785 research outputs found
Lipoteichoic acid may affect the pathogenesis of PBC-like bile duct damage and might be involved in systemic multifocal epithelial inflammations in chronic colitis-harboring TCRα−/− × AIM−/− mice
Stabilization of Ferroelectric Hf0.5Zr0.5O2 Epitaxial Films via Monolayer Reconstruction Driven by Interfacial Redox Reaction
The binary fluorite oxide Hf0.5Zr0.5O2 tends to grab a significant amount of
notice due to the distinct and superior ferroelectricity found in its
metastable phase. Stabilizing the metastable ferroelectric phase and
delineating the underlying growth mechanism, however, are still challenging.
Recent discoveries of metastable ferroelectric Hf0.5Zr0.5O2 epitaxially grown
on structurally dissimilar perovskite oxides have triggered intensive
investigations on the ferroelectricity in materials that are nonpolar in bulk
form. Nonetheless, the growth mechanism for the unique fluorite/perovskite
heterostructures has yet to be fully explored. Here we show that the metastable
ferroelectric Hf0.5Zr0.5O2 films can be stabilized even on a
one-unit-cell-thick perovskite La0.67Sr0.33MnO3 buffer layer. In collaboration
with scanning transmittance electron microscopy (STEM) based characterizations,
we show that monolayer reconstruction driven by interfacial redox reactions
plays a vital role in the formation of a unique heterointerface between the two
structurally dissimilar oxides, providing the template monolayer that
facilitates the epitaxial growth of the metastable HZO films. Our findings
offer significant insights into the stabilization mechanism of the
ferroelectric Hf0.5Zr0.5O2, and this mechanism could be extended for exploring
functional metastable phases of various metal oxides
Chirality in Bare and Passivated Gold Nanoclusters
Chiral structures have been found as the lowest-energy isomers of bare
(Au and Au_{28}(SCH_{16}_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in
the chiral clusters was calculated using the Hausdorff chirality measure. We
found that the index of chirality is higher in the passivated clusters and
decreases with the cluster size. These results are consistent with the observed
chiroptical activity recently reported for glutahione-passivated gold
nanoclusters, and provide theoretical support for the existence of chirality in
these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR
Oriented Au nanoplatelets on graphene promote Suzuki-Miyaura coupling with higher efficiency and different reactivity pattern than supported palladium
[EN] Facet 111 oriented Au nanoplatelets (20-40 nm wide, 3-4 nm height) grafted on graphene ((Au) over bar /fl-G) are about three orders of magnitude more efficient than Pd nanoparticles supported on graphene to promote Suzuki-Miyaura coupling. In contrast to Pd catalysis, it is shown here that the product yields in Suzuki-Miyaura coupling catalyzed by Au nanoparticles follow the order chlorobenzene > bromobenzene > iodobenzene. Kinetic studies show that this reactivity order is the result of the poisoning effect of halides for Au that is much higher for I- than Br- and much higher than for Cl-, due to adsorption. This strong iodide adsorption leading to Au catalyst deactivation was predicted by DFT calculations of Au clusters. (Au) over bar /fl-G are about one order of magnitude more efficient than small Au nanoparticles (4-6 nm) obtained by the polyol method supported on graphene. Our results can have impact in organic synthesis, showing the advantage of (Au) over bar /fl-G as catalyst for Suzuki-Miyaura couplings.ADM thanks University Grants Commission (UGC), New Delhi for the award of Assistant Professorship under its Faculty Recharge Programme. ADM also thanks Department of Science and Technology, India, for the financial support through Extra Mural Research funding (SB/FT/CS-166/2013) and the Generalidad Valenciana for financial aid supporting his stay at Valencia through the Prometeo programme. Financial support by the Spanish Ministry of Economy and Competitiveness (CTQ-2012-32315 and Severo Ochoa) and Generalidad Valenciana (Prometeo 2012-014) is gratefully acknowledged. The research leading to these results has received partial funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 228862.Candu, N.; Dhakshinamoorthy, A.; Apostol, N.; Teodorescu, C.; Corma Canós, A.; García Gómez, H.; Parvulescu, VI. (2017). Oriented Au nanoplatelets on graphene promote Suzuki-Miyaura coupling with higher efficiency and different reactivity pattern than supported palladium. Journal of Catalysis. 352:59-66. https://doi.org/10.1016/j.jcat.2017.04.034S596635
A QM/MM approach for the study of monolayer-protected gold clusters
We report the development and implementation of hybrid methods that combine
quantum mechanics (QM) with molecular mechanics (MM) to theoretically
characterize thiolated gold clusters. We use, as training systems, structures
such as Au25(SCH2-R)18 and Au38(SCH2-R)24, which can be readily compared with
recent crystallographic data. We envision that such an approach will lead to an
accurate description of key structural and electronic signatures at a fraction
of the cost of a full quantum chemical treatment. As an example, we demonstrate
that calculations of the 1H and 13C NMR shielding constants with our proposed
QM/MM model maintain the qualitative features of a full DFT calculation, with
an order-of-magnitude increase in computational efficiency.Comment: Journal of Materials Science, 201
Aromaticity in a Surface Deposited Cluster: Pd on TiO (110)
We report the presence of \sigma-aromaticity in a surface deposited cluster,
Pd on TiO (110). In the gas phase, Pd adopts a tetrahedral
structure. However, surface binding promotes a flat, \sigma-aromatic cluster.
This is the first time aromaticity is found in surface deposited clusters.
Systems of this type emerge as a promising class of catalyst, and so
realization of aromaticity in them may help to rationalize their reactivity and
catalytic properties, as a function of cluster size and composition.Comment: 4 pages, 3 figure
Long- and short-type double-balloon enteroscopy-assisted therapeutic ERCP for intact papilla in patients with a Roux-en-Y anastomosis
A comparative study of two different approaches for the incorporation of silver nanoparticles into layer-by-layer films
Chemically-synthesised, atomically-precise gold clusters deposited and activated on titania
Synchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Au(n)(PPh₃)(y) (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f₇/₂ peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f₇/₂ peak indicates that the size of the agglomerated clusters is still smaller than that of Au₁₀₁.David P. Anderson, Jason F. Alvino, Alexander Gentleman, Hassan Al Qahtani, Lars Thomsen, Matthew I. J. Polson, Gregory F. Metha, Vladimir B. Golovko and Gunther G. Andersso
Green electrochemical template synthesis of CoPt nanoparticles with tunable size, composition, and magnetism from microemulsions using an ionic liquid (bmimPF6)
Altres ajuts: Substrates have been prepared in IMB-CNM (CSIC),supported by the (CSIC) NGG-258 project.Electrodeposition from microemulsions using ionic liquids is revealed as a green method for synthesizing magnetic alloyed nanoparticles, avoiding the use of aggressive reducing agents. Microemulsions containing droplets of aqueous solution (electrolytic solution containing Pt(IV) and Co(II) ions) in an ionic liquid (bmimPF) define nanoreactors in which the electrochemical reduction takes place. Highly crystalline hcp alloyed CoPt nanoparticles, in the 10-120 nm range with a rather narrow size distribution, have been deposited on a conductive substrate. The relative amount of aqueous solution to ionic liquid determines the size of the nanoreactors, which serve as nanotemplates for the growth of the nanoparticles and hence determine their size and distribution. Further, the stoichiometry (PtCo) of the particles can be tuned by the composition of the electrolytic solution inside the droplets. The control of the size and composition of the particles allows tailoring the room-temperature magnetic behavior of the nanoparticles from superparaparamagnetic to hard magnetic (with a coercivity of H = 4100 Oe) in the as-obtained state. © 2014 American Chemical Society
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