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91.
A chemoselective synthesis of the macrocyclic core of leucascandrolide A has been achieved, utilizing highly enantioselective allylmetalations, an enantioselective Noyori reduction of a propargylic ketone and olefin metatheses as the key steps. 相似文献
92.
Pau Ferri Chengeng Li Reisel Millán Dr. Joaquín Martínez-Triguero Dr. Manuel Moliner Dr. Mercedes Boronat Dr. Avelino Corma 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19876-19883
The methanol-to-olefins reaction catalyzed by small-pore cage-based acid zeolites and zeotypes produces a mixture of short chain olefins, whose selectivity to ethene, propene and butene varies with the cavity architecture and with the framework composition. The product distribution of aluminosilicates and silicoaluminophosphates with the CHA and AEI structures (H-SSZ-13, H-SAPO-34, H-SSZ-39 and H-SAPO-18) has been experimentally determined, and the impact of acidity and framework flexibility on the stability of the key cationic intermediates involved in the mechanism and on the diffusion of the olefin products through the 8r windows of the catalysts has been evaluated by means of periodic DFT calculations and ab initio molecular dynamics simulations. The preferential stabilization by confinement of fully methylated hydrocarbon pool intermediates favoring the paring pathway is the main factor controlling the final olefin product distribution. 相似文献
93.
Shestivska V Nemec A Dřevínek P Sovová K Dryahina K Spaněl P 《Rapid communications in mass spectrometry : RCM》2011,25(17):2459-2467
Infection by Pseudomonas aeruginosa (PA) is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Breath analysis could potentially be a useful diagnostic of such infection, and analyses of volatile organic compounds (VOCs) emitted from PA cultures are an important part of the search for volatile breath markers of PA lung infection. Our pilot experiments using solid‐phase microextraction, SPME and gas chromatography/mass spectrometric (GC/MS) analyses of volatile compounds produced by PA strains indicated a clear presence of methyl thiocyanate. This provided a motivation to develop a method for real‐time online quantification of this compound by selected ion flow tube mass spectrometry, SIFT‐MS. The kinetics of reactions of H3O+, NO+ and O2+? with methyl thiocyanate at 300 K were characterized and the characteristic product ions determined (proton transfer for H3O+, rate constant 4.6 × 10–9 cm3 s–1; association for NO+, 1.7 × 10–9 cm3 s–1 and nondissociative charge transfer for O2+?, 4.3 × 10–9 cm3 s–1). The kinetics library was extended by a new entry for methyl thiocyanate accounting for overlaps with isotopologues of hydrated hydronium ions. Solubility of methyl thiocyanate in water (Henry's law constant) was determined using standard reference solutions and the linearity and limits of detection of both SIFT‐MS and SPME‐GC/MS methods were characterized. Thirty‐six strains of PA with distinct genotype were cultivated under identical conditions and 28 of them (all also producing HCN) were found to release methyl thiocyanate in headspace concentrations greater than 6 parts per billion by volume (ppbv). SIFT‐MS was also used to analyze the breath of 28 children with CF and the concentrations of methyl thiocyanate were found to be in the range 2–21 ppbv (median 7 ppbv). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
94.
Kato S Borgschulte A Ferri D Bielmann M Crivello JC Wiedenmann D Parlinska-Wojtan M Rossbach P Lu Y Remhof A Züttel A 《Physical chemistry chemical physics : PCCP》2012,14(16):5518-5526
The catalytic hydrogenation of CO(2) at the surface of a metal hydride and the corresponding surface segregation were investigated. The surface processes on Mg(2)NiH(4) were analyzed by in situ X-ray photoelectron spectroscopy (XPS) combined with thermal desorption spectroscopy (TDS) and mass spectrometry (MS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). CO(2) hydrogenation on the hydride surface during hydrogen desorption was analyzed by catalytic activity measurement with a flow reactor, a gas chromatograph (GC) and MS. We conclude that for the CO(2) methanation reaction, the dissociation of H(2) molecules at the surface is not the rate controlling step but the dissociative adsorption of CO(2) molecules on the hydride surface. 相似文献
95.
Artur?Ciesielski Violetta?Patroniak Maciej?KubickiEmail author 《Journal of chemical crystallography》2011,41(12):1884-1888
Abstract
The cationic tetranuclear cobalt complex of the geometry Cl-CoL-Cl-CoL-Cl-CoL-Cl-CoL (where L is 6,6′′′-dimethyl-2,2′:6′,2′′:6′′,2′′′-quaterpyridine) has been synthesized and structurally characterized. The structural unit contains one cationic ligand, two Eu(NO3)5 dianions, two solvent acetonitrile molecules and some disordered water molecules. The salt crystallizes in the monoclinic space group C2/c with a = 17.405 (3) ?, b = 28.700 (5) ? and c = 23.350 (5) ?, β = 95.14 (2)o. The cation is C 2 -symmetrical, the central Cl atom lies on the twofold axis. This structure is another example of centro-noncentro ambiguity: in the centrosymmetric model, the terminal Cl in the cation is disordered between the two ends of the chain. The Eu ion is coordinated by five nitro groups, the coordination number is 10–two oxygen atoms of every nitro group are involved in the coordination with the mean Eu–O distance of 2.52(3) ?. The quaterpyridine ligands are folded, the dihedral angle between the terminal ring planes is 29.3 (2) and 32.8 (3)o in the two symmetry independent ligands. In the crystal structure the coulombic attraction between the cations and anions seems to be a driving force; the ionic species make a chessboard-like pattern, the voids in such created structure are filled with the solvent-acetonitrile molecules as well as by some disordered waters. 相似文献96.
A. Calisti S. Ferri C. Mossé B. Talin A. Klisnick L. Meng D. Benredjem O. Guilbaud 《High Energy Density Physics》2013,9(3):516-522
We present a detailed analysis of the different processes that contribute to the spectral broadening of the Ni-like Ag XUV laser line, including the effects of particle correlations on the broadening due to the radiator motion (Doppler broadening). We consider two different regimes of collisional excitation pumping: the transient pumping for which the ionic temperature is relatively low and the plasma coupling parameter is large, and the quasi steady-state pumping for which the ionic temperature is higher and the plasma coupling parameter is of the order of 1. In both cases, by using classical molecular dynamics simulation techniques, we show that ionic correlations actually modify the radiator-motion broadened profiles and cannot be neglected in evaluating the Doppler effect. The subsequent narrowing of the Doppler component is small compared to the overall linewidth, which includes the effect of homogeneous collisional broadening. However, ionic correlations will also affect the amplification of the lasing line, especially when the laser enters the saturation regime, because it will lead to a homogenization of the spectral profile. 相似文献
97.
A variant of the statistical complexity originally advanced by López-Ruiz et al. [R. López-Ruiz, H.L. Mancini, X. Calbet, Phys. Lett. A 209 (1995) 321], is here used in conjunction with Fisher's information measure so as to explore fine details of chaotic dynamics. As a main result we can easily distinguish between (i) periodicity and chaos or (ii) between distinct chaotic dynamics belonging to different attractors. 相似文献
98.
Ferri J. M. Motoc D. Luca Bou S. Ferrandiz Balart R. 《Journal of Thermal Analysis and Calorimetry》2019,138(4):2691-2702
Journal of Thermal Analysis and Calorimetry - The objective of this study was to investigate the thermal expansivities and degradation properties for several in vitro conditioned biodegradable... 相似文献
99.
Nicol Ferri Norah Algethami Andrea Vezzoli Sara Sangtarash Maeve McLaughlin Hatef Sadeghi Colin J. Lambert Richard J. Nichols Simon J. Higgins 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16736-16742
Single‐molecule junctions that are sensitive to compression or elongation are an emerging class of nanoelectromechanical systems (NEMS). Although the molecule–electrode interface can be engineered to impart such functionality, most studies to date rely on poorly defined interactions. We focused on this issue by synthesizing molecular wires designed to have chemically defined hemilabile contacts based on (methylthio)thiophene moieties. We measured their conductance as a function of junction size and observed conductance changes of up to two orders of magnitude as junctions were compressed and stretched. Localised interactions between weakly coordinating thienyl sulfurs and the electrodes are responsible for the observed effect and allow reversible monodentate?bidentate contact transitions as the junction is modulated in size. We observed an up to ≈100‐fold sensitivity boost of the (methylthio)thiophene‐terminated molecular wire compared with its non‐hemilabile (methylthio)benzene counterpart and demonstrate a previously unexplored application of hemilabile ligands to molecular electronics. 相似文献
100.