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21.
Emmanuel Rousseau Marine Laroche Jean-Jacques Greffet 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(7-8):1005-1014
Radiative heat transfer at the nanoscale is becoming an important technological issue with the development of nano electromechanical systems (NEMS). In this article, we derive asymptotic expressions to compute near-field radiative heat transfer between two planes of silicon. We identify two physical mechanisms that give the dominant contribution at small gaps. For intrinsic and low-doped silicon, the main contribution is due to evanescent waves coming from propagating waves undergoing frustrated total internal reflections at the interfaces. For doping levels larger than Ne=1016 cm?3 surface mode coupling contributes to the heat transfer. Asymptotic expressions are also given in that case. In all cases, we compare analytical formulas with exact numerical calculations when varying the temperature and the doping concentration. We also give their range of validity. 相似文献
22.
Ritambhara Gond Dheeraj Kumar Singh Muthusamy Eswaramoorthy Prabeer Barpanda 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(25):8418-8423
Sodium cobalt metaphosphate [NaCo(PO3)3] has CoO octahedra (CoO6) and shows superior oxygen evolution reaction (OER) activity in alkaline solution, comparable with the state‐of‐the‐art precious‐metal RuO2 catalyst. OER catalysts of this metaphosphate are prepared by combustion (Cb) and solid‐state (SS) methods. The combustion‐assisted method offers a facile synthesis and one‐step carbon composite formation. Unusually high catalytic activity was observed in NCoM‐Cb‐Ar and could be due to chemical coupling effects between NaCo(PO3)3 and partially graphitized carbon. This novel electrocatalyst exhibits very small overpotential of 340 mV with high mass activity of 532 A g?1. Good charge transfer abilities and chemical coupling between NaCo(PO3)3 and amorphous carbon gives the OER activity in NCoM‐Cb‐Ar. 相似文献
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24.
Joy Ann Panis Prof. Marine Louis Arnaud Brosseau Shouhei Katao Florencio de los Reyes Prof. Takuya Nakashima Dr. Rémi Métivier Dr. Clémence Allain Prof. Tsuyoshi Kawai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202201012
We synthesized two bichromophoric difluoroboron-β-diketonates (DFB) connected in para and meta positions by using cyclohexane diamine as a chiral bridge ( para and meta (R/S)-CyDFB ). TD-DFT calculations revealed that the variation in connectivity of the DFB units leads to different spatial arrangements and a chirality inversion of the bichromophoric DFB. Higher gabs values were obtained in (R/S)-CyDFB connected in para as compared to meta position. Aggregation of para (R/S)-CyDFB in mixture of solvents increase the glum values as compared to its monomeric form. Ultrasonication and heating induced the formation of highly ordered nano-helical wires of para (R/S)-CyDFB that increased the glum values to 0.015. On the other hand, meta (R/S)-CyDFB failed to form highly ordered self-assembled wires due to hindered H-binding sites. These observations indicate that the chiroptical properties of DFB bi-chromophore system can be modulated with self-assembly and spatial arrangement of the chromophores. 相似文献
25.
Glycosyl‐Substituted Dicarboxylates as Detergents for the Extraction,Overstabilization, and Crystallization of Membrane Proteins
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Dr. Kim‐Anh Nguyen Dr. Marine Peuchmaur Sandrine Magnard Dr. Romain Haudecoeur Dr. Cédric Boyère Saravanan Mounien Ikram Benammar Veronica Zampieri Dr. Sébastien Igonet Dr. Vincent Chaptal Dr. Anass Jawhari Prof. Ahcène Boumendjel Dr. Pierre Falson 《Angewandte Chemie (International ed. in English)》2018,57(11):2948-2952
To tackle the problems associated with membrane protein (MP) instability in detergent solutions, we designed a series of glycosyl‐substituted dicarboxylate detergents (DCODs) in which we optimized the polar head to clamp the membrane domain by including, on one side, two carboxyl groups that form salt bridges with basic residues abundant at the membrane–cytoplasm interface of MPs and, on the other side, a sugar to form hydrogen bonds. Upon extraction, the DCODs 8 b , 8 c , and 9 b preserved the ATPase function of BmrA, an ATP‐binding cassette pump, much more efficiently than reference or recently designed detergents. The DCODs 8 a , 8 b , 8 f , 9 a , and 9 b induced thermal shifts of 20 to 29 °C for BmrA and of 13 to 21 °C for the native version of the G‐protein‐coupled adenosine receptor A2AR. Compounds 8 f and 8 g improved the diffraction resolution of BmrA crystals from 6 to 4 Å. DCODs are therefore considered to be promising and powerful tools for the structural biology of MPs. 相似文献
26.
The analytical performances of two triple-quadrupole instruments, which differ in their atmospheric-pressure sources, were evaluated for native amino acid analysis. The Applied Biosystems/Sciex API 300 instrument was equipped with a turboIon Spray source and a curtain gas interface while the Waters/Micromass Quattro Ultima instrument was characterized by its Z-spray source. Liquid chromatography/mass spectrometry analysis of native amino acids requires volatile ion-pairing mobile phase additives (mainly perfluorinated carboxylic acids). The effects of the structure and concentration of the ion-pairing reagents as well as the organic modifier percentage on the electrospray response of amino acids were studied in detail. The most favourable chromatographic conditions depend strongly on the mass spectrometer used. Several instrumental parameters were also studied, including spray voltage, transmission lens voltages, temperature of desolvation and auxiliary gas flow rates. The results show substantial qualitative differences depending on the instrument geometry. The quantitative performances of the two triple-quadrupole mass spectrometers were evaluated in terms of limits of detection and quantification. The effects of the matrix on the analyte ionization were also examined, and the long-term stability of the electrospray performance was studied over 12 h using a mobile phase containing the perfluorinated ion-pairing reagents. The study provides information on the robustness of the MS instrument and its detection sensitivity towards native amino acid analysis. It appears that each instrument has its good and bad points since one provides higher sensitivity while another is more robust. 相似文献
27.
Marine Pinaud Leïla Vaïtilingom Gayathiri Gnanalingam Dr. Tania Xavier Prof. Erwan Le Gall Dr. Marc Presset 《European journal of organic chemistry》2023,26(18):e202300198
The use of N-alkyl imines in decarboxylative Mannich reaction with substituted malonic acids half oxyesters (SMAHOs) has been developed to afford a direct access to secondary β2,3-aminoesters. The transformation occurs under very practical conditions (DABCO as a catalyst in bulk toluene and open to air) and can be performed with a broad range of each substrate in yields of 36 to 97 %. Importantly, the reaction was found to require the use of acidic additives in combination with the organocatalyst to limit the competitive olefination reaction. 相似文献
28.
We report concise and stereocontrolled syntheses of aculeatins (-)-A, (+)-B, (+)-D, and (+)-6-epi-D. Diastereodivergent 1,3-inductions in Mukaiyama aldol coupling contribute to reduce steps and to increase flexibility with reactants having sterically restricted proximal substituents (i.e., CH2), involving either a good anti or a moderate syn 1,3-induction, depending on the nature of protecting group (P). In addition, the 3,5-syn-diol-ketone resulting from concomitant deprotection of the beta-alkoxy (Tr = trityl) group proves to be remarkably stable whereas the 3,5-anti diastereoisomer cyclizes spontaneously to the corresponding tetrahydropyran hemiketal, thus enabling a useful and facile separation. The second part of our study is devoted to improving the yield and the diastereoselectivity of the final phenolic oxidation reaction leading to aculeatins. 相似文献
29.
The two-dimensional cyano-bridged coordination polymer Er(H(2)O)(4)[W(CN)(8)] exhibits a magnetic transition at 12 K and an unusual field-dependent transition from short-range to ferromagnetic ordering. 相似文献
30.
ChengBinCUI ChiXU QianQunGU ShiDongCHU HaiHongJI GangJING 《中国化学快报》2004,15(10):1191-1194
26-O-β-D-Glucopyranosyl-furost-5(6),20(22)-dien-3β,26-diol 1, a new furostanol saponin, was isolated from the water-extract of Dioscorea nipponica Mak., the raw material of a traditional Chinese herbal medicine Wei Ao Xin. The structure of 1 was determined on the basis of its spectral data especially by NMR spectroscopy. The result provides the first example of naturally occurring furostanol saponins with a single saccharide chain at the C-26 position. 相似文献