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971.
972.
973.
974.
Lipophilicity study of eight cephalosporins by reversed‐phase thin‐layer chromatographic method 下载免费PDF全文
Monika Dąbrowska Łukasz Komsta Jan Krzek Kinga Kokoszka 《Biomedical chromatography : BMC》2015,29(11):1759-1768
The lipophilicity (RM0) and specific hydrophobic surface area for the representatives of four generation cephalosporins have been determined by reversed‐phase thin‐layer chromatography, and the effect of different mobile‐phase modifiers (such as methanol, acetonitrile, acetone, 1,4‐dioxane and 2‐propanol) on the retention has been studied. The compounds studied showed typical retention behavior; their RM values decreased linearly with increasing concentration of the organic modifier in the eluent. The linear correlations between the volume fraction of the organic solvent and the RM values over a limited range were established for each solute, resulting in high values of correlation coefficients (>0.95 in most cases). RM values were determined by various concentrations of organic modifier, and the correlation obtained was extrapolated to 0% of organic modifier. Chromatographically established logP (RM0) parameters were compared with computationally calculated partition coefficients values (AClogP, ALOGP, KOWWIN, ALOGPs, XLOGP2, MLOGP and XLOGP3) and experimental octanol–water logP values (measured by the shake flask method). The received results demonstrate that RP‐TLC may be a good alternative technique for analytics in describing the lipophilic nature of investigated cephalosporins as well as the activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
975.
Solubility and Crystallizability: Facile Access to Functionalized π‐Conjugated Compounds with Chlorendylimide Protecting Groups 下载免费PDF全文
Dr. Jan Gebers Damien Rolland Dr. Roman Marty Dr. Stéphane Suàrez Luca Cervini Dr. Rosario Scopelliti Dr. Jan Cornelius Brauer Prof. Dr. Holger Frauenrath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1542-1553
Functional π‐conjugated molecules are relevant for the preparation of new organic electronic materials with improved performance. However, their synthesis is often rendered difficult by their inherently low solubility, and the permanent attachment of solubilizing groups may change the properties of the material. Here, we introduced the chlorendylimidyl moiety as a new temporary protecting group for the straightforward large‐scale synthesis of protected quarter‐, sexi‐, octathiophene, and perylene bisimide diamine and dicarboxylic acid derivatives. The obtained chlorendylimides and chlorendylimidyl active esters were highly soluble in organic solvents, and optical spectroscopy confirmed the low tendency of the compounds to aggregate in solution. At the same time, they could be conveniently purified by recrystallization or precipitation. Single‐crystal X‐ray structures obtained for most compounds showed supramolecular motifs highlighting the role of the rigid, polychlorinated chlorendyl moieties in their crystallization. The obtained protected diamine and dicarboxylic acid derivatives were easily deprotected and converted into various amide‐substituted oligothiophenes and perylene bisimides that are of interest as new functional materials for organic electronic thin film or nanowire devices. 相似文献
976.
Supramolecular Recognition Influences Magnetism in [X@HVIV8VV14O54]6− Self‐Assemblies with Symmetry‐Breaking Guest Anions 下载免费PDF全文
Dr. Kirill Yu. Monakhov Oliver Linnenberg Dr. Piotr Kozłowski Dr. Jan van Leusen Dr. Claire Besson Tim Secker Dr. Arkady Ellern Dr. Xavier López Prof. Dr. Josep M. Poblet Prof. Dr. Paul Kögerler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2387-2397
Mixed‐valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all‐inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self‐assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra‐weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {VIV/V22O54}‐type polyoxoanions of D2d symmetry enclosing diamagnetic VO2F2? (C2v), SCN? (C∞v), or ClO4? (Td) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V22O54} shells. We also include the synthesis and characterization of the novel [VVO2F2@HVIV8VV14O54]6? system that comprises the rarely encountered discrete difluorovanadate anion as a quasi‐isolated guest species. 相似文献
977.
Tao Wang Dr. Yuzhou Wu Dr. Seah Ling Kuan Oliver Dumele Dr. Markus Lamla Dr. David Y. W. Ng Matthias Arzt Jessica Thomas Jan O. Mueller Prof. Dr. Christopher Barner‐Kowollik Prof. Dr. Tanja Weil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):228-238
A disulfide intercalator toolbox was developed for site‐specific attachment of a broad variety of functional groups to proteins or peptides under mild, physiological conditions. The peptide hormone somatostatin (SST) served as model compound for intercalation into the available disulfide functionalization schemes starting from the intercalator or the reactive SST precursor before or after bioconjugation. A tetrazole–SST derivative was obtained that undergoes photoinduced cycloaddition in mammalian cells, which was monitored by live‐cell imaging. 相似文献
978.
Akira Inaba Hal Suzuki Jan Krawczyk Maria Massalska-Arod
《Chemical physics letters》2008,463(1-3):90-93
The heat capacity of two glass formers 5*CB and 8*OCB, each of which has two crystalline polymorphs (phases I and II) as well as a glass phase, was determined between 0.35 K and 20 K. The T-linear term of the heat capacity becomes significant below 1 K for both glasses. The glassy crystalline phase II of 5*CB also shows such contribution, which is consistent with the existence of a residual entropy. Unexpectedly, however, the ‘stable’ phase II of 8*OCB shows the similar contribution, indicating that this phase is disordered, whereas the glassy crystalline phase I shows no such contribution. 相似文献
979.
The compact trap-and-atomizer device was employed to trap stibine and bismuthine, and subsequently to volatilize collected analyte and atomize it for atomic absorption spectrometric detection. The device is actually the multiple microflame quartz tube atomizer (multiatomizer) with inlet arm modified to serve as the trap and to accommodate the oxygen delivery capillary employed for burning out hydrogen during the trapping step. The optimization of Sb and Bi collection in the device is presented based on a study of the influence of relevant experimental parameters on preconcentration efficiency of both analytes. The parameters studied were: (1) trap temperature during trapping and (2) hydrogen flow rate and (3) trap temperature during volatilization and (4) the stability of the trapped analyte species. Under optimized conditions, the preconcentration efficiency was 100% for both analytes. The trap-and-atomizer device can be replaced by the simple conventional externally heated quartz tube atomizer without any trap as demonstrated on the ultratrace antimony determination in groundwater reference material and mineral water samples. The interference of other hydride forming elements on Bi in-situ collection in the conventional externally heated quartz tube atomizer was investigated. 相似文献
980.
Kilian Muñiz Prof. Dr. Claas H. Hövelmann Esther Campos‐Gómez José Barluenga Prof. Dr. José M. González Prof. Dr. Jan Streuff Martin Nieger Dr. 《化学:亚洲杂志》2008,3(4):776-788
The oxidative intramolecular diamination of alkenes with tethered ureas and related groups as the nitrogen source has been investigated both with the iodonium reagent IPy2BF4 (Py=pyridine) and under palladium catalysis in the presence of copper(II) bromide as a reoxidant. For terminal alkenes, the two procedures enable selective and high‐yielding transformations. Studies with deuterated material led to the conclusion that the reactions proceed through different stereochemical pathways. An advanced protocol for palladium‐catalyzed diamination through six‐membered‐ring annulation was also developed, and the first examples of the intramolecular diamination of internal alkenes are described. In this case, the same stereochemical outcome was observed for the iodonium‐promoted and palladium‐catalyzed transformations. On this basis, it was possible to determine the importance of aminohalogenated intermediates in both diamination reactions. Overall, the disclosed procedures broaden significantly the synthetic applicability of the oxidative intramolecular diamination of alkenes. 相似文献