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181.
Jinxiong Lin Dr. Friedrich Wossidlo. Dr. Nathan T. Coles Manuela Weber Dr. Simon Steinhauer Priv.-Doz. Dr. Tobias Böttcher Prof. Dr. Christian Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202104135
A phosphinine-borane adduct of a Me3Si-functionalized phosphinine and the Lewis acid B(C6F5)3 has been synthesized and characterized crystallographically for the first time. The reaction strongly depends on the nature of the substituents in the α-position of the phosphorus heterocycle. In contrast, the reaction of B2H6 with various substituted phosphinines leads to an equilibrium between the starting materials and the phosphinine–borane adducts that is determined by the Lewis basicity of the phosphinine. The novel phosphinine borane adduct ( 6 -B(C6F5)3) shows rapid and facile insertion and [4+2] cycloaddition reactivity towards phenylacetylene. A hitherto unknown dihydro-1-phosphabarrelene is formed with styrene. The reaction with an ester provides a new, facile and selective route to 1-R-phosphininium salts. These salts then undergo a [4+2] cycloaddition in the presence of Me3Si−C≡CH and styrene to cleanly form unprecedented derivatives of 1-R-phosphabarrelenium salts. 相似文献
182.
Mingming Huang Dr. Jiefeng Hu Shasha Shi Dr. Alexandra Friedrich Johannes Krebs Prof. Dr. Stephen A. Westcott Prof. Dr. Udo Radius Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(24):e202200480
Defunctionalization of readily available feedstocks to provide alkenes for the synthesis of multifunctional molecules represents an extremely useful process in organic synthesis. Herein, we describe a transition metal-free, simple and efficient strategy to access alkyl 1,2-bis(boronate esters) via regio- and diastereoselective diboration of secondary and tertiary alkyl halides (Br, Cl, I), tosylates, and alcohols. Control experiments demonstrated that the key to this high reactivity and selectivity is the addition of a combination of potassium iodide and N,N-dimethylacetamide (DMA). The practicality and industrial potential of this transformation are demonstrated by its operational simplicity, wide functional group tolerance, and the late-stage modification of complex molecules. From a drug discovery perspective, this synthetic method offers control of the position of diversification and diastereoselectivity in complex ring scaffolds, which would be especially useful in a lead optimization program. 相似文献
183.
We examine the life, work, and legacy of Clara Haber, nee Immerwahr, who became the first woman to earn a doctorate from the University of Breslau, in 1900. In 1901 she married the chemist Fritz Haber. With no employment available for female scientists, Clara freelanced as an instructor in the continued education of women, mainly housewives, while struggling not to become a housewife herself. Her duties as a designated head of a posh household hardly brought fulfillment to her life. The outbreak of WWI further exacerbated the situation, as Fritz Haber applied himself in extraordinary ways to aid the German war effort. The night that he celebrated the “success” of the first chlorine cloud attack, Clara committed suicide. We found little evidence to support claims that Clara was an outspoken pacifist who took her life because of her disapproval of Fritz Haber's involvement in chemical warfare. We conclude by examining “the myth of Clara Immerwahr” that took root in the 1990s from the perspective offered by the available scholarly sources, including some untapped ones. 相似文献
184.
Dirk Pohle Sabine Ponader Thomas Rechtenwald Michael Schmidt Karl Andreas Schlegel Helmut Münstedt Friedrich Wilhelm Neukam Emeka Nkenke Cornelius von Wilmowsky 《Macromolecular Symposia》2007,253(1):65-70
Summary: The following investigation focuses on polyetheretherketone (PEEK) for bone substitutes intended for maxillofacial surgery. Different three-dimensional discs with a diameter of 12 mm and a height of 3 mm were laser sintered. As filler materials nano-sized carbon black and β-tricalciumphosphate powder with an average grain size of 35 µm were used. Human osteoblasts were cultivated on the discs and examined with scanning electron microscopy. Cell vitality and cell growth was investigated. The data shows that PEEK surfaces does not suppress osteoblast proliferation. 相似文献
185.
SYNTHESIS OF POSITIVELY CHARGED PHTHALOCYANINES and THEIR ACTIVITY IN THE PHOTODYNAMIC THERAPY OF CANCER CELLS 总被引:1,自引:0,他引:1
D. Wöhrle N. Iskander G. Graschew H. Sinn E. A. Friedrich W. Maier-Borst J. Stern P. Schlag 《Photochemistry and photobiology》1990,51(3):351-356
Positively charged zinc containing or metal free phthalocyanines 6a-c and 7a-c were prepared via a three step procedure starting from 4-nitrophthalonitrile. The phthalocyanines contain alkyl chains of different length in order to influence the hydrophilic vs lipophilic character of the compounds. The partition between a hydrophilic (water) and lipophilic (octanol-1) phase was determined, and the photoredox activities were investigated. Initial results on the photodynamic activity of these compounds were compared with those of Dougherty's Photofrin II on different malignant and non-malignant cell lines (XP 29MAmal, CX1, HeLa, S180 and NO17). Positively charged phthalocyanines in vitro showed a higher photodynamic activity than Photofrin II. 相似文献
186.
Bretting H Buck F Jacobs G Meinke S Scheppokat AM Thiem J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(25):7144-7152
Snails from the family Helicidae produce in their albumen glands a highly branched galactan, which consists almost exclusively of D- and L-galactose. The D-Gal residues are glycosydically beta(1-->6)- or beta(1-->3)-linked, whereas the L-Gal moieties are attached alpha(1-->2). Up until the present time, two beta(1-->6)-D-galactosyl transferases and one alpha(1-->2)-L-galactosyl transferase have been identified in a membrane preparation of these glands. These were used to synthesise various oligosaccharides by successive addition of the NDP-activated (NDP=nucleoside-5'-diphosphate) D-Gal or L-Fuc moieties, up to a heptasaccharide by starting from the disaccharide D-Gal-beta(1-->3)-D-Gal-beta(1-->OMe. Even larger oligosaccharides up to a tridecasaccharide were obtained by starting with the hexasaccharide D-Gal-[beta(1-->3)-D-Gal]4-beta(1-->4)-D-Glc as an acceptor substrate. This tandem exploitation process has high potential for the easy introduction of D-Gal and L-Fuc residues into a great variety of oligosaccharides, which can be used in ligand/acceptor studies. 相似文献
187.
Yvar Van Den Winkel Jeroen Van Der Laarse Frans J. J. De Kanter Thomas Van Der Does Friedrich Bickelhaupt Wilberth J. J. Smeets Anthony L. Spek 《Heteroatom Chemistry》1991,2(1):17-28
The synthesis of 2,2′-bis(bis(dimethylamino)-phosphino)-3,3′5,5′-tetra-tert-butylbiphennyl ( 5 ) is described. It was extensively studied by 1H, 13C, and 31P NMR spectroscopy. Furthermore, the X-ray analysis of 5 is reported. Crystals of 5 are tetragonal, space group P¯421c, a = b = 24.770 (3) Å, c = 12.658 (4) Å, Z = 8. The surprising reaction of 5 with proton acids leading to the formation of various phosphorus containing five- and six-membered ring compounds is discussed. On reaction of one of the six-membered ring compounds ( 9 ) with magnesium in THF, a λ3, λ5-diphosphaphenanthrene ( 19 ) was obtained. 相似文献
188.
189.
A procedure is developed that allows the calculation of chain-length distributions of polymers prepared by periodic modulation of the termination rate constant, considering termination by disproportionation. Applying some (hypothetical) field which suppresses — or at least diminishes — the termination rate constant periodically, results in step-function-like chain-length distributions. In principle, the same information may be obtained as in the case of periodical variation of the rate of initiation. 相似文献
190.
G. Woelki S. Friedrich G. Hanschmann R. Salzer 《Analytical and bioanalytical chemistry》1997,357(5):548-552
Different soil extracted humic acids as well as a commercial humic acid sodium salt were fractionated by HPLC. An almost
complete recovery could be achieved for the dissolved material. All humic samples show a typical chromatogram of at least
five fractions. The separation of humic substances is influenced by an altered hydrophobicity due to changes in the tertiary
structure. Three fractions were further investigated by Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy
and by HPLC/HPLC separation. DRIFT spectroscopy provided data on the primary structure, whereas HPLC/HPLC results gave insight
into the secondary and tertiary structure and their changes.
Received: 18 June 1996 / Revised: 9 October 1996 / Accepted: 12 October 1996 相似文献