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71.
A classical Lewis adduct derives from a covalent bond between a Lewis acid and a base. When the adduct formation is precluded by means of steric hindrance the association of the respective acid-base molecular system is defined as a frustrated Lewis pair (FLP). In this work, the archetypal FLP Mes3P/B(C6F5)3 was characterized for the first time by resonance Raman spectroscopy, and the results were supported by density functional theory (DFT) calculations. The charge transfer nature of the lowest energy electronic transition, from phosphine to borane, was confirmed by the selective enhancement of the Raman bands associated to the FLP chromophore at resonance condition. Herein, we demonstrate the use of resonance Raman spectroscopy as a distinguished technique to probe the weak interaction involved in FLP chemistry. 相似文献
72.
Leonardo Dalseno Antonino Júlia Rocha Gouveia Rogrio Ramos de Sousa Júnior Guilherme Elias Saltarelli Garcia Luara Carneiro Gobbo Lara Basílio Tavares Demetrio Jackson dos Santos 《Molecules (Basel, Switzerland)》2021,26(8)
Several efforts have been dedicated to the development of lignin-based polyurethanes (PU) in recent years. The low and heterogeneous reactivity of lignin hydroxyl groups towards diisocyanates, arising from their highly complex chemical structure, limits the application of this biopolymer in PU synthesis. Besides the well-known differences in the reactivity of aliphatic and aromatic hydroxyl groups, experimental work in which the reactivity of both types of hydroxyl, especially the aromatic ones present in syringyl (S-unit), guaiacyl (G-unit), and p-hydroxyphenyl (H-unit) building units are considered and compared, is still lacking in the literature. In this work, the hydroxyl reactivity of two kraft lignin grades towards 4,4′-diphenylmethane diisocyanate (MDI) was investigated. 31P NMR allowed the monitoring of the reactivity of each hydroxyl group in the lignin structure. FTIR spectra revealed the evolution of peaks related to hydroxyl consumption and urethane formation. These results might support new PU developments, including the use of unmodified lignin and the synthesis of MDI-functionalized biopolymers or prepolymers. 相似文献
73.
Moura Ramos Joaquim J. Diogo Hermínio P. 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3077-3085
Journal of Thermal Analysis and Calorimetry - The thermal behavior of the two glass-forming drugs bifonazole and lamotrigine was studied by differential scanning calorimetry (DSC); we reported a... 相似文献
74.
NMR spin echo measurements of 13C in C60, 89Y in Y2O3, and 29Si in silicon are shown to defy conventional expectations when more than one pi pulse is used. Multiple pi-pulse echo trains may either freeze out or accelerate the decay of the signal, depending on the pi-pulse phase. Average Hamiltonian theory, combined with exact quantum calculations, reveals an intrinsic cause for these coherent phenomena: the dipolar coupling has a many-body effect during any real, finite pulse. 相似文献
75.
Godoi C. M. Santos M. C. L. Silva A. J. Tagomori T. L. Ramos A. S. de Souza R. F. B. Neto A. Oliveira 《Research on Chemical Intermediates》2021,47(2):743-757
Research on Chemical Intermediates - PdxCuy/C catalysts combinations were employed to CH4 partial oxidation in mild condition using a solid electrolyte reactor—alkaline fuel cell type. The... 相似文献
76.
Mônica Siqueira Ferreira Diogo Noin de Oliveira Rosimeire Nunes de Oliveira Silmara Marques Allegretti Aníbal Eugênio Vercesi Rodrigo Ramos Catharino 《Journal of mass spectrometry : JMS》2014,49(1):86-92
Schistosomiasis is a neglected disease with large geographic distribution worldwide. Among the several different species of this parasite, S. mansoni is the most common and relevant one; its pathogenesis is also known to vary according to the worms' strain. High parasitical virulence is directly related to granulomatous reactions in the host's liver, and might be influenced by one or more molecules involved in a specific metabolic pathway. Therefore, better understanding the metabolic profile of these organisms is necessary, especially for an increased potential of unraveling strain virulence mechanisms and resistance to existing treatments. In this report, MALDI‐MSI and the metabolomic platform were employed to characterize and differentiate two Brazilian S. mansoni strains: males and females from Belo Horizonte (BH) and from Sergipe (SE). By performing direct analysis, it is possible to distinguish the sex of adult worms, as well as identify the spatial distribution of chemical markers. Phospholipids, diacylglycerols and triacylglycerols were located in specific structures of the worms' bodies, such as tegument, suckers, reproductive and digestive systems. Lipid profiles were found to be different both between strains and males or females, giving specific metabolic fingerprints for each group. This indicates that biochemical characterization of adult S. mansoni may help narrowing‐down the investigation of new therapeutic targets according to worm composition, molecule distribution and, therefore, aggressiveness of disease. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
77.
The π‐Back‐Bonding Modulation and Its Impact in the Electronic Properties of CuII Antineoplastic Compounds: An Experimental and Theoretical Study 下载免费PDF全文
Juan Carlos García‐Ramos Dr. Rodrigo Galindo‐Murillo Araceli Tovar‐Tovar Ana Luisa Alonso‐Saenz Virginia Gómez‐Vidales Dr. Marcos Flores‐Álamo Dr. Luis Ortiz‐Frade Dr. Fernando Cortes‐Guzmán Dr. Rafael Moreno‐Esparza Prof. Antonio Campero Prof. Lena Ruiz‐Azuara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13730-13741
78.
Trigonometrically-fitted methods have been largely used for solving second-order differential problems, and particularly for solving the radial Schrödinger equation (see for instance Alolyan and Simos in J Math Chem 50:782–804, 2012; Simos in J Math Chem 34:39–58, 2003, 44:447–466, 2008; Vigo-Aguiar and Simos in J Math Chem 29:177–189, 2001, 32:257–270, 2002 and the references therein contained). It is well-known that for periodic or oscillatory problems, trigonometrically fitted methods are more efficient than non-fitted methods. A large number of different approaches have been considered in the scientific literature to obtain analytical approximations to the frequency of oscillation in case of periodic solutions, which are valid for a large range of amplitudes of oscillation. However, these techniques have been limited to obtaining only one or two iterates because of the great amount of algebra involved. In this paper we consider the use of a trigonometrically fitted method to obtain numerical approximations for the solutions. This yields very acceptable results provided that the approximation of the parameter of the method is done with great accuracy. Many trigonometrically fitted methods have been reported in the literature, but there is no decisive way to obtain the optimal frequency value. We present a strategy for the choice of the parameter value in the adapted method, based on the minimization of the sum of the total energy error and the local truncation errors in the solution and in the derivative. We include an example solved numerically that confirms the good performance of the strategy adopted. 相似文献
79.
C. Mocuta A. Barbier A. V. Ramos M.-J. Guittet J.-B. Moussy S. Stanescu C. Gatel R. Mattana C. Deranlot F. Petroff 《The European physical journal. Special topics》2009,167(1):53-58
Epitaxial metal/oxide based magnetic tunnel-junctions
(MTJ) are valuable model systems to investigate the influence of the
crystallinity of individual layers on the magnetic properties. We
have non-destructively studied the effect of the optical lithography
procedure on the crystalline structure of MTJ’s with lateral spatial
resolution by performing local x-ray diffraction experiments using a
microfocused x-ray spot. We demonstrate that the lithography process
produces distortion effects on the crystalline structure of the
layers near the edges of the lithographed junction. These
distortions are present on all the constituent layers and are most
probably driven by the elastic constants of the materials. They
translate into tilts of the crystalline planes in the vicinity of
the edges and propagate towards the center of the junction; the
tilt’s amplitude (up to several degrees) and sign (concave or
convex) depend on the junction’s shape, size and the type of
materials (interfaces) used. We report results for junctions made
with two types of metal-oxide interfaces (Co/CoFe2O4 and
Co/Fe3O4), with sizes from 10 to 150 μm and various shapes
(square-, rectangle- and disk-like). 相似文献
80.