tumors and autoimmune disorders. Elementary in-silico studies were first performed to predict susceptible sites of metabolism and structural alerts for toxicities by StarDrop WhichP450™ module and DEREK software; respectively. Fenebrutinib metabolites and adducts were characterized in-vitro in rat liver microsomes (RLM) using MS3 method in Ion Trap LC-MS/MS. Formation of reactive and unstable intermediates was explored using potassium cyanide (KCN), glutathione (GSH) and methoxylamine as trapping nucleophiles to capture the transient and unstable iminium, 6-iminopyridin-3(6H)-one and aldehyde intermediates, respectively, to generate a stable adducts that can be investigated and analyzed using mass spectrometry. Ten phase I metabolites, four cyanide adducts, five GSH adducts and six methoxylamine adducts of fenebrutinib were identified. The proposed metabolic reactions involved in formation of these metabolites are hydroxylation, oxidation of primary alcohol to aldehyde, n-oxidation, and n-dealkylation. The mechanism of reactive intermediate formation of fenebrutinib can provide a justification of the cause of its adverse effects. Formation of iminium, iminoquinone and aldehyde intermediates of fenebrutinib was characterized. N-dealkylation followed by hydroxylation of the piperazine ring is proposed to cause the bioactivation to iminium intermediates captured by cyanide. Oxidation of the hydroxymethyl group on the pyridine moiety is proposed to cause the generation of reactive aldehyde intermediates captures by methoxylamine. N-dealkylation and hydroxylation of the pyridine ring is proposed to cause formation of iminoquinone reactive intermediates captured by glutathione. FBB and several phase I metabolites are bioactivated to fifteen reactive intermediates which might be the cause of adverse effects. In the future, drug discovery experiments utilizing this information could be performed, permitting the synthesis of new drugs with better safety profile. Overall, in silico software and in vitro metabolic incubation experiments were able to characterize the FBB metabolites and reactive intermediates using the multistep fragmentation capability of ion trap mass spectrometry.

Performance Enhancement of Polymer Electrolyte Membrane Fuel Cells with Cerium Oxide Interlayers Prepared by Aerosol-Assisted Chemical Vapor Deposition

In this study, the performance and durability of a Pt/CeOx catalyst membrane electrode assembly (MEA) fabricated by chemical vapor deposition and sputtering using aerosols were investigated for use in a polymer electrolyte membrane fuel cell (PEMFC). The cost burden of Pt-based catalysts and the degradation of performance and durability owing to corrosion of the carbon support under certain conditions limit the commercialization of PEMFCs. To solve these problems, the development of Pt alloy catalysts (Pt–Co, Pt–Ni, and Pt–Fe), Pt-based core–shell catalysts (Pt–TiO2 and Pt–CeO2), Pt bimetallic catalysts (Pt–Pd, Pt–Ru, and Pt–Sn), and Pt-based nanocomposites (Pt/graphene and Pt/carbon nanotubes) is being actively researched. Inserting a CeOx interlayer between Pt and carbon has three advantages: (i) oxygen supply to Pt due to CeOx interlayer’s ability to store oxygen improves catalyst utilization, (ii) improves the dispersibility of Pt, and (iii) solves the problem of performance and durability degradation by preventing the formation of reactive intermediates. For the deposition of ceria, the aerosol-assisted chemical vapor deposition process, which is performed at atmospheric pressure and can be uniformly deposited over a wide area with spray-based precursor delivery characteristics, was applied. The performance and electrochemical surface area of the Pt/CeOx MEA were determined using I–V measurements and cyclic voltammetry, and the durability of the Pt/CeOx MEA was analyzed using electrochemical impedance spectroscopy and an accelerated degradation test. As a result, when the Pt/CeOx on the gas diffusion layer (GDL) MEA was used, the performance improved by 46% compared to that of Pt on the GDL.

Using citric acid to suppress lignin repolymerization in the organosolv pretreatment of corn stalk

The esterification reactions that occur between citric acid (CA) and lignin on hydroxyl groups of side chains can inhibit the formation of reactive intermediates in acid-catalyzed pretreatments. The effects of CA on dilute hydrochloric acid (1.0%) pretreatments of corn stalk in hydrated 1,4–dioxane were investigated with sodium hypophosphite (0.5%) as the catalyst at 95 °C for 3.5 h. The resulting cellulose recovery (62.5–80.9%) and lignin removal (72.5–85.0%) after adding CA were significantly higher than those in the pretreatment without CA. Water content influenced pretreatment and delignification when CA was added into the treatment systems. The highest yield of total reducing sugar (97.1%) was achieved during the enzymatic hydrolysis of cellulose-rich materials obtained from the pretreatment with 11.4% water content. Meanwhile, β–O–4′ in the extracted lignin increased from 22.4/100Ar to 41.2/100Ar with increasing water content from 11.4% to 25.9%. These findings implied that CA as a stabilization agent could inhibit the repolymerization of degraded lignin fragments due to the esterification between CA and lignin and then improved the enzymatic saccharification of cellulose.

Electronic structure modulation coupling with interface effect for great improving water electrolysis by multiple dimensional S doped MnCo2O4 nanorods/N doped C nanosheets hybrids

The design of highly active, low cost and earth-abundant electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media are of great importance in practical water splitting. In this work, multiple dimensional hybrid catalysts were simply constructed by one-dimensional (1D) S-doped MnCo2O4 nanorods assembled by 0D nanoparticles composited with 2D N-doped carbon nanosheets derived from 3D chitosan carbon aerogel. Both the experimental and theoretical results confirmed that partially substitute of high-electronegative O with low-electronegative S can effectively regulate electron density of Co and Mn cations and strength of metal-O bonds, consequently, optimize the adsorption activity of active sites to reactants and the formation of reactive intermediates, change the rate-determining step and lower its energy barrier. The combined N-doped carbon nanosheets and multiple dimensional structure provided interface effect, larger specific surface, exposed more active sites, improved the conductivity and hydrophily of the hybrids. All the above superiority endowed the hybrid catalyst greatly improved electrocatalytic activities in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting with low overpotential of 180 and 258 mV for HER and OER, and 1.57 V of cell voltage for water electrolysis at 10 mA/cm2, respectively. This work provided a vivid example for rational fabricating high-performance bifunctional electrocatalysts by combined strategies of electronic structure modulation and morphology design.

Mechanistic Studies of Iron-PyBOX-Catalyzed Olefin Amino-Oxygenation with Functionalized Hydroxylamines.

Iron-catalyzed amino-oxygenation of olefins often uses discrete ligands to increase reactivity and broaden substrate scope. This work is focused on examining ligand effects on reactivity and in situ iron speciation in a system which utilizes a bisoxazoline ligand. Freeze-trapped 57Fe Mössbauer and EPR spectroscopies as well as SC-XRD experiments were utilized to isolate and identify the species formed during the catalytic reaction of amino-oxygenation of olefins with functionalized hydroxylamines, as well as in the precatalytic mixture of iron salt and ligand. Experiments revealed significant influence of ligand and solvent on the speciation in the precatalytic mixture which led to the formation of different species which had significant influence on the reactivity. In situ experiments showed no evidence for the formation of an Fe(IV)-nitrene intermediate, and the isolation of a reactive intermediate was unsuccessful, suggesting that the use of the PyBOX ligand led to the formation of more reactive intermediates than observed in the previously studied system, preventing direct detection of intermediate species. However, isolation of the seven coordinate Fe(III) species with three carboxylate units of the hydroxylamine and spin-trap EPR experiments suggest formation of a species with unpaired electron density on the hydroxylamine nitrogen, which is in accordance with formation of a potential iron iminyl radical species, as recently proposed in literature. An observed increase in yield when substrates devoid of C-H bonds as well as isolation of a ring-closed dead-end species with substrates containing these bonds suggests the identity of the functionalized hydroxylamine can dictate the reactivity observed in these reactions.