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71.
Taís Vanessa Gabbay Alves Russany Silva da Costa Antônio Taylon Aguiar Gomes Carlos Emmerson Ferreira da Costa Patrizia Perego José Otávio Carréra Silva Júnior Attilio Converti Roseane Maria Ribeiro Costa 《Journal of Thermal Analysis and Calorimetry》2018,131(2):993-1004
The mineralogical characterization and pyrolysis kinetics of raw oil shale from Moroccan Rif region and the corresponding bitumen-free material were investigated using various analytical techniques. The structural analysis results showed the siliceous character of mineral matrix and the presence of complex organic components in both oil shales studied. Non-isothermal pyrolysis kinetic measurements indicated that bitumen-free oil shale exhibits a single behavior pyrolysis in the oil-producing stage as compared to raw oil shale. The activation energies estimated by using isoconversional methods reveal that the pyrolysis reaction occurred by one-step kinetic process. The kinetic parameters, determined from a nonlinear fitting method using various kinetic models g(α) and iterative Kissinger–Akahira–Sunose energy calculations, reveal that the pyrolysis mechanism is well described by the nth order kinetics (Fn), with n = 1.071, for bitumen-free oil shale, and n = 1.550, for kerogen of raw oil shale. The mechanism of the whole pyrolysis process of raw oil shale seems not to be affected by the elimination of bitumen, but only some kinetic changes have been recorded in the reaction order mechanism. The process pyrolysis is represented by independent reactions and consequently considered as parallel processes. Besides, the thermodynamic functions of activated complexes (?S ≠ , ?H ≠ and ?G ≠) were also calculated and the pyrolysis is found as non-spontaneous process in agreement with the thermal analysis data. 相似文献
72.
Santos RP Silveira ER Uchôa DE Pessoa OD Viana FA Braz-Filho R 《Magnetic resonance in chemistry : MRC》2007,45(8):692-694
Two new bidesmoside triterpenoid saponins were isolated from stems of Cordia piauhiensis. Their structures, characterized as 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl pomolic acid 28-O-beta-D-glucopyranosyl ester (1) and 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (2), were unequivocally established after extensive NMR (1H, 13C, DEPT 135 degrees, COSY, HSQC, HMBC, TOCSY, and NOESY) studies. 相似文献
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74.
Rita de Cássia Almeida Sampaio Russany Silva da Costa Claudia Regina Fernandes de Souza Anivaldo Pereira Duarte Júnior Roseane Maria Ribeiro-Costa Carlos Emmerson Ferreira da Costa Wanderley Pereira de Oliveira Attilio Converti José Otávio Carréra Silva Júnior 《Journal of Thermal Analysis and Calorimetry》2016,123(3):2469-2475
75.
Maria Conceição M. Torres José Gustavo L. Almeida Raimundo Braz‐Filho Edilberto R. Silveira Otília Deusdênia L. Pessoa 《Magnetic resonance in chemistry : MRC》2012,50(1):74-78
From the leaves of Solanum campaniforme, two new spirosolane alkaloids β‐acetoxyl‐(25S)‐22βN‐spirosol‐4‐en‐3‐one (1) and β‐hydroxyl‐(25S)‐22βN‐spirosol‐4‐en‐3‐one (4) were isolated along with two other known alkaloids of the same class (25S)‐22βN‐spirosol‐1,4‐dien‐3‐one (2) and (25S)‐22βN‐spirosol‐4‐en‐3‐one (3), which are reported for the first time as natural products. The structures of all alkaloids were established after an extensive analysis by 1D and 2D NMR spectroscopy (COSY, HSQC, HMBC and NOESY) as well as HRESIMS. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
76.
Due to its amphoteric nature the imidazole ring can function as selective and effective anion and/or cation and even neutral organic molecules receptor system. As a result, the design of new multichannel imidazole-based receptors capable of recognizing different types of analytes is strongly demanded. This review summarizes the most recent and relevant advances in this area. 相似文献
77.
Francisco Otón Dr. Imma Ratera Dr. Arturo Espinosa Dr. Klaus Wurtz Dr. Teodor Parella Dr. Alberto Tárraga Prof. Jaume Veciana Prof. Pedro Molina Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1532-1542
The synthesis, electrochemical, optical, and cation‐sensing properties of [2.2]ferrocenophanes, in which the two ferrocene subunits are linked through two aldiminic or iminophosphorane moieties, are reported. The new compounds show remarkably selective cation‐sensing properties due to the presence of redox‐active units (ferrocene) and aza‐unsaturated functionalities that are able to act as putative cation‐binding sites. In this structural motif, the aldimine groups act as a highly selective binding site for Zn2+ cations, whereas the iminophosphorane bridges display an unusually strong binding affinity towards Li+ cations, which could be explained by an additional Li???Fe interaction. The X‐ray structure of the complex 4? Li+ as well as detailed NMR spectroscopic studies, both in solution and in the solid state, support this assessment. Experimental data and conclusions about the cation‐sensing capabilities of this family of compounds are supported by DFT calculations. 相似文献
78.
Cysne Jde B Braz-Filho R Assunção MV Uchoa DE Silveira ER Pessoa OD 《Magnetic resonance in chemistry : MRC》2006,44(6):641-643
The phytochemical investigation of carnauba wax led to the isolation of three new dammarane triterpenoids 1, 2 and 4, together with the known triterpene 3. The structures of the new compounds were determined by 1D and 2D NMR spectroscopy and by comparison with published data for closely related compounds. 相似文献
79.
[structure: see text]The guanidine bridge in the new structural motif [3,3]ferrocenophane acts as a dual binding site for anions and metal ions. Sensing of anions (Cl(-), F(-), NO(3)(-), HSO(4)(-), and H(2)PO(4)(-)) takes place by redox-ratiometric measurements, whereas metal ion (Zn(2+), Ni(2+), and Cd(2+)) recognition is achieved by fluorescence measurements. 相似文献
80.
Otón F Tarraga A Espinosa A Velasco MD Bautista D Molina P 《The Journal of organic chemistry》2005,70(17):6603-6608
The synthesis of structurally new types of azaferrocenophanes is reported in this note: 4, which comprises a 1,2-fused azaheterocycle to a 1,3-diaza[3]ferrocenophane framework; 1,3-diaza[3]ferrocenophanes 5 and 7, which can be considered as a 1,1'-ferrocenylene N,N'-guanidine or urea, respectively; and 1,3,6,8-tetraza[8]ferrocenophanes 9 and 10, bearing two ureido moieties in the ansa-bridge. These compounds were prepared directly from 1,1'-bis(isocyanato)ferrocene 1 and thoroughly characterized by spectroscopic means. Tetraza[8]ferrocenophanes 9 and 10 show spectral and electrochemical anion-sensing action: they display a selective downfield shift of the urea protons and a cathodic shift of the ferrocene/ferrocinium redox couple with dihydrogenphosphate and fluoride anions. The crystal structure of compound 4 has been determined by single-crystal X-ray methods. 相似文献