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排序方式: 共有362条查询结果,搜索用时 31 毫秒
21.
Marie Leroy Michel Lafleur Michèle Auger Gaétan Laroche Roxane Pouliot 《Analytical and bioanalytical chemistry》2013,405(27):8709-8718
The skin acts mainly as a protective barrier from the external environment, thanks to the stratum corneum which is the outermost layer of the skin. As in vitro tests on skin are essential to elaborate new drugs, the development of skin models closer to reality becomes essential. It is now possible to produce in vitro human skin substitutes through tissue engineering by using the self-assembly method developed by the Laboratoire d’Organogénèse Expérimentale. In the present work, infrared microspectroscopy imaging analyses were performed to get in-depth morpho-spectral characterization of the three characteristic layers of human skin substitutes and normal human skin, namely the stratum corneum, living epidermis, and dermis. An infrared spectral analysis of the skin is a powerful tool to gain information on the order and conformation of the lipid chains and the secondary structure of proteins. On one hand, the symmetric stretching mode of the lipid methylene groups (2,850 cm?1) is sensitive to the acyl chain conformational order. The evolution profile of the frequency of this vibrational mode throughout the epidermis suggests that lipids in the stratum corneum are more ordered than those in the living epidermis. On the other hand, the frequencies of the infrared components underneath the envelop of the amide I band provide information about the overall protein conformation. The analysis of this mode establishes that the proteins essentially adopt an α-helix conformation in the epidermis, probably associated with the presence of keratin, while modifications of the protein content are observed in the dermis (extracellular matrix made of collagen). Finally, the lipid organization, as well as the protein composition in the different layers, is similar for human skin substitutes and normal human skin, confirming that the substitutes reproduce essential features of real skin and are appropriate biomimetics. 相似文献
22.
Michèle Fee Spyridon Ntais Arnaud Weck Elena A. Baranova 《Journal of Solid State Electrochemistry》2014,18(8):2267-2277
Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P O2?=?6 kPa. With the application of positive potential, silver oxide (Ag2O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation. 相似文献
23.
Dr. Alexander Sachse Caroline Wuttke Dr. Elízio Lissner Dr. Michèle Oberson de Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):14996-14999
Hierarchically porous ZSM‐5 was achieved by using a simple bottom‐up strategy combining zeolite seeds with imidazolium‐based ionic liquids. The bimodal ZSM‐5 with hexagonal arranged mesopores (3 nm) shows important activity in the acid catalysis of bulky compounds relative to conventional ZSM‐5. 相似文献
24.
Leiming Zhu Leonard Himmel Jean Michél Merkes Prof. Dr. Fabian Kiessling Prof. Dr. Magnus Rueping Dr. Srinivas Banala 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(19):4232-4235
Atropisomerism has been observed in a variety of biaryl compounds and meso-aryl substituted porphyrins. However, in porphyrins, this phenomenon had been shown only with o-substituted 6-membered aromatic groups at the meso-position. We show herein that a 5-membered heteroaromatic (N-mesyl-pyrrol-2-yl) group at the meso-position leads to atropisomerism. In addition, we report a ‘one-pot’ synthetic route for the synthesis of ‘all-pyrrolic’ porphyrin (APP) with several N-protection groups (Boc, Cbz, Ms and Ts). Among these groups, we found that only the Ms group gave four individually separable atropisomers of meso-tetra(N-Ms-pyrrol-2-yl) porphyrin. Furthermore, the reductive removal of Cbz- was achieved to obtain meso-tetra(pyrrol-2-yl) porphyrin. Thus, our synthetic procedure provides an easy access to a group of APPs and stable atropisomers, which is expected to expand the application of novel APP-based materials. 相似文献
25.
Ahlem Bouhlel Christophe Curti Michèle P. Bertrand Patrice Vanelle 《Tetrahedron》2012,68(18):3596-3604
An easily reproducible protocol allowing inter- or intramolecular spirocyclization on β-dicarbonyl structures is described. This methodology could afford a wide variety of spirocyclic pharmacophores. As examples, highly substituted spirobenzophenanthridin-6(5H)-ones and spirolactones were synthesized. These scaffolds could be used for the design of many compounds exhibiting biological activities. 相似文献
26.
27.
Escoubet S Gastaldi S Timokhin VI Bertrand MP Siri D 《Journal of the American Chemical Society》2004,126(39):12343-12352
Thiols mediate the radical isomerization of allylic amines into enamines. The reaction results in the cleavage of the allylic C-N bond, after treatment with aqueous HCl. The mechanism involves the abstraction of an allylic hydrogen alpha to nitrogen by thiyl radical, followed by a return hydrogen transfer from the thiol to the carbon gamma to nitrogen in the intermediate allylic radical. The scope and limitations of the reaction with respect to the nature of the thiol, to the structure of the allylic chain, and to the nature of the substituents at nitrogen were investigated. The experimental results were interpreted on the ground of DFT calculations of the C-Halpha BDE in the starting allylic amines, and of the C-Hgamma BDE in the resulting enamines. The efficiency of the initial hydrogen transfer is the first requirement for the reaction to proceed. A balance must be found between the S-H BDE and the two above-mentioned C-H BDEs. The incidence of stereoelectronic factors was analyzed through NBO calculations performed on the optimized geometries of the starting allylic amines. Additional calculations of the transition structures and subsequent tracing of the reaction profiles were performed for the abstraction of Halpha from both the allyl and the prenyl derivatives by p-TolS(*). The latter allowed us to estimate the rate constant for the abstraction of hydrogen by thiyl radical from an N-prenylamine and an N-allylamine. 相似文献
28.
Le Gal J Latapie L Gressier M Coulais Y Dartiguenave M Benoist E 《Organic & biomolecular chemistry》2004,2(6):876-883
Synthetic pathways to a range of novel semi-rigid tetradentate ligands, with sulfur, amido or amino donor groups, designed to coordinate technetium 99m have been developed. The technetium-99m complexes have been prepared and their stabilities in serum and by metathesis reaction via cysteine exchange reactions were compared. HPLC comparison of two (99m)Tc-complexes and their rhenium analogues led to the first proof of the nature of our radioactive complexes. 相似文献
29.
We show that frequency and intensity noise in a Nd:YAG laser are correlated to a high degree and can be traced to the same underlying cause, namely, power fluctuations of the pump source. Because of this correlation, simultaneous suppression of frequency and intensity noise by 30 dB is achieved by means of a single actuator, the pump power. 相似文献
30.
Nechab M Campolo D Maury J Perfetti P Vanthuyne N Siri D Bertrand MP 《Journal of the American Chemical Society》2010,132(42):14742-14744
The cascade rearrangement of chiral enediynes 1c-e, involving successively 1,3-proton shift, Saito-Myers cyclization, 1,5-hydrogen atom transfer, and intramolecular coupling of the resulting biradical, proceeded at 80 °C to form tri- and tetracyclic heterocycles possessing a quaternary stereogenic center with a very high level of memory of chirality. 相似文献