178 research outputs found
Estudio cinético de la desdiazoación en medio acuoso del tetrafluorborato de bencenodiazonio
The kinetic analyses carried out at different temperatures (20ºC - 40ºC) indicate that the dediazoniation process of thebenzenediazonium ion (BZ) is of the order of one, with BZ at A = 2,3.1015 s-1 and Ea = 112,5 kJ.mol-1 for the Arrheniusequation, and ΔH‡ = 110,0 kJ.mol-1 and ΔS‡ = 40,7 J.K-1.mol-1 for the Eyring equation. The chromatographic resultsreveal that BZ decomposes through a heterolytic process mediated by the aryl ion. The presence of Cu(I) or Cu(II) saltsand ascorbic acid produce a change in the reaction mechanism. The intermediate compounds produced in these conditionsare stable species that may be transported in the bloodstream. The model studied suggests a possible explanation for thelocalisation of tumours produced by the administration of BZ in rats.Los análisis cinéticos realizados a diferentes temperaturas (20º C - 40º C) indican que el proceso de desdiazoacióndel ion bencenodiazonio (BZ) es de orden uno respecto a BZ siendo A = 2,3.1015 s-1 y Ea = 112,5 kJ.mol-1 en laecuación de Arrhenius así como ΔH‡ = 110,0 kJ.mol-1 y ΔS‡ = 40,7 J.K-1.mol-1 para la ecuación de Eyring. Losresultados cromatográficos revelan que BZ se descompone por un proceso heterolítico mediado por el catión arilo.La presencia de sales Cu(I) o de Cu(II) y ácido ascórbico produce un cambio del mecanismo de reacción. Loscompuestos intermedios originados en estas condiciones son especies estables que pueden ser transportadas en lasangre. El modelo estudiado sugiere una posible explicación para la localización descrita en la literatura para lostumores producidos por la administración de BZ a ratas
Enantioselective adsorption of ibuprofen and lysine in metal-organic frameworks
This study reveals the efficient enantiomeric separation of bioactive molecules in the liquid phase. Chiral structure HMOF-1 separates racemic mixtures whereas heteroselectivity is observed for scalemic mixtures of ibuprofen using non-chiral MIL-47 and MIL-53. Lysine enantiomers are only separated by HMOF-1. These separations are controlled by the tight confinement of the molecules
Kinetic study of the photodegradation of p-hydroxybenzenediazonium ion in polar media.
Se ha realizado un estudio sobre la fotodescomposición del ión p-hidroxibencenodiazonio (PDQ) basado en los datos
espectrofotométricos y cromatográfi cos obtenidos con disoluciones de PDQ expuestas a irradiación UV (254 nm) en
medio de acetonitrilo y agua. Los resultados de HPLC y HPLC-masa (HPLC/MS) indican que el 4-acetamidofenol
es el principal producto que se forma tras la irradiación de PDQ en acetonitrilo. Esto se explica como consecuencia
de la formación inicial del catión arilo, que posteriormente participa en una reacción de Ritter. El análisis cinético
de los datos espectrofotométricos revela que la fotodegradación de PDQ es más rápida en acetonitrilo (constante
de velocidad observada, kobs, = 0,1442 s-1) que en acetonitrilo acidifi cado (kobs = 0,009 s-1), lo que indica una mayor
fotoestabilidad de la especie protonada derivada de PDQ. La constante de segundo orden (0,062 M s-1) encontrada
para la fotodescomposición de PDQ en tampón fosfato (pH 7) se justifi ca por el establecimiento de un equilibrio
entre las especies protonada y no protonada procedentes de la disociación ácida de PDQ.A study on the photodecomposition of p-hydroxybenzenediazonium ion (PDQ) has been made using chromatographic
and spectrophotometric data obtained from UV-irradiated (254 nm) PDQ solutions in acetonitrile and aqueous media.
The HPLC and HPLC-mass results indicate that 4-acetamidophenol is the main product formed after the irradiation
of PDQ in acetonitrile. This is explained as a consequence of the initial formation of the aryl cation which is later
involved in a Ritter’s reaction. A kinetic analysis of the spectrophotometric data reveals that PDQ photodegradation is
faster in acetonitrile (observed rate constant (kobs) = 0.1442 s-1) than in acidifi ed acetonitrile (kobs = 0.009 s-1) indicating
a higher photostability of the protonated species derived from PDQ. The second order constant (0.062 M s-1) found for
the PDQ photodecomposition in phosphate buffer (pH 7) is explained in term of the equilibrium between protonated
and non-protonated species coming from the acid dissociation of PDQ
Stellar atmospheric parameters of FGK-type stars from high-resolution optical and near-infrared CARMENES spectra
With the purpose of assessing classic spectroscopic methods on high-resolution and high signal-to-noise ratio spectra in the near-infrared wavelength region, we selected a sample of 65 F-, G-, and K-type stars observed with CARMENES, the new, ultra-stable, double channel spectrograph at the 3.5 m Calar Alto telescope. We computed their stellar atmospheric parameters (T_(eff), log g, ξ, and [Fe/H]) by means of the STEPAR code, a PYTHON implementation of the equivalent width method that employs the 2017 version of the MOOG code and a grid of MARCS model atmospheres. We compiled four Fe I and Fe II line lists suited to metal-rich dwarfs, metal-poor dwarfs, metal-rich giants, and metal-poor giants that cover the wavelength range from 5300 to 17 100 Å, thus substantially increasing the number of identified Fe I and Fe II lines up to 653 and 23, respectively, We examined the impact of the near-infrared Fe and Fen lines upon our parameter determinations after an exhaustive literature search, placing special emphasis on the 14 Gala benchmark stars contained in our sample, Even though our parameter determinations remain in good agreement with the literature values, the increase in the number of Fe l and Fe II lines when the near-infrared region is taken into account reveals a deeper T_(eff) scale that might stem from a higher sensitivity of the near-infrared lines to T_(eff)
Aproximación al registro paleoambiental de la cueva de Goikoetxe (Busturia): Evidencias sedimentarias y paleontológicas
Aproximación al registro paleoambiental de la cueva de Goikoetxe (Busturia): Evidencias sedimentarias y paleontológica
Rate-equation calculations of the current flow through two-site molecular device and DNA-based junction
Here we present the calculations of incoherent current flowing through the
two-site molecular device as well as the DNA-based junction within the
rate-equation approach. Few interesting phenomena are discussed in detail.
Structural asymmetry of two-site molecule results in rectification effect,
which can be neutralized by asymmetric voltage drop at the molecule-metal
contacts due to coupling asymmetry. The results received for poly(dG)-poly(dC)
DNA molecule reveal the coupling- and temperature-independent saturation effect
of the current at high voltages, where for short chains we establish the
inverse square distance dependence. Besides, we document the shift of the
conductance peak in the direction to higher voltages due to the temperature
decrease.Comment: 12 pages, 6 figure
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