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排序方式: 共有148条查询结果,搜索用时 93 毫秒
101.
102.
Funston A Kirby JP Miller JR Pospísil L Fiedler J Hromadová M Gál M Pecka J Valásek M Zawada Z Rempala P Michl J 《The journal of physical chemistry. A》2005,109(48):10862-10869
One-electron reduction of the "extended viologen" dication 1 yields the red cation radical 2, characterized by strong near-IR absorption. It has been generated and studied by pulse radiolytic, electrochemical, redox titration, UV-visible, and electron paramagnetic resonance spectroscopic methods. All results are in agreement with a fully delocalized electronic structure for 2. 相似文献
103.
104.
Andrew M. Crawford Patrick Kurecka Tsz Kwan Yim Claire Kozemchak Aniruddha Deb Lubomír Dostál Cheng-Jun Sun Dale L. Brewe Raul Barrea James E. Penner-Hahn 《Journal of synchrotron radiation》2016,23(4):901-908
An X‐ray fluorescence flow cytometer that can determine the total metal content of single cells has been developed. Capillary action or pressure was used to load cells into hydrophilic or hydrophobic capillaries, respectively. Once loaded, the cells were transported at a fixed vertical velocity past a focused X‐ray beam. X‐ray fluorescence was then used to determine the mass of metal in each cell. By making single‐cell measurements, the population heterogeneity for metals in the µM to mM concentration range on fL sample volumes can be directly measured, a measurement that is difficult using most analytical methods. This approach has been used to determine the metal composition of 936 individual bovine red blood cells (bRBC), 31 individual 3T3 mouse fibroblasts (NIH3T3) and 18 Saccharomyces cerevisiae (yeast) cells with an average measurement frequency of ~4 cells min?1. These data show evidence for surprisingly broad metal distributions. Details of the device design, data analysis and opportunities for further sensitivity improvement are described. 相似文献
105.
Density data for dilute aqueous solutions of phenylacetic acid, benzene-1, 2-dicarboxylic acid (phtalic acid), benzene-1,2,4-tricarboxylic acid and 1,2,3-trihydroxy- benzene (pyrogallol) are presented together with the partial molar volumes at infinite dilution calculated from the experimental data. The measurements were performed at temperatures from T=298.15 K up to T=373.15 K and at three pressures up to 30 MPa. The data were obtained using a high-temperature, high-pressure flow vibrating-tube densimeter. 相似文献
106.
Sexual attraction in the silkworm moth. Nature of binding of bombykol in pheromone binding protein--an ab initio study 总被引:1,自引:0,他引:1
An analysis of the crystal structure of [BmPBP...bombykol] complex identified nine amino acid residues involved in a variety of intermolecular interactions binding the ligand. Using simple model fragments as the representatives of the residues, the interaction energies of their complexes with bombykol were calculated using high-level ab initio methods. The results were discussed in terms of the method and basis set dependence and were further corrected to account for their pair nonadditivities. This enabled us to describe quantitatively the nature and origin of the binding forces in terms of contribution of the individual amino acids and individual types of interaction to the overall stability. All of these interactions are well defined and cannot be considered as nonspecific hydrophobic interactions, one of the major conclusions of this work. 相似文献
107.
Lubomír Prokeš Michaela Vašinová Galiová Simona Hušková Tomáš Vaculovič Aleš Hrdlička Andrew Zed Mason Hector Neff Antonín Přichystal Viktor Kanický 《Chemical Papers》2015,69(6):761-778
The provenance of obsidian artefacts and raw materials was studied by the multivariate statistical analysis of forty-five samples using elemental composition data obtained by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). One ICP-MS instrument equipped with a quadrupole mass filter and the other based on a time-of-flight analyser were coupled to the same type of laser ablation device (Nd:YAG 213 nm), thereby affording a comparison of the different mass spectrometers in terms of precision and verification of the consistency of the results. The influence of surface roughness (polished raw material vs artefact) and microinhomogeneity on the LA-ICP-MS signal was studied under the optimised working conditions of the laser ablation device. Principal component analysis, correspondence analysis, independent component analysis, multi-dimensional scaling, Sammon mapping and fuzzy cluster analysis were applied and compared in order to reveal statistically significant compositional differences between particular geological sites and to disclose the provenance of the raw materials used in manufacture of the artefacts. Twenty-seven artefacts and eighteen raw material samples from natural resources in the Czech Republic, Slovakia, Italy, Greece, Syria, Iraq, Turkey, Mexico and Nicaragua were examined with special attention focused on samples from Moravia (Czech Republic) and some Near East sites (Tell Arbid, Tell Asmar). The Carpathian origin of the obsidian artefacts was investigated in the Moravian samples using the Pb, Rb and U contents. The Near East samples were classified according to their Sr, Ba, Zr and REE contents as per-alkaline obsidians (Bingöl A/Nemrut Da?) originating from Southeast Anatolia. 相似文献
108.
Cross‐Aldol Reaction of Isatin with Acetone Catalyzed by Leucinol: A Mechanistic Investigation
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Dr. Mikhail A. Kabeshov Dr. Ondřej Kysilka Dr. Lubomír Rulíšek Dr. Yury V. Suleimanov Dr. Marco Bella Prof. Dr. Andrei V. Malkov Prof. Dr. Pavel Kočovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(34):12026-12033
Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin ( 1 a ) and acetone, catalyzed by L ‐leucinol ( 3 a ), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn‐enamine 6 , catalyzed by isatin, was identified as the rate‐determining step by both the calculations (ΔG≠=26.1 kcal mol?1 for the analogous L ‐alaninol, 3 b ) and the kinetic isotope effect (kH/kD=2.7 observed for the reaction using [D6]acetone). The subsequent reaction of the syn‐enamine 6 with isatin produces (S)‐ 2 a (calculated ΔG≠=11.6 kcal mol?1). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin‐catalyzed formation of the syn‐enamine 6 , which is thermodynamically favored over its anti‐rotamer 7 by 2.3 kcal mol?1; and 2) the high preference of the syn‐enamine 6 to produce (S)‐ 2 a on reaction with isatin ( 1 a ) rather than its enantiomer (ΔΔG≠=2.6 kcal mol?1). 相似文献
109.
Lubomír Kubáček 《Mathematica Slovaca》2010,60(5):739-749
In regular linear regression model with the type II constraints the unobservable parameters in the constraints can be estimated
by the BLUE of the observable parameters. The BLUE respects the constraints. If the estimator of the observable parameters
which is the BLUE in the model without constraints is used, then the estimator of the unobservable parameters is the same. 相似文献
110.
Lubomír Kubáček 《Mathematica Slovaca》2010,60(3):411-418
In the universal linear statistical model with the type II constraints, estimates of the unbiasedly estimable linear functions
of the parameters of the mean value vector are given by special types of generalized matrix inverse. Since there exists many
versions of such matrix inverse it is of some interest to check the unambiguity of obtained estimators. The aim of the paper
is to find the best unbiased linear estimators of unbiasedly estimable functions and to show that they do not depend on the
choice of the used generalized inverse of the matrices. 相似文献