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41.
A simplified high-pressure liquid chromatograhic method for determination of furosemide in plasma and urine has been developed using a fluorometric detector directly coupled to the column effluent. The method includes an ether extraction from acidified biologic samples. The mobile phase used for chromatography on a reversed-phase column (C15 hydrocarbon permanently bonded to silica particles) is sufficiently acidic to induce fluorescence of furosemide. The methylester of furosemide is employed as an internal standard. The sensitivity is 0.1 and 0.25 microgram per ml plasma and urine, respectively. The applicability to pharmacokinetic studies of furosemide is shown. 相似文献
42.
The stereoselectivity of the α-alkylation of chiral β-hydroxy ester is discussed. The configuration of the alkylated product was proved chemically (Scheme 2). A one pot aldol-alkylation reaction was developed leading stereoselectively to racemic (s*,s*)-α-alkyl-β-hydroxy ester (Scheme 3,4). Baker's yeast reduction of 2-alkyl-3-keto ester led to valuable chiral (2RS,3S)-intermediates, which were converted via the corresponding dianion to compounds with a chiral quaternary C atom (Scheme 6). Synthetic applications of the above findings are shown in the synthesis of various chiral compounds (Scheme 8 and 9). 相似文献
43.
Brieler FJ Grundmann P Fröba M Chen L Klar PJ Heimbrodt W Krug von Nidda HA Kurz T Loidl A 《Journal of the American Chemical Society》2004,126(3):797-807
Arrays of highly ordered Zn(1-x)MnxS quantum wires with x ranging from 0.01 to 0.3 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p6m) and the high degree of order was confirmed by X-ray diffraction and transmission electron microscopy (TEM) studies. Physisorption measurements show the progressive filling of the pores of the SiO2 host structures, while TEM and Raman studies reveal the wire-like character of the incorporated Zn(1-x)MnxS nanostructures. X-ray absorption near-edge structure, extended X-ray absorption fine structure, photoluminescence excitation (PLE), and electron paramagnetic resonance studies confirm the good crystalline quality of the incorporated Zn(1-x)MnxS guest species and, in particular, that the Mn2+ ions are randomly distributed and are situated on tetrahedrally coordinated cation sites of the Zn(1-x)MnxS wires for all x up to 0.3. The amount of Mn2+ ions loosely bound to the surface of the Zn(1-x)MnxS nanowires is less than 4% of the total Mn content even for the 3 nm nanostructures up to the highest Mn content of x = 0.3. The effects of the reduction of the lateral dimensions on electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap with decreasing particle size is observed. 相似文献
44.
Xu M Brahmachary E Janco M Ling FH Svec F Fréchet JM 《Journal of chromatography. A》2001,928(1):25-40
Uniformly sized macroporous polymer beads, which can be used as chiral stationary phase (CSP), have been prepared by the staged templated suspension polymerization process using chiral monomer as one of the copolymerization components. This approach enables the preparation of CSPs for which properties such as pore size, pore volume, surface area, chemistry, and chiral ligands can be tuned over a broad range. Several types of well-defined chiral monomers were prepared and allowed to assess synergistic effect of multiple selectors attached to a branched linker as well as the effect of the length and chemistry of the linker. Microscale batch screening was used for simple and rapid evaluation of selectivity. The most promising candidate CSPs were prepared on a larger scale and packed into HPLC columns. Their performance was demonstrated on the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkylamides. The highest separation factors alpha of up to 27 were observed for CSPs prepared from monomers containing the branched spacer. These highly selective CSPs also enabled the separation of larger amounts of the target racemates upon column overload conditions. 相似文献
45.
The indolizidinium alkaloid ipalbidinium and the quinolizidinium alkaloid clathryimine B were prepared starting from brominated
2-aminopyridines using two Pd-catalyzed cross-coupling reactions and a Sandmeyer-type diazotation/iodination protocol as the key steps. 相似文献
46.
Bosman AW Vestberg R Heumann A Fréchet JM Hawker CJ 《Journal of the American Chemical Society》2003,125(3):715-728
A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction. 相似文献
47.
Resorc[4]arenes are compounds with interesting properties, mainly because of their ability to form host-guest complexes with the guest located inside the cavity. The size of the guest limits the complexation, as shown by a competition experiment with tetraalkylammonium ions of different size. By electroscopy ionization tandem mass spectrometric experiments on resorc[4]arene heterodimers bearing an alkali metal ion as guest, it was found that there must be two different binding mechanisms for alkali metal ions with high surface charge density (Li(+) and Na(+)) on the one hand compared with those with a lower surface charge density on the other hand (K(+), Rb(+), Cs(+)). 相似文献
48.
Porphyrin and pyrene photoactive cores have been encapsulated within an isolating polymeric shell using an efficient and general strategy based on the use of dendritic initiators for the ring-opening polymerization of epsilon-caprolactone to yield functional core star polymers. The isolation of the core functionalities has been studied using fluorescence quenching and fluorescence resonance energy transfer (FRET) techniques as well as solvatochromic probes. With increasing chain length as well as solvent polarity, enhanced site isolation of the core has been observed. These findings have been correlated to actual molecular dimensions independently measured by pulsed field gradient spin-echo (PGSE) NMR. The developed synthetic methodology offers a rapid route to efficient encapsulation of functional moieties and therefore has potential for the design of new materials. 相似文献
49.
[reaction: see text]. The alpha-deprotonation of alkynyl carbamates 3 with the chiral base (-)-sparteine (4)/n-butyllithium, transmetalation with ClTi(O(i)()Pr)3, and subsequent substitution with an aldehyde results in the formation of enantioenriched 4-hydroxyallenyl carbamates 11. Stereoselection is determined by dynamic resolution of the lithium/(-)-sparteine complexes by selective crystallization. 相似文献
50.
Zusammenfassung Die Polymerisation des Phosphornitrilchlorids in Substanz erweist sich als thermisch gestartete Radikalpolymerisation, die mit gleicher Geschwindigkeit und gleicher Temperaturabhängigkeit wie die durch Sauerstoff aktivierte Polymerisation in Lösung verläuft. Schon geringer Lösungsmittelzusatz bringt die thermische Polymerisation zum Erliegen. Ein Reaktionsschema mit Start-Kette-Abbruch wird diskutiert, das sowohl die Substanz- wie die Lösungspolymerisation wiedergibt. Der seinerzeit beschriebene Einfluß von Sauerstoff auf den Ablauf der Polymerisation erfährt dadurch eine wesentliche Korrektur.Die Depolymerisation von polymerem Phosphornitrilchlorid wird von 350 bis 600° C verfolgt und als gegenläufige Reaktionsfolge zur Polymerisation gefunden. Für das aus Polymerisation und Depolymerisation resultierende Gleichgewicht werden Druck- und Temperaturabhängigkeit festgestellt.Mit 8 Abbildungen.Herrn Prof. Dr.A. Klemenc zu seinem 70. Geburtstage gewidmet.Als I soll die ArbeitPatat-Kollinsky
1 Über die Polymerisation des Phosphornitrilchlorids1 gelten, die im folgenden Text auch mit (I) bezeichnet wird.— Eine Literaturzusammenstellung Phosphornitrilchlorid findet sich in der Monographie vonL. F. Audrieth, R. Steinmann undA. O. F. Toy, Chem. Rev.32, 109 (1943). 相似文献