Search results for "Nitrogen"

Reacción aza-Michael intramolecular organocatalítica sobre enonas y derivados de ácido: nuevas estrategias

2016

Una de les metodologies més importants, junt amb la reacció de Mannich, per la formació d’enllaços carboni-nitrogen i per accedir a compostos b-amino carbonílics, és la reacció aza-Michael, que consisteix en l’addició conjugada d’una font de nitrogen nucleòfila a un sistema a,b-insaturat. Aquesta reacció adquireix una especial rellevància a la seua versió intramolecular ja que condueix a la formació d’heterocicles nitrogenats de forma senzilla. A més, quan l’olefina activada conté centres proquirals, al procés d’addició es generen un o més centres estereogènics, pel que la versió asimètrica d’esta reacció permetria obtenir compostos nitrogenats funcionalitats de forma estereoselectiva. Ment…

Nuevas estrategias en la síntesis de compuestos de interés biológico: Estructuras terfenílicas y heterociclos nitrogenados fluorados enantioméricamen…

2015

Actualmente, el descubrimiento y desarrollo de nuevos fármacos es un proceso lento y económicamente exigente. En los últimos 10 años, los gastos económicos destinados al descubrimiento de nuevos compuestos se han triplicado, mientras que el número de nuevas entidades moleculares (NMEs) se ha mantenido invariable en los últimos 50 años. Es por esta razón que la búsqueda de nuevas estructuras que posean una relevante actividad terapéutica permanece como objetivo primordial en química farmacéutica. Por otra parte, la incorporación de átomos de flúor ha demostrado ser un método eficaz para alterar las propiedades biológicas, de las moléculas, incrementando la estabilidad del compuesto sin alter…

Organocatalytic approach to benzofused nitrogen-containing heterocycles: enantioselective total synthesis of (+)-angustureine.

2008

Complexes of Glycolic Acid with Nitrogen Isolated in Argon Matrices. I. Structures and Thermal Effects.

2019

Molecular complexes between glycolic acid and nitrogen were studied in a low-temperature argon matrix with FTIR spectroscopy, and supported by MP2 and BLYPD3 calculations. The calculations indicate 11 and 10 stable complex structures at the MP2 and BLYPD3 levels of theories, respectively. However, only one hydrogen-bonded complex structure involving the most stable SSC conformer of glycolic acid was found experimentally, where the nitrogen molecule is bound with the carboxylic OH group of the SSC conformer. The complex shows a rich site structure variation upon deposition of the matrix in different temperatures and upon annealing experiments, which provide interesting prospects for site-sel…

The trophic structure of a fish assemblage in a non-tidal Mediterranean Lagoon: integrating data from the Fishbase information system with results fr…

2010

Exposure to nitrogen dioxide and respiratory health at 2 years in the INMA-Valencia cohort

2018

Resumen Objetivo Analizar la relación entre la exposición a dióxido de nitrógeno (NO2) en las etapas prenatal y posnatal y la incidencia de problemas respiratorios en niños/as hasta los 2 años de edad. Método La población consistió en 624 niños/as de la cohorte INMA-Valencia. Se estimó la exposición individual al NO2 en el exterior de la vivienda durante el periodo prenatal y hasta los 2 años de edad, a partir de la combinación de datos empíricos y el desarrollo de métodos geoestadísticos. Se aplicó un cuestionario para obtener la información sobre los síntomas respiratorios a los 2 años. La asociación entre la exposición al NO2 y los eventos respiratorios se realizó mediante regresión logí…

Monolayer graphene doping and strain dynamics induced by thermal treatments in controlled atmosphere

2018

Time dynamics of doping and strain induced in single layer graphene by thermal treatments up to 300 degrees C in vacuum, nitrogen, carbon dioxide and oxygen controlled atmosphere are deeply studied by Raman spectroscopy and they are compared with its morphological evolution investigated by Atomic Force Microscopy. The reaction dynamics in oxygen treatments is determined down to a time scale of few minutes as well as that of dedoping process made by water vapor treatment. The interplay of strain modification and doping effects is separated. The strain is clarified to be strongly influenced by the cooling time. The doping removal is dominated by the water vapor, showing that the concentration…

Effects of NH3 and alkaline metals on the formation of particulate sulfate and nitrate in wintertime Beijing

2020

Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH3, or by other alkaline species such as alkaline metal ions if available. The different roles of NH3 and metal ions in neutralizing H2SO4 or HNO3, however, are seldom investigated. Here we conducted semi-continuous measurements of SO4 2−, NO3 −, NH4 +, and their gaseous precursors, as well as alkaline metal ions (Na+, K+, Ca2+, and Mg2+) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicat…

Tetraiodoethynyl resorcinarene cavitands as multivalent halogen bond donors

2014

The first examples of iodoethynyl resorcinarene cavitands as rigid 3D halogen bond (XB) donor molecules are presented. These concave macrocycles form strong, RXB = 0.78–0.83, halogen bonds with dioxane oxygen, pyridine nitrogen and a bromide anion in tetraproropyl ammonium bromide resulting in deep cavity cavitand structures.

Effect of gases on biochemical stabilization

2019

International audience; Lipid or protein are sensitive to peroxidation and inert gas limit or stop adulterations. Unsaturated lipids are peroxided by ground state dioxygen in presence of catalysts (iron, enzymes) or after thermal dissociation of C=C bond, and by excited state dioxygen without any assistance (photo-oxidation). Inerting fragile oils by bubbling with dinitrogen or carbon dioxide that are soluble gas in oil slows oxidation process during storage or frying. In a same way, limit the oxidation of the tryptophan residues of protein is possible by reducing oxygen content. Oxidation leads also to oxidation of thiol in disulfide, which induced protein cross-linked and decay of functio…