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排序方式: 共有366条查询结果,搜索用时 14 毫秒
61.
Minkyu Kim Moon Jong Han Hansol Lee Paraskevi Flouda Daria Bukharina Kellina J. Pierce Katarina M. Adstedt Madeline L. Buxton Young Hee Yoon William T. Heller Srikanth Singamaneni Vladimir V. Tsukruk 《Angewandte Chemie (International ed. in English)》2023,62(30):e202305646
Chiral metal–organic frameworks (MOFs) have gained rising attention as ordered nanoporous materials for enantiomer separations, chiral catalysis, and sensing. Among those, chiral MOFs are generally obtained through complex synthetic routes by using a limited choice of reactive chiral organic precursors as the primary linkers or auxiliary ligands. Here, we report a template-controlled synthesis of chiral MOFs from achiral precursors grown on chiral nematic cellulose-derived nanostructured bio-templates. We demonstrate that chiral MOFs, specifically, zeolitic imidazolate framework (ZIF), unc -[Zn(2-MeIm)2, 2-MeIm=2-methylimidazole], can be grown from regular precursors within nanoporous organized chiral nematic nanocelluloses via directed assembly on twisted bundles of cellulose nanocrystals. The template-grown chiral ZIF possesses tetragonal crystal structure with chiral space group of P41, which is different from traditional cubic crystal structure of I-43 m for freely grown conventional ZIF-8. The uniaxially compressed dimensions of the unit cell of templated ZIF and crystalline dimensions are signatures of this structure. We observe that the templated chiral ZIF can facilitate the enantiotropic sensing. It shows enantioselective recognition and chiral sensing abilities with a low limit of detection of 39 μM and the corresponding limit of chiral detection of 300 μM for representative chiral amino acid, D- and L- alanine. 相似文献
62.
Prasad S Pierce KM Schmidt H Rao JV Güth R Synovec RE Smith GB Eiceman GA 《The Analyst》2008,133(6):760-767
Four bacteria, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus warneri, and Micrococcus luteus, were grown at temperatures of 23, 30, and 37 degrees C and were characterized by pyrolysis-gas chromatography/differential mobility spectrometry (Py-GC/DMS) providing, with replicates, 120 data sets of retention time, compensation voltage, and ion intensity, each for negative and positive polarity. Principal component analysis (PCA) for 96 of these data sets exhibited clusters by temperature of culture growth and not by genus. Analysis of variance was used to isolate the constituents with dependences on growth temperature. When these were subtracted from the data sets, Fisher ratios with PCA resulted in four clusters according to genus at all temperatures for ions in each polarity. Comparable results were obtained from unsupervised PCA with 24 of the original data sets. The ions with taxonomic features were reconstructed into 3D plots of retention time, compensation voltage, and Fisher ratio and were matched, through GC-mass spectrometry (MS), with chemical standards attributed to the thermal decomposition of proteins and lipid A. Results for negative ions provided simpler data sets than from positive ions, as anticipated from selectivity of gas phase ion-molecule reactions in air at ambient pressure. 相似文献
63.
Benjamin A. Chalmers Hui Xing Sevan Houston Charlotte Clark Sussan Ghassabian Andy Kuo Benjamin Cao Andrea Reitsma Cody‐Ellen P. Murray Jeanette E. Stok Glen M. Boyle Carly J. Pierce Stuart W. Littler David A. Winkler Paul V. Bernhardt Cielo Pasay James J. DeVoss James McCarthy Peter G. Parsons Gimme H. Walter Maree T. Smith Helen M. Cooper Susan K. Nilsson John Tsanaktsidis G. Paul Savage Craig M. Williams 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(11)
64.
Dong X Gilbert KE Guha R Heiland R Kim J Pierce ME Fox GC Wild DJ 《Journal of chemical information and modeling》2007,47(4):1303-1307
The vast increase of pertinent information available to drug discovery scientists means that there is a strong demand for tools and techniques for organizing and intelligently mining this information for manageable human consumption. At Indiana University, we have developed an infrastructure of chemoinformatics Web services that simplifies the access to this information and the computational techniques that can be applied to it. In this paper, we describe this infrastructure, give some examples of its use, and then discuss our plans to use it as a platform for chemoinformatics application development in the future. 相似文献
65.
66.
The purpose of this research was to survey the quantity and quality of laboratory work conducted by 11th- and 12th-grade biology students in British Columbia high schools to analyze student performance on laboratory-based questions on provincial examinations, and to examine the curriculum for recommended laboratory work. A pilot survey was used to produce a valid survey instrument that identified teachers' use of laboratory activities. Examination and curriculum data were extracted from Ministry of Education documents. The frequency of laboratory work was low, with quantitative activities much less frequent than qualitative. Laboratory exercises were confirmatory rather than investigative. Critical thinking and hypotheses formulation were seldom expected of the students. Many teachers reported that they infrequently or never used laboratory simulations or computer-based data collection. Although laboratories were equipped adequately, teachers claimed that the curriculum and provincial examination limited the scope for an inquiry-based course. Provincial examination results indicated that the frequency and type of laboratory work had no effect on scores on lab-based questions. Analysis of the laboratory activities recommended in the syllabus revealed that fewer laboratory activities were being conducted than are recommended in the curriculum guide outline. This study indicates that while the current philosophy of many biology teachers supports an investigative learning experience, little change in classroom practice has occurred in British Columbia schools. 相似文献
67.
A study of the condensation of a metal vapor in an inert carrier gas is made. Superheated zinc vapor is generated in a hot
shot wind tunnel in a helium carrier gas and expanded in a converging-diverging nozzle. Static pressure measurements along
the length of the nozzle are made to determine the location of the onset of condensation. A conical nominal Mach 5 (helium)
nozzle is employed. The amount of supercooling before the onset of condensation is found to be approximately 430 K, measured
along the isentrope over a range of initial zinc mass fractions of .35 to .70 for saturation partial pressures of zinc between
10 psia and 70 psia. The measurements are compared with results of an analysis based on the classical liquid drop model of
nucleation. The computed results agree reasonably well with the measurements. 相似文献
68.
Wai Tung Lee Xin Tong Dennis Rich Yun Liu Michael Fleenor Akbar Ismaili Joshua Pierce Mark Hagen Jonny Dadras J. Lee Robertson 《Physica B: Condensed Matter》2009,404(17):2670-2672
In recent years, polarized 3He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3He to 70% polarization would require 20−40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3He gas using the SEOP method. 相似文献
69.
Comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry (GC × GC-TOFMS) provides high resolution separations of complex samples with a mass spectrum at every point in the separation space. The large volumes of multidimensional data obtained by GC × GC-TOFMS analysis are analyzed using a principal component analysis (PCA) method described herein to quickly and objectively discover differences between complex samples. In this work, we submitted 54 chromatograms to PCA to automatically compare the metabolite profiles of three different species of plants, namely basil (Ocimum basilicum), peppermint (Mentha piperita), and sweet herb stevia (Stevia rebaudiana), where there were 18 chromatograms for each type of plant. The 54 scores of the m/z 73 data set clustered in three groups according to the three types of plants. Principal component 1 (PC 1) separated the stevia cluster from the basil and peppermint clusters, capturing 61.84% of the total variance. Principal component 2 (PC 2) separated the basil cluster from the peppermint cluster, capturing 16.78% of the total variance. The PCA method revealed that relative abundances of amino acids, carboxylic acids, and carbohydrates were responsible for differentiating the three plants. A brief list of the 16 most significant metabolites is reported. After PCA, the 54 scores of the m/z 217 data set clustered in three groups according to the three types of plants, as well, yielding highly loaded variables corresponding with chemical differences between plants that were complementary to the m/z 73 information. The PCA data mining method is applicable to all of the monitored selective mass channels, utilizing all of the collected data, to discover unknown differences in complex sample profiles. 相似文献