Spectroscopic and computational insights on catalytic synergy in bimetallic aluminophosphate catalysts

A combined electronic structure computational and X-ray absorption spectroscopy study was used to investigate the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Probing the nature of the molecular species at the atomic level has led to the identification of a unique Co-O-Ti bond, which serves as the loci for the superior performance of the bimetallic catalyst, when compared with its analogous monometallic counterpart. The structural and spectroscopic features associated with this active site have been characterized and contrasted, with a view to affording structure property relationships, in the wider context of designing sustainable catalytic oxidations with porous solids

Metal-Substituted Microporous Aluminophosphates

This chapter aims to present the zeotypes aluminophosphates (AlPOs) as a complementary alternative to zeolites in the isomorphic incorporation of metal ions within all-inorganic microporous frameworks as well as to discuss didactically the catalytic consequences derived from the distinctive features of both frameworks. It does not intend to be a compilation of either all or the most significant publications involving metal-substituted microporous aluminophosphates. Families of AlPOs and zeolites, which include metal ion-substituted variants, are the dominant microporous materials. Both these systems are widely used as catalysts, in particular through aliovalent metal ions substitution. Here, some general description of the synthesis procedures and characterization techniques of the MeAPOs (metal-contained aluminophosphates) is given along with catalytic properties. Next, some illustrative examples of the catalytic possibilities of MeAPOs as catalysts in the transformation of the organic molecules are given. The oxidation of the hardly activated hydrocarbons has probably been the most successful use of AlPOs doped with the divalent transition metal ions Co2+, Mn2+, and Fe2+, whose incorporation in zeolites is disfavoured. The catalytic role of these MeAPOs is rationalized based on the knowledge acquired from a combination of the most advanced characterization techniques. Finally, the importance of the high specificity of the structure-directing agents employed in the preparation of MeAPOs is discussed taking N,N-methyldicyclohexylamine in the synthesis of AFI-structured materials as a driving force. It is shown how such a high specificity could be predicted and how it can open great possibilities in the control of parameters as critical in catalysis as crystal size, inter-and intracrystalline mesoporosity, acidity, redox properties, incorporation of a great variety of heteroatom ions or final environment of the metal site (surrounding it by either P or Al)

Using enhanced number and brightness to measure protein oligomerization dynamics in live cells

Protein dimerization and oligomerization are essential to most cellular functions, yet measurement of the size of these oligomers in live cells, especially when their size changes over time and space, remains a challenge. A commonly used approach for studying protein aggregates in cells is number and brightness (N&B), a fluorescence microscopy method that is capable of measuring the apparent average number of molecules and their oligomerization (brightness) in each pixel from a series of fluorescence microscopy images. We have recently expanded this approach in order to allow resampling of the raw data to resolve the statistical weighting of coexisting species within each pixel. This feature makes enhanced N&B (eN&B) optimal for capturing the temporal aspects of protein oligomerization when a distribution of oligomers shifts toward a larger central size over time. In this protocol, we demonstrate the application of eN&B by quantifying receptor clustering dynamics using electron-multiplying charge-coupled device (EMCCD)-based total internal reflection microscopy (TIRF) imaging. TIRF provides a superior signal-to-noise ratio, but we also provide guidelines for implementing eN&B in confocal microscopes. For each time point, eN&B requires the acquisition of 200 frames, and it takes a few seconds up to 2 min to complete a single time point. We provide an eN&B (and standard N&B) MATLAB software package amenable to any standard confocal or TIRF microscope. The software requires a high-RAM computer (64 Gb) to run and includes a photobleaching detrending algorithm, which allows extension of the live imaging for more than an hour

El desarrollo del concepto de muerte en la infancia : un análisis psicogenético

Estudiar la formación del concepto de muerte en el niño, sus creencias acerca de la muerte, partiendo de la idea de que como otros conceptos es de difícil elaboración por parte del niño porque hace referencia al contenido del pensamiento. 185 niños entre 5 y 13 años escolarizados en EGB de procedencia rural y urbana distribuidos homogéneamente. Considerando que el concepto de muerte incluye componentes de índole biológica, afectiva, social, etc. Se seleccionaron 6 aspectos: definiciones y argumentos que aporta el niño como causalidad. Sentimientos hacia ella. Creencias que mantiene y soluciones que da sobre el destino de los muertos. Posibilidad de sensaciones tras la muerte. Carácter definitivo e irreversible, reencarnación, resurrección. Alcance, carácter inevitable y universal de la muerte. Interrogatorio verbal e individual a través de un cuestionario siguiendo las pautas del método clínico de Piaget. Consta de 14 ítems sin orden fijo, según las respuestas del niño se incluían nuevas preguntas para clarificarlas, pero sin perder el núcleo. Análisis cualitativo en función de las edades y valoración global de resultados se proporcionan ejemplos de las respuestas más significativas y resultados en tablas de doble entrada (edad con las restantes variables). Aparecen tres etapas diferenciadas y coincidentes con los estadios evolutivos de Piaget. 1) De 5 a 7 años dificultad para definir la muerte, evoca sólo casos extremos como vejez por lo que no le alcanza esa posibilidad, el lugar de los muertos es el cielo o el infierno. Niegan que los muertos puedan sentir y no aceptan la posibilidad de retorno. 2) De 7 a 11 años aumenta la capacidad para definir y actuar sobre los acontecimientos no presentes. Llama la atención el cambio de la forma de exponer las causas de la muerte y conciben la existencia de razones internas biológicas. Se acepta la obligatoriedad, universalidad e inevitabilidad del fenómeno. 3) De 11 a 14 años hay un gran cambio cualitativo especula objetivamente sobre ello y se suele considerar como el fin de la historia individual, hay una mayor finura en el análisis de los sentimientos y expresan las razones de sus propias reacciones. Se comprueba que la adquisición del concepto de muerte requiere un laborioso trabajo de construcción a lo largo de un proceso evolutivo en el que se advierten errores e imperfecciones hasta la consecución correcta del mismo. A juicio de la autora este trabajo reabre líneas de investigación dentro de este tema ya que plantea dudas e interrogantes.AsturiasES

Cooperative structure-directing effect of fluorine-containing organic molecules and fluoride anions in the synthesis of zeolites

Dibenzyldimethylammonium (DBDM) cations, singly fluorinated at the ortho, meta, and para positions of the aromatic ring, have been investigated as structure-directing agents (SDAs) for the synthesis of all-silica zeolites in fluoride media and compared with the nonfluorinated molecule. The nonfluorinated DBDM cation can direct the synthesis either to an all-silica zeolite beta or to an all-silica zeolite ZSM-50 with the EUO framework topology. Under the same conditions that DBDM gives zeolite beta, benzyl-orthofluorobenzyldimethylammonium (o-FDBDM) readily directs the crystallization of pure all-silica ZSM-50 [Cmma, a = 13.726(3) angstrom, b = 22.171(5) angstrom, c = 20.254(4) angstrom]. Replacing o-FDBDM by the para fluoro derivative (p-FDBDM) results in a much slower crystallization of ZSM-50 whereas no crystalline product results if the meta fluoro derivative (m-FDBDM) is added. Single-crystal diffraction studies of selected ZSM-50 crystals prepared using DBDM and o-FDBDM determine the location of the template and of charge-balancing fluoride atoms bound to framework silicon atoms and included within [41516 2] cages in the framework. Furthermore, the o-FDBDM is found to order within the structure, with the fluorine-containing aromatic rings occupying channel, rather than cavity, locations. Computer simulations indicate how the position of fluorine in the SDA influences the template ordering.</p

Cooperative structure-directing effect of fluorine-containing organic molecules and fluoride anions in the synthesis of zeolites

Dibenzyldimethylammonium (DBDM) cations, singly fluorinated at the ortho, meta, and para positions of the aromatic ring, have been investigated as structure-directing agents (SDAs) for the synthesis of all-silica zeolites in fluoride media and compared with the nonfluorinated molecule. The nonfluorinated DBDM cation can direct the synthesis either to an all-silica zeolite beta or to an all-silica zeolite ZSM-50 with the EUO framework topology. Under the same conditions that DBDM gives zeolite beta, benzyl-orthofluorobenzyldimethylammonium (o-FDBDM) readily directs the crystallization of pure all-silica ZSM-50 [Cmma, a = 13.726(3) angstrom, b = 22.171(5) angstrom, c = 20.254(4) angstrom]. Replacing o-FDBDM by the para fluoro derivative (p-FDBDM) results in a much slower crystallization of ZSM-50 whereas no crystalline product results if the meta fluoro derivative (m-FDBDM) is added. Single-crystal diffraction studies of selected ZSM-50 crystals prepared using DBDM and o-FDBDM determine the location of the template and of charge-balancing fluoride atoms bound to framework silicon atoms and included within [41516 2] cages in the framework. Furthermore, the o-FDBDM is found to order within the structure, with the fluorine-containing aromatic rings occupying channel, rather than cavity, locations. Computer simulations indicate how the position of fluorine in the SDA influences the template ordering.</p

Purely Visible-Light-Induced Photochromism in Ag-TiO2 Nanoheterostructures

We report titania nanoheterostructures decorated with silver, exhibiting tuneable photochromic properties for the first time when stimulated only by visible white light (domestic indoor lamp), with no UV wavelengths. Photochromic materials show reversible color changes under light exposure. However, all inorganic photochromic nanoparticles (NPs) require UV light to operate. Conventionally, multicolor photochromism in Ag-TiO2 films involves a change in color to brownish-gray during UV-light irradiation (i.e., reduction of Ag+ to Ag0) and a (re)bleaching (i.e., (re)oxidation of Ag0 to colorless Ag+) upon visible-light exposure. In this work, on the contrary, we demonstrate visible-light-induced photochromism (ranging from yellow to violet) of 1-10 mol % Ag-modified titania NPs using both spectroscopic and colorimetric CIEL ab∗ analyses. This is not a bleaching of the UV-induced color but a change in color itself under exposure to visible light, and it is shown to be a completely different mechanism - driven by the interfacial charge transfer of an electron from the valence band of TiO2 to that of the AgxO clusters that surround the titania - to the usual UV-triggered photochromism reported in titania-based materials. The quantity of Ag or irradiation time dictated the magnitude and degree of tuneability of the color change, from pale yellow to dark blue, with a rapid change visible only after a few seconds, and the intensity and red shift of surface plasmon resonance induced under visible light also increased. This effect was reversible after annealing in the dark at 100 °C/15 min. Photocatalytic activity under visible light was also assessed against the abatement of nitrogen oxide pollutants, for interior use, therefore showing the coexistence of photochromism and photocatalysis - both triggered by the same wavelength - in the same material, making it a multifunctional material. Moreover, we also demonstrate and explain why X-ray photoelectron spectroscopy is an unreliable technique with such materials