Compuestos N-carbenos heterocíclicos como catalizadores para producir hidrógeno a partir de glicerol

El hidrógeno juega un papel importante en la industria debido a sus diversas aplicaciones. Existen varios procesos para producir hidrógeno, entre los cuales el reformado con vapor es el más rentable; sin embargo, es necesario desarrollar procesos alternativos para reducir la dependencia de los combustibles fósiles. Una forma alternativa y viable de obtener hidrógeno es generarla a partir de glicerol, que se produce excesivamente en el mercado porque es un subproducto del biodiesel. Por otra parte, la reacción de los líquidos iónicos con metales para preparar complejos N-carbenos heterocíclicos (NHC), ofrecen una oportunidad en aplicaciones industriales ya que ofrecen un mínimo impacto sobre el medio ambiente. En este trabajo se evaluó la actividad catalítica de los complejos (NHC) Pt y (NHC) Ni en la reacción en fase acuosa del glicerol; la reacción se llevó a cabo a temperaturas relativamente bajas y altas presiones en comparación con otros métodos.Hydrogen plays an important role in the industry due to its diverse applications. There are several processes to produce hydrogen, among which steam reforming is the most profitable; however, it is necessary to develop alternative processes to reduce dependence on fossil fuels. An alternative and viable way to obtain hydrogen is to generate it from glycerol, which produced excessively in the market because it is by product of biodiesel. In the other hand, the reaction of ionic liquids with metals was used to prepare N-heterocyclic carbene (NHC) complexes, offering an opportunity for industrial applications with minimal impact on the environment, they used as catalysts. In this work, the catalytic activity of the complexes (NHC) Pt and (NHC) Ni was evaluated in the reaction in aqueous phase of the glycerol; the reaction was carried out at relatively low temperatures and at high pressures compared with other methods

Structure-Function Relationships of the Follicle-Stimulating Hormone Receptor

The follicle-stimulating hormone receptor (FSHR) plays a crucial role in reproduction. This structurally complex receptor is a member of the G-protein coupled receptor (GPCR) superfamily of membrane receptors. As with the other structurally similar glycoprotein hormone receptors (the thyroid-stimulating hormone and luteinizing hormone-chorionic gonadotropin hormone receptors), the FSHR is characterized by an extensive extracellular domain, where binding to FSH occurs, linked to the signal specificity subdomain or hinge region. This region is involved in ligand-stimulated receptor activation whereas the seven transmembrane domain is associated with receptor activation and transmission of the activation process to the intracellular loops comprised of amino acid sequences, which predicate coupling to effectors, interaction with adapter proteins, and triggering of downstream intracellular signaling. In this review, we describe the most important structural features of the FSHR intimately involved in regulation of FSHR function, including trafficking, dimerization, and oligomerization, ligand binding, agonist-stimulated activation, and signal transduction

The Youngest Victims: Children and Youth Affected by War

In 1989, the United Nation Convention on the Rights of the Child declared, “[state parties] shall take all feasible measures to ensure protection and care of children who are affected by an armed conflict.” In addition to attempting to secure the welfare of children in armed conflict, the Convention went on to ban the recruitment and deployment of children during armed conflict. Despite the vast majority of sovereign nations signing and ratifying this agreement, this treaty, unfortunately, has not prevented children and youth from witnessing, becoming victims of, or participating in political, ethnic, religious, and cultural violence across the past three decades. This chapter offers an “ecological perspective” on the psychosocial consequences of exposure to the trauma of war-related violence and social disruption

Estudio del efecto de un simbiótico sobre el perfil lipídico en modelos murinos de hiperlipidemia

Tesis (Maestría en Ciencias en Alimentos), Instituto Politécnico Nacional, SEPI, ENCB, 2009, 1 archivo PDF, (88 páginas). tesis.ipn.m

El Kataminó y la percepción geométrica de un grupo de estudiantes de preparatoria

La investigación se ubica en los estudios de didáctica de la geometría, es de orden cualitativo y versa sobre el desarrollo de la percepción geométrica que manifestaron nueve estudiantes de preparatoria al resolver situaciones de construcción (considerando condiciones que deben cumplirse) o de reproducción (cuando se hace con base en un modelo) de una configuración geométrica particular. Interesa poner a esta habilidad humana en la mesa de la didáctica de la geometría, proponiendo para ello una definición que caracteriza sus cualidades y propiedades. Los referentes teórico-metodológicos se rastrean en: los conceptos de estímulo y percepción para definir a la percepción geométrica, la Teoría de las Situaciones Didácticas para el montaje experimental, los conceptos táctica y estrategia para el análisis de los datos y, por último, los antecedentes de experiencias sobre geometría obtenidos de una entrevista semi-estructurada aplicada a cada miembro de la muestra. Además, se proponen mecanismos para «medir», indirectamente, la percepción geométrica, mediante las tácticas y estrategias que usaron los estudiantes para resolver los retos de cuatro juegos didáctico- geométricos estudiados, por razones de espacio, solamente se analiza el Kataminó, cuyos resultados se correlacionan con los de los otros tres

Molecular dynamics simulation of the follicle-stimulating hormone receptor. Understanding the conformational dynamics of receptor variants at positions N680 and D408 from in silico analysis.

Follicle-stimulating hormone receptor (FSHR) is a G-protein coupled receptor (GPCR) and a prototype of the glycoprotein hormone receptors subfamily of GPCRs. Structural data of the FSHR ectodomain in complex with follicle-stimulating hormone suggests a "pull and lift" activation mechanism that triggers a conformational change on the seven α-helix transmembrane domain (TMD). To analyze the conformational changes of the FSHR TMD resulting from sequence variants associated with reproductive impairment in humans, we set up a computational approach combining helix modeling and molecular simulation methods to generate conformational ensembles of the receptor at room (300 K) and physiological (310 K) temperatures. We examined the receptor dynamics in an explicit membrane environment of polyunsaturated phospholipids and solvent water molecules. The analysis of the conformational dynamics of the functional (N680 and S680) and dysfunctional (mutations at D408) variants of the FSHR allowed us to validate the FSHR-TMD model. Functional variants display a concerted motion of flexible intracellular regions at TMD helices 5 and 6. Disruption of side chain interactions and conformational dynamics were detected upon mutation at D408 when replaced with alanine, arginine, or tyrosine. Dynamical network analysis confirmed that TMD helices 2 and 5 may share communication pathways in the functional FSHR variants, whereas no connectivity was detected in the dysfunctional mutants, indicating that the global dynamics of the FSHR was sensitive to mutations at amino acid residue 408, a key position apparently linked to misfolding and variable cell surface plasma membrane expression of FSHRs with distinct mutations at this position

Normal testicular function without detectable follicle-stimulating hormone. A novel mutation in the follicle-stimulating hormone receptor gene leading to apparent constitutive activity and impaired agonist-induced desensitization and internalization

Activating mutations in the follicle-stimulating hormone (FSH) receptor (FSHR) gene are rarely detected due to the absence of a clearly defined phenotype, particularly in men. We here report the biochemical features of a novel mutation in the first extracellular loop of the FSHR. The mutation (N431I) was detected in an asymptomatic man exhibiting normal spermatogenesis, suppressed serum FSH, and normal or elevated levels of biochemical markers of FSH action. Employing different experimental strategies on HEK-293 cells transiently expressing the N431I FSHR mutant, we found that the mutation led to decreased cell surface plasma membrane expression of the receptor protein, but conferred a low level of constitutive activity associated with markedly altered agonist-stimulated desensitization and internalization. These latter features may contribute and/or amplify the persistent activation of the receptor in both absence and presence of agonist and provide new insights into opportunities for adjuvant therapies based on disruption of these processes

Role of cysteine residues in the carboxyl-terminus of the follicle-stimulating hormone receptor in intracellular traffic and postendocytic processing

Posttranslational modifications occurring during the biosynthesis of G protein-coupled receptors include glycosylation and palmitoylation at conserved cysteine residues located in the carboxyl-terminus of the receptor. In a number of these receptors, these modifications play an important role in receptor function and particularly, in intracellular trafficking. In the present study, the three cysteine residues present in the carboxyl-terminus of the human FSHR were replaced with glycine by site-directed mutagenesis. Wild-type and mutant (Cys627/629/655Gly) FSHRs were then transiently expressed in HEK-293 cells and analyzed for cell-surface plasma membrane expression, agonist-stimulated signaling and internalization, and postendocytic processing in the absence and presence of lysosome and/or proteasome inhibitors. Compared with the wild-type FSHR, the triple mutant FSHR exhibited ~70% reduction in plasma membrane expression as well as a profound attenuation in agonist-stimulated cAMP production and ERK1/2 phosphorylation. Incubation of HEK-293 cells expressing the wild-type FSHR with 2-bromopalmitate (palmitoylation inhibitor) for 6 h, decreased plasma membrane expression of the receptor by ~30%. The internalization kinetics and β-arrestin 1 and 2 recruitment were similar between the wild-type and triple mutant FSHR as disclosed by assays performed in non-equilibrium binding conditions and by confocal microscopy. Cells expressing the mutant FSHR recycled the internalized FSHR back to the plasma membrane less efficiently than those expressing the wild-type FSHR, an effect that was counteracted by proteasome but not by lysosome inhibition. These results indicate that replacement of the cysteine residues present in the carboxyl-terminus of the FSHR, impairs receptor trafficking from the endoplasmic reticulum/Golgi apparatus to the plasma membrane and its recycling from endosomes back to the cell surface following agonist-induced internalization. Since in the FSHR these cysteine residues are S-palmitoylated, the data presented emphasize on this posttranslational modification as an important factor for both upward and downward trafficking of this receptor