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21.
Clovis Piovezan Fábio da Silva Lisboa Fábio Souza Nunes Sueli Maria Drechsel 《Transition Metal Chemistry》2011,36(1):79-85
We report the reactivity of three binuclear non-heme Fe(III) compounds, namely [Fe2(bbppnol)(μ-AcO)(H2O)2](ClO4)2 (1), [Fe2(bbppnol)(μ-AcO)2](PF6) (2), and [Fe2(bbppnol)(μ-OH)(Cl)2]·6H2O (3), where H3bbppnol = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)–1,3-propanediamine-2-ol, toward the hydrolysis of bis-(2,4-dinitrophenyl)phosphate as models for phosphoesterase
activity. The synthesis and characterization of the new complexes 1 and 3 was also described. The reactivity differences observed for these complexes show that the accessibility of the substrate
to the reaction site is one of the key steps that determinate the hydrolysis efficiency. 相似文献
22.
Manzano R Andrés JM Álvarez R Muruzábal MD de Lera ÁR Pedrosa R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5931-5938
A series of chiral thioureas derived from easily available diamines, prepared from α-amino acids, have been tested as catalysts in the enantioselective Michael additions of nitroalkanes to α,β-unsaturated ketones. The best results are obtained with the bifunctional catalyst prepared from L-valine. This thiourea promotes the reaction with high enantioselectivities and chemical yields for aryl/vinyl ketones, but the enantiomeric ratio for alkyl/vinyl derivatives is very modest. The addition of substituted nitromethanes led to the corresponding adducts with excellent enantioselectivity but very poor diastereoselectivity. Evidence for the isomerization of the addition products has been obtained from the reaction of chalcone with [D(3)]nitromethane, which shows that the final addition products epimerize under the reaction conditions. The epimerization explains the low diastereoselectivity observed in the formation of adducts with two adjacent tertiary stereocenters. Density functional studies of the transition structures corresponding to two alternative activation modes of the nitroalkanes and α,β-unsaturated ketones by the bifunctional organocatalyst have been carried out at the B3LYP/3-21G* level. The computations are consistent with a reaction model involving the Michael addition of the thiourea-activated nitronate to the ketone activated by the protonated amine of the organocatalyst. The enantioselectivities predicted by the computations are consistent with the experimental values obtained for aryl- and alkyl-substituted α,β-unsaturated ketones. 相似文献
23.
Four novel benzamido-functionalized prolinamides have been prepared and tested as organocatalysts for enantioselective aldol reaction of aldehydes and cyclic ketones in water. In particular, prolinamide derived from achiral ethylene diamine was the best catalyst leading to anti aldols in excellent diastereomeric (up to 98/2) and enantiomeric (up to 99/1) ratios, thereby showing that lateral amide functionalities might be a key issue for facilitating "in water" chemistry. These catalysts are cheaper and easier to prepare than those previously described. 相似文献
24.
A. V. Melnikov L. G. Eliseev S. A. Grashin A. V. Gudozhnik S. E. Lysenko V. A. Mavrin S. V. Perfilov V. A. Vershkov L. I. Krupnik A. A. Chmyga A. D. Komarov A. S. Kozachok C. Hidalgo A. Alonso J. L. dePablos M. A. Pedrosa 《Czechoslovak Journal of Physics》2005,55(12):1569-1578
Comparison of the plasma electric potential evolution in the T-10 tokamak and TJ-II stellarator was performed. The core potential
was measured by the heavy-ion beam probing and the edge potential was measured by Langmuir probe. The intrinsic potentials
in both devices are different in sign, positive in TJ-II low-density discharge and negative in T-10 higher-density discharges,
but during ECRH they evolve similarly: the potential becomes more positive, and increase of ECRH power leads to stronger rise
of core potential.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
25.
26.
H. Th. Schneider B. P. Lisboa und H. Breuer 《Fresenius' Journal of Analytical Chemistry》1976,279(2):161-162
Ohne Zusammenfassung
Identification of hormone metabolites in tissue by radio gas chromatography相似文献
27.
We report that measurements of the Raman intensity versus applied voltage are sensitive to filling of the density of states and enable us to measure the second band gap in specific semiconducting single-walled carbon nanotubes (SWNTs). Raman scattering preferentially selects sets of SWNTs whose excitonic transitions are resonant with the incident or scattered photon energies. Simultaneous measurement of the electronic gap and exciton resonance allows us to infer binding energies for the exciton of 0.49+/-0.05 and 0.62+/-0.05 eV for tubes of (10, 3) and (7, 5), respectively. Metallic SWNTs exhibit no excitonic feature. 相似文献
28.
Lisboa Thalles Pedrosa de Faria Lucas Vincius Alves Guilherme Figueira Matos Maria Auxiliadora Costa Matos Renato Camargo 《Journal of Solid State Electrochemistry》2021,25(8):2301-2308
Journal of Solid State Electrochemistry - This work describes a simple, rapid, and cost-effective method for fabrication of paper-based carbon electrode (US$ <0.01) using conductive ink... 相似文献
29.
30.
In this contribution, we investigate quantum effects of relic gravitons in a Friedmann–Robertson–Walker (FRW) cosmological background. We reduce the problem to that of a generalized time-dependent harmonic oscillator and find the corresponding exact Schrödinger states with the help of linear invariants and of the dynamical invariant method. Afterwards, we construct Gaussian wave packet states and calculate the quantum dispersions as well as the quantum correlations for each mode of the quantized field. 相似文献