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991.
Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde 下载免费PDF全文
Andreas Peter Samuel M. Fehr Valentin Dybbert Dr. Daniel Himmel Ines Lindner Dr. Eberhard Jacob Mohamed Ouda Dr. Achim Schaadt Dr. Robin J. White Dr. Harald Scherer Prof. Dr. Ingo Krossing 《Angewandte Chemie (International ed. in English)》2018,57(30):9461-9464
Oxymethylene dimethyl ethers (OMEn; CH3(‐OCH2‐)nO‐CH3, n=3–5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot‐free combustion. Herein a novel anhydrous OMEn synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OMEn at temperatures of 25–30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OMEn emanating from CO2 and H2. 相似文献
992.
C. Popescu P. Budrugeac F.-J. Wortmann L. Miu D.E. Demco M. Baias 《Polymer Degradation and Stability》2008,93(5):976-982
The thermal degradation of collagen-based materials, viz. collagen, recently manufactured parchments and tanned leathers, a heritage parchment and patrimonial (historical) leathers, was investigated by thermal analysis methods. With progressive heating, all these materials exhibit three main successive processes, associated with dehydration, protein denaturation and pyrolysis/oxidation. The analysis of both denaturation and thermo-oxidation revealed significant differences between aged leather, collagen, recently manufactured parchments and tanned leathers in terms of the number of overlapping processes (reflected in the number of peaks recorded at denaturation) and of the oxidative degradation rates, given by the normalised curves of differential thermal gravimetry (DTG). The various observations are proposed as qualitative indices for assessing the age and storage conditions of leather. A three-phase model was used for explaining the results. This consists of crystalline collagen filaments that are embedded in an amorphous matrix with an interface zone between the crystalline and amorphous regions. Solid-state 1H NMR investigations corroborate the thermal analysis results and enhance the understanding of the ageing processes. 相似文献
993.
Maria Carolina de CeglieLeonardo Degennaro Aurelia FalcicchioRenzo Luisi 《Tetrahedron》2011,67(48):9382-9388
‘Gear-like’ rotations of simple C-C bonds have been observed in some aziridine methanol derivatives. These restricted rotations have been studied by dynamic and multinuclear magnetic resonance experiments, and the barrier for rotations of Csp3-Csp3 and Csp3-Csp2 bonds have been calculated. The role of an intramolecular hydrogen bond on the stereodynamics has also been demonstrated. 相似文献
994.
Alan R. Katritzky Megumi Yoshioka-Tarver Bahaa El-Dien M. El-Gendy C. Dennis Hall 《Tetrahedron letters》2011,52(17):2224-2227
GFP chromophore analogs (7a-e, 8, and 10a,b) containing 2-thienyl-, 5-methyl-2-furyl-, 2-pyrryl, and 6-methyl-2-pyridyl-groups were synthesized and their fluorescence spectra recorded in the pH range 1-7. NMR studies showed that protonation of 8 (2-thienyl system) inhibited photoisomerization (Z-E) about the exocyclic double bond but that protonation of 7c (E + Z) (2-pyrryl system) gave only 7cE. Fluorescence studies revealed enhancement of fluorescence intensity of 7c and 7b,e (furyl system) below pH 2.5 and gave a similar result for 10a (pyridyl system) below pH 6. Quantum yields at pH 1 were low, probably due to excited state proton transfer (ESPT). 相似文献
995.
The epitope mapping of nucleotides bound to three chromatography supports is accomplished using saturation transfer difference (STD)-NMR spectroscopy. This experiment involves subtracting a spectrum in which the support was selectively saturated from one recorded without support saturation. In the difference spectrum only the signals of the ligands that bind to the support and received saturation transfer remain. The nucleotide protons in closer contact with the support have more intense signals due to a more efficient transfer of saturation. We investigate the effects on the binding to the nucleotides by the introduction of a spacer arm between l-histidine and Sepharose. Our NMR experiments evidence a clear contribution of the spacer to the interaction with all the nucleotides, increasing the mobility of the amino acid and giving different STD responses. This enhanced mobility originates the reinforcement of the interactions with the sugar moiety and phosphate group of 5'-CMP and 5'-TMP or the base of 5'-GMP and 5'-UMP. Hence, with this study we show that by using STD NMR technique on chromatographic systems it is possible to provide a fast, robust and efficient way of screening the atoms involved in the binding to the supports. 相似文献
996.
Two new guaiane-type sesquiterpenoid glucosides (1 and 2) were isolated from the fruit of Gardenia jasminoides Ellis. Their structures were elucidated to be (1R,7R,10S)-11-O-β-D-glucopyranosyl-4-guaien-3-one (1) and (1R,7R,10S)-7-hydroxy-11-O-β-D-glucopyranosyl-4-guaien-3-one (2) by one- and two-dimensional NMR techniques ((1)H NMR, (13)C NMR, HSQC, HMBC and NOESY), MS, CD spectrometry and chemical methods. 相似文献
997.
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999.
During the past few years, the electrochemical sensing techniques based on ion channels have attracted considerable attention. Nowadays, these techniques have been widely used in DNA sequencing, measurement of molecular interactions, and detection of inorganic ions and biological species. Hence, in this review, the research progresses of the ion channel-based electrochemical techniques including amperometry, conductometry and potentiometry in chemical and biological sensing are addressed from the perspective of different electrochemical methods. The sensing mechanism and fabrication process of these sensing methods are mainly introduced. In addition, the further research orientations of the electrochemical sensing based on ion channels are prospected. 相似文献
1000.