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61.
Yejia Li Boyu Zhang Jessica N. Hoskins Scott M. Grayson 《Journal of polymer science. Part A, Polymer chemistry》2012,50(6):1086-1101
The copper (I)‐catalyzed azide‐alkyne cycloaddition “click” reaction was successfully applied to prepare well‐defined 3, 6, and 12‐arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well‐defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL‐b‐PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
62.
Jessica Cid Dr. Jorge J. Carbó Dr. Elena Fernández 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(40):12794-12802
Most trivalent boron reagents are electrophiles owing to the vacancy for two electrons to fill the outer orbital of boron; however, interestingly, trivalent boron compounds can change their electrophilic character to a nucleophilic character by only changing the nature of the substituents on the boron atoms. With the help of computational tools, we have analyzed the structural‐ and electronic properties of boryl fragments that were either bonded to main‐group metals or coordinated to transition‐metals/rare‐earth‐metals and we have designed a map that might help to identify certain trends. This trend map will be useful for selecting an appropriate trivalent boron compound, depending on the sought reactivity. 相似文献
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Craig T. Archbold Jessica L. Andrews Stephen J. Cowling John W. Goodby 《Liquid crystals》2017,44(12-13):2079-2088
ABSTRACTThe twist-bend phase (NTB) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the NTB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the NTB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the NTB phase. 相似文献
65.
Eva C. Sonnenschein Marc Stierhof Stephan Goralczyk Floriane M. Vabre Leonie Pellissier Kine Østnes Hanssen Mercedes de la Cruz Caridad Díaz Peter de Witte Daniëlle Copmans Jeanette Hammer Andersen Espen Hansen Venke Kristoffersen José R. Tormo Rainer Ebel Bruce F. Milne Hai Deng Lone Gram Jioji N. Tabudravu 《Tetrahedron》2017,73(18):2633-2637
A new siderophore containing a 4,5-dihydroimidazole moiety was isolated from Pseudoalteromonas piscicida S2040 together with myxochelins A and B, alteramide A and its cycloaddition product, and bromo- and dibromoalterochromides. The structure of pseudochelin A was established by spectroscopic techniques including 2D NMR and MS/MS fragmentation data. In bioassays selected fractions of the crude extract of S2040 inhibited the opportunistic pathogen Pseudomonas aeruginosa. Pseudochelin A displayed siderophore activity in the chrome azurol S assay at concentrations higher than 50 μM, and showed weak activity against the fungus Aspergillus fumigatus, but did not display antibacterial, anti-inflammatory or anticonvulsant activity. 相似文献
66.
de Oliveira Elcio Cruz de Santana Maia Lúcio Abdala da Costa Lívio Garcia Lourenço Túlio Campos 《Accreditation and quality assurance》2018,23(6):365-369
Accreditation and Quality Assurance - In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is... 相似文献
67.
Brynne E. Lazarus Matthew J. Germino Jessica L. Vander Veen 《Isotopes in environmental and health studies》2016,52(3):309-325
Application of stable isotopes of water to studies of plant–soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics. 相似文献
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Jorge‐Aarn Rangel‐Mndez Manlio‐Joaquin Graniel‐Sabido Juan‐Francisco Snchez‐Cruz Rosa Moo‐Puc 《Biomedical chromatography : BMC》2019,33(4)
To date, several methods for the quantification of tamoxifen and its metabolites have been developed, most of which employ liquid chromatography tandem–mass spectrometry (LC–MS/MS). These methods are highly sensitive and reproducible, but are also time‐consuming and require expensive equipment; one of their main disadvantages is matrix ionization effects. A more viable option, particularly in developing countries, is high‐performance liquid chromatography coupled with UV or fluorescence detection. We developed and validated a method for simultaneous quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen based on high‐performance liquid chromatography with fluorescence detection in a reverse‐phase column. The method is rapid (16 min plus 5 min of column re‐equilibrium), accurate (80–100%) and precise (0.23–6.00%), and does not require any additional irradiation process. Sample pretreatment consists of protein precipitation with acetonitrile under alkaline conditions, employing only 200 μL plasma. The validated method's wide range allowed quantification of steady‐state levels in patients under standard tamoxifen treatment (20 mg/day). This assay is ready for application in clinical studies and routine quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen in healthcare institutions. 相似文献
70.