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21.
Tárraga A Otón F Espinosa A Desamparados Velasco M Molina P Evans DJ 《Chemical communications (Cambridge, England)》2004,(4):458-459
The synthesis of the first tetraaza[3,3]ferrocenophane, from the previously unreported 1,1'-bis(triphenylphosphoranylidenamino)ferrocene and its conversion into a nitrogen-rich [2,2]bis[3,3]ferrocenophane is described. The electronic behaviour of these multinuclear ferrocenophanes indicates a strong electronic coupling between the iron centers. 相似文献
22.
D. Levy F. Del Monte J.M. Otón G. Fiksman I. Matías P. Datta M. López-amo 《Journal of Sol-Gel Science and Technology》1997,8(1-3):931-935
Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems. 相似文献
23.
Silva da Costa Russany Pinheiro Wandson Braamcamp de Souza Arruda Mara Silvia Pinheiro Costa Carlos Emmerson Ferreira Converti Attilio Ribeiro Costa Roseane Maria Silva Júnior José Otávio Carrera 《Journal of Thermal Analysis and Calorimetry》2022,147(1):275-284
Journal of Thermal Analysis and Calorimetry - Cupuassu (Theobroma grandiflorum Schum.) is a typical Amazonian fruit, whose seed is used as raw material to produce cupulate. The by-product of its... 相似文献
24.
Gomes Antonio Taylon Aguiar Pereira Rayanne Rocha Duarte Junior Anivaldo Pereira da Cruz Rodrigues Antonio Manoel Remédios Claudio Marcio Rocha Brasil Davi do Socorro Barros Morais Luiz Roberto Barbosa Silva-Júnior José Otávio Carréra Ribeiro-Costa Roseane Maria 《Journal of Thermal Analysis and Calorimetry》2022,147(1):355-365
Journal of Thermal Analysis and Calorimetry - Native Amazon palm trees have been target of research and product development especially because of their oil and fat. Tucumã-do-Pará... 相似文献
25.
Otón F Tárraga A Espinosa A Velasco MD Molina P 《The Journal of organic chemistry》2006,71(12):4590-4598
The synthesis of structurally new types of ferrocene-based ureas, in which the ferrocene moiety is simultaneously attached to two urea groups, have been prepared directly from 1,1'-bis(isocyanato)ferrocene 1. Homoditopic receptors 2a-e 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 hydrogen phosphate and fluoride anions. In addition, receptor 2d based on an unprecedent tetraaza[9]ferrocenophane architecture, shows spectral, electrochemical, and selective fluorescent responses to fluoride anion. 相似文献
26.
Liquid crystal microdroplets can be trapped into silica gel-glasses by sol-gel processes. Several silica matrices containing different non-reacting organic radicals have been employed for preparing gel-glass dispersed liquid crystals (GDLC). The optical properties of thin GDLC layers may be modified by coating the material with transparent electrodes and applying external AC-voltage signals. Switching between opaque and transparent states is achieved. The sample transmission depends on the scattering properties of the material; no polarizers are required. The transmission of the transparent state is improved by matching the refractive indices of the gel-glass matrix and the liquid crystal. This can be achieved by adding high refractive index dopants to the starting mixture, or by substituting the non-reacting organic group of the silica matrix. Both approaches have been tested. Phenyl and methyl monomers have been used as well as titanium-based dopants. The resulting GDLC materials have been optimized by controlling the starting mixture composition, the reaction conditions, and the film preparation. The optics, dynamics, and stability of GDLC films are analyzed. 相似文献
27.
A method for automatic classification of the shape of graphite particles in cast iron is proposed. In a typical supervised classification procedure, the standard charts from the ISO-945 standard are used as a training and validation population. Several shape and size parameters are described and used as discriminants. A new parameter, the average internal angle, is proposed and is shown to be relevant for accurate classification. The ideal parameter sets are determined, leading to validation success rates above 90%. The classifier is then applied to real cast iron samples and provides results that are consistent with visual examination. The method provides classification results per particle, different from the traditional per field chart comparison methods. The full procedure can run automatically without user interference. 相似文献
28.
Santos RP Silveira ER Lemos TL Viana FA Braz-Filho R Pessoa OD 《Magnetic resonance in chemistry : MRC》2005,43(6):494-496
A careful NMR analysis with full assignment of the 1H and 13C spectral data for two minor saponins isolated from stems of Cordia piauhiensis is reported. These saponins were isolated by high-performance liquid chromatography and characterized as 3beta-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl]pomolic acid 28-O-[beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl] ester (1) and 3beta-O-[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl]oleanolic acid 28-O-[beta-D-xylopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl] ester (2). Their structures were established using a combination of 1D and 2D (1H, 1H-COSY, TOCSY, NOESY, gs-HMQC and gs-HMBC) NMR techniques, electrospray ionization mass spectrometry and chemical evidence. 相似文献
29.
Jaécio Carlos Diniz Francisco Arnaldo Viana Odaci Fernandes Oliveira Maria Aparecida M. Maciel Maria da Conceição de Menezes Torres Raimundo Braz‐Filho Edilberto R. Silveira Otília Deusdênia L. Pessoa 《Magnetic resonance in chemistry : MRC》2009,47(2):190-193
From the roots of Cordia leucocephala (Boraginaceae), two new meroterpenoid naphthoquinones, 6‐[10‐(12,12‐dimethyl‐13α‐hydroxy‐16‐methenyl‐cyclohexyl)ethyl]‐1,4‐naphthalenedione (cordiaquinone L) and 5‐methyl‐6‐[10‐(12,12‐dimethyl‐13β‐hydroxy‐16‐methenyl‐cyclohexyl)methyl‐1,4‐naphthalenedione (cordiaquinone M) were isolated. Their structures were elucidated after detailed 1D and 2D NMR (COSY, HSQC, HMBC and NOESY) data analyses and comparison with literature data for analogous compounds. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
30.
Ezequiel F. V. Leitão Elizete Ventura Otávio L. de Santana Silmar A. do Monte 《International journal of quantum chemistry》2014,114(8):508-520
The unusual O‐coordination mode of nitrosamines to Fe(III) heme models has been observed in the bis(dimethylnitrosamine)(meso‐tetraphenylporphyrinate)iron(III) cation. For the first time, this latter as well as the simpler bis(dimethylnitrosamine)(porphinate)iron(III) heme model cations have been studied through ab initio methods. The sextet, quartet, and doublet spin states of both cations have been studied through single‐point calculations based on the experimental (X‐ray) geometry. Their energies, charges, and spin densities have been analyzed. The obtained results (at the UHF/cc‐pVDZ and ROHF/cc‐pVDZ levels) indicate that the peripheral benzene rings are of secondary importance for the coordination of dimethylnitrosamine to the Fe(III) porphyrin core. The obtained energy ordering is sextet < quartet < doublet, at all computational levels. The UHF, ROHF, and UMP2 results indicate an excess of alpha spin density around the Fe atom, a low covalency for the Fe? O bond and a substantial charge transfer to the Fe atom. Our best estimates [obtained at ROMP2 level with the mixed cc‐pVDZ/cc‐pVTZ‐DK(Fe) basis set] for the energy differences (in eV) between the three spin states considered are 0.929 for the sextet‐quartet gap and 0.812 for the quartet‐doublet gap, which indicate that the spin crossover (at room temperature) is very unlikely. These results represent the substantial decrease in the uncorrelated values. The implications of spin contaminations at the UHF and UMP2 levels for subsequent geometry optimizations to be performed in the smaller cation have also been discussed. © 2013 Wiley Periodicals, Inc. 相似文献