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21.
Summary In this paper a database of atomic residual charges has been constructed for all the molecular fragments defined previously in a combinatorial search of the Cambridge Structural Database. The charges generated for the atoms in each fragment are compared with charges calculated for whole molecules containing those fragments. The fragment atomic charges lie within 1 S.D. of the mean for 68%, and within 2 S.D. for 91%, of the atoms whose charges were computed for whole molecules. The actual charges on any atom are strongly influenced by the adjacent connected atoms. There is a large spread of atomic residual charge within the fragments database. 相似文献
22.
Siya Ram William Evans Dean S. Wise Leroy B. Townsend John W. Mccall 《Journal of heterocyclic chemistry》1989,26(4):1053-1059
A series of methyl 2-substituted purine 8-carbamates was prepared and evaluated for antifilarial activity. These purines were synthesized as aza congeners of benzimidazole carbamates which have shown significant anthelmintic activity to determine the effect that this modification might have on anthelmintic activity. The compounds were tested against the filarial infection, B. pahangi, in jirds. None of the compounds prepared in this study demonstrated antifilarial activity. 相似文献
23.
A novel approach to the fabrication of metal ring-disk (RD) microelectrodes is presented that employs flexible chemical vapor deposition (CVD) and electrode modification techniques. Specifically, the development of a copper ring-disk microelectrode is described utilizing a combination of CVD coating, electroetching, and electroplating. Initially, a 25 μm diameter tungsten wire is concentrically coated by CVD with an insulating layer of silica, a layer of tungsten metal, and finally, a second outer layer of silica. The copper surface was prepared by first creating micrometer cavities by electrochemical etching the tungsten in hydroxide solutions followed by electrodeposition of copper from aqueous solutions of Cu(II). Each step of the process was characterized by scanning electron microscopy, optical microscopy, and cyclic voltammetry, demonstrating the preparation of a viable metal-based dual ring-disk microelectrode system. For the purpose of demonstrating the concept of introducing specific selectivity into the device, amperometric detection of galactose in 0.1 M NaOH was performed at +0.60 V in bulk solution and after flow injection analysis in a capillary column. 相似文献
24.
The adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase. 相似文献
25.
Friedman LA You F Sabat M Harman WD 《Journal of the American Chemical Society》2003,125(49):14980-14981
The rhenium furan complexes TpRe(CO)(MeIm)(eta2-2-methylfuran) (1) and TpRe(CO)(MeIm)(eta2-2,5-dmethylfuran) (2) undergo Lewis acid-promoted cyclopentannulation reactions with enones and enals to generate 3-acetylcyclopentene complexes. During the reaction, a rearrangement occurs such that the alpha and beta carbons of the enone are incorporated into the new carbocycle. Treatment of these complexes with an oxidant (H2O2 or silver triflate) liberates the acetylcyclopentene. When a resolved form of the rhenium complex is used, the acetylcyclopentenes can be obtained enantioselectively. 相似文献
26.
Trost BM Shen HC Horne DB Toste FD Steinmetz BG Koradin C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2577-2590
The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates. 相似文献
27.
OPAL Collaboration G. Alexander J. Allison N. Altekamp K. Ametewee K. J. Anderson S. Anderson S. Arcelli S. Asai D. Axen et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):543-560
Symmetric three-jet events are selected from hadronic Z0 decays such that the two lower energy jets are each produced at an angle of about 150° with respect to the highest energy
jet. In some cases, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other
lower energy jet to be identified as a gluon jet through anti-tagging. In other cases, the highest energy jet is tagged as
a b jet or as a light quark (uds) jet using secondary vertex or track impact parameter and momentum information. Comparing
the two lower energy jets of the events with a tag in the highest energy jet to the anti-tagged gluon jets yields a direct
comparison of b, uds and gluon jets, which are produced with the same energy of about 24 GeV and under the same conditions.
We observe b jets and gluon jets to have similar properties as measured by the angular distribution of particle energy around
the jet directions and by the fragmentation functions. In contrast, gluon jets are found to be significantly broader and to
have a markedly softer fragmentation function than uds jets. For thek
⊥ jet finder withy
cut=0.02, we find
as the ratios of the mean charged particle multiplicity in the gluon jets compared to the b and uds jets. Results are also
reported using the cone jet finder. 相似文献
28.
R. Akers G. Alexander J. Allison K. Ametewee K. J. Anderson S. Arcelli S. Asai D. Axen G. Azuelos A. H. Ball et al. 《Zeitschrift fur Physik C Particles and Fields》1995,67(1):45-55
The properties of hadronic Z0 decays with final state photons, measured with OPAL at LEP, have been compared with predictions from two different matrix element calculations ofO(
s
). Two calculations, GNJETS and EEPRAD, have been investigated which use different schemes to restrict the phase space around the poles of the cross section. Assuming the E0-JADE jet definition, both calculations describe the data well in large regions of phase space fory
cut
values around 0.06. For very large and very small jet-photon masses some deviations from the predictions have been found, indicating the importance of higher order corrections. Significant differences between the calculations are only apparent in the predicted rate of 1-jet plus photon events. The rate is higher in GNJETS which reproduces the data better than EEPRAD. 相似文献
29.
用原子吸收光谱法测下了“东北水三七”根、茎、叶的21种化学元素,结果表明,不同部位的元素含量有一定差别。 相似文献
30.
Ruey-Jen Jang-Lewis Harold Dean Victory Jr. 《Integral Equations and Operator Theory》1994,18(1):88-108
LetE be a Banach lattice having order continuous norm. Suppose, moreover,T is a nonnegative reducible operator having a compact iterate and which mapsE into itself. The purpose of this work is to extend the previous results of the authors, concerning nonnegative solvability of (kernel) operator equations on generalL
p-spaces. In particular, we provide necessary and sufficient conditions for the operator equation x=T
x+y to possess a nonnegative solutionxE wherey is a given nonnegative and nontrivial element ofE and is any given positive parameter. 相似文献