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排序方式: 共有1087条查询结果,搜索用时 15 毫秒
941.
Daniel Kamzol Maxime Neuville Chloé Cocaud Killian Tiger Baptiste Taffoureau Prof. Dr. Krzysztof Lewiński Justyna Jaszczyk Prof. Dr. Olivier R. Martin Dr. Sebastian Baś Prof. Dr. Sylvain Routier Prof. Dr. Isabelle Gillaizeau Dr. Frédéric Buron Dr. Cyril Nicolas 《European journal of organic chemistry》2023,26(39):e202300762
A comprehensive study of the preparation and reactivity of N-tert-butanesulfinyl glycosylamines with simple Grignard and organo lithium reagents in batch vs. continuous flow chemistry is reported. As they readily react as latent imine equivalents with a variety of carbon nucleophiles, these carbohydrate derivatives constitute very useful precursors for the diastereoselective synthesis of bioactive compounds such as iminosugar-C-glycosides. A hybrid protocol, involving the addition of benzylmagnesium chloride to a (SR)-arabinofuranosylamine substrate in flow, at room temperature, combined with a cyclization protocol in batch is also described for the first time. Of note, this semi-continuous flow process shortens the synthesis of imino-C-glycoside scaffolds to a single workday. 相似文献
942.
Julien Lavie Van Binh Vu Daniel Medina-Lopez Yannick Dappe Thomas Liu Loïc Rondin Jean-Sébastien Lauret Sylvain Latil Stéphane Campidelli 《Helvetica chimica acta》2023,106(6):e202300034
Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years now; first with fullerene, then with nanotubes and now with graphene and graphene related materials. Graphene quantum dots (GQDs) are nanoparticles of graphene that can be synthesized following two approaches, namely top-down and bottom-up methods. The top-down synthesis used harsh chemical and/or physical treatments of macroscopic graphitic materials to obtain nanoparticles, while the second is based on organic chemistry through the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. The main drawback of this approach is related to the low solubility of carbon materials that prevents the synthesis of nanoparticles containing more than few hundreds of sp2 carbon atoms. Here we report on the synthesis of a family of rectangular-shaped graphene quantum dots containing up to 162 sp2 carbon atoms. These graphene quantum dots are not functionalized on their periphery in order to keep the maximum similarity with nanoparticles of pure graphene. We chose water with sodium deoxycholate surfactant to study their dispersion and their optical properties (absorption, photoluminescence and photoluminescence excitation). The electronic structure of the particles and of their aggregates are studied using Tight-Binding (TB). We observe that the larger particles ( GQD 3 and GQD 4 ) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water. 相似文献
943.
Rocío Rivera Sánchez Siva Bandi Marie-Désirée Scheidt Hanna Laaroussi Bennett William Fox Yojiro Ishida Gaétan Glauser Sylvain Sutour Stephan H. von Reuss 《Helvetica chimica acta》2023,106(11):e202300131
Ceramide biosynthesis and its connection to iso-fatty acid metabolism in the model organism Caenorhabditis elegans was investigated using a combination of reverse genetics and comparative ESI-(+)-HR-MSe ceramide profiling along with incorporation experiments with bacterial mutants specifically enriched with isotopically labeled branched-chain amino acids or branched-chain fatty acids. Incorporation of a l -leucine-derived isovalerate unit into the conserved d17 : 1iso sphingosine building block proceeds through elo-5 dependent chain elongation and depends on peroxisomal β-oxidation by the 3-ketoacyl-CoA thiolase daf-22, although ceramide profiles of N2 wildtype and daf-22(ok693) are indistinguishable. Biosynthesis of the homologous N-iso-acyl moieties also depends on l -leucine and isovalerate chain elongation but proceeds independently of elo-5 and daf-22. Biosynthesis of the dominating N-docosanoyl moiety depends on elo-3-catalyzed chain elongation of bacteria-derived palmitic acid, whereas the N-tetracosanoyl moiety is derived from de novo lipogenesis. 相似文献
944.
Trépout S Mornet S Benabdelhak H Ducruix A Brisson AR Lambert O 《Langmuir : the ACS journal of surfaces and colloids》2007,23(5):2647-2654
Mimetic functional membranes on solid support are now emerging for the development of membrane biosensor or for the study of membrane-mediated processes and should have an important impact on biodiagnostics. We established a method to reconstitute a membrane protein into a lipid membrane in a selective orientation on a solid support. Membrane protein OprM, a component of OprM-MexA-MexB multidrug efflux pump, solubilized in detergent was immobilized via its extracellular domain on aminosilane-modified silica surface. The oriented protein was reconstituted into a lipid membrane by detergent removal. The membrane protein reconstitution process carried out on silica nanoparticles and on planar silica surfaces was followed by cryo-electron microscopy (cryo-EM) and quartz crystal microbalance with dissipation monitoring (QCM-D) respectively. The selective protein orientation on aminosilane-modified silica surface was assessed by cryo-EM and was compared to the nonspecific protein deposition on silica surface. Finally, the binding of MexA, a periplasmic component of the tripartite efflux complex, was monitored with QCM-D on the oriented OprM protein monolayer. The large adsorbed mass gave a direct evidence of the high affinity of MexA with the periplasmic helical part of OprM. 相似文献
945.
Baillargeon P Bernard S Gauthier D Skouta R Dory YL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(33):9223-9235
The synthesis of four C(n) symmetric macrocyclic lactams cyclo-[NH-CH(2)-CH=CH-CH(2)-CO](n) (1, n=2; 2, n=3; 3, n=4) and cyclo-[NH-CH(2)-CH(2)-CH=CH-CO](3) (4) has been achieved by two approaches. A linear route leads to precursors that are subsequently macrocyclized in a separate step. The second, convergent approach relies on the symmetry of the targets: it includes suitably activated subunits, which are subjected to macrocyclization conditions. The subunits first oligomerize, then cyclize to form either pure macrolactams or mixtures. The macrolactam units 1, 2 and 4 stack on top each other through weak interactions (hydrogen bond and van der Waals), to form endless square, rectangular and triangular prisms, respectively. These stacks are further packed side by side in crystals grown from isotropic media. The overall dipoles in the crystals from lactams 1 and 4, which result mostly from the alignment of amide groups, are zero and large, respectively. Macrolactam 2 displays an astonishing isomorphism when allowed to cool down in anisotropic liquid crystal solutions. Large hollow hexagonal tubes are then obtained through a fractal process. Contrary to the three previous rings, 3 yields crystals where prisms of any shape are absent. 相似文献
946.
A solid-phase tandem ene-reaction/intramolecular Sakurai cyclization sequence has been developed to synthesize highly substituted tetrahydropyran derivatives in two steps from aldehydes and with complete control of the relative stereochemistry of the three newly formed stereocenters. The compounds are obtained with high purity after release from the solid support and can be easily isolated in multimilligram amounts. Moreover, we have shown that asymmetric induction is possible on solid phase and that enantiomerically pure tetrahydropyrans containing four stereocenters can be effectively synthesized with this method. 相似文献
947.
Alladoum J Roland S Vrancken E Mangeney P Kadouri-Puchot C 《The Journal of organic chemistry》2008,73(24):9771-9774
Amino alcohols, having an enol ether function, cyclized in acidic medium to give quantitatively diastereosomerically pure bicyclic compounds that were transformed in five steps in enantiopure trans-5-alkylproline derivatives. 相似文献
948.
Gas-phase basicity of methionine 总被引:1,自引:0,他引:1
Proton affinity and protonation entropy of methionine (Met) were determined by the extended kinetic method from ESI-Q-TOF tandem mass spectrometry experiments. The values, PA(Met) = 937.5 +/- 2.9 kJ mol(-1) and Delta(p)S degrees (Met) = - 22 +/- 5 J mol(-1) K(-1), lead to gas-phase basicity GB(Met) = 898.2 +/- 3.2 kJ.mol(-1). Quantum chemical calculations using density functional theory confirm that the proton affinity of Met is indeed in the 940 kJ mol(-1) range and that a significant entropy loss, of at least - 25 J mol(-1) K(-1), occurs upon protonation. This last point is evidenced here for the first time and suggests revision of the tabulated protonation thermochemistry of Met. A comparison with previous experimental data allows us to propose the following evaluated thermochemical values: PA(Met) = 943 +/- 4 kJ mol(-1) and Delta(p)S degrees (Met) = - 35 +/- 15 J mol(-1) K(-1) and GB(Met) = 900 +/- 2 kJ mol(-1). 相似文献
949.
Iterative use of Cr-mediated catalytic asymmetric allylation could give a simple access to 1,3-polyols. Using syn/syn- and anti/anti-1,3,5-triols as representative examples, the feasibility of this approach is studied, thereby demonstrating that (1) the pre-existing TMS-protected alcohol at the beta-position does not give a significant effect on the Cr-mediated catalytic asymmetric allylation and (2) this synthetic route furnishes the expected syn/syn- and anti/anti-1,3,5-triols at the useful level of asymmetric induction and yield. 相似文献
950.
Hantal G Jedlovszky P Hoang PN Picaud S 《Physical chemistry chemical physics : PCCP》2008,10(42):6369-6380
The adsorption isotherm of acetone at the surface of I(h) ice has been determined by a set of grand canonical Monte Carlo simulations at 200 K, by varying the chemical potential of acetone in the simulations. The obtained isotherm can be described by the Langmuir theory up to a certain relative pressure value (i.e., about 0.07); above which the isotherm increasingly deviates from the Langmuir form. This deviation mainly originates from the increasing importance of the lateral dipolar interactions. Further, above this pressure the adsorption sites are no longer equivalent: the adsorbed acetone molecules are aligned in three different ways. In one of these orientations the acetone molecule forms two, while in another one it forms one hydrogen bond with the surface waters, whereas in the third preferred orientation no hydrogen bonding occurs between the adsorbed molecule and the ice surface. 相似文献