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61.
R. L. O. Rezende M. I. R. M. Santoro J. R. Matos 《Journal of Thermal Analysis and Calorimetry》2008,93(3):881-886
This paper demonstrates the application of thermal analysis in compatibility and stability studies between an ACE inhibitor
(enalapril maleate) and excipients. The results have helped to elucidate the reason of a stability problem observed during
the storage of enalapril maleate tablets. Incompatibility between enalapril maleate and colloidal silicon dioxide was detected.
Besides, it was confirmed that the reaction between enalapril maleate and NaHCO3 increases the thermal stability of the drug. This study supports the importance of using thermoanalytical methods in the
development of pharmaceuticals. 相似文献
62.
Cloud point extraction for determination of cadmium in soft drinks by thermospray flame furnace atomic absorption spectrometry 总被引:3,自引:0,他引:3
Cloud point extraction (CPE) is proposed as a preconcentration procedure for the determination of Cd in soft drinks by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The cadmium reacted with pyridyl-azo-naphthol (PAN) to form hydrophobic chelates, which were extracted into the micelles of Triton X-114 in a solution buffered at pH 9. NaCl was used for the phase separation. The variables which affect the preconcentration were optimized using a 23 factorial design and central composite design (CCD). A response surface maximum point was obtained, and the critical values were a concentration of 0.13 mmol L? 1 PAN, 0.03% m/v Triton X-114 and 2.3% m/v NaCl. Under the optimized conditions, after the extraction and preconcentration steps, a sample volume of 100 μL was introduced into the hot Ni tube using water as the carrier at a flow rate of 0.4 mL min? 1. The values obtained for the detection limit, relative standard deviation and preconcentration factor were 0.0178 μg L? 1, 4.1% (n = 8) and 55.5, respectively. The accuracy of the proposed method was demonstrated by performing addition-recovery experiments. Recoveries varied from 88 to 104%. 相似文献
63.
Fernanda M. B. Coutinho Luiz Cludio Rezende Juan Raul Quijada 《Journal of polymer science. Part A, Polymer chemistry》1986,24(11):3021-3032
A comparative kinetic study of the reaction of three different hydroxylated liquid poly-butadienes (M?n ? 3000)–R-45M, R-45HT and H-034–with 3-isocyanatomethyl–3,5,5-trimethylclohexylisocyanate (IPDI) and dimer diacid diisocyanate (DDI) was carried out in toluene solution. An analytical method was used to follow the kinetics of the reactions, at four different temperatures. In the second-order plots, a discontinuity was observed in the reaction with IPDI, in contrast to the reactions with DDI which showed straight-line plots. In all studied reactions, the R-45M polybutadiene was about twice as reactive as R-45HT and H-034. The latter hydroxylated polybutadienes (R-45HT and H-034) showed similar reactivities. 相似文献
64.
65.
M. F. S. Rezende R. A. Mansur H. -D. Pfannes A. I. C. Persiano 《Hyperfine Interactions》1991,66(1-4):319-323
Two distinct phases of the Fe?Co?Nb and three of the Fe?Co?V systems have been studied by means of X-ray diffraction and Mössbauer spectroscopy. The dependence of the lattice parameter of the alpha phase on the nominal solute content in equiatomic FeCo together with the alterations of the Mössbauer spectra have shown a very limited solubility of niobium in alpha FeCo. There are indications that the solubility of vanadium in alpha FeCo increases with increasing nominal content of solute in the alloy. A mechanism involving the withdrawal of cobalt from the alpha matrix to form a phase rich in Co and V (gamma) is proposed to explain such a varying solubility. The vanadium content of the sigma phase in equiatomic FeCo alloys with 22 wt% V is proposed to be less than 50 at%. 相似文献
66.
67.
Iriux Almodovar Marcos Caroli Rezende Bruce K. Cassels Macarena García‐Arriagada 《Journal of Physical Organic Chemistry》2017,30(8)
The mechanism of the cyclization step of the Pictet‐Spengler reaction between acetaldehyde and dopamine to give salsolinol and isosalsolinol was studied computationally, using density functional theory. The preferential formation in acidic media of salsolinol, the product of para‐cyclization, and the requirement of a neutral pH for the formation of the ortho‐cyclized isosalsolinol are explained in terms of 2 different mechanistic routes with an iminium ion or a phenolate‐iminium zwitterion as starting reactants. 相似文献
68.
De Lazari Ferreira Luiza Calado Hállen Daniel Rezende 《Journal of Solid State Electrochemistry》2018,22(5):1507-1515
Journal of Solid State Electrochemistry - Polythiophenes are conjugated polymers that are highly promising candidates for use as an active layer in flexible optoelectronic devices. The... 相似文献
69.
Iriux Almodovar Wilson Cardona Tomás Delgado-Castro Gerald Zapata-Torres Marcos Caroli Rezende Ramiro Araya-Maturana 《Journal of the Iranian Chemical Society》2014,11(4):1021-1026
Competing reduction and cycloaddition products were formed in the reaction of 8,8-dimethylnaphthalene-1,4,5(8H)-trione with a hydroxysulfinyldiene. The ratio of reduction to cycloaddition products depended on the stereochemistry of the diene and on the solvent employed, being higher in ethanol than in benzene. The ratio was also affected by the addition of Lewis acids, decreasing in the order BF3 = Al2O3 > MgCl2 > ZnCl2. The results help to explain and predict the occurrence of these competing processes in Diels–Alder cycloadditions involving quinonedienophiles. 相似文献
70.
M. F. S. Rezende A. M. Lacerda H. -D. Pfannes R. A. Mansur J. D. Ardisson A. I. C. Persiano 《Hyperfine Interactions》1994,83(1):231-234
The effects of filing FeCoV alloys with equiatomic FeCo and up to 14 at% V is studied by Mössbauer spectroscopy and X-ray diffraction. We observed that filing eliminates the paramagnetic component observed in samples in the form of plates. The filed material also presents a linear increase of the lattice parameter and a linear decrease of the average hyperfine field of the alpha phase due to extra low-field satellites with increasing vanadium contents. This indicates that filing produces a gamma to alpha phase transformation, which increases the amount of vanadium in solid solution in the FeCo alpha phase. 相似文献