Abstract
Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, ...the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts.
Early detection and effective treatment of severe COVID-19 patients remain major challenges. Here, we performed proteomic and metabolomic profiling of sera from 46 COVID-19 and 53 control ...individuals. We then trained a machine learning model using proteomic and metabolomic measurements from a training cohort of 18 non-severe and 13 severe patients. The model was validated using 10 independent patients, 7 of which were correctly classified. Targeted proteomics and metabolomics assays were employed to further validate this molecular classifier in a second test cohort of 19 COVID-19 patients, leading to 16 correct assignments. We identified molecular changes in the sera of COVID-19 patients compared to other groups implicating dysregulation of macrophage, platelet degranulation, complement system pathways, and massive metabolic suppression. This study revealed characteristic protein and metabolite changes in the sera of severe COVID-19 patients, which might be used in selection of potential blood biomarkers for severity evaluation.
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•93 proteins show differential expression in severe COVID-19 patient sera•204 metabolites in COVID-19 patient sera correlate with disease severity•A model composed of 29 serum factors shows patient stratification potential•Pathway analysis highlights metabolic and immune dysregulation in COVID-19 patients
Proteomic and metabolomic analysis of COVID-19 sera identifies differentially expressed factors that correlate with disease severity and highlights dysregulation of multiple immune and metabolic components in clinically severe patients.
Microglia/macrophages are the major immune cells involved in the defence against brain damage. Their morphology and functional changes are correlated with the release of danger signals induced by ...stroke. These cells are normally responsible for clearing away dead neural cells and restoring neuronal functions. However, when excessively activated by the damage-associated molecular patterns following stroke, they can produce a large number of proinflammatory cytokines that can disrupt neural cells and the blood-brain barrier and influence neurogenesis. These effects indicate the important roles of microglia/macrophages in the pathophysiological processes of stroke. However, the modifiable and adaptable nature of microglia/macrophages may also be beneficial for brain repair and not just result in damage. These distinct roles may be attributed to the different microglia/macrophage phenotypes because the M1 population is mainly destructive, while the M2 population is neuroprotective. Additionally, different gene expression signature changes in microglia/macrophages have been found in diverse inflammatory milieus. These biofunctional features enable dual roles for microglia/macrophages in brain damage and repair. Currently, it is thought that the proper inflammatory milieu may provide a suitable microenvironment for neurogenesis; however, detailed mechanisms underlying the inflammatory responses that initiate or inhibit neurogenesis remain unknown. This review summarizes recent progress concerning the mechanisms involved in brain damage, repair and regeneration related to microglia/macrophage activation and phenotype transition after stroke. We also argue that future translational studies should be targeting multiple key regulating molecules to improve brain repair, which should be accompanied by the concept of a "therapeutic time window" for sequential therapies.
Celestial Berends-Giele current Tao, Yi-Xiao
The journal of high energy physics,
09/2023, Volume:
2023, Issue:
9
Journal Article
Peer reviewed
Open access
A
bstract
Celestial amplitude plays an important role in the understanding of holography. Computing celestial amplitudes by recursion can deepen our understanding of the structure of celestial ...amplitudes. As an important recursion method, the Berends-Giele (BG) currents on the celestial sphere are worth studying. In this paper, we study the celestial BG recursion and utilize this to calculate some typical examples. We also explore the OPE behavior of celestial BG currents. Moreover, we generalize the “sewing procedure” for BG currents to the celestial case.
Impacts of sudden stratospheric warming (SSW) on three severe cold events (C1–C3) over Northern Hemisphere in early 2021 were investigated using subseasonal‐to‐seasonal ensemble forecasts. The SSW ...was characterized by successive displacement and split of the stratospheric polar vortex (SPV). Ensemble‐based sensitivity analyses showed that C1 over Siberia and C2 over western Canada were more related to SPV variations at a lead time of 1–2 weeks than C3 over central U.S. Within ensemble forecasts, a more elongated SPV with higher geopotential height over northern Eurasia were conducive to C1, whereas a SPV with the more poleward retreat from displacement contributed to C2. The forecast accuracy of stratospheric heights over the sensitive region at 2 weeks lead was significantly correlated with the forecast skill of the tropospheric circulation pattern preceding C1, implying that prediction of specific cold weather events may be improved by a better forecast of key features in SPV variations.
Plain Language Summary
Unusually extreme cold events have frequently occurred during the boreal winter in recent decades. These cold air outbreaks at the surface can be profoundly influenced by variations in the stratospheric polar vortex (SPV) with a lead time of weeks. The winter of early 2021 was characterized by successive extreme cold events over Asia and North America, leading to huge societal impacts, such as the unprecedented power outages over central U.S. in mid‐February 2021. These cold events were accompanied by a weak SPV that had been successively displaced and then split. Based on real‐time ensemble forecasts, we show that weakening and stretching of the SPV contributed to the cold event over Siberia. By contrast, the return of the SPV from displacement favored the cold event over western Canada. The subsequent cold surge over central U.S. was more related to mid‐latitude tropospheric processes than stratospheric processes. The prediction of some extremely cold weather events may be significantly improved by more accurate forecasts of the key features of the evolution of the SPV with a lead time of about two weeks.
Key Points
Sudden stratospheric warming with a displaced‐to‐split polar vortex in early 2021 had significant influences on surface cold events
Cold event in Siberia (Canada) was related to weakening (poleward retreat between displacement and split) of stratospheric polar vortex
Accurate forecasts of stratospheric variations improved forecast of the tropospheric pattern preceding the cold event over Siberia
The development of efficient catalysts for the dehydrogenation of formic acid (FA) through molecular level control and precise regulation remains challenging. Herein, we report the newly developed ...complexes of iridium and ruthenium with nitrogen‐rich ligand for aqueous FA dehydrogenation. The Cp*Ir complex 1 (Cp*=cyclopentadienyl) and Ru(p‐cym) complex 2 (p‐cym=p‐Cymene) were synthesized and fully characterized. The single crystal structures of these complexes have a typical piano‐stool structure. A turnover frequency of 12468 h−1 was achieved for FA dehydrogenation at 90 °C by using complex 1 bearing 3,3’‐diamino‐5,5’‐bis(1H‐1,2,4‐triazole) (DABT). The effects of pH, temperature, concentration of formic acid and amount of catalyst on the reaction kinetics were studied in detail. Kinetic isotope effect (KIE) experiments and 1H NMR detection of reaction revealed that a plausible mechanism involves the decarboxylation of formate and the formation of H2. More importantly, the influence of H2O and H+ was involved in the rate‐determining step. This study demonstrated the effectiveness of nitrogen‐rich ligand for FA dehydrogenation, which would contribute to the development of new and effective hydrogen release systems.
The newly developed complexes of iridium and ruthenium with nitrogen‐rich ligand were reported for aqueous FA dehydrogenation. KIE experiments and 1H NMR detection revealed that a plausible mechanism involves the decarboxylation of formate and formation of H2. This study demonstrated the effectiveness of nitrogen‐rich ligand for FA dehydrogenation, which would contribute to the development of new and effective catalysts for hydrogen release systems.
Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as NH4(UO2)3(HTTDS)(H2O) (1), (UO2)4(HTTDS)2(HIM)6 (2, IM=imidazole), (UO2)4(TTDS)(H2O)2(Phen)2 (3, ...Phen=1,10‐phenanthroline), Zn(H2O)40.5(UO2)3(HTTDS)(H2O)4 (4), and {(UO2)2Zn(H2O)32(TTDS)} (5), {Zn(UO2)2(H2O)(Dib)0.5(HDib)(HTTDS)} (6, Dib=1,4‐di(1H‐imidazol‐1‐yl)benzene) and Na{(UO2)4Cu3(u3‐OH)(H2O)7(TTDS)2} (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5‐dicarboxyphenyl)silicon(H8TTDS). These UOFs have different 3D self‐assembled structures as a function of co‐ligands, structure‐directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO7 pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N‐donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to UO22+ units as co‐ligands. The second metal centers were introduced in the syntheses of 4–7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5−7). Interesting, in 7, a rare polyoxometalate Cu3(μ3‐OH)O7(O2CR)4 cluster was found in the structure. It acts as an inorganic building unit together with the dimer (UO2)2(O2CR)4 unit. Those uranyl carboxylates were sufficiently determined by single crystal X‐ray diffraction, and their topological structures and luminescence properties were analyzed in detail.
Seven 3D uranyl organic frameworks have been hydrothermally prepared using a rigid octadentate carboxylate linker. These UOFs have diverse 3D self‐assembled architectures as a function of pH, co‐ligands, structure‐directing agents and transition metals.
Metal-nitrogen-co-doped graphene has great potential for use as a high-efficiency catalyst in energy applications. In this paper, density functional theory (DFT) with the projector-augmented wave and ...generalized gradient approximation (PAW-GGA) method was used to explore the catalytic activity of M@Gra (M = Ni, Pd, Pt, and Ru) on different types of graphene for oxygen reduction reaction (ORR) applications. Both the direct hydrogenation and dissociative mechanism of O2 are used to evaluate the ORR performance, and the binding energy of the intermediates, rate-determining step, overpotential, and activation energy of metal-nitrogen-co-doped graphene are considered. The catalytic properties of 4Ru@Gra and 1Pt@Gra make them the best candidates for ORRs, as 4Ru@Gra and 1Pt@Gra exhibit a stronger interaction (ΔG *OH) with the nanosheets and excellent ORR catalytic performance compared to other compounds. Precious metals have a significant influence on reducing O2 and decreasing the reaction energy, and the strong interaction of *O may lead to a high overpotential for the ORR process. This demonstrates that these compounds can moderately bind with the ORR intermediates by tuning the relative free energy, resulting in the ORR intermediates binding neither too strongly nor too weakly, and this may lead to slow or fast kinetics. The 1Ni@Gra support has a higher activation energy for O2 dissociation of 0.74 eV as well as a small activation energy of 0.13 eV, and the rate-determining step is controlled by the binding of *OH. The ORR reduction pathway occurs via direct hydrogenation with four-electron reduction, and it was determined that the energy barrier was 0.35 eV for the *OOH form, which is lower than the energy barrier (0.74 eV) of the 2O* species produced from the O2 dissociation in 1Ni@Gra. This indicates that the direct hydrogenation pathway is preferred as the most favorable of the ORR mechanisms.
Biofilm infections can induce chronic inflammation and stall the normal orchestrated course of wound-healing cascades. Herein, pH-switchable antimicrobial hydrogel with nanofiber networks for biofilm ...eradication and rescuing stalled healing in chronic wounds is reported on the basis of the self-assembly of a designed octapeptide (IKFQFHFD) at neutral pH. This hydrogel is biocompatible and exhibits an acidic pH (pathological environment of infected chronic wounds)-switchable broad-spectrum antimicrobial effect via a mechanism involving cell wall and membrane disruption. The antimicrobial activity of hydrogel is derived from its acidic pH-dependent nanofiber network destabilization and activated release of IKFQFHFD, which is antimicrobial only at acidic pH due to the antimicrobial peptide-like molecular structure. In addition, supramolecular nanofiber networks loaded with drugs of cypate (photothermal agent) and proline (procollagen component) are further developed. In vitro experiments show that loaded drugs exhibit acidic pH (pH ∼ 5.5)-responsive release profiles, and synergistic biofilm eradication and subsequent healing cascade activation of cells proliferation are achieved on the basis of the supramolecular nanofiber networks. Remarkably, the nanofiber networks of hydrogel enable in vivo complete healing of MRSA biofilm infected wound in diabetic mice within 20 days, showing great potential as promising chronic wound dressings. The proposed synergistic strategy for eradicating biofilm and activating subsequent healing cascades may offer a powerful modality for the management of clinical chronic wounds.
Pyridyl‐pyrrole ligands usually mimic the polypyridine ligand, and their metal complexes are interesting due to their rich coordination chemistry and their use in molecular devices, biological ...therapeutics, and catalytic transformations. Cs‐symmetric HL3 ligand Br‐substituted on one of the pyridyl rings was designed and synthesized by Paal–Knorr pyrrole condensation. Ligand HL4 was synthesized by Suzuki‐coupling reaction between HL3 and 2‐thiopheneboronic acid in the presence of K2CO3 and Pd(PPh3)4 in degassed THF/H2O solution. Zinc complexes 1–5 with HL1 to HL5 were prepared by treatment of the corresponding pyridyl‐pyrrole ligands with diethylzinc in toluene at 0 °C in high yield. Ligand HL3 and all zinc complexes are characterized by X‐ray diffraction analysis. The structure of free HL3 is planar. The geometries at Zn in 1, 2, and 5 are compressed octahedra, while in 3 and 4 they are perhaps best described as being between cis‐divacant octahedral and distorted tetrahedral. In these zinc complexes, shorter Zn–Npyrrole 1.878(5)‐1.950(4) Å and longer Zn–Npyridine 2.108(5)‐2.509(3) Å, Zn‐Npendant pyridine 2.802(2)‐3.039(3) Å bond lengths are observed. Complexes 2 and 3 were used as catalysts to promote the coupling reaction of CO2 and various epoxides under solvent‐free conditions, and the catalytic mechanism was investigated by 1H NMR spectroscopy.
Zinc complexes with tridentate pyridyl‐pyrrole ligands were synthesized and fully characterized by NMR, IR, and UV/Vis spectroscopy and X‐ray diffraction. These zinc complexes were used as efficient catalyst for the coupling reaction of epoxides and CO2 to form cyclic carbonates with low catalyst loading at ambient temperature and normal pressure under solvent‐free conditions.
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