Search results for "Inorganic Chemical"
showing 10 items of 491 documents
Gold(I)-catalyzed intermolecular oxyarylation of alkynes: unexpected regiochemistry in the alkylation of arenes.
2009
The reaction between acetylenes and sulfoxides, studied as a test case for gold-catalyzed intermolecular addition, provides the oxyarylation compounds 3 in good yields. Unpredictably, in all cases a single regioisomer arising from the electrophilic aromatic alkylation at the position adjacent to the sulfur atom is obtained instead of the expected Friedel−Crafts regioisomer. A new concerted mechanism based on DFT calculations is proposed to account for the products in this intermolecular gold(I)-catalyzed reaction.
Enhanced Heterogeneous Catalytic Conversion of Furfuryl Alcohol into Butyl Levulinate
2014
We study the catalytic condensation of furfuryl alcohol with 1-butanol to butyl levulinate. A screening of several commercial and as-synthesized solid acid catalysts shows that propylsulfonic acid-functionalized mesoporous silica outperforms the state-of-the-art phosphotungstate acid catalysts. The catalyst is prepared via template-assisted sol-gel polycondensation of TEOS and MPTMS. It gives 96 % yield (and 100 % selectivity) of butyl levulinate in 4h at 110 °C. Reaction profiles before and after a hot filtration test confirm that the active catalytic species do not leach into the solution. The catalyst synthesis, characterization, and mode of operation are presented and discussed. Sour ca…
Exposure to nitrogen dioxide and respiratory health at 2 years in the INMA-Valencia cohort
2018
Resumen Objetivo Analizar la relación entre la exposición a dióxido de nitrógeno (NO2) en las etapas prenatal y posnatal y la incidencia de problemas respiratorios en niños/as hasta los 2 años de edad. Método La población consistió en 624 niños/as de la cohorte INMA-Valencia. Se estimó la exposición individual al NO2 en el exterior de la vivienda durante el periodo prenatal y hasta los 2 años de edad, a partir de la combinación de datos empíricos y el desarrollo de métodos geoestadísticos. Se aplicó un cuestionario para obtener la información sobre los síntomas respiratorios a los 2 años. La asociación entre la exposición al NO2 y los eventos respiratorios se realizó mediante regresión logí…
Monolayer graphene doping and strain dynamics induced by thermal treatments in controlled atmosphere
2018
Time dynamics of doping and strain induced in single layer graphene by thermal treatments up to 300 degrees C in vacuum, nitrogen, carbon dioxide and oxygen controlled atmosphere are deeply studied by Raman spectroscopy and they are compared with its morphological evolution investigated by Atomic Force Microscopy. The reaction dynamics in oxygen treatments is determined down to a time scale of few minutes as well as that of dedoping process made by water vapor treatment. The interplay of strain modification and doping effects is separated. The strain is clarified to be strongly influenced by the cooling time. The doping removal is dominated by the water vapor, showing that the concentration…
The effect of gold addition on the catalytic performance of copper manganese oxide catalysts for the total oxidation of propane
2011
Mixed copper manganese oxide catalysts (Hopcalite) have been studied for the total oxidation of propane, as a model for hydrocarbon volatile organic compound emission control. Catalysts were prepared using coprecipitation with and without gold. Calcination temperature influenced the catalyst activity and those prepared at 300 °C were the most active. Characterization showed that the catalysts had a nanowire-type morphology, and for those containing gold it was present as metallic particles occluded within the nanowires. The incorporation of gold into the catalyst enhanced the activity for propane conversion, but the presence of gold did not noticeably enhance the light-off activity. Althou…
A DFT study of the Diels–Alder reaction between methyl acrolein derivatives and cyclopentadiene. Understanding the effects of Lewis acids catalysts b…
2006
Abstract The effects of Lewis acid catalysts based on sulfur containing boron heterocycles on the Diels–Alder reactions of two methyl acroleins with cyclopentadiene have been studied using DFT methods. These reactions take place along highly asynchronous concerted processes. While the reaction with crotonaldehyde leads to the expected endo adduct, the reaction with methacrolein leads to exo one in agreement with the experiments. The catalytic effect can be explained through the analysis of the electrophilicity index (ω) of the reagents, and the molecular structure of the corresponding transition structures.
The reduction of molecular oxygen by iron porphyrins
2002
Abstract Molecular assemblies have been synthesised to reproduce the structure of the cytochrome c oxidase (C c O) active site and to explore the roles played by its different features. It was discovered that a single iron porphyrin, adsorbed at the surface of a graphite electrode, is a selective catalyst for the four-electron reduction of dioxygen to water, at pH 7. To cite this article: D. Ricard et al., C. R. Chimie 5 (2002) 33–36
Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12
2005
ABSTRACT Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) possessing an ability to bind uranium and other heavy metals. Purified and recrystallized S-layer proteins were shown to be phosphorylated by phosphoprotein-specific staining, inductive coupled plasma mass spectrometry analysis, and a colorimetric method. We used extended X-ray absorption fine-structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-laye…
Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion
2000
Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO(3) into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l(-1); the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6-3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100-106…
Electrothermal Atomic Absorption Determination of Chromium in Sediments
1999
Abstract An electrothermal atomic absorption spectrometric method has been developed to determine total chromium concentration in natural sediment samples. Samples were mineralized by dry ashing at 550°C and fused at 1100°C for 30 min with lithium metaborate. Dissolved samples were injected in graphite tubes, mineralized at 1100°C, and atomized at 2600°C. Standard addition calibration made unnecessary the use of chemical modifiers. The method provided a limit of detection from 23 to 45 ng liter −1 . The relative standard deviation for chromium determination was between 3 and 14%. Results obtained for a standard reference material agree well with the certified value. A series of natural samp…