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showing 10 items of 13601 documents
Tetraiodoethynyl resorcinarene cavitands as multivalent halogen bond donors
2014
The first examples of iodoethynyl resorcinarene cavitands as rigid 3D halogen bond (XB) donor molecules are presented. These concave macrocycles form strong, RXB = 0.78–0.83, halogen bonds with dioxane oxygen, pyridine nitrogen and a bromide anion in tetraproropyl ammonium bromide resulting in deep cavity cavitand structures.
Bioavailability of inorganic arsenic in cooked rice: practical aspects for human health risk assessments.
2005
Arsenic is present in rice grain mainly as inorganic arsenic. Little is known about the effect of cooking on inorganic arsenic content in rice and its bioavailability. This study evaluated total arsenic and inorganic arsenic in rice cooked with arsenic-contaminated water, the bioaccessibility of As(III) and As(V) after simulated gastrointestinal digestion, and the extent of arsenic retention and transport by Caco-2 cells used as a model of intestinal epithelia. After cooking, inorganic arsenic contents increase significantly. After simulated gastrointestinal digestion, the bioaccessibility of inorganic arsenic reached 63-99%; As(V) was the main species found. In Caco-2 cells, arsenic retent…
Graphitically encapsulated cobalt nanocrystal assemblies
2010
Graphitically encapsulated cobalt nanocrystal assemblies are chemically prepared by one-pot reaction at380 degrees C followed by a reversed etching process to produce porous graphitic structure for revealing their self-assembling nature.
Combined NC-AFM and DFT study of the adsorption geometry of trimesic acid on rutile TiO2(110)
2010
The adsorption behavior of trimesic acid (TMA) on rutile TiO(2)(110) is studied by means of non-contact atomic force microscopy (NC-AFM) and density-functional theory (DFT). Upon low-coverage adsorption at room temperature, NC-AFM imaging reveals individual molecules, centered above the surface titanium rows. Based on the NC-AFM results alone it is difficult to deduce whether the molecules are lying flat or standing upright on the surface. To elucidate the detailed adsorption geometry, we perform DFT calculations, considering a large number of different adsorption positions. Our DFT calculations suggest that single TMA molecules adsorb with the benzene ring parallel to the surface plane. In…
Cocrystal trimorphism as a consequence of the orthogonality of halogen- and hydrogen-bonds synthons.
2019
True trimorphic cocrystals, i.e. multi-component molecular crystals of identical composition that exhibit three polymorphic structures, are exceedingly rare and so far no halogen-bonded cocrystal system has been reported to exhibit trimorphism. Here we describe a unique example of a trimorphic cocrystal exhibiting both hydrogen and halogen bonds in which the differences between polymorphs reveal their orthogonality, evident by the apparently independent variation of well-defined hydrogen- and halogen-bonded motifs. peerReviewed
The enrichment ratio of atomic contacts in crystals, an indicator derived from the Hirshfeld surface analysis
2014
An enrichment ratio is derived from the decomposition of the crystal contact surface between pairs of interacting chemical species. The propensity of different contact types to form is investigated.
Phosphororganische Verbindungen, 68. Darstellung und Eigenschaften von Tetrakis(diphenylphosphin)‐nickel(0)
1971
Die Titelsubstanz 1 wurde durch Einwirkung von Diphenylphosphin auf Bis-π-allyl-nickel, Tetrakis(triphenylphosphin)-nickel(0) (2), Nickelpulver oder Nickel(II)-bromid dargestellt. Ihre Struktur wurde durch Zerewitinoff-Bestimmung, IR- und NMR-Spektren abgesichert. Eine Alkylierung von metalliertem 1 gelang nicht. Organic Phosphorus Compounds, 68. Preparation and Properties of Tetrakis(diphenylphosphine)nickel(0) The title compound, 1, was prepared by reacting of diphenylphosphine with bis(π-allyl)nickel, tetrakis(triphenylphosphine)nickel(0) (2), nickel-powder, or nickel(II) bromide. The structure of 1 was elucidated by Zerewitinoff method, i. r. and n. m. r. spectra. The alkylation of meta…
Improvement of catalytic activity over Cu--Fe modified Al-rich Beta catalyst for the selective catalytic reduction of NOx with NH3
2016
Copper and iron bimetal modified Al-rich Beta zeolites from template-free synthesis were prepared for selective catalytic reduction (SCR) of NOx with NH3 in exhaust gas streams. Comparing to the Cu-based and Fe-based mono-component Beta catalysts, Cu(3.0)-Fe(1.3)-Beta bi-component catalyst shows better low-temperature activity and wider reaction-temperature window. Over 80% of NO conversion can be achieved at the temperature region of 125–500 °C. Due to the synergistic effect of copper and iron evidenced by XRD, UV–Vis–NIR, EPR and XPS measurements, the dispersion state of active components as well as the ratio of Cu2+/Cu+ and Fe3+/Fe2+ were improved over Cu(3.0)-Fe(1.3)-Beta. Isolated Cu2+…
Pumice-Supported Nickel Catalysts
1997
A series of nickel catalysts supported on pumice was prepared by precipitation and impregnation techniques. The influence of the calcination and reduction temperatures on the structural properties such as lattice parameters and particle dimensions of the oxide precursors and of the reduced catalysts was investigated by X-ray diffraction measurements. The effect of structural changes on the catalytic activity in the hydrogenation of carbon monoxide has been evaluated. The turnover frequencies, as well as product distributions, are discussed in terms of the influence of the support properties and of its interaction with the metal. Changes of the C2+yield over CH4yield ratio versus nickel disp…
DFT insights into the oxygen-assisted selective oxidation of benzyl alcohol on manganese dioxide catalysts
2020
Abstract The reactivity pattern of the MnO2 catalyst in the selective aerobic oxidation of benzyl alcohol is assessed by density functional theory (DFT) analysis of adsorption energies and activation barriers on a model Mn4O8 cluster. DFT calculations predict high reactivity of defective Mn(IV) sites ruling a surface redox mechanism, L-H type, involving gas-phase oxygen. Bare and promoted (i.e., CeOx and FeOx) MnOx materials with high surface exposure of Mn(IV) sites were synthesized to assess kinetic and mechanistic issues of the selective aerobic oxidation of benzyl alcohol on real catalysts (T, 333–363 K). According to DFT predictions, the experimental study shows: i) comparable activity…