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41.
MacKinnon SL Cembella AD Burton IW Lewis N LeBlanc P Walter JA 《The Journal of organic chemistry》2006,71(23):8724-8731
Biosynthetic origins of the cyclic imine toxin 13-desmethyl spirolide C were determined by supplementing cultures of the toxigenic dinoflagellate Alexandrium ostenfeldii with stable isotope-labeled precursors [1,2-13C2]acetate, [1-13C]acetate, [2-13CD3]acetate, and [1,2-13C2,15N]glycine and measuring the incorporation patterns by 13C NMR spectroscopy. Despite partial scrambling of the acetate labels, the results show that most carbons of the macrocycle are polyketide-derived and that glycine is incorporated as an intact unit into the cyclic imine moiety. This work represents the first conclusive evidence that such cyclic imine toxins are polyketides and provides support for biosynthetic pathways previously defined for other polyether dinoflagellate toxins. 相似文献
42.
Alan R. Bassindale Iain A. MacKinnon Peter G. Taylor Yuxing Yang Peter N. Horton 《Journal of organometallic chemistry》2004,689(21):3287-3300
The recently-reported reaction of triethoxysilanes with tetrabutylammonium fluoride in the presence of scarce water provides a higher yielding route to substituted octasilsesquioxane cages. Further cages have now been prepared in good yield using this route and their X-ray crystal structures demonstrate that their cage geometries in the solid state are very similar with the packing constraints of the crystal lattices appearing to have the greatest influence on the geometry of the cage core. The mechanism of the reaction has been examined and the proposed mechanism of cage formation validated, though its exclusivity has not been categorically proven. By careful choice of reaction conditions, dramatic increases in rate and yield have been demonstrated. 相似文献
43.
Amanda L. MacKinnon 《Journal of organometallic chemistry》2003,683(1):114-119
The compound trans-NiCl2(IPr)2 (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) is synthesized and characterized crystallographically. In combination with MAO, it is converted to an intermediate which catalyses the dimerization of ethylene but which not the polymerization of ethylene, propylene or 1-hexene. 相似文献
44.
Ruth A. Perez Nils Rehmann Sheila Crain Patricia LeBlanc Cheryl Craft Shawna MacKinnon Kelley Reeves Ian W. Burton John A. Walter Philipp Hess Michael A. Quilliam Jeremy E. Melanson 《Analytical and bioanalytical chemistry》2010,398(5):2243-2252
The production and certification of a series of azaspiracid (AZA) calibration solution reference materials is described. Azaspiracids were isolated from contaminated mussels, purified by preparative liquid chromatography and dried under vacuum to the anhydrous form. The purity was assessed by liquid chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The final concentration of each AZA in a CD3OH stock solution was determined by quantitative NMR spectroscopy. This solution was then diluted very accurately in degassed, high purity methanol to a concentration of 1.47?±?0.08 μmol/L for CRM-AZA1, 1.52?±?0.05 μmol/L for CRM-AZA2, and 1.37?±?0.13 μmol/L for CRM-AZA3. Aliquots were dispensed into argon-filled glass ampoules, which were immediately flame-sealed. The calibration solutions are suitable for method development, method validation, calibration of liquid chromatography or mass spectrometry instrumentation and quality control of shellfish monitoring programs. 相似文献
45.
Kathryn Frey MacKinnon 《Tetrahedron letters》2007,48(45):8074-8077
Polycyclic aromatic hydrocarbons were found to be promising universal bases in PNA·DNA double helices. Several of the arenes paired promiscuously with any of the four canonical bases. However, the stabilities of the duplexes depended on the size and shape of the arene. 相似文献
46.
Horvath TD Matthews NI Stratton SL Mock DM Boysen G 《Analytical and bioanalytical chemistry》2011,401(9):2805-2810
Measurement of 3-hydroxyisovaleric acid (3HIA) in human urine has been shown to be a useful indicator of biotin status for a variety of clinical situations, including pregnancy. The work described herein presents a novel UPLC-MS/MS method for accurate and precise quantitation of urinary 3HIA. This method utilizes sample preparation prior to quantitation that has been simplified compared to the previous GC-MS method. To demonstrate the suitability of the UPLC-MS/MS method for human bio-monitoring, this method was used to measure 3-HIA in 64 human urine samples from eight healthy adults in whom marginal biotin deficiency had been induced experimentally by egg white feeding. 3HIA was detected in all specimens; the mean concentration [±standard deviation (SD)] was 80.6 ± 51 μM prior to inducing biotin deficiency. Mean excretion rate for 3HIA (expressed per mol urinary creatinine) before beginning the biotin-deficient diet was 8.5 ± 3.2 mmol 3HIA per mol creatinine and the mean increased threefold with deficiency. These specimens had been previously analyzed by GC-MS; the two data sets showed strong linear relationship with a correlation coefficient of 0.97. These results provide evidence that this method is suitable for bio-monitoring of biotin status in larger populations. 相似文献
47.
48.
R. R. Freeman C. Anderson J. M. Hill J. King R. Snavely S. Hatchett M. Key J. Koch A. MacKinnon R. Stephens T. Cowan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,26(1):73-77
The use of high-intensity lasers to cause ignition in inertial confinement fusion is presented, with emphasis on current experimental programs and physical concepts that are at the forefront of the field. In particular, we highlight the issues of fast electron transport through dense materials, an essential element of the Fast Ignitor concept.Received: 22 November 2002, Published online: 5 August 2003PACS:
52.20.Fs Electron collisions - 52.38.Kd Laser-plasma acceleration of electrons and ions 相似文献
49.
Timothy P. Bender Sean M. MacKinnon Zhi Yuan Wang 《Journal of polymer science. Part A, Polymer chemistry》2000,38(4):758-763
The synthesis of a new diamine monomer, N‐n‐butyl 3,12‐diamino‐5,6,9,10‐tetrahydro[5]helicene‐7,8‐dicarboxylic imide (4), that contains a helically locked, U‐shaped 4′,4″‐o‐terphenyl moiety is described. The monomer was polymerized with 3,3′,4,4′‐oxydiphthalic dianhydride and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane to form a series of copoly(ether imide)s (5a–e). The incorporation of 4 into the poly(ether imide)s varied the glass‐transition temperature of the copolymers of which it was a part. There was a tendency to form macrocyclic materials at higher molar percentages of 4 during polymerization. The fluorescence of all the copoly(ether imide)s gradually decreased as the content derived from monomer 4 increased in the polymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 758–763, 2000 相似文献
50.
Delta wells can become charge-depleted through background doping, or as part of asymmetric n-i-p-i structures. For moderate depletions, the electronic properties of the residual 2DEGs in these cases are similar. For moderate depletion by background doping, the charge removed from the well varies inversely with the square-root of the background intensity, independent of the strength of the delta well. Depletion of delta wells is found to procede in a ‘top-down’ fashion in a 2-dimensional analogue to atomic ionization. 相似文献