Boron-based mixed anhydrides are rapidly reactive, easy to prepare, cheap, efficient, and general acylating reagents capable of selectivity when chelation is possible. High yields of various esters, amides and thioesters are quickly obtainable and the products are easy to isolate in high purity. The method is readily used under multiple parallel synthesis conditions and is readily scaleable. 相似文献
A simple technique for the determination of environmental levels of plutonium in a highly complex matrix (sediments containing very high amounts of iron and other metals) is reported. The sediments, collected from the Hudson River Estuary with an Emory dredge, were hand-homogenized before a sample aliquot was taken. Samples were airdried, weighed, spiked with 242Pu tracer, and heated at 400°C for 24 h. Plutonium was leached from the sediment with an acid mixture. The leachate was filtered, and plutonium coprecipitated with iron by adding ammonia solution. After dissolution, plutonium was extracted with 20% trilaurylamine in xylene, the extracts were thoroughly acid-washed to remove uranium and thorium traces, and plutonium was then back-extracted with 2 M sulfuric acid prior to electrodeposition onto a platinum planchet. The isotopic composition of plutonium was determined by α-spectrometry. Tracer yield and plutonium concentrations determined on aliquots of the same samples by this method and by an ion-exchange technique were not significantly different. 相似文献
Pyrolysis—mass spectrometry in combination with discriminant analysis and a newly development non-supervised mixture analysis approach is shown to provide valuable information about the biochemical composition of wood and wood products. The application of this technique to the chemotaxonomy of sagebrush (Artemisia) species as well as to the quality control of wood pulping processes is discussed. With regard to the latter application strong correlations are found between classical lignin and xylan determinations and direct pyrolysis—mass spectrometric analysis results. 相似文献
Summary The development and implementation of a parallel direct self consistent field (SCF) Hartree-Fock algorithm, with gradients and random phase approximation solutions is presented. Important details of the structure of the parallel version of DISCO and preliminary results for calculations using the Concurrent Supercomputing Consortium Intel Touchstone Delta parallel computer system are reported. The data show that the algorithms are efficiently parallelized and that throughput of a one processor CRAY X-MP is reached with about 16 nodes on the Delta. The data also indicate sequential code which was not a bottleneck on traditional supercomputers, can become time critical on parallel computers.This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy, under contract DE-AC06-76RLO 1830 for Pacific Northwest Laboratory which is operated by Battelle Memorial Institute for the U.S. Department of Energy. 相似文献
Access to the synthetically important tetrahydropyridine motif has been achieved by radical rearrangement of pyrrolines obtained from the Birch reduction of electron-deficient pyrroles. 相似文献
Summary A distributed memory programming model was used in a fully parallel implementation of theab initio integral evaluation program ARGOS (R. Pitzer (1973)J. Chem. Phys. 58:3111), on shared memory UNIX computers. The method used is applicable to many similar problems, including derivative integral evaluation. Only a few lines of the existing sequential FORTRAN source required modification. Initial timings on several multi-processor computers are presented. A simplified version of the programming tool used is also presented, and general consideration is given to the parallel implementation of quantum chemistry algorithms.Work performed at Argonne National Laboratory under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract W-31-109-Eng-38. Pacific Northwest Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830 相似文献
A dideoxyribonucleotide, 2′-amino-2′-deoxyuridylyl 3′,5′-deoxyuridine, containing an unsual base (2′-amino-2′-deoxyuridine) that isresistant to nucleases was investigated by ′H NMR. The pKa of the protonation of the amino group (5.8) was determined by profiles of chemical shifts of protons in the vicinity of amino group versus pH. However, protonation of the amino group has little effect on the conformation of the dimer, assumed to be B-form DNA. This conclusion is drawn from the chemical shift data and coupling constants of H1-H2. Thus, 2′-amino-2′-deoxyuridine can be used in antisense and anticode oligonucleotides. 相似文献
Saccharomyces cerevisiae was supported on chrysotile, crocidolite and lixiviated chrysotile. Samples of the supported cells and free cells were observed by confocal laser scanning microscopy. After 30 days, the free cells showed no viability when stored at 30 °C, and a viability of 40% when stored at 4 °C. Supported cells stored at 30 °C were more viable than the free cells at early times, but showed no viability after 30 days. Samples stored at 4 °C showed that the adhered cells are more viable than the free cells, up to 30 days. Cells supported on chrysotile and lixiviated chrysotile had 80% viability, and on crocidolite 70% viability. Scanning electron microscopy showed that cells supported on lixiviated chrysotile are fully covered by the support, but crocidolite fibers adhere less, since they are stiffer. Fermentation experiments performed after 3 years storage showed that four from the five lixiviated chrysotile samples and one of the three crocidolite samples were active. In all cases, a delay time for the onset of fermentation was observed indicating a state of latency. 相似文献
Partitioning of lactic acid between aqueous phase and kerosene containing trin-octyl phosphine oxide (TOPO) as a reactive agent was measured and analyzed in terms of an association model between lactic acid and TOPO. Equilibrium association was calculated to involve 1.1 mol of lactic acid/mol of TOPO.31P-NMR and FTIR analyses found no evidence of covalent bond formation between lactic acid and TOPO in solutions in kerosene, and pointed to hydrogen bond formation between the two chemicals. In a hydrophobic, microporous, hollow-fiber-membrane module, the simultaneous presence of lactic acid, TOPO, and the back-extractant NaOH resulted in drastic membrane fouling as evidenced by the loss of kerosene flux through the membrane. The membrane could be restored back to the original kerosene flux after extensive washing.