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排序方式: 共有186条查询结果,搜索用时 15 毫秒
71.
[reaction: see text] alpha,beta-Unsaturated acetals afford, in the presence of the LIC-KOR superbase, 1-alkoxybuta-1,3-dienes. These substrates cross couple with aryl derivatives in the presence of Pd catalyst (Heck conditions) in a regio- and stereoselective mode. With dialkyl acetals, the reaction affords arylated dienes; on the other hand, in the case of 1,3-dioxane derivatives, the final outcome of the process formally corresponds to the direct gamma-arylation reaction of the starting alpha,beta-unsaturated material. 相似文献
72.
Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization. 相似文献
73.
Annamaria Canino Berardino Sciunzi Alessandro Trombetta 《NoDEA : Nonlinear Differential Equations and Applications》2016,23(2):8
We consider quasilinear elliptic equations involving the p-Laplacian and singular nonlinearities. We prove comparison principles and we deduce some uniqueness results. 相似文献
74.
Blangetti M Deagostino A Prandi C Zavattaro C Venturello P 《Chemical communications (Cambridge, England)》2008,(14):1689-1691
A new approach to the synthesis of pyrimidines and cyclopentenones is described. The method exploits the reactivity of alpha,beta-unsaturated acetals with aromatic nitriles in the presence of the Schlosser's superbase LIC-KOR. 相似文献
75.
Annamaria Barbagallo Giovanni Scilla 《Journal of Mathematical Analysis and Applications》2018,457(2):1118-1134
A class of stochastic weighted variational inequalities in non-pivot Hilbert spaces is proposed. Existence and continuity results are proved. These theoretical results play a prominent role in order to introduce a new weighted transportation model with uncertainty. Moreover, they allow to establish the equivalence between the random weighted equilibrium principle and a suitable stochastic weighted variational inequality. At the end, a numerical model is discussed. 相似文献
76.
Annamaria Visco Cristina Scolaro Daniela Iannazzo 《International Journal of Polymer Analysis and Characterization》2019,24(2):97-104
In this article, we compared the sealing strength, flexibility, thermal stability, and moisture-barrier properties of two polymeric films, both based on linear low density poly ethylene (LLDPE), which can be successfully used as sealant materials in electrical devices. One example is the dye-sensitized solar cell (DSSC), a low-cost third generation device, based on a photo-electrochemical system. Characterization of LLDPE modified with maleic anhydride (PE-MAH) or with ionomeric ethylene-acrylic acid co-polymer (EMAA) was carried out. Results highlighted as PE-MAH exhibits better adhesion features toward glass, higher thermal stability, and lower wet ability even at high temperatures (80?°C) compared to EMAA. Sealant’s features have been correlated to their chemical and structural composition. 相似文献
77.
78.
Dr. Philipp Gotico Dr. Dooshaye Moonshiram Dr. Cunming Liu Dr. Xiaoyi Zhang Dr. Régis Guillot Dr. Annamaria Quaranta Dr. Zakaria Halime Dr. Winfried Leibl Prof. Ally Aukauloo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(13):2859-2868
Inspired by the sulfur-rich environment found in active hydrogenase enzymes, a Ni-based proton reduction catalyst with pentadentate N2S3 ligand was synthesised. When coupled with [Ru(bpy)3]2+ (bpy=2,2′-bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time-resolved X-ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal-centred reduction to form a NiI intermediate with distorted square-bipyramidal geometry. Further kinetic analyses revealed differences in charge-separation dynamics between the pentadentate and tetradentate forms. 相似文献
79.
Groom CA Halasz A Paquet L Thiboutot S Ampleman G Hawari J 《Journal of chromatography. A》2005,1072(1):73-82
An Agilent 3DCE capillary electrophoresis system using sulfobutylether-beta-cyclodextrin (SB-beta-CD)-ammonium acetate separation buffer pH 6.9 was coupled to a Bruker Esquire 3000+ quadrupole ion trap mass detector via a commercially available electrospray ionization interface with acetonitrile sheath flow. The CE-MS system was applied in negative ionization mode for the resolution and detection of nitroaromatic and polar cyclic or caged nitramine energetic materials including TNT [2,4,6-trinitrotoluene, formula mass (FW) 227.13], TNB (1,3,5-trinitrobenzene, FW 213.12), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine, FW 222.26) HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, FW 296.16), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, FW 438.19). The CE-MS system conformed to the high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) and HPLC-MS reference methods for the identification of energetic contaminants and their degradation products in soil and marine sediment samples. 相似文献
80.
Philipp Gotico Bernard Boitrel Rgis Guillot Marie Sircoglou Annamaria Quaranta Zakaria Halime Winfried Leibl Ally Aukauloo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(14):4552-4557
Inspired by nature's orchestra of chemical subtleties to activate and reduce CO2, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO2) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO2 reduction in this family of molecular catalysts and importantly increased the CO2 binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO2 reduction. 相似文献