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Adam?HarrisEmail author Sergey?Kazachenko Robert?Bateman Jarett?Nickerson Michael?Emanuel 《Journal of Thermal Analysis and Calorimetry》2014,116(3):1309-1314
Heat transfer fluids are often a critical performance component in industrial processes and system design. Fluids are used in heat dissipation to maintain stable operating temperatures in a variety of applications, such as diesel engines, chemical production, asphalt storage, and high-power electric transformers. A wide range of fluids specific to various applications are available, thus a reliable and accurate thermal conductivity characterization is extremely important. Thermal conductivity analysis of heat transfer fluids with traditional methods is time-consuming and error-prone due to the impact of convection. Convection often distorts effective thermal conductivity measurement as an additional source of heat transfer. The modified transient plane source method implemented in the C-Therm Technologies TCi Analyzer provides an easy way to accurately measure the thermal conductivity and distinguish this form of heat transfer in negating the impact of convection by (a) employing the shortest test time in commercially available sensors (0.8 s), (b) offering a minimal sample volume requirement (1.25 mL), and (c) employing a low-energy power flux to the specimen under test (approximately 2,600 W m?2). This work presents thermal conductivity results generated on three types of heat transfer fluids over a wide temperature range and discusses the significance of the data in relevance to the application. 相似文献
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Dr. Chi Chung Lee Dr. Jarett Wilcoxen Caleb J. Hiller Prof. Dr. R. David Britt Prof. Dr. Yilin Hu 《Angewandte Chemie (International ed. in English)》2018,57(13):3411-3414
Binding and activation of CO by nitrogenase is a topic of interest because CO is isoelectronic to N2, the physiological substrate of this enzyme. The catalytic relevance of one‐ and multi‐CO‐bound states (the lo‐CO and hi‐CO states) of V‐nitrogenase to C−C coupling and N2 reduction was examined. Enzymatic and spectroscopic studies demonstrate that the multiple CO moieties in the hi‐CO state cannot be coupled as they are, suggesting that C−C coupling requires further activation and/or reduction of the bound CO entity. Moreover, these studies reveal an interesting correlation between decreased activity of N2 reduction and increased population of the lo‐CO state, pointing to the catalytic relevance of the belt Fe atoms that are bridged by the single CO moiety in the lo‐CO state. Together, these results provide a useful framework for gaining insights into the nitrogenase‐catalyzed reaction via further exploration of the utility of the lo‐CO conformation of V‐nitrogenase. 相似文献
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Stereoselective Synthesis of the Halaven C14–C26 Fragment from D‐Quinic Acid: Crystallization‐Induced Diastereoselective Transformation of an α‐Methyl Nitrile 下载免费PDF全文
Francis Belanger Dr. Charles E. Chase Dr. Atsushi Endo Dr. Francis G. Fang Dr. Jing Li Steven R. Mathieu Dr. Annie Z. Wilcoxen Huiming Zhang 《Angewandte Chemie (International ed. in English)》2015,54(17):5108-5111
Crystallization‐induced diastereoselective transformation (CIDT) of an α‐methyl nitrile completes an entirely non‐chromatographic synthesis of the halichondrin B C14–C26 stereochemical array. The requisite α‐methyl nitrile substrate is derived from D ‐quinic acid through a series of substrate‐controlled stereoselective reactions via a number of crystalline intermediates that benefit from a rigid polycyclic template. Therefore, all four stereogenic centers in the Halaven C14–C26 fragment were derived from the single chiral source D ‐quinic acid. 相似文献
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Cyclic peptides have come under scrutiny as potential antimicrobial therapeutic agents. Combinatorial split-and-pool synthesis of cyclic peptides can afford single compound per well libraries for antimicrobial screening, new lead identification, and construction of quantitative structure-activity relationships (QSAR). Here, we report a new sequencing protocol for rapid identification of the members of a cyclic peptide library based on automated computer analysis of mass spectra, obviating the need for library encoding/decoding strategies. Furthermore, the software readily integrates with common spreadsheet and database packages to facilitate data visualization and archiving. The utility of the new MS-sequencing approach is demonstrated using sonic spray ionization ion trap MS and MS/MS spectrometry on a single compound per bead cyclic peptide library and validated with individually synthesized pure cyclic D,L-alpha-peptides. 相似文献
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Carbon monoxide dehydrogenase from Oligotropha carboxidovorans catalyzes the aerobic oxidation of carbon monoxide to carbon dioxide, providing the organism both a carbon source and energy for growth. The active site of the native enzyme is a unique binuclear molybdenum- and copper-containing center. Here we show that silver can be substituted for copper in the active site to yield a functional enzyme. The characteristic hyperfine coupling of the I = ? nucleus of Ag is evident in the EPR signal of the binuclear active site observed upon reduction with CO, indicating both the incorporation of silver into the active site and, remarkably, retention of the catalytic activity. The silver-substituted enzyme is reduced by CO with an observed limiting rate constant of 8.1 s(-1), which can be compared with the value of 51 s(-1) for the wild-type enzyme. Steady-state kinetics for the Ag-substituted enzyme yielded k(cat) = 8.2 s(-1) and K(m) = 2.95 μM at pH 7.2. 相似文献
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Weixing Wang Jarett C. Martin Ning Zhang Chao Ma Aijie Han Luyi Sun 《Journal of nanoparticle research》2011,13(12):6981-6990
Biogenic silica nanoparticles were synthesized using rice husks (RHs) as the raw material via controlled pyrolysis. The characterization
results showed that the morphology of the synthesized silica was highly related to the pretreatment of RHs and the pyrolysis
conditions. Particularly, potassium cations in RHs were found to catalyze the melting of silica, during which the amorphous
silica were converted to crystalline phase. Two hours of pyrolysis at 700 °C appeared to be ideal to synthesize silica nanoparticles
with a diameter of ca. 20–30 nm. Higher temperature and longer duration of pyrolysis led to undesired melting of silica nanoparticles,
while too low a temperature cannot effectively remove carbonous residues. Such amorphous silica nanoparticles with narrow
size distribution and high purity are expected to replace silica gel and fumed silica for various applications. 相似文献
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Andrew J. Jasniewski Jarett Wilcoxen Kazuki Tanifuji Britt Hedman Keith O. Hodgson R. David Britt Yilin Hu Markus W. Ribbe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14845-14849
Nitrogenases catalyze the reduction of N2 to NH4+ at its cofactor site. Designated the M‐cluster, this [MoFe7S9C(R‐homocitrate)] cofactor is synthesized via the transformation of a [Fe4S4] cluster pair into an [Fe8S9C] precursor (designated the L‐cluster) prior to insertion of Mo and homocitrate. We report the characterization of an eight‐iron cofactor precursor (designated the L*‐cluster), which is proposed to have the composition [Fe8S8C] and lack the “9th sulfur” in the belt region of the L‐cluster. Our X‐ray absorption and electron spin echo envelope modulation (ESEEM) analyses strongly suggest that the L*‐cluster represents a structural homologue to the l ‐cluster except for the missing belt sulfur. The absence of a belt sulfur from the L*‐cluster may prove beneficial for labeling the catalytically important belt region, which could in turn facilitate investigations into the reaction mechanism of nitrogenases. 相似文献
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Inside Cover: Stereoselective Synthesis of the Halaven C14–C26 Fragment from D‐Quinic Acid: Crystallization‐Induced Diastereoselective Transformation of an α‐Methyl Nitrile (Angew. Chem. Int. Ed. 17/2015) 下载免费PDF全文