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21.
Allan J. Canty R. Thomas Honeyman Brian W. Skelton Allan H. White 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(1):o98-o99
The title compound, C14H13BrN4, has a planar central unit, (C)2C6H3Br, the pendant pyrazole rings forming dihedral angles of 83.8 (3) and 89.3 (3)° with this plane. The pyrazole rings are oriented such that there is an approximate twofold axis coincident with the C—Br bond. 相似文献
22.
Clegg W Dale SH Drummond AM Hevia E Honeyman GW Mulvey RE 《Journal of the American Chemical Society》2006,128(23):7434-7435
The new concept of alkali-metal-mediated zincation (AMMZ), formally a zinc-hydrogen exchange reaction but one that requires the participation of an alkali metal, is applied here to the alkyl aryl ether anisole, an important molecule for studying directed ortho-metalation (DoM) chemistry. Treating one molar equivalent of anisole with the lithium dialkyl-TMP zincate reagent [THF.Li(mu-TMP)(mu-tBu)Zn(tBu)] (1) in hexane solution affords the mono-ortho-zincated complex [THF.Li(mu-TMP)(mu-o-C6H4OMe)Zn(tBu)] (2), which establishes that 1 functions as an alkyl base although previously it was regarded as an amido (TMP) base in other DoM applications. Treating two molar equivalents of anisole with 1, and increasing the reaction time, affords the bis-ortho-zincated complex [THF.Li(mu-TMP)(mu-o-C6H4OMe)Zn(o-C6H4OMe)] (3), which establishes that 1 can also function as a dual alkyl base. Omitting THF and rerunning the reaction with one or two molar equivalents of anisole affords [Ph(Me)O.Li(mu-TMP)(mu-o-C6H4OMe)Zn(tBu)] (4), which remarkably contains a combination of neutral and ortho-deprotonated anisole ligands. On isolating crystalline 4 from solution and adding THF, it converts to 2 and then to 3 on further stirring of the solution, as determined by NMR studies. This fact, along with other observations, would suggest that a complex-induced proximity effect does not need to be invoked to explain the observed zincation of anisole. The crystal structures of 2-4 are presented, as are their 1H, 13C, and 7Li NMR spectra recorded in C6D6 solution. 相似文献
23.
Humic substances are natural complexed mixtures of organic compounds originated from the decomposition of plant and animal residues. These compounds are ubiquitous in soils, sediments, surface waters and groundwaters. They contain both hydrophobic and hydrophilic moieties, able to interact with hydrophobic organic contaminants and with heavy metals. These sorption interactions play a crucial role in contaminants fate and transport and their understanding and quantification are essential for modeling and predictions. However, sorption analyses frequently suffer from experimental problems. A novel idea presented in this study is to use sol-gel as an inert matrix to immobilize (entrap) specific, well defined, humic molecules which then be used in sorption studies. We developed a successful procedure for the immobilization of humic acid (HA) in a sol-gel matrix. After gelation and drying, the doped gel was crushed and washed several times, yielding a very stable product. It was then used in a series of batch experiments, studying the sorption of several polycyclic aromatic hydrocarbons (PAHs) with Aldrich HA. The sorption coefficients (K
oc) obtained with the immobilized HA were highly correlated with the values expected based on the hydrophobicity of the contaminants. We concluded that the entrapped HA retained its original properties and that it was accessible to the external contaminants through the pore network. 相似文献
24.
This paper considers the solution of the geodetic Doppler multi-stationadjustment, i.e. the problem of computing the positions of severalstations observing the Doppler shift on radio frequencies emittedby several artificial satellites passing over the horizon. Amodification of an algorithm due to Golub and Plemmons, forsolving large linear least-squares problems where the observationmatrix has a block dual angular form, is proposed in this framework.This modification is shown to reduce substantially both datatransfer between the tracking stations and the main computingcentre, and the total computational effort required to obtainthe solution of the problem. Preliminary numerical results arediscussed and some further comments presented. 相似文献
25.
C. Schmitt A. Guessous J.P. Bocquet H.-G. Clerc R. Brissot D. Engelhardt H.R. Faust F. Gönnenwein M. Mutterer H. Nifenecker J. Pannicke CH. Ristori J.P. Theobald 《Nuclear Physics A》1984,430(1):21-60
At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of 239Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even-Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd-Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data 1) for thermal-neutron-induced fission of 235U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for 235U and 239Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σz2. for thermal-neutron fission of 235U and 239Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σz2 is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed. 相似文献
26.
Inhaltsübersicht. Es ist gelungen, ein durch BeO stabilisiertes Bariumoxoiridat der Zusammensetzung BaIr0,67Be0,33O3 in der Kristallform eines kubischen Perowskits mit kleiner Elementarzelle erstmals darzustellen. Raumgruppe O1h–Pm3m, a = 4,1009 Å, Z = 1. Ir5+ und Be2 + besetzen die Oktaederposition des Perowskits statistisch. BaIr0,67Be0,33O3: A Stabilized Cubic Form of BaIrO3 For the first time it was possible to prepare a new barium-oxoiridate of the formula BaIr0,67Be0,33O3, stabilized by BeO. It crystallizes in a small cubic unit cell of the perovskite type. Space group O1h–Pm3m; a = 4.1009 Å; Z = 1. Ir5+ and Be2+ occupy the octahedra positions of the perovskite structure statistically. 相似文献
27.
28.
KM Clauwaert Van Bocxlaer JF HJ Major JA Claereboudt WE Lambert Van den Eeckhout EM Van Peteghem CH De Leenheer AP 《Rapid communications in mass spectrometry : RCM》1999,13(14):1540-1545
This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
29.
30.
P. A. Kumar Swathi Pisupati V. G. K. M. Pisipati CH. Srinivasu P. Narayana Murty 《Liquid crystals》2002,29(7):967-977
A systematic kinetic study leading to the crystallization process from the kinetophases (which occur prior to crystal phase) smectic B, crystal G and smectic F is performed on representative compounds of the homologous series p-phenylbenzylidene-p'-alkylanilines (PBnA) and p-n-alkoxybenzylidene-p'-alkylanilines (nO.m) these compounds are p-phenylbenzylidene-p'-nonylaniline (PB9A), p-phenylbenzylidene-p'-tetradecylaniline (PB14A), p-n-pentadecyloxybenzylidene p'-tetradecylaniline (15O.14) and p-n-octadecyloxybenzylidene-p'-nonylaniline (18O.9). The molecular mechanism and dimensionality in crystal growth from the kineto phases are computed from the Avrami equation, while the characteristic crystalline time (t*) at each crystallization temperature is deduced from the individual plots of log t vs. ΔH. The low magnitudes of the dimensionality parameter n infers the occurrence of diffusion-controlled transformations leading to the formation of plates or needles of finite size possessing impinged edges. The degree of variation in the value of n at each crystallization temperature also reveals the existence of an independent nucleation mechanism for any individual member of the series. The influence of the terminal alkyl chain lengths on the rate of crystallization is determined from a comparative study with the reported analogous compounds. 相似文献