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排序方式: 共有284条查询结果,搜索用时 15 毫秒
221.
222.
A Wittig reaction employing the ylide generated from isopropyl triphenylphosphonium bromide with THP-protected aldol intermediate 8 constitutes the key step in a regiospecific synthesis of olefin 1 in the total synthesis of zoapatanol analogue 2a. 相似文献
223.
Gem-substituted aryl, aralkenyl and 2-furyl ethynyl vinyi carbinols as well as 2,5-disubstituted furans can be obtained by a novel addition and rearrangement reaction of acetylene with the appropriate aldehydes. 相似文献
224.
225.
The complexation of Cu+ by the potentially tripod like ligand cis, cis-1, 3, 5 cyclohexanetriamine (chta) has been studied potentiometrically in aqueous acetonitrile (an). The expected tetracoordinated species Cu (chta) ? (an)+ was formed only at rather high pH with log K (Cu (an)+ + chta ? Cu (chta) · (an)+) = 6.94. Quite unexpectedly the most stable complex in neutral solution was the trimetric species Cu3 (chta) with log K (3 Cu+ + 2 chta ? Cu3 (chta)) = 31.75. In addition, the ternary complexes Cu (LH2) · (an)3+ and Cu (LH) · (an)2+ (L = chta) are formed at low pH. From model considerations, Cu3 (chta) must contain two ligand molecules with all amino groups in equatorial position, linked by three linearly coordinated Cu+-ions. Cu3 (chta)3+2 shows no measurable reactivity towards dioxygen. At pH values above 9, very rapid O2-uptake due to Cu (chta) · (an)+ is observed. In this reaction, Cu+-autoxidation is stoichiometrically coupled to ligand oxidation, followed by a much slower Cu-catalyzed secondary reaction of the primary oxidation product of chta. Hydrogen peroxide and likely also superoxide, are involved in the coupled Cu+/ligand oxidation. 相似文献
226.
Patricia Grinberg Zoltan Mester Alessandro D'Ulivo Ralph E. Sturgeon 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(7):714-716
Ultraviolet irradiation of aqueous solutions of iodide/iodate ion containing low molecular weight organic acids generates volatile iodine species that are amenable to detection by atomic spectrometry. In the presence of formic, acetic or propionic acids, photo-chemical generation results in the formation of HI, methyl- and ethyl-iodide respectively, the latter two products being directly identified by gas chromatography–mass spectrometry. Deuterium and 13C-labeled reagents were employed to elucidate the provenance of the alkyl group. Use of 13CH3–COOH produced 13CH3–I; deuterated acetic acid (D3C-COOD) resulted in the formation of CD3–I. These observations indicate direct transfer of the alkyl group from the carboxylic acid to iodide, consistent with the suggestion that the mechanism of synthesis involves radical induced reactions. 相似文献
227.
Michal Stransky Zoltan Jurek Robin Santra Adrian P. Mancuso Beata Ziaja 《Molecules (Basel, Switzerland)》2022,27(13)
In this work, we report on incorporating for the first time tree-algorithm based solvers into the molecular dynamics code, XMDYN. XMDYN was developed to describe the interaction of ultrafast X-ray pulses with atomic assemblies. It is also a part of the simulation platform, SIMEX, developed for computational single-particle imaging studies at the SPB/SFX instrument of the European XFEL facility. In order to improve the XMDYN performance, we incorporated the existing tree-algorithm based Coulomb solver, PEPC, into the code, and developed a dedicated tree-algorithm based secondary ionization solver, now also included in the XMDYN code. These extensions enable computationally efficient simulations of X-ray irradiated large atomic assemblies, e.g., large protein systems or viruses that are of strong interest for ultrafast X-ray science. The XMDYN-based preparatory simulations can now guide future single-particle-imaging experiments at the free-electron-laser facility, EuXFEL. 相似文献
228.
Jocelyn Tillner Vincen Wu Emrys A. Jones Steven D. Pringle Tamas Karancsi Andreas Dannhorn Kirill Veselkov James S. McKenzie Zoltan Takats 《Journal of the American Society for Mass Spectrometry》2017,28(10):2090-2098
A new, more robust sprayer for desorption electrospray ionization (DESI) mass spectrometry imaging is presented. The main source of variability in DESI is thought to be the uncontrolled variability of various geometric parameters of the sprayer, primarily the position of the solvent capillary, or more specifically, its positioning within the gas capillary or nozzle. If the solvent capillary is off-center, the sprayer becomes asymmetrical, making the geometry difficult to control and compromising reproducibility. If the stiffness, tip quality, and positioning of the capillary are improved, sprayer reproducibility can be improved by an order of magnitude. The quality of the improved sprayer and its potential for high spatial resolution imaging are demonstrated on human colorectal tissue samples by acquisition of images at pixel sizes of 100, 50, and 20 μm, which corresponds to a lateral resolution of 40–60 μm, similar to the best values published in the literature. The high sensitivity of the sprayer also allows combination with a fast scanning quadrupole time-of-flight mass spectrometer. This provides up to 30 times faster DESI acquisition, reducing the overall acquisition time for a 10 mm × 10 mm rat brain sample to approximately 1 h. Although some spectral information is lost with increasing analysis speed, the resulting data can still be used to classify tissue types on the basis of a previously constructed model. This is particularly interesting for clinical applications, where fast, reliable diagnosis is required. 相似文献
229.
Juris Meija Zoltan Mester Alessandro D’Ulivo 《Journal of the American Society for Mass Spectrometry》2007,18(2):337-345
Mass spectra of fully and partially deuterated As, Sb, Bi, Ge, and Sn hydrides have been obtained using several mathematical
approaches aimed at signal extraction and reconstruction. Study of such hydride mixtures is important for the elucidation
of hydride generation mechanisms. In this approach, mass spectra of partially deuterated isotopomers, i.e., AsH2D and AsHD2, are extracted using the weighted two-band target entropy minimization method. Alternatively, these mass spectra were constructed
from the mass spectra of fully deuterated and hydrogenated hydrides using the statistical approach in fragmentation pathways.
Concentration profiles of all deuterated hydrides were obtained from their overlapping mixture mass spectra using least-squares
deconvolution. 相似文献
230.
Erzsebet Varga Tamas Sohajda Zoltan Juvancz Rita Bodane Kendrovics Edit Szekely Gyorgy Bansaghi 《Chromatographia》2015,78(13-14):881-888
Obtaining enantiomeric pure compounds is—among other techniques—possible in a resolvation experiment via diastereomeric salt formation, excellently exemplified by a modified Pope–Peachy method performed in supercritical carbon dioxide as solvent. The salt precipitation is followed by supercritical fluid extraction (SFE) to separate the diastereomeric salts and the unreacted enantiomers. To evaluate the extraction efficiency, conversion and enantioselectivity achieved, it is essential to determine the enantiomer excess and the residual resolving agent content in extracts and raffinates. Carefully chosen experimental parameters enable the simultaneous determination of certain anions and cations in capillary electrophoresis in a single run, which has not been reported for diastereomeric mixtures so far. In this paper, a partially validated chiral selective cyclodextrin enabled capillary electrophoresis method is presented for the characterization of cis-permethrinic acid samples resolved with (R)-1-phenylethylamine prepared by the SFE-based resolvation technique. To evaluate the efficiency of the resolvation, a cyclodextrin enabled chiral separation method was developed applying permethylated-β-cyclodextrin as chiral selector. The theoretical possibility of the widespread application of the developed method (with minor adjustments) is justified for other selectands and selectors. The developed methods can be thereby applied for the fast and reliable control of resolvation experiments. 相似文献