Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

Spatial intensity distributions from electron impact scattering modes: W{100}(1 × 1)H

The detailed mechanism of electron energy loss vibrational spectroscopy has been examined in the present study by recording a large data base of spectra with the detector moved both in and out of the incidence plane, for saturation coverage of atomic H adsorbed on W{1OO} at 300 K. In agreement with earlier work we find only a single electron loss (130 meV) in the specular direction, while away from the specular direction additional losses at 80 meV and 160 meV appear. These losses correspond to the symmetric stretching, the wagging and the asymmetric stretching modes respectively of H atoms occupying a C_2V bridge site. Large intensity variations of all these modes are found in backscattering directions and out of the incidence plane, in general agreement with recent theoretical predictions. The usefulness of these spatial intensity variations in adsorbate structure determination will be discussed. The signal enhancement with electron collection in the plane orthogonal to the incidence plane may allow the observation of otherwise weak impact modes.     

A Heck–Matsuda Process for the Synthesis of β‐Arylethenesulfonyl Fluorides: Selectively Addressable Bis‐electrophiles for SuFEx Click Chemistry

A Heck–Matsuda process for the synthesis of the otherwise difficult to access compounds, β‐arylethenesulfonyl fluorides, is described. Ethenesulfonyl fluoride (i.e., vinylsulfonyl fluoride, or ESF) undergoes β‐arylation with stable and readily prepared arenediazonium tetrafluoroborates in the presence of the catalyst palladium(II) acetate to afford the E‐isomer sulfonyl analogues of cinnamoyl fluoride in 43–97 % yield. The β‐arylethenesulfonyl fluorides are found to be selectively addressable bis‐electrophiles for sulfur(VI) fluoride exchange (SuFEx) click chemistry, in which either the alkenyl moiety or the sulfonyl fluoride group can be the exclusive site of nucleophilic attack under defined conditions, making these rather simple cores attractive for covalent drug discovery.     

Electronic properties and charge transfer phenomena in Pt nanoparticles on γ-Al(2)O(3): size, shape, support, and adsorbate effects

This study presents a systematic detailed experimental and theoretical investigation of the electronic properties of size-controlled free and γ-Al(2)O(3)-supported Pt nanoparticles (NPs) and their evolution with decreasing NP size and adsorbate (H(2)) coverage. A combination of in situ X-ray absorption near-edge structure (XANES) and density functional theory (DFT) calculations revealed changes in the electronic characteristics of the NPs due to size, shape, NP-adsorbate (H(2)) and NP-support interactions. A correlation between the NP size, number of surface atoms and coordination of such atoms, and the maximum hydrogen coverage stabilized at a given temperature is established, with H/Pt ratios exceeding the 1?:?1 ratio previously reported for bulk Pt surfaces.     

Biocompatible SuFEx Click Chemistry: Thionyl Tetrafluoride (SOF4)‐Derived Connective Hubs for Bioconjugation to DNA and Proteins

We report here the development of a suite of biocompatible SuFEx transformations from the SOF₄‐derived iminosulfur oxydifluoride hub in aqueous buffer conditions. These biocompatible SuFEx reactions of iminosulfur oxydifluorides (R‐N=SOF₂) with primary amines give sulfamides (8 examples, up to 98 %), while the reaction with secondary amines furnish sulfuramidimidoyl fluoride products (8 examples, up to 97 %). Likewise, under mild buffered conditions, phenols react with the iminosulfur oxydifluorides (Ar‐N=SOF₂) to produce sulfurofluoridoimidates (13 examples, up to 99 %), which can themselves be further modified by nucleophiles. These transformations open the potential for asymmetric and trisubstituted linkages projecting from the sulfur(VI) center, including versatile S?N and S?O connectivity (9 examples, up to 94 %). Finally, the SuFEx bioconjugation of iminosulfur oxydifluorides to amine‐tagged single‐stranded DNA and to BSA protein demonstrate the potential of SOF₄‐derived SuFEx click chemistry in biological applications.     

Bioconversion of a L-carnitin precursor in a one- or two-phase system

Applied Biochemistry and Biotechnology - The ability of the yeastSaccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol,...     

Orientation of chemisorbed species from electron impact and dipole selection rules: The formate ion on Pt{110}

Selection rules in high resolution electron energy loss spectroscopy are shown to permit a determination of the structure of formate ions adsorbed on Pt{110} from data obtained on and off specular along three different azimuthal directions. Long-range dipole scattering indicates that the ion is adsorbed upright bonding, through the two oxygen atoms. Shorter-range impact scattering provides the further information that the ion is coplanar with the 〈110〉 direction and tilted (in the same plane) through at most 10^° from the surface normal.     

Split-pool method for synthesis of solid-state material combinatorial libraries

The synthesis and analysis of inorganic material combinatorial libraries by the split-pool bead method were demonstrated at the proof-of-concept level. Millimeter-size spherical beads of porous gamma-alumina, a commonly used support material for heterogeneous catalysts, were modified with Al(13)O(4)(OH)(24)(H(2)O)(12)(7+) cations in order to promote irreversible adsorption of the anionic fluorescent dyes Cascade Blue, Lucifer Yellow, and Sulforhodamine 101. The compositions of individual beads were easily determined through three split-pool cycles using a conventional fluorescence plate reader. Small split-pool material libraries were made by adsorbing noble metal salts (H(2)PtCl(6), H(2)IrCl(6), and RhCl(3)) into the beads. Analysis of these beads by micro-X-ray fluorescence showed that quantitative adsorption of metal salts without cross-contamination of beads could be achieved at levels (0.3 wt % metal loading) relevant to heterogeneous catalysis. The method offers the potential for synthesis of rather large libraries of inorganic materials through relatively simple benchtop split-pool chemistry.     

Ultrasonics promoted synthesis of thiazolidinones from 2-aminopyridine and 2-picolilamine

The efficient multicomponent synthesis of thiazolidinones from the reaction of arenealdehydes, mercaptoacetic acid and 2-picolilamine or 2-aminopyridine under ultrasound irradiation are reported. The reaction with 2-aminopyridine needs a Lewis acid catalysis to afford the corresponding 2-aryl-3-(pyridin-2-yl)-1,3-thiazolidin-4-ones. All novel compounds were identified and characterized by (1)H and (13)C NMR spectra. Applying the sonochemical methodology, two series of heterocyclic thiazolidinones were synthesized in good yields after short reaction times.     

怀孕期头发中一些元素含量的变化趋势

用同步辐射激发X射线荧光分析,对11个产妇怀孕期间头发内一些元素含量的变化趋势进行了测量,在各自对比的基础上,得到了一些结果。