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At least 973 records · Page 54

Improvement in synthesis of (K 0.5 Na 0.5 )NbO 3 powders by Ge 4+ acceptor doping

In this study, the effects of doping with GeO 2 on the synthesis temperature, phase structure and morphology of (K 0.5 Na 0.5 )NbO 3 (KNN) ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900°C for 2 h. Introducing 0.5 mol.% GeO 2 into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800°C, which can be ascribed to the formation of the liquid phase during the synthesis.

36 MATERIALS SCIENCE↗

Exsolution of NiCo alloys over Ruddlesden-Popper perovskite for mild electrochemical synthesis of ammonia on protonic ceramic electrochemical cells

Ammonia synthesis from renewable energies on protonic ceramic electrochemical cells (PCECs) shows great potential. The primary challenges in ammonia synthesis on PCECs include sluggish catalytic activity, competition from the hydrogen evolution reaction, and unsatisfactory durability of the cathode, which is the active site of ammonia generation. Here, in this study, we report an elaborate design of the cathode with an intended formula of Pr 4 Ni 1.79 Co 1.2R u 0.01 O 10-δ , where NiCo alloy nanoparticles are exsolved from Ruddlesden-Popper perovskite substrates after the reduction in 5 % H 2 /Ar at 400 °C for 1 h, for electrocatalysis of the nitrogen reduction reaction to ammonia. The host material Pr 4 Ni 1.8 Co 1.2 O 10-δ with embeddable layered structure and stability was deliberately chosen to fix the Ru cation and maximize the catalytic activity of NiCo. Also, density functional theory calculations suggest that Ru doping provides an optimal balance between structural stability and redox activity, facilitating the controlled exsolution of NiCo nanoparticles and enhancing catalytic performance. As a result, the composite electrode with exsolved NiCo alloy and abundant oxygen vacancies on fuel-electrode-supported PCECs achieves a superior electrochemical activity towards ammonia synthesis: a peak ammonia formation rate of 27.84 μg h −1 cm −2 and excellent Faradaic efficiencies of 62.6 % at 350 °C.

30 DIRECT ENERGY CONVERSION↗

Impact of high altitude on the hepatic fatty acid oxidation and synthesis in rats

Highlights: • Acute exposure to high altitude (HA) increased hepatic fatty acid (FA) β-oxidation. • Acute exposure of rats to HA increased hepatic FA synthesis. • PPARα and AMPK can regulate the FA metabolism. • FA may be a key energy fuel and a compensation for CHO during acute exposure to HA. • The acute changes of FA metabolism may be a mechanism of acclimatization. - Abstract: High altitude (HA) affects energy metabolism. The impact of acute and chronic HA acclimatization on the major metabolic pathways is still controversial. In this study, we aimed to unveil the impact of HA on the key enzymes involved in the fatty acid (FA) metabolism in liver. Rats were exposed to an altitude of 4300 m for 30 days and the expressions of two key proteins involved in FA β-oxidation (carnitine palmitoyl transferase I, CPT-I; and peroxisome proliferator-activated receptor alpha, PPARα), two proteins involved in FA synthesis (acetyl CoA carboxylase-1, ACC-1; and AMP-activated protein kinase, AMPK), as well as the total ketone body in the liver and the plasma FFAs were examined. Rats without HA exposure were used as controls. We observed that the acute exposure of rats to HA (3 days) led to a significant increase in the expressions of CPT-I and PPARα and in the total hepatic ketone body. Longer exposure (15 days) caused a marked decrease in the expression of CPT-I and PPARα. By 30 days after HA exposure, the expression levels of CPT-I and PPARα returned to the control level. The hepatic ACC-1 level showed a significant increase in rats exposed to HA for 1 and 3 days. In contrast, the hepatic level of AMPK showed a significant reduction throughout the experimental period. Plasma FFA concentrations did not show any significant changes following HA exposure. Thus, increased hepatic FA oxidation and synthesis in the early phase of HA exposure may be among the important mechanisms for the rats to respond to the hypoxic stress in order to acclimatize themselves to the stressful environments.

60 APPLIED LIFE SCIENCES↗

Assessment of DNA synthesis in Islet-1{sup +} cells in the adult murine heart

Highlights: • Islet-1 was expressed in the adult heart. • Islet-1-positive cells did not proliferate in the adult heart. • Sinoatrial node cells did not proliferate in the adult heart. - Abstract: Rationale: Islet-1 positive (Islet-1{sup +}) cardiac progenitor cells give rise to the right ventricle, atria and outflow tract during murine cardiac development. In the adult heart Islet-1 expression is limited to parasympathetic neurons, few cardiomyocytes, smooth muscle cells, within the proximal aorta and pulmonary artery and sinoatrial node cells. Its role in these cells is unknown. Here we tested the hypothesis that Islet-1{sup +} cells retain proliferative activity and may therefore play a role in regenerating specialized regions in the heart. Methods and results: DNA synthesis was analyzed by the incorporation of tritiated thymidine ({sup 3}H-thymidine) in Isl-1-nLacZ mice, a transgenic model with an insertion of a nuclear beta-galactosidase in the Islet-1 locus. Mice received daily injections of {sup 3}H-thymidine for 5 days. DNA synthesis was visualized throughout the heart by dipping autoradiography of cryosections. Colocalization of an nLacZ-signal and silver grains would indicate DNA synthesis in Islet-1{sup +} cells. Whereas Islet{sup −} non-myocyte nuclei were regularly marked by accumulation of silver grains, colocalization with nLacZ-signals was not detected in >25,000 cells analyzed. Conclusions: Islet-1{sup +} cells are quiescent in the adult heart, suggesting that, under normal conditions, even pacemaking cells do not proliferate at higher rates than normal cardiac myocytes.

60 APPLIED LIFE SCIENCES↗

Inhibition of 3-phosphoglycerate dehydrogenase (PHGDH) by indole amides abrogates de novo serine synthesis in cancer cells

Cancer cells reprogram their metabolism to support growth and to mitigate cellular stressors. The serine synthesis pathway has been identified as a metabolic pathway frequently altered in cancers and there has been considerable interest in developing pharmacological agents to target this pathway. In this study, we report a series of indole amides that inhibit human 3-phosphoglycerate dehydrogenase (PHGDH), the enzyme that catalyzes the first committed step of the serine synthesis pathway. Using X-ray crystallography, we show that the indole amides bind the NAD + pocket of PHGDH. Through structure-based optimization we were able to develop compounds with low nanomolar affinities for PHGDH in an enzymatic IC50 assay. In cellular assays, the most potent compounds inhibited de novo serine synthesis with low micromolar to sub-micromolar activities and these compounds successfully abrogated the proliferation of cancer cells in serine free media. The indole amide series reported here represent an important improvement over previously published PHGDH inhibitors as they are markedly more potent and their mechanism of action is better defined.

3-phosphoglycerate dehydrogenase↗

Autonomous continuous flow reactor synthesis for scalable atom-precision

With new instrumentation design, robotics, and in-operando hyphenated analytical tool automation, the intelligent discovery of synthesis pathways is becoming feasible. It can potentially bridge the gap for the scale-up of new materials. In this article, we review current progress and describe a new system that uses an autonomous continuous flow chemistry framework to translate high-quality lead molecules and materials to quantities that can meet scalability demands. At the core is a continuous flow synthesis platform that can design its viable synthesis pathway to a particular molecule or material and then autonomously carry it out. This is realized by integrating: (1) A workflow/architecture for multimode chemical/materials characterization in-line. The in-line characterization modes are NMR, ESR, IR, Raman, UV-Vis, GC-MS, and HPLC, along with ex-situ modes for X-Ray and neutron scattering; (2) Integration for feedback/analysis/data storage of the control variables; (3) A core software stack that includes deep learning and reinforcement learning alongside quantum chemistry and molecular dynamics; (4) On-demand compute architectures that parse calculations to compute resources needed which include light-weight edge, mid-level edge (NVIDA DGX-2), and high-performance computing. We demonstrate preliminary results on how this autonomous reactor system can enhance our ability to deliver deuterated materials, copolymers, and site-substituted molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Effects of support and promoter on Ru catalyst activity in microwave-assisted ammonia synthesis

Microwave-assisted ammonia synthesis is a promising alternative to the energy-intensive Haber-Bosch process, specially at small- and medium-scale with renewable H 2 as resource. Here, we report that Cs promoted Ru/CeO 2 catalyst exhibits considerable activity at 533 K and ambient pressure. In this work, the combined theoretical and experimental approaches are adopted to optimize the electronic and geometric structures of Ru on the catalysts. Both DFT modeling work and structural characterization show that the strong interaction between Ru and CeO 2 results in the formation of highly dispersed Ru particles favoring ammonia synthesis. The higher electron donating ability of CeO 2 and lower electronegativity of Cs promoter result in higher electron density on Ru reducing the N≡N dissociation barrier. Finally, the work demonstrates the potential of microwave-assisted catalytic process in activating stable molecules for ammonia synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Laboratory synthesis of C3S on the kilogram scale

An optimized process using amorphous silica for efficient C{sub 3}S synthesis in the laboratory is reported: an estimated production capacity of ~2 kg C{sub 3}S within a week is possible. Amorphous silica (fumed silica) was used as raw material and inter-ground with CaCO{sub 3} and water for C{sub 3}S synthesis, the dried raw mixture has sufficient green strength to be self-supporting, which allows large cylinders to be placed in Platinum crucibles. The mineral composition of the sintered sample was quantified with X-ray powder diffraction using Rietveld analysis. C{sub 3}S with 3 S synthesis was dramatically enhanced because of 1) increased burnability of the raw mix due to amorphous silica and very fine CaCO{sub 3} particles after grinding, 2) simplified sample preparation process avoiding pressing discs and 3) improved capacities of the crucible and furnace.

36 MATERIALS SCIENCE↗

Toward a tunable fabrication of multifunctional iron-aluminum spinels via solution combustion synthesis: The effects of fuel, heating mode, and Fe:Al precursor ratio

The solid solutions of iron and aluminum spinels (hercynite, maghemite, magnetite, and γ-alumina) are promising materials for emerging technologies such as solar thermochemical fuel production and clean dehydrogenation of fossil fuels. Solution combustion synthesis (SCS) is an attractive technique for the fabrication of these materials as it has been used for synthesis of many nanoscale oxides. However, the design space of SCS is large with many synthesis parameters affecting the properties of the combustion products. To optimize the SCS of these materials, it is important to determine which parameters yield the best properties. In the present work, FeAlO x nanocomposites were obtained by SCS using iron nitrate and aluminum nitrate as precursors and oxidizers. Two fuels (citric acid and glycine), three Fe:Al molar ratios (1:2, 1:1, and 2:1) in the precursors, and three heating modes (hotplate, muffle furnace, and microwave oven) were compared. The products were characterized by X-ray diffraction analysis, scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, and laser diffraction particle size analysis. The fuel used had the largest impact on the combustion behavior and hence the material properties. The high combustion temperature of glycine allowed for the formation of an FeAl 2 O 4 /Fe 3 O 4 solid solution, while the lower-temperature combustion of citric acid yielded Al-substituted γ-Fe 2 O 3 with high amorphous content. With citric acid, the specific surface area as high as 200 m 2 /g was achieved. The effect of Fe:Al precursor ratio was clearly seen in variations of the lattice parameter, which demonstrated the ability to tune the phase composition. The heating mode had minor effects on material properties, but some differences were observed. As a result, all products obtained by SCS in a microwave oven had low specific surface areas compared to those obtained with a hotplate and a muffle furnace.

Alumina↗

Aqueous solution-based synthesis approach for carbon-disordered rocksalt composite cathode development and its limitations

Disordered rocksalt cathodes exhibit high specific capacities and high energy density; however, their low electronic conductivity poses a great challenge. Herein, we explored an aqueous-solution-based synthesis route that involves controlling the surface charges of Li 1.2 Mn 0.6 Ti 0.2 O 1.8 F 0.2 (LMTOF) to be anchored by a few-layer reduced graphene oxide (rGO) for the first time. The uniform rGO wrapping on the surface of the LMTOF particles is achieved by electrostatic attraction between the negatively charged rGO and positively charged LMTOF particles. Although the initial specific capacity of rGO-LMTOF composite increased by 58 % compared to the pristine LMTOF, the composite experienced a severe capacity fade over cycling. The synthesis process in an aqueous medium resulted in Li + /H + exchange and TM dissolution as evidenced from inductively coupled plasmon analysis and X-ray diffraction analysis. Therefore, this work suggests the search for alternative media or conditions for the synthesis of carbon-disordered rock salt cathode composite.

25 ENERGY STORAGE↗

Carbon isotope evidence for the substrates and mechanisms of prebiotic synthesis in the early solar system

Meteorites contain prebiotic, bio-relevant organic compounds including amino acids. Their syntheses could result from diverse sources and mechanisms and provide a window on the conditions and materials present in the early solar system. Here we constrain alanine’s synthetic history in the Murchison meteorite using site-specific 13 C/ 12 C measurements, reported relative to the VPDB standard. The δ 13 C VPDB values of -29 ± 10‰, 142 ± 20‰, and -36 ± 20‰ for the carboxyl, amine-bound, and methyl carbons, respectively, are consistent with Strecker synthesis of interstellar-medium-derived aldehydes, ammonia, and low-δ 13 C nebular or interstellar-medium-derived CN. We report experimentally measured isotope effects associated with Strecker synthesis, and use them to constrain the δ 13 C values of the alanine precursors, which we then use to construct a model that predicts the molecular-average δ 13 C values of 19 other organic compounds of prebiotic significance found in Murchison if they were made by our proposed synthetic network. Finally, most of these predictions agree with previous measurements, suggesting that interstellar-medium-derived aldehydes and nebular and/or pre-solar CN could have served as substrates for synthesis of a wide range of prebiotic compounds in the early solar system.

79 ASTRONOMY AND ASTROPHYSICS↗

Sol-gel synthesis of nano-scale, end-member albite feldspar (NaAlSi 3 O 8 )

Feldspars are the most abundant minerals in the Earth’s crust, and are also important constituents of many lunar rocks and some stony meteorites. Albite (NaAlSi 3 O 8 ) makes up the sodium corner of the feldspar ternary diagram (KAlSi 3 O 8 - NaAlSi 3 O 8 – CaAl 2 Si 2 O 8 ) and connects the alkali-feldspar and plagioclase binary joins. Synthesis of albite, however, has long been a problem, even at high temperatures and even at high pressures when dry. In fact, most successful syntheses require the combination of high-pressure, high-temperature, and hydrothermal environments. Here, this paper presents a sol–gel method of albite synthesis that requires hydrothermal processing followed by high-temperature recrystallization, but no high-pressure environments. This has the advantage of allowing synthesis of relatively large amounts of material and controlled elemental substitutions.

Albite↗

Towards green synthesis of Mn 4+ -doped fluoride phosphors: a review

Mn 4+ -doped fluoride phosphors are attractive for application in white solid-state lighting devices because their distinct red emission can improve the color rendering index, while the earth-abundance of Mn 4+ ions can reduce the production cost. However, highly hazardous HF is used as the fluoride source in the synthesis processes, which requires extreme caution. In this review, we introduce various methods for synthesizing Mn 4+ -doped fluoride phosphors, categorized according to the presence or absence of HF in the synthesis. The underlying optical properties of the phosphors fabricated using the various methods are discussed. In addition, in the discussion of each method, we emphasize on the key factors and strategies for developing phosphors. Finally, this review highlights perspectives on and future directions for the safe synthesis of Mn 4+ -doped fluoride phosphors to achieve solid-state lighting devices with superior optical properties.

36 MATERIALS SCIENCE↗

Modular Electrochemical Synthesis Using a Redox Reservoir Paired with Independent Half-Reactions

Electrochemical synthesis of high-value chemicals using renewable electricity could lead to sustainability advantages over conventional chemical manufacturing. The tight coupling between paired anodic and cathodic reactions in conventional electrochemical processes, however, constrains the products and their efficiencies. Here, we demonstrate a strategy to achieve modular electrochemical synthesis (ModES) of different chemicals by decoupling and pairing the oxidative and reductive half-reactions with a heterogeneous redox reservoir (RR). Specifically, sodium nickel hexacyanoferrate (NaNiHCF) can serve as a robust and reversible RR that enables the modular production of several strong oxidants, hydrogen peroxide (H 2 O2) and sodium persulfate (Na 2 S 2 O 8 ) or active chlorine, in separate RR-coupled electrochemical processes. The system’s excellent performance and operational stability is demonstrated by continuous operation over 100 cycles (~36 h) to produce H 2 O 2 and Na 2 S 2 O 8 with a high voltage efficiency. The concept presented here highlights the prospects for using RRs to enable efficient, modular, and on-demand electrochemical synthesis of valuable chemicals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Mild hydrothermal synthesis, crystal structure, photoluminescence properties and emission quantum yield of a new zirconium germanate with garnet-type structure

The mild hydrothermal synthesis, crystal structure, photoluminescence properties and emission quantum yield of a new sodium zirconium germanate are reported. This material and the method for its preparation represent for the first time a germanium garnet-type material synthesized at autogenous pressure and temperature at 230 Degree-Sign C. The crystal structure was determined by starting from the crystallographic parameters of a common garnet structure and it represents not only a new chemical combination of atoms but also combination of oxidation states in garnet structure. The framework consists of interconnected corner sharing GeO{sub 4} tetrahedra and ZrO{sub 6} octahedra which form small cavities that accommodate charge compensation Na{sup +} cations. In the course of synthesis the structure can be functionalized by in situ doping with different percentage of Eu{sup 3+} ions. This structural flexibility is used to explore the photoluminescent behavior of the active centers embedded in garnet-type host. The materials display the Eu{sup 3+5}D{sub 0}{yields}{sup 7}F{sub 0-4} transitions under excitation via intra-{sup 4}f{sub 6} excitation levels and through the O{sup 2-}{yields}Eu{sup 3+} ligand-to-metal charge transfer. A maximum {sup 5}D{sub 0} quantum efficiency and emission quantum yield values (ca. 0.28 and 0.04{+-}0.01, respectively) were found for the low Eu{sup 3+}-containing sample, suggesting the presence of concentration quenching effects at higher Eu{sup 3+}-content (5%). - Graphical abstract: Na{sub 3}Zr{sub 1.8}Ge{sub 3}O{sub 10}(OH){sub 2} prepared at mild hydrothermal conditions. Highlights: Black-Right-Pointing-Pointer New zirconogermanate with garnet-type structure. Black-Right-Pointing-Pointer Hydrothermal synthesis. Black-Right-Pointing-Pointer Crystal structure. Black-Right-Pointing-Pointer Photoluminescent properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Synthesis, crystal growth, structural and physicochemical studies of novel binary organic complex: 4-chloroaniline-3-hydroxy-4-methoxybenzaldehyde

The solid-state reaction, which is solvent free and green synthesis, has been adopted to explore the novel compound. The phase diagram of 4-chloroaniline (CA) and 3-hydroxy-4-methoxybenzaldehyde (HMB) system shows the formation of a novel 1:1 molecular complex, and two eutectics on either sides of complex. Thermochemical studies of complex and eutectics have been carried out for various properties such as heat of fusion, entropy of fusion, Jackson's parameters, interfacial energy and excess thermodynamic functions. The formation of molecular complex was also studied by IR, NMR, elemental analysis and UV-Vis absorption spectra. The single crystal of molecular complex was grown and its XRD study confirms the formation of complex and identifies the crystal structure and atomic packing of crystal of complex. Transmission spectra of grown crystal of the complex show 70% transmittance efficiency with cut off wavelength 412 nm. The band gap and refractive index of the crystal of complex have also been studied. - Graphical abstarct: Exploiting phase diagram study and solvent free synthesis a novel compound was synthesized and its single crystal growth, atomic packing, energy band gap and refractive index were studied. Highlights: Black-Right-Pointing-Pointer Novel organic complex was synthesized using Green or solvent free synthesis. Black-Right-Pointing-Pointer Phase diagram study provided the information to identify the worthy composition of novel complex. Black-Right-Pointing-Pointer The single crystal of the sufficient size was grown from the ethanol solution. Black-Right-Pointing-Pointer Crystal analysis suggested that the covalent bond is formed between the two parent compounds. Black-Right-Pointing-Pointer The transmittance of the crystal was found to be 70% and it was transparent from 412 to 850 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Synthesis of metastable rare-earth-iron mixed oxide with the hexagonal crystal structure

Rare-earth-iron mixed oxides with the rare earth/iron ratio=1 have either orthorhombic (o-REFeO{sub 3}) or hexagonal (h-REFeO{sub 3}) structure. h-REFeO{sub 3} is a metastable phase and the synthesis of h-REFeO{sub 3} is usually difficult. In this work, the crystallization process of the precursors obtained by co-precipitation and Pechini methods was investigated in detail to synthesize h-REFeO{sub 3}. It was found that the crystallization from amorphous to hexagonal phase and the phase transition from hexagonal to orthorhombic phase occurred at a similar temperature range for rare earth elements with small ionic radii (Er-Lu, Y). For both co-precipitation and Pechini methods, single-phase h-REFeO{sub 3} was obtained by shortening the heating time during calcination process. The hexagonal-to-orthorhombic phase transition took place by a nucleation growth mechanism and vermicular morphology of the thus-formed orthorhombic phase was observed. The hexagonal YbFeO{sub 3} had higher catalytic activity for C{sub 3}H{sub 8} combustion than orthorhombic YbFeO{sub 3}. - Graphical abstract: Although the synthesis of metastable hexagonal REFeO{sub 3} by the conventional method is difficult, we found that this phase is obtained by shortening the heating time of the precursor prepared by co-precipitation method. Highlights: Black-Right-Pointing-Pointer Synthesis of metastable REFeO{sub 3} with hexagonal structure by the co-precipitation method. Black-Right-Pointing-Pointer Hexagonal REFeO{sub 3} is obtained for the rare earth elements with small ionic radii. Black-Right-Pointing-Pointer Hexagonal-to-orthorhombic transformation of REFeO{sub 3}. Black-Right-Pointing-Pointer Catalytic activity of hexagonal REFeO{sub 3} for C{sub 3}H{sub 8} combustion.

36 MATERIALS SCIENCE↗

Synthesis and single crystal structure refinement of the one-layer hydrate of sodium brittle mica

A sodium brittle mica with the ideal composition [Na{sub 4}]{sup inter}[Mg{sub 6}]{sup oct}[Si{sub 4}Al{sub 4}]{sup tet}O{sub 20}F{sub 4} was synthesized via melt synthesis in a gas tight crucible. This mica is unusual inasmuch as the known mica structure holds only room for two interlayer cations per unit cell and inasmuch as it readily hydrates despite the high layer charge while ordinary micas and brittle micas are non-swelling. The crystal structure of one-layer hydrate sodium brittle mica was determined and refined from single crystal X-ray data. Interlayer cations reside at the center of the distorted hexagonal cavities and are coordinated by the three inner basal oxygen atoms. The coordination of the interlayer cation is completed by three interlayer water molecules residing at the center of the interlayer region. The relative position of adjacent 2:1-layers thus is fixed by these octahedrally coordinated interlayer cations. Pseudo-symmetry leads to extensive twinning. In total five twin operations generate the same environment for the interlayer species and are energetically degenerate. - Graphical abstract: The sodium brittle mica has been successfully synthesized by melt synthesis and the crystal structure of the one-layer hydrate of sodium brittle mica was determined from single crystal X-ray diffraction data. Highlights: Black-Right-Pointing-Pointer Melt synthesis yielded coarse grained sodium brittle mica which showed little disorder. Black-Right-Pointing-Pointer Sodium brittle mica hydrated completely to the state of one-layer hydrate. Black-Right-Pointing-Pointer Structure of one-layer hydrate of sodium brittle mica could therefore be determined and refined. Black-Right-Pointing-Pointer Arrangement of upper and lower tetrahedral sheet encompassing interlayer cation were clarified.

36 MATERIALS SCIENCE↗