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81.
Gema González Werner Stracke Zoraya Lopez Ulrike Keller Andrea Ricker Rudolf Reichelt 《Microscopy and microanalysis》2004,10(2):224-235
High-resolution transmission (HRTEM) and high-resolution scanning electron microscopy as well as atomic force microscopy (AFM), X-ray diffraction, and electron diffraction were used for studying the zeolites MFI, MEL, and the MFIMEL intergrowth system. All three zeolites consisted of individual particles having a size in the range of approximately 0.5 m to 5 m. The particle habits varied from rather cubelike to almost spherelike with many intermediate habits. Typically, the particles of these three zeolites were assembled by many individual blocks that differed in the dimension from about 25 nm to 140 nm as well as in the shape from very frequently almost rectangular (for MFI, MEL, and MFIMEL) to sometimes roundish or irregular habits (mainly for MFIMEL). An estimate shows that some 104 up to more than 106 densely packed blocks typically may assemble each individual zeolite particle or, related to the corresponding unit cell dimension, about 108 up to 1010 unit cells. The fine surface structure of zeolite particles was terracelike with steps between adjacent terraces typically in the range of 20 nm to 60 nm; the minimum step measured was approximately 4 nm. A detailed study of the surface topography was performed by AFM, detecting organic molecules at the block intersections. The presence of topological defects was observed by HRTEM and electron diffraction. 相似文献
82.
Cuesta A Cabello G Gutiérrez C Osawa M 《Physical chemistry chemical physics : PCCP》2011,13(45):20091-20095
The electrooxidation of formic acid on Pt and other noble metal electrodes proceeds through a dual-path mechanism, composed of a direct path and an indirect path through adsorbed carbon monoxide, a poisoning intermediate. Adsorbed formate had been identified as the reactive intermediate in the direct path. Here we show that actually it is also the intermediate in the indirect path and is, hence, the key reaction intermediate, common to both the direct and indirect paths. Furthermore, it is confirmed that the dehydration of formic acid on Pt electrodes requires adjacent empty sites, and it is demonstrated that the reaction follows an apparently paradoxical electrochemical mechanism, in which an oxidation is immediately followed by a reduction. 相似文献
83.
Let A be a commutative ring and M be a projective module of rank k with n generators. Let h=n-k. Standard computations show that M becomes free after localizations in comaximal elements (see Theorem 5). When the base ring A contains a field with at least hk+1 non-zero distinct elements we construct a comaximal family G with at most (hk+1)(nk+1) elements such that for each g∈G, the module Mg is free over A[1/g]. 相似文献
84.
Rita Vaickelionienė Vytautas Mickevičius Gema Mikulskienė Maryna Stasevych Olena Komarovska-Porokhnyavets Volodymyr Novikov 《Research on Chemical Intermediates》2011,37(8):1009-1027
N′-(4-Oxo-1,4-dihydronaphthalen-1-ylidene)-1-phenyl-5-oxopyrrolidine-3-carbohydrazides and N′-(3-methyl-4-oxo-1,4-dihydronaphthalen-1-ylidene)-1-phenyl-5-oxopyrrolidine-3-carbohydrazides were synthesized by reactions
of 5-oxo-1-phenylpyrrolidine-3-carbohydrazides with 1,4-naphthoquinone or 2-methyl-1,4-naphthoquinone. The alkylated analogues
of the above products were obtained using ethyl iodide. The interaction of 5-oxo-1-phenylpyrrolidine-3-carbohydrazides with
2,3-dichloro-1,4-naphthoquinone was followed by formation of N′-(3-chloro-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-1-phenyl-5-oxopyrrolidine-3-carbohydrazides. All these compounds were characterized
using 1H, 13C NMR, IR and mass spectra. Some of the new compounds were tested for the antimicrobial and antifungal activity. 相似文献
85.
M. Carmen Calzada Gema Camacho Enrique Fernández-Cara Mercedes Marín 《Journal of computational physics》2011,230(4):1335-1358
In this work we present a new strategy for solving numerically a (relatively simple) model of tumor growth. In principle, this is devoted to describe avascular growth although, by choosing the parameters appropriately, it also permits to give an idea of the behavior after vascularization. The numerical methods rely on fictitious domain and level set techniques, with a combination of quadratic finite elements and finite differences approximations. We present a collection of numerical results that essentially coincide with others, previously obtained with other techniques. 相似文献
86.
87.
Sarah?Brice?o Ana?C.?Hernandez Juan?Sojo Luis?Lascano Gema?GonzalezEmail author 《Journal of nanoparticle research》2017,19(4):140
Magnetic nanoparticles (NPs) of magnetite Fe3O4 obtained by coprecipitation (COP), thermal decomposition (DT), and commercial sample (CM) have been degraded in similar conditions to physiological medium at pH 4.7 and in simulated body fluid (SBF) at pH 7.4. The formation of the nanoparticles was confirmed by FTIR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In view of medical and environmental applications, the stability of the particles was measured with dynamic light scattering. The degradation processes were followed with atomic absorption spectroscopy (EAA) and TEM. Magnetic measurements were carried out using vibrating sample magnetometry (VSM). Our results revealed that the structural and magnetic properties of the remaining nanoparticles after the degradation process were significantly different to those of the initial suspension. The degradation kinetics is affected by the pH, the coating, and the average particle size of the nanoparticles. 相似文献
88.
Blanco-Urgoiti J Añorbe L Pérez-Serrano L Domínguez G Pérez-Castells J 《Chemical Society reviews》2004,33(1):32-42
There are still some synthetic chemists who hesitate to use metal-mediated or -catalysed reactions. The Pauson-Khand reaction (PKR) is a powerful transformation that has now been sufficiently well developed to be routinely considered when planning a synthesis, especially of polycyclic complex molecules. This tutorial review aims to encourage the use of this process explaining the best ways of performing a PKR both in the stoichiometric and the catalytic version, showing the scope of the process and its limitations. Additionally, asymmetry can be introduced in the reaction using several strategies, which will be discussed. The most recent examples of the synthetic applications of the PKR in natural product synthesis will give the reader an idea of the great usefulness of this reaction. 相似文献
89.
Sani M Bruché L Chiva G Fustero S Piera J Volonterio A Zanda M 《Angewandte Chemie (International ed. in English)》2003,42(18):2060-2063
90.
Pilar Sánchez-Andrada Marta Marín-Luna Ibon Alkorta José Elguero Gema Percho Dolores Santa María Rosa M. Claramunt 《Journal of heterocyclic chemistry》2021,58(5):1130-1140
Conformational exploration of five 2,5-diaryl-4-methyl-2,4-dihydro-3H-1,2,4-triazol-3-ones has been carried out based on a combination of their NMR chemical shifts determined in CDCl3 and the scrutiny of their computed relative energies and absolute shieldings calculated at the DFT/GIAO/B3LYP/6–311++G(d,p) level. The very flat potential energy curves corresponding to the three relevant single bond rotations were explored by calculating the energy of the rotational barriers and comparing the experimental chemical shifts with those theoretically calculated in each rotamer by statistical analysis. 相似文献