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361.
362.
Flavia C. De Sousa Fonseca Flavia M. Araujo Tanus J. Nagem Tânia T. de Oliveira Carlos Roque D. Correia 《合成通讯》2013,43(5):768-773
N-Boc-allenylaniline undergoes cyclization in the presence of a catalytic amount of a cationic gold complex to exclusively form 2-oxazolidinones, whereas the N-Moc-allenylaniline affords dihydroquinolines. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
363.
Tiago Fidemann Gabriela Aparecida de Araujo Pereira Lia Bossard Nascimento Milena Cristina Moraes Mônica Rosa Bertão Regildo Márcio Gonçalves da Silva 《Natural product research》2018,32(9):1109-1117
Plants endue a key role against illnesses caused by oxidative stress. These attributes are frequently associated with polyphenolic compounds. However, presence and concentration of secondary metabolites are affected by abiotic factors. The in vitro culture techniques can solve these drawbacks. Peppers can be a suitable alternative to obtain polyphenols. Aiming to optimise the callus culture stage from Capsicum baccatum to produce polyphenols, this work evaluated systemically the effects of the explant’s origin (root, hypocotyl and cotyledon), growth hormone type (2,4-dichlorophenoxyacetic acid (2,4-D), benzylaminopurine (BAP) and a combination of 2,4-D/BAP at five-to-one ratio) and concentration (0.023–10.000 mg L?1) on callus culture efficiency parameters using a multilevel factorial design. The root explant in combination with BAP at 1.138 mg L?1 ensured the optimal values of the assessed responses; ?callus mass (225.03 mg), antioxidant activity (35.95%), total phenols (11.48 mg of GAE/g DE) and flavonoids (15.92 mg of RU/g DE) production. 相似文献
364.
Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries
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Suman Das Dr. Diptikanta Swain Dr. Rafael B. Araujo Dr. Songxin Shi Prof. Rajeev Ahuja Prof. Tayur N. Guru Row Prof. Aninda J. Bhattacharyya 《化学:亚洲杂志》2018,13(3):299-310
We discuss here a unique flexible non‐carbonaceous layered host, namely, metal titanium niobates (M‐Ti‐niobate, M: Al3+, Pb2+, Sb3+, Ba2+, Mg2+), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M‐Ti‐niobate is formed by ion exchange of the K+ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol‐gel synthesized potassium titanium niobate (KTiNbO5). Drastic volume changes (approximately 300–400 %) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M‐Ti‐niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50–75 % of total K+) in the M‐Ti‐niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M‐Ti‐niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li+ and Na+ ion cyclability (>2 Li+/Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al‐titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M‐Ti‐niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries. 相似文献
365.
Francisco D. Avila Orozco Antonio C. Sousa Claudia E. Domini Mario Cesar Ugulino Araujo Beatriz S. Fernández Band 《Ultrasonics sonochemistry》2013,20(3):820-825
Biodiesel is considered an alternative energy because it is produced from fats and vegetable oils by means of transesterification. Furthermore, it consists of fatty acid alkyl esters (FAAS) which have a great influence on biodiesel fuel properties and in the storage lifetime of biodiesel itself. The biodiesel storage stability is directly related to the oxidative stability parameter (Induction Time – IT) which is determined by means of the Rancimat® method. This method uses condutimetric monitoring and induces the degradation of FAAS by heating the sample at a constant temperature. The European Committee for Standardization established a standard (EN 14214) to determine the oxidative stability of biodiesel, which requires it to reach a minimum induction period of 6 h as tested by Rancimat® method at 110 °C. In this research, we aimed at developing a fast and simple alternative method to determine the induction time (IT) based on the FAAS ultrasonic-accelerated oxidation. The sonodegradation of biodiesel samples was induced by means of an ultrasonic homogenizer fitted with an immersible horn at 480 Watts of power and 20 duty cycles. The UV–Vis spectrometry was used to monitor the FAAS sonodegradation by measuring the absorbance at 270 nm every 2. Biodiesel samples from different feedstock were studied in this work. In all cases, IT was established as the inflection point of the absorbance versus time curve. The induction time values of all biodiesel samples determined using the proposed method was in accordance with those measured through the Rancimat® reference method by showing a R2 = 0.998. 相似文献
366.
José Luis Vílchez Avismelsi Prieto Lilia Araujo Alberto Navalón 《Mikrochimica acta》2006,155(3-4):435-439
A method using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry with selected
ion monitoring (GC–MS, SIM) has been developed for the determination of trace amounts of anthracene in sea water, wastewater,
honey and saliva samples. Anthracene was extracted on to a fused-silica fibre coated with 85 μm polyacrylate (PA). Quantification
of anthracene was carried out by isotope dilution mass spectrometry. The detection limit and the quantification limit found
were 0.02 and 0.06 ng mL−1, respectively. The method was validated by analysis of spiked matrix samples and used to investigate the presence of anthracene
above the stated detection limit in sea water, wastewater, honey and saliva samples. 相似文献
367.
V. J. Fernandes Jr. A. S. Araujo G. J. T. Fernandes 《Journal of Thermal Analysis and Calorimetry》2001,64(2):807-811
Thermogravimetry is used for regeneration of the alumina catalyst which was deactivated by coke, formed in the transformation
of 1,3-butadiene in a fixed bed continuous flow reactor. The Vyazovkin model-free kinetic analysis has been applied to data
on thermal oxidation of carbonaceous deposits on the catalyst. This analysis has allowed us to estimate the activation energy
(E) as a function of α (conversion) and to predict the time required to remove coke at a given temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
368.
369.
Anderson L. A. de Araujo Paulo M. D. de Magalhães 《Mathematical Methods in the Applied Sciences》2017,40(13):4802-4811
In this paper, we prove that if the initial data is small enough, we obtain an explicit L∞(QT)‐estimate for a two‐dimensional mathematical model of cancer invasion, proving an explicit bound with respect to time T for the estimate of solutions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献