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161.
Frontispiece: Monitoring and Understanding the Paraelectric–Ferroelectric Phase Transition in the Metal–Organic Framework [NH4][M(HCOO)3] by Solid‐State NMR Spectroscopy 下载免费PDF全文
162.
Determination of nicotine and its metabolites accumulated in fish tissue using hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry 下载免费PDF全文
Yun‐Wei Chang S. Rebekah Burket Bryan W. Brooks Kevin A. Schug 《Journal of separation science》2015,38(14):2414-2422
The determination of nicotine and its major metabolites (cotinine and anabasine) in fish tissue was performed using liquid chromatography and tandem mass spectrometry. Marine and freshwater fish were purchased from local grocery stores and were prepared based on a quick, easy, cheap, effective, rugged, and safe sample preparation protocol. To determine the highly polar compounds, hydrophilic interaction liquid chromatography was also used. There were modest suppressions on measured nicotine signals (10%) due to the matrix effects from marine fish but no obvious effects on freshwater fish signals. Method validation was incorporated with internal standards and carried out with matrix‐matched calibration. The detection limits for nicotine, cotinine, and anabasine were 9.4, 3.0, and 1.5 ng/g in fish, respectively. Precision was quite acceptable returning less than 8% RSD at low, medium, and high concentrations. Acceptable and reproducible extraction recoveries (70–120%) of all three compounds were achieved, except for anabasine at low concentration (61%). The method was then applied to define nicotine bioaccumulation in a fathead minnow model, which resulted in rapid uptake with steady state internal tissue levels, reached within 12 h. This developed method offers a fast, easy, and sensitive way to evaluate nicotine and its metabolite residues in fish tissues. 相似文献
163.
Andrew N. Norris 《International Journal of Solids and Structures》1998,35(36):5237-5252
The potential energy of the elastic surface of an elastic body which is growing by the coherent addition of material is derived. Several equivalent expressions are presented for the energy required to add a single atom, also known as the chemical potential. The simplest involves the Eshelby stress tensors for the bulk medium and for the surface. Dual Lagrangian/Eulerian expressions are obtained which are formally similar to each other. The analysis employs two distinct types of variations to derive the governing bulk and surface equations for an accreting elastic solid. The total energy of the system is assumed to comprise bulk and surface energies, while the presence of an external medium can be taken into account through an applied surface forcing. A detailed account is given of the various formulations possible in material and current coordinates, using four types of bulk and surface stresses: the Piola-Kirchhoff stress, the Cauchy stress, the Eshelby stress and a fourth, called the nominal energy-momentum stress. It is shown that inhomogeneity surface forces arise naturally if the surface energy density is allowed to be position dependent. 相似文献
164.
Iulia A. SacuiPeter Norris 《Tetrahedron letters》2011,52(21):2670-2672
Attempted diazo transfer to 1-O-(2-phenylacetyl)-2,3;5,6-di-O-isopropylidene-α-d-mannofuranose using p-acetamidobenzenesulfonyl azide (p-ABSA) and DBU as base affords 1-O-(2-diazo-2-phenylacetyl)-2,3;5,6-di-O-isopropylidene-α-d-mannofuranose in low yield along with 2,3;5,6-di-O-isopropylidene-α-d-mannofuranose, 1-azido-2,3;5,6-di-O-isopropylidene-β-d-mannofuranose, as well as the unreacted starting material. The azido sugar likely arises from α-mannofuranosyl sulfonate ester formation, through displacement of azide from p-ABSA by the sugar lactol, followed by stereospecific displacement by azide anion on the furanosyl sulfonate ester. This outcome has been studied further with the conditions being applied to several common monosaccharide derivatives. Accessible substrates afford the azido sugar in an overall one-pot alcohol-to-azide conversion, while hindered substrates yield the sulfonate esters. 相似文献
165.
Jacek PecynaRichard P. Denicola Bryan RingstrandAleksandra Jankowiak Piotr Kaszynski 《Polyhedron》2011,30(15):2505-2513
The preparation of iodo acid [closo-1-CB9H8-1-COOH-10-I]− (1) is optimized and scaled from 1 to 40 g of B10H14. The improved preparation of the [arachno-6-CB9H13-6-COOH]− (5) uses four times smaller volume and can be run conveniently in up to 40 g scale in a 3-L vessel. The optimized oxidation of 5 to [closo-2-CB9H9-2-COOH]− (4) requires less oxidant, 12 times smaller volume, and significantly shorter reaction time. The overall yields of the iodo acid 1 as the [NMe4]+ salt are typically 8-10% (10-12 g) for 40 g of B10H14. The iodo acid 1 was transformed to amino acid 8, then to dinitrogen acid 10, and finally to sulfonium acid 2[3] in overall yield of about 13%. The search for a more efficient phosphine ligand for the Pd-catalyzed amination process was not fruitful. Three routes to the sulfonium acid 2[n] were investigated, and the best yield of about 47% was obtained for Cs2CO3-assisted cycloalkylation. Liquid crystalline ester of acid 2[3] and 4-butoxyphenol was prepared and investigated. 相似文献
166.
McCullough BJ Bristow T O'Connor G Hopley C 《Rapid communications in mass spectrometry : RCM》2011,25(10):1445-1451
The design and development of a novel extractive electrospray ionisation (EESI) device for on-line reaction monitoring is described. The EESI apparatus uses a secondary, grounded nebuliser to produce an analyte aerosol and a Venturi pump is then used to transfer a sample of the aerosol to an electrospray source where it is ionised. The EESI apparatus was then tested with a variety of small, organic molecules to assess sensitivity, linearity and dynamic range. The performance of the technique will depend on the mass spectrometer used for the experiments; in the configurations used here it has a usable dynamic range of around 3.5 orders of magnitude with a linear range of around 2.5 orders of magnitude and is capable of analysing species present down to low μg/mL with signal-to-noise ratio greater than 2.5. The use of EESI for reaction monitoring was validated using a series of mock reaction mixtures and then used to monitor the base hydrolysis of ethyl salicylate to salicylic acid. 相似文献
167.
Edison SE Lin LA Gamble BM Wong J Zhang K 《Rapid communications in mass spectrometry : RCM》2011,25(1):127-139
A rapid screening method for pesticides has been developed to promote more efficient processing of produce entering the United States. Foam swabs were used to recover a multiclass mixture of 132 pesticides from the surfaces of grapes, apples, and oranges. The swabs were analyzed using direct analysis in real time (DART) ionization coupled with a high‐resolution Exactive Orbitrap? mass spectrometer. By using a DART helium temperature gradient from 100–350°C over 3 min, a minimal separation of analytes based on volatility differences was achieved. This, combined with the Exactive's mass resolution of 100 000, allowed the chromatographic step, along with the typical compositing and extraction steps associated with gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS) approaches, to be eliminated. Detection of 86% of the analytes present was consistently achieved at levels of 2 ng/g (per each apple or orange) and 10 ng/g (per grape). A resolution study was conducted with four pairs of isobaric compounds analyzed at a mass resolution of 100 000. Baseline separation was achieved with analyte ions differing in mass by 25 ppm and analyte ions with a mass difference of 10 ppm were partially resolved. In addition, field samples that had undergone traditional sample preparation using QuEChERS (quick, easy, cheap, rugged, and safe) were analyzed using both LC/MS and DART‐MS and the results from the two techniques were found to be comparable in terms of identification of the pesticides present. The use of swabs greatly increased sample throughput by reducing sample preparation and analysis time. Published in 2010 by John Wiley & Sons, Ltd. 相似文献
168.
Sahu A Qi L Kang MS Deng D Norris DJ 《Journal of the American Chemical Society》2011,133(17):6509-6512
A general, one-pot, single-step method for producing colloidal silver chalcogenide (Ag(2)E; E = Se, S, Te) nanocrystals is presented, with an emphasis on Ag(2)Se. The method avoids exotic chemicals, high temperatures, and high pressures and requires only a few minutes of reaction time. While Ag(2)S and Ag(2)Te are formed in their low-temperature monoclinic phases, Ag(2)Se is obtained in a metastable tetragonal phase not observed in the bulk. 相似文献
169.
Matsuura BS Condie AG McBee IA Buff RC Karahalis GJ Stephenson CR 《Organic letters》2011,13(23):6320-6323
An intramolecular cyclization cascade reaction has been developed utilizing a high valent palladium intermediate that generates a carbon-carbon and carbon-oxygen bond in a single transformation. This method provides rapid access to highly functionalized tricyclic scaffolds, including spirocyclic cyclohexadienones. Good yields and mild conditions are reported with high tolerance toward oxygen and water. 相似文献
170.
Petrov AP Cherney LT Dodgson B Okhonin V Krylov SN 《Journal of the American Chemical Society》2011,133(32):12486-12492
Noncovalent binding of DNA with multiple proteins is pivotal to many regulatory cellular processes. Due to the lack of experimental approaches, the kinetics of assembly and disassembly of DNA-multiple proteins complexes have never been studied. Here, we report on a first method capable of measuring disassembly kinetics of such complexes. The method is based on continuous spatial separation of different complexes. The kinetics of multiple complex dissociation processes are also spatially separated, which in turn facilitates finding their rate constants. Our separation-based approach was compared with a conventional no-separation approach by using computer simulation of dissociation kinetics. It proved to be much more accurate than the no-separation approach and to be a powerful tool for testing hypothetical mechanisms of the disassembly of DNA-multiple proteins complexes. An experimental implementation of the separation-based approach was finally demonstrated by using capillary electrophoresis as a separation method. The interaction between an 80 nucleotide long single-stranded DNA and single-stranded DNA binding protein was studied. DNA-protein complexes with one and two proteins were observed, and rate constants of their dissociation were determined. We foresee that a separation approach will be also developed to study the kinetics of the formation of DNA-multiple protein complexes. 相似文献