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11.
Wilfried A. Knig Detlef Icheln Torsten Runge Ingo Pforr Adolf Krebs 《Journal of separation science》1990,13(10):702-707
Transferring the site of specific substitution of dipentylated cyclodextrins with methyl or acyl residues from the secondary 3-hydroxyl group to the primary 6-hydroxyl group was expected to provide new information on the mechanism of chiral recognition. The 3-position points towards and the 6-position points away from the cyclodextrin cavity which via inclusion complex formation is supposed to play a major role in chiral separation. The “inverse” 6-O-acyl-2,3-di-O-pentyl-cyclodextrins displayed almost no enantioselectivity but the corresponding 6-O-methyl derivatives are a versatile supplement to the chiral capillary GC phases nowadays available. Among the compounds that could be enantiomerically resolved are alcohols, amino acids, alkyl halides, bicyclic ethers, acetals, olefins, other hydrocarbons and chiral pharmaceuticals. 相似文献
12.
The intermolecular cyclotrimerisation of terminal and internal alkynes can be catalysed by simple cobalt complexes such as a CoBr2(diimine) under mild reaction conditions when treated with zinc and zinc iodide with high regioselectivity in excellent yields. 相似文献
13.
Joanna Szpunar-Łobińska Michiel Ceulemans Wilfried Dirkx Claudia Witte Ryszard Łobiński Freddy C. Adams 《Mikrochimica acta》1994,113(3-6):287-298
Interferences in trace and ultratrace speciation analysis of organotin and organolead compounds in various samples by gas chromatography coupled with atomic absorption spectrometry (AAS) and/or microwave induced plasma atomic emission spectrometry (MIP AES) are investigated. Particular attention is given to the effects of matrix co-extractives and reagents impurities introduced during sample preparation. Their influence on the detection limits is discussed in terms of baseline noise level, blank value, formation of artefacts and signal suppression. Loss of column resolution during the analysis of some matrices is observed. 相似文献
14.
Wilfried Heller 《Journal of Polymer Science.Polymer Physics》1966,4(2):209-226
The principles of a method are outlined whereby one can determine the partial specific volume of a solute, V?, by means of measurements of dn/dc using a suitable pair of equations and a simple graphical interpolation procedure. The method yields V? data which compare well with densitometrically obtained V? data if the polarizability of both solvent and solute molecules is unaffected by the solution process. It is tested successfully on solutions of polystyrene in various solvents. The method appears to be particularly attractive for measurements of the change of V? with temperature and also for conveniently following the time rate of changes in - such as during the coil → helix transition. 相似文献
15.
Zusammenfassung Es wird eine qualitative und eine quantitative Methode zum Nachweis und zur Bestimmung der Haupt- und einiger Nebenprodukte in den Laugen des technischen Dicyandiamid/Melamin-Prozesses vorgeschlagen. Der in bezug auf ihre Zusammensetzung komplexe Charakter dieser Laugen erfordert insbesondere bei der quantitativen Analyse (Ammelin, Melamin, Rhodanid, Thioharnstoff, Eisenverbindungen) die Beachtung einer Reihe von Störmöglichkeiten. Die Verfahren wurden mit synthetischen Gemischen getestet und in der betrieblichen Praxis überprüft.
Mitteilung aus dem Institut für Organische Chemie der E.-M.-A.-Universität Greifswald (Direktor: Prof. Dr. H. Beyer). Die Arbeit wurde im Rahmen der Vertragsforschung mit dem VEB Stickstoffwerk Piesteritz durchgeführt.
Wir danken den Herren Dr. H. Brandner und Dr. H. Lemke vom VEB Stickstoffwerk Piesteritz für die erwiesene Unterstützung sowie der Werkleitung für die Genehmigung zur Veröffentlichung dieser Arbeit. 相似文献
Summary A qualitative and a quantitative procedure is described for the analysis of the main and by-products in the liquors of the industrial dicyanodiamide/melamine process. The complex composition of the liquors requires consideration of a number of interferences, especially in quantitative analysis (ammeline, melamine, thiocyanate, thiourea, iron compounds). The procedures have been tested by means of synthetic mixtures and controlled in commercial-scale production.
Mitteilung aus dem Institut für Organische Chemie der E.-M.-A.-Universität Greifswald (Direktor: Prof. Dr. H. Beyer). Die Arbeit wurde im Rahmen der Vertragsforschung mit dem VEB Stickstoffwerk Piesteritz durchgeführt.
Wir danken den Herren Dr. H. Brandner und Dr. H. Lemke vom VEB Stickstoffwerk Piesteritz für die erwiesene Unterstützung sowie der Werkleitung für die Genehmigung zur Veröffentlichung dieser Arbeit. 相似文献
16.
Zachariasse KA Druzhinin SI Bosch W Machinek R 《Journal of the American Chemical Society》2004,126(6):1705-1715
Fast and efficient intramolecular charge transfer (ICT) and dual fluorescence is observed with the planarized aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) in a series of solvents from n-hexane to acetonitrile and methanol. Such a reaction does not take place for the related molecules with 1-isopropyl (NIC6) and 1-methyl (NMC6) groups, nor with the 1-alkyl-5-cyanoindolines with methyl (NMC5), isopropyl (NIC5), or tert-butyl (NTC5) substituents. For these molecules, a single fluorescence band from a locally excited (LE) state is found. The charge transfer reaction of NTC6 is favored by its relatively small energy gap DeltaE(S(1),S(2)), in accordance with the PICT model for ICT in aminobenzonitriles. For the ICT state of NTC6, a dipole moment of around 19 D is obtained from solvatochromic measurements, similar to micro(e)(ICT) = 17 D of 4-(dimethylamino)benzonitrile (DMABN). For NMC5, NIC5, NTC5, NMC6, and NIC6, a dipole moment of around 10 D is determined by solvatochromic analysis, the same as that of the LE state of DMABN. For NTC6 in diethyl ether at -70 degrees C, the forward ICT rate constant (1.3 x 10(11) s(-1)) is much smaller than that of the back reaction (5.9 x 10(9) s(-1)), showing that the equilibrium is on the ICT side. The results presented here make clear that ICT can very well take place with a planarized molecule such as NTC6, when DeltaE(S(1),S(2)) is sufficiently small, indicating that a perpendicular twist of the amino group relative to the rest of the molecule is not necessary for reaching an ICT state with a large dipole moment. The six-membered alicyclic ring in NMC6, for example, prevents ICT by increasing DeltaE(S(1),S(2)) relative to that of DMABN. 相似文献
17.
David Falck Anna J. Oosthoek-de Vries Ard Kolkman Henk Lingeman Maarten Honing Sybren S. Wijmenga Arno P. M. Kentgens Wilfried M. A. Niessen 《Analytical and bioanalytical chemistry》2013,405(21):6711-6720
Flow-through electrochemical conversion (EC) of drug-like molecules was hyphenated to miniaturized nuclear magnetic resonance spectroscopy (NMR) via on-line solid-phase extraction (SPE). After EC of the prominent p38α mitogen-activated protein kinase inhibitor BIRB796 into its reactive products, the SPE step provided preconcentration of the EC products and solvent exchange for NMR analysis. The acquisition of NMR spectra of the mass-limited samples was achieved in a stripline probe with a detection volume of 150 nL offering superior mass sensitivity. This hyphenated EC–SPE–stripline-NMR setup enabled the detection of the reactive products using only minute amounts of substrate. Furthermore, the integration of conversion and detection into one flow setup counteracts incorrect assessments caused by the degradation of reactive products. However, apparent interferences of the NMR magnetic field with the EC, leading to a low product yield, so far demanded relatively long signal averaging. A critical assessment of what is and what is not (yet) possible with this approach is presented, for example in terms of structure elucidation and the estimation of concentrations. Additionally, promising routes for further improvement of EC–SPE–stripline-NMR are discussed. 相似文献
18.
Richard A. Bunce James E. Schammerhorn Jessica Sigle 《Journal of heterocyclic chemistry》2013,50(2):373-380
A tandem imine addition‐SNAr annulation reaction has been developed as a new approach to the synthesis of 4‐oxo‐1,2,3,4‐tetrahydroquinoline‐3‐carboxylic esters. A series of these structures has been generated by reacting selected imines with tert‐butyl 2‐fluoro‐5‐nitrobenzoylacetate. Structural variations in the final products are accomplished by changing the substituents on the imine and the alkyl group of the ester. The title compounds are isolated as their enols in 55–97% yield without the need for added base or catalysts. The synthesis of the starting materials as well as mechanistic studies and further synthetic conversions of the products are presented. 相似文献
19.
Prof. Dr. Sjoerd Harder Dominik Naglav Dr. Christian Ruspic Prof. Dr. Claudia Wickleder Dr. Matthias Adlung Dr. Wilfried Hermes Dr. Matthias Eul Prof. Dr. Rainer Pöttgen Dr. Daniel B. Rego Prof. Dr. Frederic Poineau Prof. Dr. Kenneth R. Czerwinski Prof. Dr. Rolfe H. Herber Prof. Dr. Israel Nowik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12173-12173
20.
Gerda Rogl Viktor Soprunyuk Wilfried Schranz Michael J. Zehetbauer Jiri Bursik Herbert Müller Ernst Bauer Peter F. Rogl 《无机化学与普通化学杂志》2020,646(14):1267-1272
Thermoelectric materials with a high figure of merit, ZT, are the essential basis to build thermoelectric generators, which can directly convert heat into electricity. Severe plastic deformation (SPD) via high-pressure torsion (HPT) was successfully applied to enhance ZT of ball-milled and hot-pressed skutterudites as well as to produce bulk nanostructured skutterudites directly from powders. SPD introduces many defects into the sample and in parallel the crystallite size is significantly reduced. During measurement-induced heating these defects anneal partially out, and the grains grow. In this work for the first time systematically the changes of the temperature-dependent electrical resistivity and of thermal expansion were compared. It could be shown that for p- and n-type skutterudites, being hot-pressed and HPT-processed as well as directly HPT-processed from compacted powder, these changes occur more or less simultaneously within the same temperature ranges. This evaluation gives a much deeper insight into the thermoelectric behavior of HPT samples under the influence of changing temperature. 相似文献