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排序方式: 共有121条查询结果,搜索用时 125 毫秒
91.
Ingrid F. Zattoni Lais D. Guanaes Letícia B. Cerqueira Roberto Pontarolo Diogo R.B. Ducatti M. Eugênia R. Duarte Miguel D. Noseda Angela C.L.B. Trindade Alan G. Gonçalves 《Tetrahedron letters》2019,60(40):151129
We have evaluated four 1,4-dihydropyridines (DHPs 1a, 1b, 1c and 1d) as reducing agents, which presented free (hydrogenated) or phenyl-substituted N-1 and C-4 positions of the DHP ring. Reactions combining each of the DHP and different amounts of BF3OEt2 were evaluated for the reduction of imine 2a (N-benzylideneaniline). DHP simultaneously substituted at N-1 and C-4 (1a), and DHP substituted at C-4 (1b) gave lower yields for reduction of 2a in comparison with DHPs 1c and 1d (both unsubstituted at the C-4 position). By evaluating the amount of added BF3OEt2 to the reaction mixture, we have found that DHP 1c (substituted at N-1) provided its best yield for amine 3a (82%) when associated with stoichiometric amounts BF3OEt2, while DHP 1d (N-1- and C-4-unsubstituted derivative) was more effective (90% yield) with catalytic quantities of the Lewis acid. The reaction system using DHP 1c under stoichiometric BF3OEt2 could also be successfully applied with additional imine examples and under reductive amination conditions. 相似文献
92.
Nunes Ernane Nogueira Rocha Ana Paula Trindade de Araújo Gilmar Trindade de Paz Adeilton Padre Rodrigues Larissa Monique de Sousa Batista Rayanne Sales de Araújo Melo Taynara Batista Lins 《Journal of Thermal Analysis and Calorimetry》2019,135(6):3281-3288
Journal of Thermal Analysis and Calorimetry - Large amounts of plant biomass generated daily and not harnessed for lack of adequate technologies. Based on this context, this study aimed to perform... 相似文献
93.
M.O.?FigueiredoEmail author T.P.?Silva J.P.?Veiga A.M.?Dias Diogo L.?Trindade 《Applied Physics A: Materials Science & Processing》2004,79(2):327-329
During an emergency archaeological intervention conducted in downtown Lisbon (the Old City), ceramic foundry crucibles were collected in a layer of embankment debris used after the earthquake that destroyed the city in 1755. A chemical and phase-constitution study was undertaken to complement the dating and to ascertain the kind of foundries (metallurgical or glass-working) concerning two intact cup-shaped crucibles and a fragment displaying glassy outflows. Non-destructive methodologies were used – namely, laboratory techniques (X-ray fluorescence spectrometry and X-ray diffraction) combined with synchrotron-radiation-induced micro-fluorescence (SRXRF). Analytical results are presented and discussed. SRXRF analysis of the glassy outflow on the larger crucible revealed the presence of mercury and traces of gold, along with copper, suggesting that it might have been used to manipulate gold amalgams. A possible Islamic origin was disclosed for the smaller crucible as only tin was detected in the external outflow and further confirmed by minute cassiterite (SnO2) grains. PACS 81.05.Kf; 41.60.Ap; 78.70.En 相似文献
94.
Thermal analysis of the rice and by-products 总被引:2,自引:0,他引:2
J. A. Amorim S. A. Eliziário D. S. Gouveia A. S. M. Simőes J. C. O. Santos M. M. Conceiçăo A. G. Souza M. F. S. Trindade 《Journal of Thermal Analysis and Calorimetry》2004,75(2):393-399
The thermogravimetry (TG) is a technique used in the quality control of foods. In this work the moisture and ash contents
in the rice and by-products (bran and husk), the thermal stability and the gelatinization process by conventional, thermogravimetric
and calorimetric methods were studied. The moisture and ash contents obtained by TG and conventional methods did not present
significant differences. The rice presented higher starch content, while the bran presented higher protein content. The thermogravimetric
data presented the following thermal stability order: rice>bran>husk. The calorimetric curves indicated the gelatinization
of the starch. The kinetic parameters were compatible.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
95.
Trindade JR Visak ZP Blesic M Marrucho IM Coutinho JA Lopes JN Rebelo LP 《The journal of physical chemistry. B》2007,111(18):4737-4741
The effects of the addition of three inorganic salts, namely, NaCl, Na(2)SO(4), and Na(3)PO(4), on the liquid-liquid (L-L) phase diagram of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], were investigated. All three inorganic salts trigger salting-out effects, leading to significant upward shifts of the L-L demixing temperatures of the systems. The magnitude of the shifts depends on both the water-structuring nature of the salt and its concentration; that is, the effects are correlated with the ionic strength of the solution and the Gibbs free energy of hydration of the inorganic salt. The pH effect and the occurrence of salt precipitation in concentrated solutions are also discussed. 相似文献
96.
Trindade AF Gois PM Veiros LF André V Duarte MT Afonso CA Caddick S Cloke FG 《The Journal of organic chemistry》2008,73(11):4076-4086
An efficient new methodology for the arylation of aldehydes is disclosed which uses dirhodium(II) catalysts and N-heterocyclic carbene (NHC) ligands. Complexes of Rh 2(OAc) 4 with one and two NHCs attached on the axial positions were successfully isolated, fully characterized, and used as catalysts in the reaction. The saturated monocomplex ((NHC 5)Rh 2(OAc) 4) 31 was shown to be the most active catalyst and was particularly efficient in the arylation of alkyl aldehydes. DFT calculations support participation of complexes with one axial NHC in the reaction as the catalysts active species and indicate that hydrogen bonds involving dirhodium unit, reactants, and solvent (alcohol) play an important role on the reaction mechanism. 相似文献
97.
The drift, the risk-free interest rate, and the volatility change over time horizon in realistic financial world. These frustrations
break the necessary assumptions in the Black-Scholes model (BSM) in which all parameters are assumed to be constant. To better
model the real markets, a modified BSM is proposed for numerically evaluating options price-changeable parameters are allowed
through the backward Markov regime switching. The method of fundamental solutions (MFS) is applied to solve the modified model
and price a given option. A series of numerical simulations are provided to illustrate the effect of the changing market on
option pricing. 相似文献
98.
Dennys Reis Ana C. Trindade Maria Helena Godinho Laura C. Silva Maria do Carmo Gonçalves Antônio M. Figueiredo Neto 《Brazilian Journal of Physics》2017,47(1):19-25
The nanostructure of urethane/urea elastomeric membranes was investigated by small-angle X-ray scattering (SAXS) in order to establish relationships between their structure and mechanical properties. The networks were made up of polypropylene oxide (PPO) and polybutadiene (PB) segments. The structural differences were investigated in two types of membranes with the same composition but with different thermal treatment after casting. Type I was cured at 70–80 °C and type II at 20 °C. Both membranes showed similar phase separation by TEM, with nanodomains rich in PB or PPO and 25 nm dimensions. The main difference between type I and type II membranes was found by SAXS. The type I membrane spectra showed, besides a broad band at a 27-nm q value (modulus of the scattering vector), an extra band at 6 nm, which was not observed in the type II membrane. The SAXS spectra were interpreted in terms of PPO, PB soft segments, and urethane/urea links, as well as hard moiety segregation in the reaction medium. This additional segregation (q = 7 nm), although subtle, results in diverse mechanical behavior of in both membranes. 相似文献
99.
J. Zukerman‐Schpector Antonio Carlos Trindade P. O. Dunstan 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):763-765
In both title compounds, (acetylacetonato‐O,O′)bis(3‐cyanopyridine‐N)nickel(II), (I), and (acetylacetonato‐O,O′)bis(4‐cyanopyridine‐N)nickel(II), (II), both [Ni(C5H7O2)2(C6H4N2)2], the NiII atom, which is situated on a centre of symmetry, is octahedrally coordinated. Distances and angles for (I) and (II), respectively, are: Ni—O 2.009 (2)/2.016 (2) and 2.0110 (16)/2.0238 (18) Å, Ni—N 2.116 (3) and 2.179 (2) Å, O—Ni—O 91.86 (10) and 90.19 (7)°, and O—Ni—N 91.27 (11)/90.19 (11) and 89.65 (8)/90.79 (7)°. 相似文献
100.
de Souza Poliana Santos Clain Almir Faria Filho Octávio Luiz Trindade de Oliveira Estela Maria Delgado Jose Ubiratan Lopes Ricardo Tadeu 《Journal of Radioanalytical and Nuclear Chemistry》2019,321(3):851-856
Journal of Radioanalytical and Nuclear Chemistry - The production of environmental reference materials such as soil, sediment, water and vegetation containing radionuclides for interlaboratory... 相似文献