In situ study of the evolution of NiFe nanocatalysts in reductive and oxidative environments upon thermal treatments.

The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H2 but with a change in structure and chemical ordering.

Coronary Artery Vasospasm Requiring Cardiac Autotransplantation Yet Controlled With Tobacco.

Coronary artery vasospasm is typically managed through avoidance of triggers and with symptomatic treatments with calcium channel blockers and long-acting nitrates. Here, we report a rare case of medically refractory coronary artery vasospasm associated with genetic predispositions that initially required cardiac autotransplantation followed paradoxically by nicotine for long-term symptomatic control. (Level of Difficulty: Intermediate.).

The Smoking Paradox: A Twist in the Tale of Vasospastic Angina.

Cigarette smoking is undoubtedly the single most important risk factor and trigger for vasospastic angina, a condition also known as Prinzmetal angina secondary to coronary artery vasospasm. Even decades before vasospastic angina was first described by Dr. Myron Prinzmetal and his colleagues in 1959, there had been suspected connections between smoking and coronary artery vasospasm in what was alluded to then as "tobacco angina." The intimate relationship between smoking and vasospastic angina has since been extensively researched and validated through decades of epidemiological and clinical studies. The fact that smoking would aggravate vasospastic angina comes with very little surprise, as it has been shown to adversely impact many of the disease processes thought to underlie vasospastic angina, including autonomic dysfunction, endothelial dysfunction, smooth muscle hyperactivity, and genetic susceptibility. While avoidance of smoking is the first logical step in managing smokers with vasospastic angina, there have been reported cases of vasospastic angina paradoxically triggered by smoking cessation or relieved with smoking resumption or nicotine replacement therapy. Thus, there appears to be patient-specific factors that could significantly alter the close connection between smoking and vasospastic angina, warranting further mechanistic investigations. In this review, we will examine this complicated relationship between smoking and vasospastic angina from multiple perspectives (historical, mechanistic, and clinical) and call attention to the "smoking paradox," which, with further elucidation, may provide additional insight into the complex mechanisms of VSA and potentially new strategies to treat medically refractory VSA, at least in selected individuals.

Mobility and versatility of the liquid bismuth promoter in the working iron catalysts for light olefin synthesis from syngas.

Liquid metals are a new emerging and rapidly growing class of materials and can be considered as efficient promoters and active phases for heterogeneous catalysts for sustainable processes. Because of low cost, high selectivity and flexibility, iron-based catalysts are the catalysts of choice for light olefin synthesis via Fischer-Tropsch reaction. Promotion of iron catalysts supported by carbon nanotubes with bismuth, which is liquid under the reaction conditions, results in a several fold increase in the reaction rate and in a much higher light olefin selectivity. In order to elucidate the spectacular enhancement of the catalytic performance, we conducted extensive in-depth characterization of the bismuth-promoted iron catalysts under the reacting gas and reaction temperatures by a combination of cutting-edge in situ techniques: in situ scanning transmission electron microscopy, near-atmospheric pressure X-ray photoelectron spectroscopy and in situ X-ray adsorption near edge structure. In situ scanning transmission electron microscopy conducted under atmospheric pressure of carbon monoxide at the temperature of catalyst activation showed iron sintering proceeding via the particle migration and coalescence mechanism. Catalyst activation in carbon monoxide and in syngas leads to liquid bismuth metallic species, which readily migrate over the catalyst surface with the formation of larger spherical bismuth droplets and iron-bismuth core-shell structures. In the working catalysts, during Fischer-Tropsch synthesis, metallic bismuth located at the interface of iron species undergoes continuous oxidation and reduction cycles, which facilitate carbon monoxide dissociation and result in the substantial increase in the reaction rate.

How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural.

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Isopropanol Dehydration on Amorphous Silica-Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo-Bridging Silanols.

The mechanism of isopropanol dehydration on amorphous silica-alumina (ASA) was unraveled by a combination of experimental kinetic measurements and periodic density functional theory (DFT) calculations. We show that pseudo-bridging silanols (PBS-Al) are the most likely active sites owing to the synergy between the Brønsted and Lewis acidic properties of these sites, which facilitates the activation of alcohol hydroxy groups as leaving groups. Isopropanol dehydration was used to specifically investigate these PBS-Al sites, whose density was estimated to be about 10-1  site nm-2 on the silica-doped alumina surface under investigation, by combining information from experiments and theoretical calculations.

Amphiphilic polyoxometalates for the controlled synthesis of hybrid polystyrene particles with surface reactivity.

Amphiphilic organo-polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50-100 nm polystyrene-POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM-mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.

Muscarinic excitation of parvalbumin-positive interneurons contributes to the severity of pilocarpine-induced seizures.

OBJECTIVE: A common rodent model in epilepsy research employs the muscarinic acetylcholine receptor (mAChR) agonist pilocarpine, yet the mechanisms underlying the induction of pilocarpine-induced seizures (PISs) remain unclear. Global M1 mAChR (M1 R) knockout mice are resistant to PISs, implying that M1 R activation disrupts excitation/inhibition balance. Parvalbumin-positive (PV) inhibitory neurons express M1 Rs, participate in cholinergically induced oscillations, and can enter a state of depolarization block (DB) during epileptiform activity. Here, we test the hypothesis that pilocarpine activation of M1 Rs expressed on PV cells contributes to PISs. METHODS: CA1 PV cells in PV-CRE mice were visualized with a floxed YFP or hM3Dq-mCherry adeno-associated virus, or by crossing PV-CRE mice with the RosaYFP reporter line. To eliminate M1 Rs from PV cells, we generated PV-M1 knockout (KO) mice by crossing PV-CRE and floxed M1 mice. Action potential (AP) frequency was monitored during application of pilocarpine (200 µm). In behavioral experiments, locomotion and seizure symptoms were recorded in wild-type (WT) or PV-M1 KO mice during PISs. RESULTS: Pilocarpine significantly increased AP frequency in CA1 PV cells into the gamma range. In the continued presence of pilocarpine, a subset (5/7) of PV cells progressed to DB, which was mimicked by hM3Dq activation of Gq-receptor signaling. Pilocarpine-induced depolarization, AP firing at gamma frequency, and progression to DB were prevented in CA1 PV cells of PV-M1 KO mice. Finally, compared to WT mice, PV-M1 KO mice were associated with reduced severity of PISs. SIGNIFICANCE: Pilocarpine can directly depolarize PV+ cells via M1 R activation, but a subset of these cells progress to DB. Our electrophysiologic and behavioral results suggest that this mechanism is active during PISs, contributing to a collapse of PV-mediated γ-aminobutyric acid (GABA)ergic inhibition, dysregulation of excitation/inhibition balance, and increased susceptibility to PISs.

EXAFS spectroscopy as a tool to probe metal-support interaction and surface molecular structures in oxide-supported catalysts: application to Al2O3-supported Ni(II) complexes and ZrO2-supported tungstates.

EXAFS spectroscopy is shown as a tool of prime importance to probe the formation of metal-oxygen-support bonds and unravel the surface molecular structure in oxide-supported systems through two examples: (i) a molecular metal complex (Ni(II) bisglycinate) characterized after impregnation and drying on Al2O3, and (ii) a tungsten oxide nanophase characterized after deposition on zirconia and high temperature thermal treatment (tungstated zirconia catalysts, i.e. WOx/ZrO2). Unlike other spectroscopic techniques, EXAFS at the Ni K-edge proves that a modest thermal activation during the impregnation step triggers the grafting of nickel(II) bisglycinate onto the support: Al next-nearest neighbours are detected when the impregnation is carried out at 60 degrees C instead of room temperature. Characterization of WOx/ZrO2 catalysts shows the presence of W next-nearest neighbours around tungsten, with W-W distances distinctive of edge-shared WO6 octahedra only. The WOx overlayer can thus be described as bidimensional, nanometric slabs of 4 to 5 WO6 units on each side. In these slabs, W octahedra are interconnected to form a more condensed structure than the one present in bulk WO3 (in which linkage through corners exists). Moreover, EXAFS results conclusively demonstrate that the WOx overlayer is directly anchored to the ZrO2 surface by means of W-O-Zr bonds with a W-Zr distance of 3.14 A.

Profiling of alpha-dicarbonyl content of commercial honeys from different botanical origins: identification of 3,4-dideoxyglucoson-3-ene (3,4-DGE) and related compounds.

The alpha-dicarbonyl contents of commercial honey samples from different botanical origins were analyzed as their quinoxaline derivatives using HPLC-DAD, HPLC-MS, HPLC-MS/MS, and HPLC-TOF-MS. A total of nine such compounds were detected, of which five were previously reported in honey (glucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, and 2,3-butanedione) and three were reported only from sources other than honey [3-deoxypentulose, 1,4-dideoxyhexulose, and 3,4-dideoxyglucoson-3-ene (3,4-DGE)]. An unknown alpha-dicarbonyl compound was also tentatively identified as an oxidation product of 3,4-DGE and was termed 3,4-dideoxyglucosone-3,5-diene (3,4-DGD). Only glyoxal (0.3-1.3 mg/kg), methylglyoxal (0.8-33 mg/kg), and 2,3-butanedione (0-4.3 mg/kg) were quantified in all honey samples. Furthermore, analysis of the alpha-dicarbonyl profile of various honey samples indicated that certain alpha-dicarbonyl compounds are found in specific honey samples in much higher proportions relative to the average amounts. The free radical scavenging activity as measured by DPPH method has also indicated that the darker honey samples such as buckwheat, manuka, blueberry, and eucalyptus had higher antioxidant properties compared to lighter-colored samples.

Transformations of gamma-alumina in aqueous suspensions 1. Alumina chemical weathering studied as a function of pH.

Hydration of gamma-Al2O3 is often reported to occur via the superficial transformation of the alumina surface into aluminum hydroxide-like layers. However, very little evidence has been given so far to support this hypothesis. It is demonstrated here by X-ray diffraction, TEM, electron diffraction, and solubility studies that a second process of hydration takes place that involves the dissolution of alumina and subsequent precipitation of well-shaped Al(OH)3 particles from supersaturated alumina aqueous solution. This process can be observed on a macroscopic scale (XRD, TEM) for any pH5, provided that the contact time between alumina and water exceeds 10 h. The least thermodynamically stable phase of aluminum hydroxide, bayerite, becomes favored compared with gibbsite when the pH of the solution is increased. It is assumed that the rate of formation of bayerite germs is greater than that of gibbsite due to variations in aluminum speciation in solution as a function of pH.

Sorption of Cu(II) onto vineyard soils: macroscopic and spectroscopic investigations.

The sorption of Cu on five vineyard soils was examined via macroscopic and spectroscopic investigations. The composition of the soils was previously determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) was employed to determine the metal environment with regard to the identity and interaction of the nearest atomic neighbors, the bond distances, and the coordination numbers. The five soils present similar sorption properties and there is no XAS evidence that the nature of the soil samples affects the local chemical environment of Cu(II). The kinetics of the Cu sorption reactions is rapid, with the equilibrium loading of Cu on the surface achieving approximately 200 mumol g(-1), i.e., 12.7 mg g(-1). The XAS data indicate that Cu is adsorbed in the form of inner-sphere complexes with first shell CuO parameters of four equatorial CuO bonds equal to 1.93 A and two axial CuO bonds at 2.43 A. This is in accordance with a Jahn-Teller distorted octahedron environment around copper. Our results provide evidence of the complexation of Cu(II) onto soil organic matter coated with an inorganic surface (quartz, clay, and goethite).

Evolution of nickel speciation during preparation of Ni-SiO(2) catalysts: effect of the number of chelating ligands in [Ni(en)x(H2O)6-2x]2+ precursor complexes.

The evolution of nickel speciation during the successive preparation steps of Ni-SiO(2) catalysts is studied by UV-Vis-NIR, FT-IR, DTG, TPR and TEM. The study focuses on the effect of the number of chelating ligands in the precursor complexes [Ni(en)(x)(H(2)O)((6-2x))](2+) (en = ethylenediamine, x = 1, 2, 3) on the adsorption on silica, and on nickel speciation after thermal treatment. When the en:Ni ratio in solution increases from 1 to 3, the most abundant complex is [Ni(en)(H(2)O)(4)](2+) (64% of all Ni complexes), [Ni(en)(2)(H(2)O)(2)](2+) (81%) and [Ni(en)(3)](2+) (61%), respectively. Equilibrium adsorption of [Ni(en)(x)(H(2)O)((6-2x))](2+) on SiO(2) results in the selective grafting of [Ni(en)(H(2)O)(4)](2+) and [Ni(en)(2)(H(2)O)(2)](2+), through the substitution of two labile H(2)O ligands by two surface SiO(-) groups. The surface [Ni(en)(H(2)O)(2)(SiO)(2)] complex formed by the grafting of [Ni(en)(H(2)O)(4)](2+) onto silica tends to transform into NiO and nickel phyllosilicate after calcination, which consequently leads to large and heterogeneously distributed metallic Ni particles upon reduction. In contrast, [Ni(en)(2)(SiO)(2)], resulting from the grafting of [Ni(en)(2)(H(2)O)(2)](2+) onto silica, no longer has aqua ligands able to react with other nickel complexes or silicium-containing species. Calcination transforms these complexes into isolated Ni(2+) ions, which are reduced into small metallic Ni particles with a more homogeneous size distribution, even at higher Ni loading.

A systematic study of the interactions between chemical partners (metal, ligands, counterions, and support) involved in the design of Al2O3-supported nickel catalysts from diamine-Ni(II) chelates.

1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina.