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1.
Nature ; 2021 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-34823256

RESUMO

During the current SARS-CoV-2 pandemic, a variety of mutations have accumulated in the viral genome, and currently, four variants of concern (VOCs) are considered potentially hazardous to human society1. The recently emerged B.1.617.2/Delta VOC is closely associated with the COVID-19 surge that occurred in India in the spring of 20212. However, its virological properties remain unclear. Here, we show that the B.1.617.2/Delta variant is highly fusogenic and notably more pathogenic than prototypic SARS-CoV-2 in infected hamsters. The P681R mutation in the spike protein, which is highly conserved in this lineage, facilitates spike protein cleavage and enhances viral fusogenicity. Moreover, we demonstrate that the P681R-bearing virus exhibits higher pathogenicity than its parental virus. Our data suggest that the P681R mutation is a hallmark of the virological phenotype of the B.1.617.2/Delta variant and is associated with enhanced pathogenicity.

2.
Chem Sci ; 12(13): 4940-4948, 2021 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-34163741

RESUMO

Loading Ag and Co dual cocatalysts on Al-doped SrTiO3 (AgCo/Al-SrTiO3) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H2O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO3 (52.7 µmol h-1) was a dozen times higher than that over Ag/Al-SrTiO3 (4.7 µmol h-1). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO3 was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 µmol h-1). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O2, respectively, on the Al-SrTiO3 surface.

3.
Inorg Chem ; 60(13): 9359-9367, 2021 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-34137588

RESUMO

Relationship between the local structures of middle lanthanoid elements (Ln; Eu, Gd, Tb, and Dy) in their complex oxides and the characteristic features of the L1-edge and L3-edge X-ray absorption near edge structure (XANES) was investigated. There was a significant correlation between the pre-edge peak areas of the Ln L1-edge or the full widths at half maximum of the white line of the Ln L3-edge XANES spectra and the abstract physical indexes defined by bond angles formed by the middle Ln elements and the two adjacent oxygen atoms, which act as indicators of local configurational disorder of the target element. Theoretical simulation based on multiple scattering theory revealed that the pre-edge peak in the Ln L1-edge XANES spectra originates due to the p-d hybridization that occurs above the Fermi energy. This systematic survey demonstrated a universal method to estimate the local structure of the middle Ln elements by means of XANES spectroscopy.

4.
Artigo em Inglês | MEDLINE | ID: mdl-34133123

RESUMO

Pt-based catalysts are commonly employed as NOx-trapping catalysts for automobiles, while perovskite oxides have received attention as Pt-free NOx-trapping catalysts. However, the NOx storage performance of perovskite catalysts is significantly inferior at low temperatures and with coexisting gases such as H2O, CO2, and SO2. This study demonstrates that NOx storage reactions proceed over redox site (Mn, Fe, and Co)-doped SrTiO3 perovskites. Among the examined catalysts, Mn-doped SrTiO3 exhibited the highest NOx storage capacity (NSC) and showed a high NSC even at a low temperature of 323 K. Moreover, the high NOx storage performance of Mn-doped SrTiO3 was retained in the presence of poisoning gases (H2O, CO2, and SO2). NO oxidation experiments revealed that the NSC of Co-doped SrTiO3 was dependent on the NO oxidation activity from NO to NO2 via lattice oxygen, which resulted in an inferior NSC at low temperatures. On the other hand, Mn-doped SrTiO3 successfully adsorbed NO molecules onto its surface at 323 K without the NO oxidation process using lattice oxygens. This unique adsorption behavior of Mn-doped SrTiO3 was concluded to be responsible for the high NSC in the presence of poisoning gases.

5.
ACS Appl Mater Interfaces ; 13(21): 24615-24623, 2021 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-34013728

RESUMO

We evaluated the catalytic performance of the Rh-Fe/Al2O3 catalyst during a three-way catalytic reaction and found, by chance, that a part of Fe species was dissolved into the γ-Al2O3 support and worked as an oxygen storage material, which adjusts the oxygen concentration around the catalytically active sites to a suitable level for three-way catalysis. In this study, we demonstrated that the Fe-doped γ-Al2O3 can reversibly store and release oxygen by the redox of Fe2+/Fe3+ at the tetrahedral (Td) site of the spinel structure without its structure deformation. The finding that a spinel-structured metal oxide, Fe-doped γ-Al2O3, could work as an oxygen storage material suggested a new opportunity for the development of oxygen storage materials without rare metals.

6.
Angew Chem Int Ed Engl ; 60(26): 14420-14428, 2021 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-33729669

RESUMO

Electronic metal-support interactions (EMSI) describe the electron flow between metal sites and a metal oxide support. It is generally used to follow the mechanism of redox reactions. In this study of CuO-CeO2 redox, an additional flow of electrons from metallic Cu to surface carbon species is observed via a combination of operando X-ray absorption spectroscopy, synchrotron X-ray powder diffraction, near ambient pressure near edge X-ray absorption fine structure spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. An electronic metal-support-carbon interaction (EMSCI) is proposed to explain the reaction pathway of CO oxidation. The EMSCI provides a complete picture of the mass and electron flow, which will help predict and improve the catalytic performance in the selective activation of CO2 , carbonate, or carbonyl species in C1 chemistry.

7.
Viruses ; 13(2)2021 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-33573054

RESUMO

Recently, we experienced an outbreak of acute hepatitis A virus (HAV) infection between 2018 and 2020. Herein, we describe this male-dominant HAV infection outbreak observed among non-human immunodeficiency virus (HIV)-infected persons in the northern part of Tokyo, Japan. Clinical information was collected from patient interviews and from medical record descriptions. In the present study, 21 patients were retrospectively analyzed. A total of 90.4 and 33.3% of patients were males, and men who have sex with men (MSM), respectively. The total bilirubin levels and platelet counts tended to be lower in the MSM group than in the non-MSM group. C-reactive protein (CRP) levels tended to be higher in acute liver failure (ALF) patients than in non-ALF patients. Prolonged cholestasis was observed in one patient (4.8%). We also found that 18 HAV isolates belonged to HAV subgenotype IA/subgroup 13 (S13), which clustered with the HAV isolate (KX151459) that was derived from an outbreak of HAV infection among MSM in Taiwan in 2015. Our results suggest that the application of antivirals against HAV, as well as HAV vaccines, would be useful for the treatment and prevention of severe HAV infection.


Assuntos
Surtos de Doenças , Hepatite A/epidemiologia , Adulto , Feminino , Genótipo , Hepatite A/virologia , Vírus da Hepatite A/classificação , Vírus da Hepatite A/genética , Vírus da Hepatite A/isolamento & purificação , Homossexualidade Masculina , Humanos , Tempo de Internação , Falência Hepática Aguda/epidemiologia , Falência Hepática Aguda/virologia , Masculino , Pessoa de Meia-Idade , Filogenia , Estudos Retrospectivos , Fatores de Risco , Minorias Sexuais e de Gênero , Tóquio/epidemiologia
8.
Angew Chem Int Ed Engl ; 60(3): 1212-1219, 2021 01 18.
Artigo em Inglês | MEDLINE | ID: mdl-32978789

RESUMO

RuII compounds are widely used in catalysis, photocatalysis, and medical applications. They are usually obtained in a reductive environment as molecular O2 can oxidize RuII to RuIII and RuIV . Here we report the design, identification and evolution of an air-stable surface [bipy-RuII (CO)2 Cl2 ] site that is covalently mounted onto a polyphenylene framework. Such a RuII site was obtained by reduction of [bipy-RuIII Cl4 ]- with simultaneous ligand exchange from Cl- to CO. This structural evolution was witnessed by a combination of in situ X-ray and infrared spectroscopy studies. The [bipy-RuII (CO)2 Cl2 ] site enables oxidation of CO with a turnover frequency of 0.73×10-2  s-1 at 462 K, while the RuIII site is completely inert. This work contributes to the study of structure-activity relationship by demonstrating a practical control over both geometric and electronic structures of single-site catalysts at molecular level.

9.
ACS Appl Mater Interfaces ; 12(50): 55994-56003, 2020 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-33287543

RESUMO

It is important to understand the reduction processes of mixed metal oxides or metal oxide interfaces in three-way catalytic reactions toward replacing the currently used high-cost Pt group metal catalysts. The redox behavior of simple Ni-Cu alloy catalysts, which exhibit high catalytic activity and durability during a three-way catalytic reaction, was studied by operando X-ray absorption spectroscopy (XAS). The operando XAS analyses revealed that Ni-Cu species changed from the NiO-Cu2O to Ni-Cu alloy and vice versa under reductive and oxidative conditions, respectively. The real-time monitoring of the oxidation states of Ni and Cu species indicated that the Cu species assisted the reduction of Ni species, in agreement with the density functional theory-based study of NiO reduction by carbon monoxide in the presence of metallic Cu nanoparticles.

10.
Phys Chem Chem Phys ; 22(42): 24181-24190, 2020 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-33000816

RESUMO

Improvement of the low-temperature activity for NO oxidation catalysts is a crucial issue to improve the NOx storage performance in automotive catalysts. We have recently reported that the lattice oxygen species in SrFeO3-δ (SFO) are reactive in the oxidation of NO to NO2 at low temperatures. The oxidation of NO using lattice oxygen species is a powerful means to oxidize NO in such kinetically restricted temperature regions. This paper shows that Fe-site substitution of SFO with Mn or Co improves the properties of lattice oxygen such as the temperature and amount of oxygen release/storage, resulting in the enhancement of the activity for NO oxidation in a low-temperature range. In particular, NO oxidation on SrFe0.8Mn0.2O3-δ is found to proceed even at extremely low temperatures <423 K. From oxygen release/storage profiles obtained by temperature-programmed reactions, Co doping into SFO increases the amount of released oxygen owing to the reducibility of the Co species and promotes the phase transformation to the brownmillerite phase. On the other hand, Mn doping does not increase the oxygen release amount and suppresses the phase transformation. However, it significantly decreases the oxygen migration barrier of SFO. Substitution with Mn renders the structure of SFO more robust and maintains the perovskite structure after the release of oxygen. Thus, the oxygen release properties are strongly dependent on the crystal structure change before and after oxygen release from the perovskite structure, which has a significant effect on NO oxidation and the NOx storage performance.

11.
Angew Chem Int Ed Engl ; 59(45): 20183-20191, 2020 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-32770613

RESUMO

A CO2 -mediated hydrogen storage energy cycle is a promising way to implement a hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, sub-nanometer Pd-Mn clusters were encaged within silicalite-1 (S-1) zeolites by a ligand-protected method under direct hydrothermal conditions. The obtained zeolite-encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO2 hydrogenation into formate and formic acid (FA) dehydrogenation back to CO2 and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bimetallic components, the PdMn0.6 @S-1 catalyst afforded a formate generation rate of 2151 molformate molPd -1 h-1 at 353 K, and an initial turnover frequency of 6860 mol H 2 molPd -1 h-1 for CO-free FA decomposition at 333 K without any additive. Both values represent the top levels among state-of-the-art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite-encaged metallic catalysts hold great promise to realize CO2 -mediated hydrogen energy cycles in the future that feature fast charge and release kinetics.

13.
Angew Chem Int Ed Engl ; 59(6): 2289-2293, 2020 02 03.
Artigo em Inglês | MEDLINE | ID: mdl-31773819

RESUMO

Chemical synthesis of amino acids directly from biomass feedstock is rare. Reported here is a one-step protocol to convert crude glycerol, from the biodiesel industry, into 43 % alanine over a Ru1 Ni7 /MgO catalyst. The multifunctional catalytic system promotes glycerol conversion into lactic acid, and then into alanine. X-ray absorption spectroscopy and scanning transmission electron microscopy revealed the existence of bimetallic RuNi species, whereas density-functional theory calculations suggested Ni-doped Ru substantially decreased the Ea of C-H bond dissociation of lactate alkoxide to form pyruvate, which is the rate-determining step. The catalytic route established in this work creates new opportunities for glycerol utilization and enriches the substrate scope of renewable feedstock to access value-added amino acids.


Assuntos
Alanina/biossíntese , Glicerol/metabolismo , Amônia/química , Biocombustíveis , Catálise , Complexos de Coordenação/química , Teoria da Densidade Funcional , Glicerol/química , Ácido Láctico/química , Níquel/química , Rutênio/química , Espectroscopia por Absorção de Raios X
14.
ACS Appl Mater Interfaces ; 11(41): 37875-37884, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31550116

RESUMO

Sr1.6K0.37Na1.43Ta5O15, which belongs to the Na-substituted Sr2KTa5O15 series of compounds with a tetragonal tungsten bronze structure, was fabricated using a flux mixture of KCl and NaCl (KCl/NaCl molar ratio = 55:45). It exhibited higher CO formation rate (94.6 µmol h-1), better selectivity for CO evolution (85.5%), and better stability of the photocatalytic activity than those of bare Sr2KTa5O15 and other Na-substituted Sr2KTa5O15 samples synthesized from flux mixtures with different KCl/NaCl ratios. X-ray photoelectron spectroscopic studies revealed that the surface atomic Sr/Ta ratio of Sr1.6K0.37Na1.43Ta5O15 was larger than that of Sr2KTa5O15. To clarify the factor responsible for the improvement in the photocatalytic activity facilitated by Na substitution, as well as to elucidate the reaction mechanism, the surface species were characterized by in situ Fourier transform infrared spectroscopy. It was observed that the bicarbonate species (HCO3-) adsorbed on the active Sr sites of Sr1.6K0.37Na1.43Ta5O15 was reduced to CO via the formate species during photoirradiation. The plot of the CO formation rate vs. the surface atomic Sr/Ta ratio for tetragonal tungsten bronze-type Sr-K-Ta-O complex oxides had the summit, indicating that Sr atoms on the surface enhance the photocatalytic activity, while an excessive amount of Sr on the surface leads to the decrease in the photocatalytic activity. Hence, it can be concluded that while the presence of Sr on the surface has a determining effect on the adsorption of CO2 and eventually on the photocatalytic activity, excess Sr on the surface that exists as SrCO3 or Sr2Ta2O7 suppresses the photocatalytic activity. Thus, Sr1.6K0.37Na1.43Ta5O15 showed higher CO formation rate than Sr2KTa5O15 did.

15.
ACS Appl Mater Interfaces ; 11(30): 26985-26993, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31262168

RESUMO

The development of NOx-trapping catalysts for automobiles is highly desired to meet the current strict exhaust emission regulations. This study demonstrates that NOx oxidation and storage reactions proceed over Pt-free Sr3Fe2O7-δ with a Ruddlesden-Popper-type layered perovskite structure. Two types of Sr-Fe perovskite with oxygen storage capacity, namely, SrFeO3-δ and Sr3Fe2O7-δ, are studied as NOx-trapping catalysts. Sr3Fe2O7-δ shows higher NOx storage capacity than SrFeO3-δ; its activity is comparable to that of Pt/Ba/Al2O3 calcined at 1273 K. NOx temperature-programmed desorption and diffuse reflectance infrared Fourier transform experiments confirm the superior NOx-trapping ability of Sr3Fe2O7-δ over SrFeO3-δ. In addition, NO temperature-programmed reactions and O2 temperature-programmed desorption experiments reveal that these catalysts operate through a novel NO oxidation mechanism involving the consumption of their lattice oxygens and topotactic structural changes at a temperature of around 350-400 K. The reduction performance of trapped NOx on Pd-modified Sr-Fe perovskites is investigated by lean-rich cycle experiments using H2 as the reductant. Pd/Sr3Fe2O7-δ shows significantly high NOx removal efficiency over the entirety of each lean-rich period. Modifying Sr3Fe2O7-δ with Pd is also effective for NOx storage in the presence of H2O and CO2 and the regeneration of the catalyst following SOx sorption. Sr3Fe2O7-δ, with both NOx adsorption and NO oxidation capabilities, acts as a Pt-free NOx-trapping catalyst, exhibiting both high NOx storage capacity and high thermal tolerance.

16.
Phys Chem Chem Phys ; 21(35): 18816-18822, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31187809

RESUMO

Ni-Cu alloy supported on γ-Al2O3 catalysts prepared by high-temperature hydrogen reduction exhibit high catalytic activity and durability for a three-way catalytic reaction under both oxidative and reductive conditions because of their self-regenerating feature. DFT calculations showed that Ni-oxide was reduced to Ni metal by CO in the presence of Cu metal because of the Ni-Cu alloy effect but was not in the absence of Cu metal.

17.
J Am Chem Soc ; 141(20): 8185-8197, 2019 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-31030515

RESUMO

Unlike nanostructured metal catalysts, supported single-atom catalysts (SACs) contain only atomically dispersed metal atoms, hinting at much more pronounced metal-support effects. Herein, we take a series of polyoxometalate-supported Pt catalysts as examples to quantitatively investigate the stability of Pt atoms on oxide supports and how the Pt-support interaction influences the catalytic performance. For this entire series, we show that the Pt atoms prefer to stay at a 4-fold hollow site of one polyoxometalate molecule and that the least adsorption energy to obtain sintering-resistant Pt SACs is 5.50 eV, which exactly matches the cohesive energy of bulk Pt metal. Further, we compared their catalytic performance in several hydrogenation reactions and simulated the reaction pathways of propene hydrogenation by density functional theory (DFT) calculations. Both experimental and theoretical approaches suggest that despite the Pt1-support interactions being different, the reaction pathways of various Pt1-polyoxometalate catalysts are very similar and their effective reaction barriers are close to each other and as low as 24 kJ/mol, indicating the possibility of obtaining SACs with improved stability without compromising activity. DFT calculations show that all reaction elementary steps take place only on the Pt atom without involving neighboring O atoms and that hydrogenation proceeds from the molecularly adsorbed H2 species. Pt SACs give a weaker H2 adsorption energy than Pt clusters or surfaces, resulting in small adsorption equilibrium constants and small apparent activation barriers, which agree between experiment and theory.

18.
Nat Commun ; 10(1): 1330, 2019 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-30902990

RESUMO

Single-atom catalysts have recently been applied in many applications such as CO oxidation. Experimental in situ investigations into this reaction, however, are limited. Hereby, we present a suite of operando/in situ spectroscopic experiments for structurally well-defined atomically dispersed Rh on phosphotungstic acid during CO oxidation. The identification of several key intermediates and the steady-state catalyst structure indicate that the reactions follow an unconventional Mars-van Krevelen mechanism and that the activation of O2 is rate-limiting. In situ XPS confirms the contribution of the heteropoly acid support while in situ DRIFT spectroscopy consolidates the oxidation state and CO adsorption of Rh. As such, direct observation of three key components, i.e., metal center, support and substrate, is achieved, providing a clearer picture on CO oxidation on atomically dispersed Rh sites. The obtained information are used to engineer structurally similar catalysts that exhibit T20 values up to 130 °C below the previously reported Rh1/NPTA.

19.
Chem Rec ; 19(7): 1420-1431, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30663225

RESUMO

This paper describes a systematic study of the spectra and local structures of lanthanide (Ln) L-edge XANES. We found that Ln L1 and L3 -edge XANES spectra exhibit characteristic features correlated to their local symmetry through experimental and theoretical simulations. We also propose a simple local structure index criterion for a combination of XANES study and theoretical simulation. Possible solutions of intrinsic problems such as low resolution of characteristic features in the Ln L-edge XANES and site distributions are also discussed.

20.
Chempluschem ; 84(5): 442, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31943895

RESUMO

Invited for this month's cover is the group of Dr. Katsutoshi Sato and Prof. Dr. Katsutoshi Nagaoka (Kyoto University) and collaborators at Oita and Kyushu Universities. The cover picture shows the proposed mechanism for automotive exhaust purification over a Pt-Co alloy nanoparticle catalyst with an extremely low Pt/Co molar ratio. In the catalyst, the isolated electron-rich Pt atoms are present on the surface of the nanoparticles and play an important role in NOx capture and activation, which are important elementary steps in exhaust purification. Read the full text of the article at 10.1002/cplu.201800542.

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