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81.
Feng H Ermolat'ev DS Song G Van der Eycken EV 《The Journal of organic chemistry》2012,77(11):5149-5154
A novel microwave-assisted approach for the one-pot Cu(I)-catalyzed A(3)-coupling/decarboxylative coupling (PA(2)-coupling) of a propiolic acid, an aldehyde, and an amine, resulting in the formation of diversely substituted 1,4-diamino-2-butynes,is described. It is noteworthy that this new multicomponent coupling provides an efficient access to introduce alkyl and aryl group at the 1,4-position of the 1,4-diamino-2-butynes. 相似文献
82.
He Z Zajdlik A St Denis JD Assem N Yudin AK 《Journal of the American Chemical Society》2012,134(24):9926-9929
A reaction exemplifying migration of boron-substituted carbon is described. We show that α-boroalkyl groups of transient boroalkyl acyl azide intermediates readily migrate from carbon to nitrogen. This process allows access to a new class of stable molecules, α-boryl isocyanates, from α-borylcarboxylic acid precursors. The methodology facilitates synthesis of a wide range of α-aminoboronic acid derivatives, including α,α-disubstituted analogues. 相似文献
83.
We implemented explicitly correlated second-order M?ller-Plesset perturbation theory with numerical quadratures using pseudospectral construction of grids. Introduction of pseudospectral approach for the calculation of many-electron integrals gives a possibility to use coarse grids without significant loss of precision in correlation energies, while the number of points in the grid is reduced about nine times. The use of complementary auxiliary basis sets as the sets of dealiasing functions is justified at both theoretical and computational levels. Benchmark calculations for a set of 16 molecules have shown the possibility to keep an error of second-order correlation energies within 1 milihartree (mH) with respect to MP2-F12 method with dense grids. Numerical tests for a set of 13 isogyric reactions are also performed. 相似文献
84.
Quideau S Deffieux D Pouységu L 《Angewandte Chemie (International ed. in English)》2012,51(28):6824-6826
A votre Santé! The mechanism by which resveratrol, a hydroxystilbenoid polyphenol found in grapes and present in wine, exerts antiaging metabolic benefits has been uncovered. Chung and co-workers have found that it works by inhibiting cAMP phosphodiesterases, thus triggering a signaling cascade that leads to the possible activation of the mammalian enzyme sirtuin?1. 相似文献
85.
86.
Zeng Y Zhang W Xu C Xiao N Huang Y Yu DY Hng HH Yan Q 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):4026-4030
Single-crystalline TiOF(2) nanotubes were prepared by a one-step solvothermal method. The nanotubes are rectangular in shape with a length of 2-3?μm, width of 200-300?nm, and wall thickness of 40-60?nm. The formation of TiOF(2) nanotubes is directly driven by the interaction between TiF(4) and oleic acid in octadecane to form the 1D nanorods, and this is followed by a mass diffusion process to form the hollow structures. The synthesis approach can be extended to grow TiOF(2) nanoparticles and nanorods. Compared with TiO(2), which is the more commonly considered anode material in lithium-ion batteries, TiOF(2) has the advantages of a lower Li-intercalation voltage (e.g., to help increase the total voltage of the battery cell) and higher specific capacities. The TiOF(2) nanotubes showed good Li-storage properties with high specific capacities, stable cyclabilities, and good rate capabilities. 相似文献
87.
The formation and properties of carbonate adducts of some organic hydroxy compounds in aqueous medium were investigated. Fatty alcohols and sugars were chosen as representative classes of biological interest, and the medium was carbonated aqueous solution with pH ranging from 3.0 to 8.3. Capillary electrophoresis with two capacitively coupled contactless conductivity detectors (C4Ds) was used for quantitation and to obtain the mobility of the monoalkyl carbonates (MACs), which were used to determine the equilibrium and kinetic constants of the reaction as well as the diffusion coefficients. For increasing chain length of the alcohols, the equilibrium constant tends to the unit, which suggests that fatty alcohols can form the corresponding MACs. The formation of MACs for cyclohexanol and cyclopentanol also suggest the existence of similar species for sterols. Carbonate adducts of fructose, glucose, and sucrose were also detected, which suggests that these counterparts of the well‐known phosphates can also occur in the cytosol. Our calculations suggest that one in 1000 to one in 10 000 molecules of these hydroxy compounds would be available as the corresponding MAC in such a medium. Experiments carried out at pH values less than 3.0 showed that there is a catalytic effect of hydronium on the interconversion of bicarbonate and a MAC. Taking into account the great number of hydroxy compounds similar to the ones investigated and that bicarbonate is ubiquitous in living cells, one can anticipate the existence of a whole new class of carbonate adducts of these metabolites. 相似文献
88.
Barsan MM Butler IS Gilson DF Moyer RO Zhou W Wu H Udovic TJ 《The journal of physical chemistry. A》2012,116(10):2490-2496
The vibrational spectra of the ternary metal hydride (deuteride) salts, A(2)MH(5) and A(2)MD(5), where A = calcium, strontium and europium and M = iridium(I) and rhodium(I), have been assigned using Raman, Fourier transform infrared, photoacoustic infrared, and inelastic neutron scattering spectroscopies and density functional theory (DFT) calculations. The wavenumbers of the infrared-active stretching vibrations depend upon the ionization energies of the central metal atom and the cation. The phase transition in calcium pentahydridoiridate(I) was studied as a function of temperature and pressure. 相似文献
89.
Farid Ichou Denis Lesage Xavier Machuron‐Mandard Christophe Junot Richard B. Cole Jean‐Claude Tabet 《Journal of mass spectrometry : JMS》2013,48(2):179-186
Control of the ion internal energy in mass spectrometry is needed to establish a workable mass spectral library. The purpose of this study is to understand and to compare the pressure effects on the collision‐induced dissociation (CID) spectrum pattern recorded using triple quadrupole instruments. The monoprotonated Leucine enkephalin [YGGFL, H+] was used as a thermometer molecule to calibrate the electrospray ionization (ESI) and the CID internal energies deposited on the molecular species and the time scale of ion decompositions. The survival yield and the ratio of a4/b4 fragment ions were mainly monitored. The energy uptake for the ESI source geometry used in our study has no impact on the CID spectrum fingerprint. The collision cell pressure for the [YGGFL, H+] has a major influence on the SY curves slope and on the experimental time scale. To demonstrate the pressure effect on internal energy distribution, three models (threshold, thermal and collisional) based on RRKM theory were built using the Masskinetics software. As a result, the limit of each model is discussed, and the investigation demonstrates that the thermal model, using truncated Maxwell‐Boltzmann internal energy distribution, is well‐suited for simulating the experimental data at high pressure widely used in the analytical conditions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
90.
Adrián Schwarzenberg Farid Ichou Richard B. Cole Xavier Machuron‐Mandard Christophe Junot Denis Lesage Jean‐Claude Tabet 《Journal of mass spectrometry : JMS》2013,48(5):576-586
Organophosphorus compounds have played important roles as pesticides, chemical warfare agents and extractors of radioactive material. Structural elucidation of phosphonates poses a particular challenge because their initial forms can be hydrolyzed, thus, degradation products may predominate in samples acquired in the field. The analysis of non‐volatile organophosphorus compounds and their degradation products is possible using electrospray tandem mass spectrometry ESI‐MS/MS. Here, we present a generic strategy that allows the unambiguous identification of substituents for two families of organophosphorus compounds: the phosphonates and phosphates. General fragmentation rules were deduced based on the study of decomposition pathways of 55 organophosphorus esters, including examples found in the literature. Multistage MS (MSn) experiments at high resolution in a hybrid mass spectrometer provide accurate mass measurements, whereas collision‐induced dissociation experiments in a triple quadrupole give access to small fragment ions. The creation of a specific nomenclature for each possible structure of organophosphorus compound, depending on the alkyl side chain linked to the oxygen, was achieved by applying these fragmentation rules. This led to the creation of an ‘identification tree’ based upon the unique consecutive decomposition pathways uncovered for each individual compound. Hence, seven structural motifs were created that orient an unequivocal identification using the ‘identification tree’. Despite the similar structures of the ensemble of phosphate and phosphonate esters, distinct identifications based upon characteristic neutral losses and diagnostic fragment ions were possible in all cases. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献