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81.
Schmidt GT Vlasova N Zuzaan D Kersten M Daus B 《Journal of colloid and interface science》2008,317(1):228-234
Arsenate [As(V)] and arsenite [As(III)] sorption at the solid-water interface of activated carbon impregnated with zirconyl nitrate (Zr-AC) was investigated using X-ray absorption spectroscopy (XAS) and surface complexation modeling. The XAS data at the Zr K-edge suggest that the structure of the zirconyl nitrate coating is built from chains of edge-sharing ZrO8 trigonal dodecahedra bound to each other through two double hydroxyl bridges. The 8-fold coordination of each Zr atom is completed by four O atoms, which share a bit less than the two theoretically possible bidentate nitrate groups. On impregnation, two of the O atoms may lose their nitrate group and be transformed to hydroxyl groups ready for binding to carboxylic or phenolic ligands at the AC surface. As K-edge XANES results showed the presence of only As(V) on adsorption regardless of the initial As oxidation state. Oxidation to As(V) is probably mediated by available carbon species on the AC surface as found by batch titration. Zr K-edge EXAFS data indicate that arsenate tetrahedra form monodentate mononuclear surface complexes with free hydroxyl groups of zirconyl dodecahedra, whereby each bidentate nitrate group is exchanged by up to two arsenate groups. The inner-sphere arsenate binding to the Zr-AC surface sites constrained with the spectroscopic results was used in the formulation of a surface complexation model to successfully describe the adsorption behavior of arsenate in the pH range between 4 and 12. The results suggest therefore that Zr-AC is an effective adsorbent for arsenic removal due to its high surface area and the presence of high affinity surface hydroxyl groups. 相似文献
82.
Mathias Kersten Eberhard Wenschuh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):335-336
Abstract The Thio-ARBUZOV-Reactions has proved to be a facile synthetic route for the conversion of alkoxysulfanes into sulfinyl derivatives. Scope and limitations of the reaction are discussed. BEcause of their donor properties the alkoxysulfanes are suitable ligands which has been confirmed by the preparatoin of palladium(II) complexes. 相似文献
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86.
An efficient method to construct Hamiltonian structures for nonlinear evolution equations is described. It is based on the notions of variational Schouten bracket and ℓ*-covering. The latter serves the role of the cotangent bundle in the category of nonlinear evolution PDEs. We first consider two illustrative examples (the KdV equation and the Boussinesq system) and reconstruct for them the known Hamiltonian structures by our methods. For the coupled KdV–mKdV system, a new Hamiltonian structure is found and its uniqueness (in the class of polynomial (x,t)-independent structures) is proved. We also construct a nonlocal Hamiltonian structure for this system and prove its compatibility with the local one. 相似文献
87.
Sonja Klee Sascha Albrecht Valerie Derpmann Hendrik Kersten Thorsten Benter 《Analytical and bioanalytical chemistry》2013,405(22):6933-6951
We provide experimental and theoretical evidence that the primary ionization process in the dopant-assisted varieties of the atmospheric pressure ionization methods atmospheric pressure photoionization and atmospheric pressure laser ionization in typical liquid chromatography–mass spectrometry settings is—as suggested in the literature—dopant radical cation formation. However, instead of direct dopant radical cation–analyte interaction—the broadly accepted subsequent step in the reaction cascade leading to protonated analyte molecules—rapid thermal equilibration with ion source background water or liquid chromatography solvents through dopant ion–molecule cluster formation occurs. Fast intracluster chemistry then leads to almost instantaneous proton-bound water/solvent cluster generation. These clusters interact either directly with analytes by ligand switching or association reactions, respectively, or further downstream in the intermediate-pressure regions in the ion transfer stages of the mass spectrometer via electrical-field-driven collisional decomposition reactions finally leading to the predominantly observed bare protonated analyte molecules [M?+?H]+. 相似文献
88.
Liu WT Kersten RD Yang YL Moore BS Dorrestein PC 《Journal of the American Chemical Society》2011,133(45):18010-18013
Here, we described the discovery of anti-infective agent arylomycin and its biosynthetic gene cluster in an industrial daptomycin producing strain Streptomyces roseosporus. This was accomplished via the use of MALDI imaging mass spectrometry (IMS) along with peptidogenomic approach in which we have expanded to short sequence tagging (SST) described herein. Using IMS, we observed that prior to the production of daptomycin, a cluster of ions (1-3) was produced by S. roseosporus and correlated well with the decreased staphylococcal cell growth. With a further adopted SST peptidogenomics approach, which relies on the generation of sequence tags from tandem mass spectrometric data and query against genomes to identify the biosynthetic genes, we were able to identify these three molecules (1-3) to arylomycins, a class of broad-spectrum antibiotics that target type I signal peptidase. The gene cluster was then identified. This highlights the strength of IMS and MS guided genome mining approaches in effectively bridging the gap between phenotypes, chemotypes, and genotypes. 相似文献
89.
Kersten H Lorenz M Brockmann KJ Benter T 《Journal of the American Society for Mass Spectrometry》2011,22(6):1063-1069
The performance of a KrF* bench top excimer laser and a compact diode pumped UV solid state (DPSS) Nd:YAG laser as photo-ionizing source in LC-APLI
MS is compared. The commonly applied bench-top excimer laser, operating at 248 nm, provides power densities of the order of
low MW/cm2 on an illuminated area of 0.5 cm2 (8 mJ/pulse, 5 ns pulse duration, beam waist area 0.5 cm2, 3 MW/cm2). The DPSS laser, operating at 266 nm, provides higher power densities, however, on a two orders of magnitude smaller illuminated
area (60 μJ/pulse, 1 ns pulse duration, beam waist area 2 × 10–3 cm2, 30 MW/cm2). In a common LC-APLI MS setup with direct infusion of a 10 nM pyrene solution, the DPSS laser yields a significantly smaller
ion signal (0.9%) and signal to noise ratio (1.4%) compared with the excimer laser. With respect to the determined low detection
limits (LODs) for PAHs of 0.1 fmol using an excimer laser, LODs in DPSS laser LC-APLI MS in the low pmol regime are expected.
The advantages of the DPSS laser with respect to applicability (size, cost, simplicity) may render this light source the preferred
one for APLI applications not focusing on ultimately high sensitivities. Furthermore, the impact of adjustable ion source
parameters on the performance of both laser systems is discussed in terms of the spatial sensitivity distribution described
by the distribution of ion acceptance (DIA) measurements. Perspectives concerning the impact on future APLI-MS applications
are given. 相似文献
90.
On the Plasma Chemistry of an RF Discharge Containing Aluminium Tri‐Isopropoxide Studied by FTIR Spectroscopy
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In Ar and Ar/N2 radio frequency (RF) discharges with admixtures of aluminium tri‐isopropoxide (ATI) the fragmentation of this metal‐organic precursor was studied by means of Fourier Transform Infrared (FTIR) spectroscopy using an optical long path cell providing an optical length of l = 17.2 m. The experiments were performed in an asymmetric capacitively coupled process plasma at a frequency of f = 13.56 MHz and at pres‐sure values in the range of p = 1–10.5 Pa. The discharge power was chosen between P = 10–100 W. Using FTIR spectroscopy the evolution of the concentrations of ATI and of six stable molecules, CH4, C2H2, C2H4, C2H6, CO and HCN, was monitored under flowing conditions at gas flows of Φtotal = 0.5–14.5 sccm in the discharge. The concentrations of the reaction products were measured tobe between 2 x 1012 molecules cm–3 as e.g. found for C2H4and C2H6, and 5 x 1013 molecules cm–3, as e.g. in the case of CO. In the plasma a complete dissociation of the precursor ATI was found at a power value of about P = 80 W independent on the admixture of Ar or N2. The fragmentation efficiency (FE) of the reaction products which originate from the ATI molecules ranges between 0.2 and 4 x 1016 molecules J–1 while the fragmentation rate (FR) reached up to 2.5 x 1018 molecules s–1. The multi component detection ability of the spectrometer served to analyse the carbon balance of the by‐product formation. For all experiments, the carbon balance never exceeded 25%. Therefore, in the plasmas the majority of the provided carbon is most likely deposited at the reactor walls or forms dust particles or higher molecular CxHy. The conversion efficiencies (CE) of the produced molecular species ranges between 0.1 x 1015 molecules J–1 for C2H4 and 5 x 1015 molecules J–1 for C2H6 depending on the discharge conditions of the RF plasma. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献