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21.
A rapid and inexpensive method for the large-scale purification of C60 is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C60 with ethyl and tert-butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene-bridged isomers 1a – 3a and 1b – 3b , respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b , respectively. Isomers 1a / b possess the methano bridge at the 6–6 ring junction, whereas structures 2a / b and 3a / b are bridged at the 6–5 junction. A dramatic influence of local and π-ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a / b and over a hexagon ring in 3a / b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the 13C-NMR chemical shifts of the bridgehead C-atoms and the 1J(C,H) coupling constants for the methano-bridge atoms reveals conclusively that the 6-5-ring-bridged structures 2a / 2b and 3a / 3b are π-homoaromatic (‘open’ transannular bond) and the 6-6-ring-bridged structures 1a / b are π-homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π-homoconjugation in 2a / b and 3a / b represents a much smaller electronic perturbation of the original C60 chromophore than σ-homoconjugation in 1a / b . The results of this study demonstrate an impressive linkage between the chemistry of methano-bridged annulenes and methano-bridged fullerenes. 相似文献
22.
Brigitte Sarry und Arno Lange 《Fresenius' Journal of Analytical Chemistry》1968,241(3):186-196
Zusammenfassung Die optimalen Bedingungen für die photometrische Bestimmung von Tantal mit Pyrogallol in schwefelsaurer Lösung bei 405 nm wurden ausgearbeitet. Das Verfahren wurde statistisch überprüft.
Für die Durchführung der Untersuchungen standen Mittel aus dem ERP-Sondervermögen und dem Fonds der Chemischen Industrie zur Verfügung, für die wir auch an dieser Stelle bestens danken.
Herrn Professor Dr. E. Asmus zum 60. Geburtstag gewidmet. 相似文献
Investigations on the photometric determination of tantalum with pyrogallol
The optimum conditions for the photometric determination of tantalum with pyrogallol in sulphuric acid solution at 405 nm have been elaborated. The method has been checked statistically.
Für die Durchführung der Untersuchungen standen Mittel aus dem ERP-Sondervermögen und dem Fonds der Chemischen Industrie zur Verfügung, für die wir auch an dieser Stelle bestens danken.
Herrn Professor Dr. E. Asmus zum 60. Geburtstag gewidmet. 相似文献
23.
Philipp Wagener Marcus Lau Sandra Breitung-Faes Arno Kwade Stephan Barcikowski 《Applied Physics A: Materials Science & Processing》2012,108(4):793-799
Combination of wet-grinding and laser fragmentation is a promising approach to advance both methods: Laser fragmentation will be more efficient when combined with mechanical treatment and wet-grinding may take advance of the abrasion-free laser process to achieve fabrication of smaller particles. By mechanical pre-treatment of zinc oxide microparticles in a stirred-media mill, the starting material is activated by generation of crystallographic defects, which strongly enhance the efficiency of subsequent laser fragmentation. Picosecond-laser irradiation of mechanically treated and untreated microparticles suspended in water yielded in colloidal zinc oxide nanoparticles. Furthermore, nanoparticle productivity and properties can be controlled by variation of anionic surfactant concentration. 相似文献
24.
Some cases of the LFED Conjecture, proposed by the second author [15], for certain integral domains are proved. In particular, the LFED Conjecture is completely established for the field of fractions of the polynomial algebra , the formal power series algebra and the Laurent formal power series algebra , where denotes n commutative free variables and k a field of characteristic zero. Furthermore, the relation between the LFED Conjecture and the Duistermaat–van der Kallen Theorem [3] is also discussed and emphasized. 相似文献
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Arno M. Bieser 《Supramolecular chemistry》2013,25(4):363-367
This article highlights the aggregation behaviour of potential low molecular weight hydrogelators on attracting surfaces. Our goal was the development of a method, which enables the finding of new hydrogelators that are not easily recognizable as such because they only form instable or no hydrogels in aqueous solution. To this end, a series of negatively charges azo-dyes was synthesized and positive charged glass slides were immersed into their aqueous solutions. All dyes showed supramolecular organization and significant concentration on the attracting glass surface. Microscopic investigations mostly revealed the formation of crystals. However, one compound, (1-(2-n-octylphenylazo)-2-hydroxy-6-naphthalenesulphonate, selectively formed a hydrogel on the surface whereas it does not gel in aqueous solution. This reveals the hydrogel as the stable form of this compound under equilibrium conditions. This method of surface-induced hydrogelation might facilitate the identification of new hydrogelators. Further more, it might also allow the mimicking of surface gelation as a process of biological relevance. 相似文献
29.
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
30.
Highly Selective Dimerization and Trimerization of Isobutene to Linearly Linked Products by Using Nickel Catalysts
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Prof. Arno Behr Nils Rentmeister Thomas Seidensticker Jonas Vosberg Dr. Stephan Peitz Dr. Dietrich Maschmeyer 《化学:亚洲杂志》2014,9(2):596-601
The unique linear linkage of isobutene to generate highly valuable C8 precursors for plasticizers is feasible by using special nickel catalysts. (4‐Cyclooctene‐1‐yl)(1,1,1,5,5,5‐hexafluoro‐2,4‐acetylacetonato)nickel and aluminum‐alkyl‐activated nickel acetylacetonates produce isobutene dimers with high selectivities of up to 95 %. Moreover, selectivity for the head‐to‐head products (2,5‐dimethylhexenes) is remarkably high at up to 99 %. Additionally, novel C12 isobutene trimers are also formed with a very high selectivity of up to 99 % for the linear linkage. The trimer structure (2,5,8‐trimethylnonenes) reflects the stepwise characteristic of the reaction mechanism. Pathways of insertion and activation and the deactivation processes of the catalyst are discussed in detail. 相似文献