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511.
Revealing the Dynamic Structure of Complex Solid Catalysts Using Modulated Excitation X‐ray Diffraction
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Dr. Davide Ferri Dr. Mark A. Newton Dr. Marco Di Michiel Dr. Gian Luca Chiarello Dr. Songhak Yoon Dr. Ye Lu Dr. Jérôme Andrieux 《Angewandte Chemie (International ed. in English)》2014,53(34):8890-8894
X‐ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach, time‐resolved high‐energy XRD is able to provide the detailed redox dynamics of palladium nanoparticles with a diameter of 2 nm in 2 wt % Pd/CZ (CZ=ceria–zirconia), which is a difficult sample for extended X‐ray absorption fine structure (EXAFS) measurements because of the cerium component. The temporal evolution of the Pd(111) and Ce(111) reflections together with surface information from synchronous diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements reveals that Ce maintains Pd oxidized in the CO pulse, whereas reduction is detected at the beginning of the O2 pulse. Oxygen is likely transferred from Pd to Ce3+ before the onset of Pd re‐oxidation. In this context, adsorbed carbonates appear to be the rate‐limiting species for re‐oxidation. 相似文献
512.
Rancan M Newton GN Muryn CA Pritchard RG Timco GA Cronin L Winpenny RE 《Chemical communications (Cambridge, England)》2008,(13):1560-1562
Synthetic and structural studies of Cr horseshoes are reported which show that these compounds demonstrate a rich supramolecular chemistry through H-bonding interactions, and can act as ligands for metal clusters. 相似文献
513.
Nano-scale superhydrophobicity: suppression of protein adsorption and promotion of flow-induced detachment 总被引:1,自引:0,他引:1
Wall adsorption is a common problem in microfluidic devices, particularly when proteins are used. Here we show how superhydrophobic surfaces can be used to reduce protein adsorption and to promote desorption. Hydrophobic surfaces, both smooth and having high surface roughness of varying length scales (to generate superhydrophobicity), were incubated in protein solution. The samples were then exposed to flow shear in a device designed to simulate a microfluidic environment. Results show that a similar amount of protein adsorbed onto smooth and nanometer-scale rough surfaces, although a greater amount was found to adsorb onto superhydrophobic surfaces with micrometer scale roughness. Exposure to flow shear removed a considerably larger proportion of adsorbed protein from the superhydrophobic surfaces than from the smooth ones, with almost all of the protein being removed from some nanoscale surfaces. This type of surface may therefore be useful in environments, such as microfluidics, where protein sticking is a problem and fluid flow is present. Possible mechanisms that explain the behaviour are discussed, including decreased contact between protein and surface and greater shear stress due to interfacial slip between the superhydrophobic surface and the liquid. 相似文献
514.
Lifen Yan Dr. Vladimir Pelmenschikov Christie H. Dapper Aubrey D. Scott Prof. William E. Newton Prof. Stephen P. Cramer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16349-16357
Fourier transform infrared spectroscopy (FTIR) was used to observe the photolysis and recombination of a new EPR‐silent CO‐inhibited form of α‐H195Q nitrogenase from Azotobacter vinelandii. Photolysis at 4 K reveals a strong negative IR difference band at $\tilde \nu $ =1938 cm?1, along with a weaker negative feature at 1911 cm?1. These bands and the associated chemical species have both been assigned the label “Hi‐3”. A positive band at $\tilde \nu $ =1921 cm?1 was assigned to the “Lo‐3” photoproduct. By using an isotopic mixture of 12C 16O and 13C 18O, we show that the Hi‐3 bands arise from coupling of two similar CO oscillators with one uncoupled frequency at approximately $\tilde \nu $ =1917 cm?1. Although in previous studies Lo‐3 was not observed to recombine, by extending the observation range to 200–240 K, we found that recombination to Hi‐3 does indeed occur, with an activation energy of approximately 6.5 kJ mol?1. The frequencies of the Hi‐3 bands suggest terminal CO ligation. This hypothesis was tested with DFT calculations on models with terminal CO ligands on Fe2 and Fe6 of the FeMo‐cofactor. An S=0 model with both CO ligands in exo positions predicts symmetric and asymmetric stretches at $\tilde \nu $ =1938 and 1909 cm?1, respectively, with relative band intensities of about 3.5:1, which is in good agreement with experiment. From the observed IR intensities, Hi‐3 was found to be present at a concentration about equal to that of the EPR‐active Hi‐1 species. The relevance of Hi‐3 to the nitrogenase catalytic mechanism and its recently discovered Fischer–Tropsch chemistry is discussed. 相似文献
515.
Nigel J. Newton 《Journal of Functional Analysis》2012,263(6):1661-1681
We construct an infinite-dimensional Hilbert manifold of probability measures on an abstract measurable space. The manifold, M, retains the first- and second-order features of finite-dimensional information geometry: the α-divergences admit first derivatives and mixed second derivatives, enabling the definition of the Fisher metric as a pseudo-Riemannian metric. This is enough for many applications; for example, it justifies certain projections of Markov processes onto finite-dimensional submanifolds in recursive estimation problems. M was constructed with the Fenchel–Legendre transform between Kullback–Leibler divergences, and its role in Bayesian estimation, in mind. This transform retains, on M, the symmetry of the finite-dimensional case. Many of the manifolds of finite-dimensional information geometry are shown to be -embedded submanifolds of M. In establishing this, we provide a framework in which many of the formal results of the finite-dimensional subject can be proved with full rigour. 相似文献
516.
Pereira JB Carvalho EF Faustino MA Fernandes R Neves MG Cavaleiro JA Gomes NC Cunha A Almeida A Tomé JP 《Photochemistry and photobiology》2012,88(3):537-547
This study describes the synthesis of three new tetra- and octa-thio-pyridinium phthalocyanine derivatives. PSs 3a and 4a were prepared from the tetramerization of phthalonitriles 1 and 2, respectively, whereas PS 5 was prepared from the nucleophilic substitution of the 8 beta fluor atoms of hexadecafluorophthalocyaninatozinc(II) by mercaptopyridine, followed by cationization. The recombinant bioluminescent Escherichia coli strain was used to assess, in real time, the photoinactivation efficiency of these cationic phthalocyanines, under white and red light. The cellular localization and uptake were also determined to assess the potential of the new phthalocyanines as antibacterial agents. Derivative 3a was the most effective PS, causing a 5 logs reduction in bioluminescence after 30 min of irradiation under white or red lights. The photoinactivation efficiency of the phthalocyanine 4a was similar (5 logs reduction in bioluminescence) to that of 3a when irradiated with white light, but the efficiency of inactivation was reduced (2.1 logs reduction in bioluminescence) under red light. The tetra-substituted phthalocyanine 3a also generates high amounts of singlet oxygen, does not aggregate in PBS and is highly fluorescent, which makes it an effective PS and a promising fluorescent labeling. 相似文献
517.
In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexadecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)3N(C16H33)]+ ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded on the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. 相似文献
518.
Tuytten R Lemière F Esmans EL Herrebout WA van der Veken BJ Dudley E Newton RP Witters E 《Journal of the American Society for Mass Spectrometry》2006,17(8):1050-1062
In-source collision induced dissociation was applied to access second generation ions of protonated guanosine. The in-source gas-phase behavior of [BH2]+-NH3 (m/z 135, C5H3N4O+) was investigated. Adduct formation and reactions with available solvent molecules (H2O and CH3OH) were demonstrated. Several addition/elimination sequences were observed for this particular ion and solvent molecules. Dissociation pathways for the newly formed ions were developed using a QqTOF mass spectrometer, permitting the assignment of elemental compositions of all product ions produced. Reaction schemes were suggested arising from the ring-opened intermediate of the protonated base moiety [BH2]+, obtained from fragmentation of guanosine. The mass spectral data revealed that the in-source CH3OH-reaction product underwent more complex fragmentations than the comparable ion following reaction with H2O. A rearrangement and a parallel radical dissociation pathway were discerned. Apart from the mass spectrometric evidence, the fragmentation schemes are supported by density functional theory calculations, in which the reaction of the ring-opened protonated guanine intermediate with CH3OH and a number of subsequent fragmentations were elaborated. Additionally, an in-source transition from the ring-opened intermediate of protonated guanine to the ring-opened intermediate of protonated xanthine was suggested. For comparison, a low-energy collision induced dissociation study of xanthosine was performed. Its dissociation pathways agreed with our assumption. 相似文献
519.
Johannes Wieser Dr. Amy J. Knorpp Dr. Dragos C. Stoian Dr. Przemyslaw Rzepka Dr. Mark A. Newton Prof. Jeroen A. van Bokhoven 《Angewandte Chemie (International ed. in English)》2023,62(40):e202305140
The methane-to-methanol (MtM) conversion via the oxygen looping approach using copper-exchanged zeolites has been extensively studied over the last decade. While a lot of research has focussed on maximizing yield and selectivity, little has been directed toward productivity—a metric far more meaningful for evaluating industrial potential. Using copper-exchanged zeolite omega (Cu-omega), a material highly active and selective for the MtM conversion using the isothermal oxygen looping approach, we show that this material exhibits unprecedented potential for industrial valorization. In doing so, we also present a novel methodology combining operando XAS and mass spectrometry for the screening of materials for the MtM conversion in oxygen looping mode. 相似文献
520.
Rory C. McNulty Keir Penston Sharad S. Amin Sandro Stal Jie Yie Lee Mario Samperi Lluïsa Pérez-García Jamie M. Cameron Lee R. Johnson David B. Amabilino Graham N. Newton 《Angewandte Chemie (International ed. in English)》2023,62(12):e202216066
The mixing of [V10O28]6− decavanadate anions with a dicationic gemini surfactant ( gem ) leads to the spontaneous self-assembly of surfactant-templated nanostructured arrays of decavanadate clusters. Calcination of the material under air yields highly crystalline, sponge-like V2O5 ( gem -V2O5 ). In contrast, calcination of the amorphous tetrabutylammonium decavanadate allows isolation of a more agglomerated V2O5 consisting of very small crystallites ( TBA -V2O5 ). Electrochemical analysis of the materials’ performance as lithium-ion intercalation electrodes highlights the role of morphology in cathode performance. The large crystallites and long-range microstructure of the gem -V2O5 cathode deliver higher initial capacity and superior capacity retention than TBA -V2O5 . The smaller crystallite size and higher surface area of TBA -V2O5 allow faster lithium insertion and superior rate performance to gem -V2O5 . 相似文献