排序方式: 共有31条查询结果,搜索用时 46 毫秒
21.
Millán A Campaña AG Bazdi B Miguel D de Cienfuegos LA Echavarren AM Cuerva JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3985-3994
The allylation, crotylation and prenylation of aldehydes and ketones with stable and easily handled allylic carbonates is promoted by a Ti/Pd catalytic system. This Ti/Pd bimetallic system is especially convenient for the allylation of ketones, which are infrequent substrates in other related protocols, and can be carried out intramolecularly to yield five- and six-membered cyclic products with good stereoselectivities. In addition, Ti/Pd-mediated reductions and Würtz-type dimerisation reactions can be readily carried out from allyl carbonates and carboxylates. 相似文献
22.
A. B. Voitkiv B. Najjari J. Ullrich 《Journal of Experimental and Theoretical Physics》2005,100(3):516-520
We consider an interesting realization of the fundamental four-body problem: double ionization of helium in superintense electromagnetic fields generated by highly charged ions in relativistic collisions. We show how the simultaneous interaction of such fields with all three target constituents (which is not described by first-order theory) strongly influences the collision dynamics even at very high collision energies and how a “genuine” photoemission-like pattern may emerge in collisions at extreme relativistic energies. A very good agreement with available experimental data is obtained. 相似文献
23.
Viscous dissipation and its contribution to turbulent kinetic energy (TKE) budget are investigated in the asymmetric jet–wake flow of a forward-curved centrifugal turbomachine. Single-plane three-dimensional turbulent data are obtained using stereoscopic particle image velocimetry (SPIV). Viscous dissipation is indirectly estimated from subgrid-scale (SGS) dissipation (SGS energy flux) by filtering velocity field using a top-hat filter. The filter scale should be within the inertial sub-range and this is ensured by spectral analysis of the measured field. Reduction of turbulent energy flux for smaller filter scales plus underestimation of viscous dissipation as compared with other TKE terms both suggest the presence of spectral shortcut. This bypass energy transfer (from intermediate scales towards dissipative scales) works in parallel with direct SGS energy transfer and affects the classical energy cascade. Analysis of TKE budget in the rotor exit region shows significant radial/circumferential variations in the contributing terms. These variations are mainly due to jet–wake–volute interactions, circumferential asymmetry of volute area and expansion of flow toward the fan outlet. 相似文献
24.
25.
Rosa E. Estévez José Justicia Dr. Btissam Bazdi Noelia Fuentes Miguel Paradas Duane Choquesillo‐Lazarte Dr. Juan M. García‐Ruiz Prof. Rafael Robles Dr. Andreas Gansäuer Prof. Juan M. Cuerva Dr. J. Enrique Oltra Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(12):2774-2791
Versatility of titanium : Titanocene(III) complexes catalyze Barbier‐type allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. These reactions take place at RT under mild conditions compatible with many functional groups; provide good yields of open‐chain and cyclic homoallylic alcohols, including heterocyclic derivatives; and can be conducted enantioselectively by using enantiomerically pure titanium catalysts.
26.
27.
28.
Hafssa El Cadi Hajar El Bouzidi Ginane Selama Btissam Ramdan Yassine Oulad El Majdoub Filippo Alibrando Katia Arena Miguel Palma Lovillo Jamal Brigui Luigi Mondello Francesco Cacciola Tania M. G. Salerno 《Molecules (Basel, Switzerland)》2021,26(9)
The aim of this study was to characterize the phytochemical content as well as the antioxidant ability of the Moroccan species Chamaerops humilis L. Besides crude ethanolic extract, two extracts obtained by sonication using two solvents with increased polarity, namely ethyl acetate (EtOAc) and methanol-water (MeOH-H2O) 80:20 (v/v), were investigated by both spectroscopy and chromatography methods. Between the two extracts, the MeOH-H2O one showed the highest total polyphenolic content equal to 32.7 ± 0.1 mg GAE/g DM with respect to the EtOAc extract (3.6 ± 0.5 mg GAE/g DM). Concerning the antioxidant activity of the two extracts, the EtOAc one yielded the highest value (1.9 ± 0.1 mg/mL) with respect to MeOH-H2O (0.4 ± 0.1 mg/mL). The C. humilis n-hexane fraction, analyzed by GC–MS, exhibited 69 compounds belonging to different chemical classes, with n-Hexadecanoic acid as a major compound (21.75%), whereas the polyphenolic profile, elucidated by HPLC–PDA/MS, led to the identification of a total of sixteen and thirteen different compounds in both EtOAc (major component: ferulic acid: 104.7 ± 2.52 µg/g) and MeOH-H2O extracts (major component: chlorogenic acid: 45.4 ± 1.59 µg/g), respectively. The attained results clearly highlight the potential of C. humilis as an important source of bioactive components, making it a valuable candidate to be advantageously added to the daily diet. Furthermore, this study provides the scientific basis for the exploitation of the Doum in the food, pharmaceutical and nutraceutical industries. 相似文献
29.
Single ionization of He by 1 keV electron impact in the presence of an intense (I=4 x 10(12) W/cm(2)) laser field (lambda=1064 nm) has been explored in a kinematically complete experiment using a reaction microscope. Distinct differences in the singly to fully differential cross sections compared to the field-free situation are observed which cannot be explained by a first-order quantum calculation. Major features, such as the number of photons exchanged and the modification of the energy spectrum of emitted electrons, can be understood qualitatively within a simple classical model. 相似文献
30.