Browsing by Subject "Selectivity"
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- PublicationEmbargoContribution of ion binding affinity to ion selectivity and permeation in KcsA, a model potassium channel(2012-04-17) Renart Pérez, María Lourdes; Montoya Díaz, Estefanía; Fernández Carvajal, Asia María; Molina Gallego, María Luisa; Poveda Larrosa, José Antonio; Encinar Hidalgo, José Antonio; Ayala Torres, Antonio Vicente; Gómez Pérez, Francisco Javier; Morales Calderón, Andrés; González Ros, José Manuel; Bioquímica y Biología Molecular B e InmunologíaIon permeation and selectivity, key features in ion channel function, are believed to arise from a complex ensemble of energetic and kinetic variables. Here we evaluate the contribution of pore cation binding to ion permeation and selectivity features of KcsA, a model potassium channel. For this, we used E71A and M96V KcsA mutants in which the equilibrium between conductive and nonconductive conformations of the channel is differently shifted. E71A KcsA is a noninactivating channel mutant. Binding of K+ to this mutant reveals a single set of low-affinity K+ binding sites, similar to that seen in the binding of K+ to wild-type KcsA that produces a conductive, low-affinity complex. This seems consistent with the observed K+ permeation in E71A. Nonetheless, the E71A mutant retains K+ selectivity, which cannot be explained on the basis of just its low affinity for this ion. At variance, M96V KcsA is a rapidly inactivating mutant that has lost selectivity for K+ and also conducts Na+. Here, low-affinity binding and high-affinity binding of both cations are detected, seemingly in agreement with both being permeating species in this mutant channel. In conclusion, binding of the ion to the channel protein seemingly explains certain gating, ion selectivity, and permeation properties. Ion binding stabilizes greatly the channel and, depending upon ion type and concentration, leads to different conformations and ion binding affinities. High-affinity states guarantee binding of specific ions and mediate ion selectivity but are nonconductive. Conversely, low-affinity states would not discriminate well among different ions but allow permeation to occur.
- PublicationOpen Access¿Desigualdad territorial en Selectividad? Analizando la asignatura de matemáticas en Ciencias Sociales(Universidad de Murcia. Servicio de Publicaciones, 2022) Faura-Martínez, Úrsula; Lafuente-Lechuga, Matilde; Cifuentes Faura, JavierAnte el debate sobre la posible desigualdad territorial en la Prueba de Acceso a la Universidad, conocida como Selectividad, este trabajo pretende arrojar un poco de luz a cerca de esta creciente preocupación. Se analiza la estructura y resultados de las 17 pruebas autonómicas en la materia de Matemáticas Aplicadas a las Ciencias Sociales II, examinando el grado de dificultad de los ejercicios con la opinión de un panel de expertos. Se detectan diferencias en la estructura del examen de acceso que han podido influir en los resultados obtenidos por el alumnado. A través del panel de expertos se constata el diferente grado de dificultad de los ejercicios y su posible correlación con la calificación media obtenida en cada región. Los resultados evidencian la necesidad de llevar a cabo una revisión de la forma actual de las pruebas de acceso que elimine las desigualdades que puedan existir. Quizás habría que plantearse la realización de una única prueba a nivel nacional que garantice la igualdad en los contenidos y en los criterios de evaluación.
- PublicationOpen AccessFAIR data for compounds included in the article "Mechanically Planar-to-Point Chirality Transmission in [2]Rotaxanes"(ACS, 2024-03) Puigcerver, Julio; Marin Luna, Marta; Alajarin, Mateo; Martínez Cuezva, Alberto; Berna, Jose; Química orgánica
- PublicationOpen AccessFAIR Data for compounds included in the article "Reactivity of Glutaconamides Within [2]Rotaxanes: Mechanical Bond Controlled Chemoselective Synthesis of Highly Reactive α-KetoAmides and their Light-Triggered Cyclization" Angew. Chem. Int. Ed. 2023, e202302681(2023-03-23) Perez, Jesus de Maria; Alajarin, Mateo; Martinez-Cuezva, Alberto; Berna, Jose; Química orgánica
- PublicationOpen AccessFAIR data for compounds included in the article "Ring-to-Thread Chirality Transfer in [2]Rotaxanes for the Synthesis of Enantioenriched Lactams".(Universidad de Murcia, 2022-08-02) López Leonardo, Carmen; Saura Sanmartín, Adrián; Marín Luna, Marta; Alajarín, Mateo; Martínez Cuezva, Alberto; Berná Cánovas, José; Química orgánica
- PublicationOpen AccessKinetically-controlled ni-catalyzed direct carboxylation of unactivated secondary alkyl bromides without chain walking(American Chemical Society, 2024-01-09) Davies, Jacob; Lyonnet, Julien R.; Carvalho, Bjorn; Sahoo, Basudev; Day, Craig S.; Juliá Hernández, Francisco; Duan, Yaya; Obst, Marc; Norrby, Per-Ola; Velasco-Rubio, Álvaro; Hopmann, Kathrin H; Martin, Ruben; Obst, Marc; Per-OLa, Norrby; Química InorgánicaHerein, we report the direct carboxylation of unactivated secondary alkyl bromides enabled by the merger of photoredox and nickel catalysis, a previously inaccessible endeavor in the carboxylation arena. Site-selectivity is dictated by a kinetically controlled insertion of CO2 at the initial C(sp3 )−Br site by the rapid formation of Ni(I)−alkyl species, thus avoiding undesired β-hydride elimination and chain-walking processes. Preliminary mechanistic experiments reveal the subtleties of stereoelectronic effects for guiding the reactivity and site-selectivity.
- PublicationOpen AccessProblemas de los sistemas de provisión escolar mixta: análisis de la red privada subvencionada en Chile(Universidad de Murcia. Servicio de Publicaciones, ) Carrasco Bahamonde, Juan A.; Gedda Muñoz, RelmuEl sistema educativo chileno se caracteriza por un tipo de provisión mixta y la participación del sector privado en la provisión escolar, que se consolida como la red con mayor matrícula del país. No obstante, las razones que están en la base de su consolidación, sus características y cuáles son los efectos de su expansión en la organización de la provisión escolar permanecen subrepresentados en el debate educacional. Por esto, resulta relevante preguntarse cómo se compone la red privada subvencionada y cómo interactúan sus atributos con las características institucionales de la provisión escolar en un contexto de cambios regulatorios. El estudio se centra en cuáles son las características de los centros educativos, indagando en los atributos de estatus reconocido por las familias, las prácticas de selectividad de los centros conectando con la discusión más amplia sobre los sistemas de provisión mixta. Para este propósito, se utiliza una técnica factorial exploratoria que permite caracterizar descriptivamente los centros educativos, considerando para esto a los 906 establecimientos del Área Metropolitana de Santiago. Entre los principales hallazgos, los resultados son confirmatorios respecto de los atributos vinculados teóricamente a estatus en contextos de competición y elección escolar, destacando que sus fuentes tradicionales –el cobro de aranceles, composición y desempeño– presentan un patrón de agrupamiento y constituyen una base estable de estatus para las escuelas. Por otro lado, las prácticas de selectividad en el acceso interactúan más directamente sobre la demanda de escolaridad, ofreciendo una diferenciación al interior de escuelas de mayor estatus.
- PublicationOpen AccessRoom-temperature direct β-arylation of thiophenes and benzo[b]thiophenes and kinetic evidence for a Heck-type pathway(American Chemical Society, 2016-01-20) Colletto, Chiara; Islam, Saidul; Juliá Hernández, Francisco; Larrosa, Igor; Química InorgánicaThe first example of a regioselective β-arylation of benzo[b]thiophenes and thiophenes at room temperature with aryl iodides as coupling partners is reported. This methodology stands out for its operational simplicity: no prefunctionalization of either starting material is required, the reaction is insensitive to air and moisture, and it proceeds at room temperature. The mild conditions afford wide functional group tolerance, often with complete regioselectivity and high yields, resulting in a highly efficient catalytic system. Initial mechanistic studies, including 13C and 2 H KIEs, suggest that this process occurs via a concerted carbo-palladation across the thiophene double bond, followed by a base-assisted anti-elimination.
- PublicationOpen AccessRu-catalyzed C–H arylation of fluoroarenes with aryl halides(American Chemical Society, 2016-03-04) Simonetti, Marco; Perry, Gregory J. P.; Cambeiro, Xacobe C.; Juliá Hernández, Francisco; Arokianathar, Jude N.; Larrosa, Igor; Química InorgánicaAlthough the ruthenium-catalyzed C−H arylation of arenes bearing directing groups with haloarenes is wellknown, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η6-arene-ligandfree Ru(II) catalyst. Indeed, upon initial pivalate-assisted C−H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C−H activation is both reversible and kinetically significant. Computational studies support a concerted metalation−deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.
- PublicationOpen AccessValor pronóstico de las pruebas de acceso al INEFC respecto al rendimiento académico(2003-07-01) Planas Anzano, Antoni; Doménech i Massons, Josep M.The establiment of selective mechanisms that limitate the acces to some studies or jobs is a widely extended practise nowadays. This report talks about the analysis of the entry test tojoin the Physical Education studies in INEFC, center of Lleida. In this test both physical and intellectual requeriments are combined. The analysis of the results in this case based on three consecutive promotions of students (1997-1999) shows that the measurings done have a poor predictable value of the academic performance, coinciding with the trend pointend in other researchings, for exemple Herrera Garcia, et. al. (1999). Given the singularity of the degree taught in this center and opposite to other reports, in this one a representative measure of the «physical ability» is inclued. Abilities such as the different tests of the entry aptitude test, with the intention of achieving a greater predictable power. According to the results this intention is quite far away from reality.