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41.
42.
Dr. Shengwen Liu Maoyu Wang Xiaoxuan Yang Dr. Qiurong Shi Zhi Qiao Marcos Lucero Qing Ma Prof. Karren L. More Dr. David A. Cullen Prof. Zhenxing Feng Prof. Gang Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21882-21889
Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a facile chemical vapor deposition (CVD) strategy to synthesize the promising M-N-C catalysts. The deposition of gaseous 2-methylimidazole onto M-doped ZnO substrates, followed by an in situ thermal activation, effectively generated single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst exclusively contains atomically dispersed FeN4 sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance. 相似文献
43.
Paola L. Lucero Walter J. Peláez Zsuzsanna Riedl György Hajós Elizabeth L. Moyano Gloria I. Yranzo 《Tetrahedron》2012,68(4):1299-1305
2-Aryl-5-acroleinyl-1,2,3,4-tetrazoles (1a–d) and 2-aryl-5-butadienyl-1,2,3,4-tetrazoles (1e–g) were subjected to flash vacuum pyrolysis. Acroleinyl derivatives resulted in nitrogen extrusion to give nitrilimines followed by ring closure to give the corresponding indazoles 3a–d in good yields. On the other hand, butadiene derivatives underwent ring fragmentation to give p-substituted anilines without formation of the expected indazoles. Differences between thermal behaviour of 2-(4-chlorophenyl)-5-acroleinyl-1,2,3,4-tetrazole (1c) and 1-(4-chlorophenyl)-4-acroleinyl-1,2,3-triazole (2) were studied in details. DFT calculations have been used to examine the nitrilimine and carbene nature of the intermediates involved in the thermal reactions of azolyl derivatives. 相似文献
44.
Reed JA Love SA Lucero AE Haynes CL Canavan HE 《Langmuir : the ACS journal of surfaces and colloids》2012,28(4):2281-2287
Poly(N-isopropyl acrylamide) or pNIPAM is a thermoresponsive polymer that is widely studied for use in bioengineering applications. The interest in this polymer lies in the polymer's unique capability to undergo a sharp property change near physiological temperature, which aids in the spontaneous release of biological cells from substrates. Currently, there are many methods for depositing pNIPAM onto substrates, including atom-transfer radical polymerization (ATRP) and electron beam ionization. Each method yields pNIPAM-coated substrates with different surface characteristics that can influence cell behavior. In this work, we compare two methods of pNIPAM deposition: plasma deposition and codeposition with a sol-gel. The resulting pNIPAM films were analyzed for use as substrates for mammalian cell culture based on surface characterization (XPS, ToF-SIMS, AFM, contact angles), cell attachment/detachment studies, and an analysis of exocytosis function using carbon-fiber microelectrode amperometry (CFMA). We find that although both methods are useful for the deposition of functional pNIPAM films, plasma deposition is much preferred for cell-sheet engineering applications because of the films' thermoresponse, minimal change in cell density, and maintenance of supported cell exocytosis function. 相似文献
45.
A systematic study of C-glycosylations of acetals related to mannose and other pyranoses was conducted. The C-5 alkoxyalkyl group provides only a modest influence on stereoselectivity. On the other hand, studies of pentopyranoses bearing alkoxy groups at C-2, C-3, and C-4 showed that the alkoxy groups exerted powerful influences on selectivity. In the case of mannose, the high alpha selectivity observed with C-mannosylation was reversed to high beta selectivity if the C-5 alkoxyalkyl group were removed. An analysis of the conformational preferences of the intermediate oxocarbenium ions, including the mannosyl cation, as well as consideration of steric effects that develop in the transition states for nucleophilic attack provide explanations for these phenomena. 相似文献
46.
García J Márquez A Ruiz R López LF Claro C Lucero MJ 《Biomedical chromatography : BMC》2006,20(10):1024-1027
An isocratic high-performance liquid chromatographic method with UV detection has been developed and validated for the quantitative determination of foscarnet in isoosmotic sodium chloride aqueous solution. The mobile phase consisted of mixture of methanol:water (30:70 v/v), containing 1 mm tetrahexylammonium hydrogen sulphate at pH 5.80. The analyte was separated on a reversed-phase C(18) column packed with 4 microm spherical particles of octadecylsilane. Hydrochlorothiazide was used as internal standard. UV detection at 232 nm allowed a quantification limit of 50 microg/mL. The assay was linear from 50 to 4000 microg/mL. The coefficient of variation was < or =2.52% for intra-assay precision and < or =3.49% for inter-assay precision. The deviation from the nominal value ranged from -0.57 to 0.47% for the same-day accuracy and from -0.75 to 3.06% for day-to-day accuracy. 相似文献
47.
N-Aminophthalimide (I) reacted with a variety of aromatic aldehydes to give the related arylideneaminophthalimides (III-X), although typical ketones such as acetone and benzophenone did not under the specific conditions employed. Catalytic reduction of benzylideneaminophthalimide (III) led to N-benzylaminophthalimide (XI), a stable acid-free precursor of benzylhydrazine. 相似文献
48.
This Letter presents an extension of a previous equation for the phonation threshold pressure by Titze [I. R. Titze, J. Acoust. Soc. Am. 83, 1536-1552 (1988)]. The extended equation contains the vocal-fold oscillation frequency as an explicit factor. It is derived from the mucosal wave model of the vocal folds by considering the general case of an arbitrary time delay for the mucosal wave to travel the glottal height. The results are illustrated with a numerical example, which shows good qualitative agreement with experimental measures. 相似文献
49.
In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness. 相似文献
50.
Particle image velocimetry (PIV) was used to measure velocity fields inside and around oscillating methane-air diffusion flames
with a slot fuel orifice. PIV provided velocity and directional information of the flow field comprised of both the flame
and air. From this, information on flow paths of entrained air into the flame were obtained and visualized. These show that
at low fuel flow rates for which the oscillations were strongest, the responsible mechanism for the oscillating flow appeared
to be the repetitive occurrence of flame quenching. PIV findings indicated that quenching appears to be associated primarily
with air entrainment. Velocity was found to be considerably larger in regions where quenching occurred. The shedding of vortices
in the shear layer occurs immediately outside the boundary of the flame envelope and was speculated to be the primary driving
force for air entrainment. 相似文献