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191.
192.
Zyryanov GV Kang Y Stampp SP Rudkevich DM 《Chemical communications (Cambridge, England)》2002,(23):2792-2793
Reaction of NO2 with simple calix[4]arenes in chloroform in the presence of a Lewis acid rapidly results in intense coloration caused by the encapsulation of nitrosonium cation. 相似文献
193.
Burke AJ Davies SG Garner AC McCarthy TD Roberts PM Smith AD Rodriguez-Solla H Vickers RJ 《Organic & biomolecular chemistry》2004,2(9):1387-1394
Conjugate addition of lithium (S)-N-benzyl-N-alpha-methylbenzylamide to a range of alpha, beta-unsaturated Weinreb amides proceeds with high levels of diastereoselectivity (>95% de). The beta-amino Weinreb amide products may be transformed into beta-amino ketones via reactions with Grignard reagents, while treatment with DIBAL-H furnishes beta-amino aldehydes. Trapping of the aldehyde via Wadsworth-Emmons reaction and subsequent manipulation offers an efficient route to homochiral delta-amino acid derivatives and 2-substituted piperidines. The application of this methodology for the synthesis of (S)-coniine is demonstrated. 相似文献
194.
Tomasino SF 《Journal of AOAC International》2005,88(1):355-358
The U.S. Environmental Protection Agency's (EPA) Office of Pesticide Programs (OPP) has the responsibility for regulating antimicrobial products, including sporicides, used to treat and decontaminate inanimate surfaces. In response to the anthrax (Bacillus anthracis) attacks of 2001 and the associated need for verifying the performance of chemicals for building decontamination, the EPA initiated research in late 2003 to evaluate and improve efficacy test methods for sporicides. The OPP Microbiology Laboratory located at the Environmental Science Center, Ft. Meade, MD is the lead laboratory. Through funding provided by EPA's Office of Research and Development (Safe Buildings Program), a collaborative research plan has been established to address several key issues. Research is currently being conducted on 2 fronts: (1) the evaluation of quantitative methodology for assessing the efficacy of sporicides, and (2) the development and comparative testing of selected modifications to improve the AOAC Sporicidal Activity Test (AOAC Method 966.04). Future studies will include the evaluation of candidate surrogates of B. anthracis using a quantitative method, and a multilaboratory validation study of a quantitative method-surrogate combination. The General Referee is serving as the Principal Investigator for all research described in this report, and has the overall responsibility for the technical conduct of the projects. In cases where the General Referee has oversight of projects that involve official collaborative studies and validation support from AOAC INTERNATIONAL, AOAC officials and the Committee Chair will determine the appropriate mechanism for formal study review. The 2003 General Referee report provides the background on the development and direction of the research projects. The preliminary data, general conclusions, next steps, and recommendations are provided in this report. 相似文献
195.
The separation of wide molecular mass (Mr) ranges of macromolecules using frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF) has been improved by implementing a combination of field and flow programming. In this first implementation, field strength (governed by the cross flow-rate through the membrane-covered accumulation wall) is decreased with time to obtain faster elution and improved detection of the more strongly retained (high Mr) materials. The channel outlet flow-rate is optionally held constant, increased, or decreased with time. With circulation of the flow exiting the accumulation wall to the inlet frit, the dual programming of cross flow and channel outlet flow could be implemented using just two pumps. With this flow configuration, the channel outlet flow-rate is always equal to the channel inlet flow-rate, and these may be programmed independently of the cross flow-rate through the membrane. FI-AFlFFF retains its operational advantage over conventional asymmetrical flow FFF (AFlFFF). Unlike conventional AFlFFF, FI-AFlFFF does not require time consuming, and experimentally inconvenient, sample focusing and relaxation steps involving valve switching and interruption of sample migration. The advantages of employing dual programming with FI-AFlFFF are demonstrated for sets of polystyrene sulfonate standards in the molecular mass range of 4 to 1000 kDa. It is shown that programmed FI-AFlFFF successfully expands the dynamic separation range of molecular mass. 相似文献
196.
Ottenberg CM McDonald FC O'Donnell ET Skrabal SA White DP 《Inorganic chemistry》2002,41(26):7151-7158
Increased preorganization can be achieved by immobilizing ligands on solid supports. Photoluminescent porous silicon, which can undergo facile hydrosilylation, was used as a support for open chain neutral N- and O-donor ligands. The abilities of these ligands to bind the divalent metal ions Ni(2+), Cu(2+), Zn(2+), and Pb(2+) are examined. Immobilized ligands selectively complexed Cu(II) over the other metal ions studied. Ligands immobilized on photoluminescent porous silicon also removed a significant amount, up to 98%, of Cu(II) from copper(II)-spiked, organic-rich, seawater samples. 相似文献
197.
Trimethylsilyl bromide is an effective reagent for the deprotection of methoxymethyl ethers under mild conditions. 相似文献
198.
Lonnon DG Craig DC Colbran SB Bernhardt PV 《Dalton transactions (Cambridge, England : 2003)》2004,(5):778-787
Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C2-symmetric, chiral [Cu2(L)Br2]2+ 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu2(L)Cl3]+ tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described. 相似文献
199.
Orbital correlation diagrams for the black phosphorus to A7 (arsenic) phase transformation for various points in the Brillouin zone are presented and analyzed in symmetry terms. The level doublings observed at the black phosphorus geometry for several points are directly attributable to the nonsymmorphic nature of the space group (Herring's theorem). Doublings observed at the A7 structure derive from the choice of a four-atom, rather than two-atom, unit cell to view the geometrical transformation. The space group requirements at the beginning and end points of the transformation process simply control the form of orbital correlation diagrams. In general, crossings are found at where bonds are made and broken along the x direction, a result with simple analogies to more easily visualized one-dimensional problems. 相似文献
200.
Stephen de Mora Jean-Pierre Villeneuve Eric Wyse 《Accreditation and quality assurance》2007,12(11):587-592
Aspects of the International Atomic Energy Agency (IAEA) Analytical Quality Control Services (AQCS) for marine environmental
studies are discussed, focusing on recent laboratory performance studies (LPS) and the production of reference materials for
trace metals and organic compounds in various marine matrices. The IAEA has organized seventeen global interlaboratory studies
for a range of organic contaminants. Of note has been the inclusion of numerous polychlorinated biphenyl congeners (PCBs)
and some sterols of anthropogenic origin. Concurrently, there have been eleven worldwide intercomparison exercises for trace
metals in the marine environment, most of which included methylmercury. Although such interlaboratory studies can help improve
performance in individual laboratories and regional laboratory networks, the results reveal that problems remain in the determination
of some metals and many organic contaminants. 相似文献