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Vargas E.,Chilean Center of Nanosciences and Nanotechnology | Denardin J.C.,Chilean Center of Nanosciences and Nanotechnology | Escrig J.,Chilean Center of Nanosciences and Nanotechnology | Marco J.F.,Institute Quimica Fisica Rocasolano
Materials Characterization | Year: 2014

Cobalt oxide nanocrystals of size 17-21 nm were synthesized by a simple reaction between cobalt acetate (II) and dodecylamine. On the other hand, micrometric Co3O4 was prepared using the ceramic method. The structural examination of these materials was performed using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM and HRTEM). XRD studies showed that the oxides were pure, well-crystallized, spinel cubic phases with a-cell parameter of 0.8049 nm and 0.8069 nm for the nano and micro-oxide, respectively. The average particle size was 19 nm (nano-oxide) and 1250 μm (micro-oxide). Morphological studies carried out by SEM and TEM analyses have shown the presence of octahedral particles in both cases. Bulk and surface properties investigated by X-ray photoelectron spectroscopy (XPS), point zero charge (pzc), FTIR and cyclic voltammetry indicated that there were no significant differences in the composition on both materials. The magnetic behavior of the samples was determined using a vibrating sample magnetometer. The compounds showed paramagnetic character and no coercivity and remanence in all cases. Galvanostatic measurements of electrodes formed with nanocrystals showed better performance than those built with micrometric particles. © 2014 Elsevier Inc.

Mompean M.,Institute Quimica Fisica Rocasolano | Hervas R.,Instituto Cajal | Hervas R.,IMDEA Madrid Institute for Advanced Studies | Xu Y.,Columbia University | And 9 more authors.
Journal of Physical Chemistry Letters | Year: 2015

TDP-43 can form pathological proteinaceous aggregates linked to ALS and FTLD. Within the putative aggregation domain, engineered repeats of residues 341-366 can recruit endogenous TDP-43 into aggregates inside cells; however, the nature of these aggregates is a debatable issue. Recently, we showed that a coil to β-hairpin transition in a short peptide corresponding to TDP-43 residues 341-357 enables oligomerization. Here we provide definitive structural evidence for amyloid formation upon extensive characterization of TDP-43(341-357) via chromophore and antibody binding, electron microscopy (EM), solid-state NMR, and X-ray diffraction. On the basis of these findings, structural models for TDP-43(341-357) oligomers were constructed, refined, verified, and analyzed using docking, molecular dynamics, and semiempirical quantum mechanics methods. Interestingly, TDP-43(341-357) β-hairpins assemble into a novel parallel β-turn configuration showing cross-β spine, cooperative H-bonding, and tight side-chain packing. These results expand the amyloid foldome and could guide the development of future therapeutics to prevent this structural conversion. © 2015 American Chemical Society.

Velez E.,University of Medellín | Ruiz P.,National University of Colombia | Quijano J.,National University of Colombia | Notario R.,Institute Quimica Fisica Rocasolano
International Journal of Chemical Kinetics | Year: 2015

The gas-phase elimination reaction of ethyl (5-cyanomethyl-1,3,4-thiadiazol-2-yl)carbamate has been studied computationally at the MP2/6–31++G(2d,p) level of theory. The values of the activation parameters and rate constants for the thermal decomposition were evaluated over a temperature range from 405.0 to 458.0 K. The temperature dependence of the rate constants was used to deduce the modified Arrhenius expression: log k405–458 K = (9.01 ± 0.49) + (1.32 ± 0.16) log T – (6946 ± 30) 1/T, which is in good agreement with the expression obtained from experimental data. The results confirm that the mechanism is a cis-concerted elimination that occurs in two steps: The first one corresponds to the formation of ethylene and an intermediate, 5-(cyanomethyl)-1,3,4-thiadiazol-2-yl-carbamic acid, via a six-membered cyclic transition state, and the second one is the decarboxylation of this intermediate via a four-membered cyclic transition step, leading to carbon dioxide and the corresponding 1,3,4-thiadiazole derivative (5-amino-1,3,4-thiadiazole-2-acetonitrile). The connectivity of transition states with their respective minima was verified through intrinsic reaction coordinate calculations, and the progress of the reaction was followed by means of Wiberg bond indices, resulting that both transition states have an “early” character, nearer to the reactants than to the products. © 2015 Wiley Periodicals, Inc.

Zoogman P.,Harvard - Smithsonian Center for Astrophysics | Liu X.,Harvard - Smithsonian Center for Astrophysics | Suleiman R.M.,Harvard - Smithsonian Center for Astrophysics | Pennington W.F.,NASA | And 49 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2016

TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch between 2018 and 2021. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO observes from Mexico City, Cuba, and the Bahamas to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (~2.1. km N/S×4.4. km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry, as well as contributing to carbon cycle knowledge. Measurements are made hourly from geostationary (GEO) orbit, to capture the high variability present in the diurnal cycle of emissions and chemistry that are unobservable from current low-Earth orbit (LEO) satellites that measure once per day. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies.TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), formaldehyde (H2CO), glyoxal (C2H2O2), bromine monoxide (BrO), IO (iodine monoxide), water vapor, aerosols, cloud parameters, ultraviolet radiation, and foliage properties. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides these near-real-time air quality products that will be made publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring together with the European Sentinel-4 (S4) and Korean Geostationary Environment Monitoring Spectrometer (GEMS) instruments. © 2016 Elsevier Ltd.

Garcia E.,CSIC - Institute of Ceramics and Glass | Gancedo J.R.,Institute Quimica Fisica Rocasolano | Gracia M.,Institute Quimica Fisica Rocasolano
Materials Characterization | Year: 2010

A combination of 57Fe-Mössbauer spectroscopy and X-ray Powder Diffraction analysis has been employed to study modifications in chemical and mechanical stability occurring in a cordierite burner aged under combustion conditions which simulate the working of domestic boilers. Mössbauer study shows that Fe is distributed into the structural sites of the cordierite lattice as Fe2+ and Fe3+ ions located mostly at octahedral sites. Ferric oxide impurities, mainly hematite, are also present in the starting cordierite material accounting for ≅40% of the total iron phases. From Mössbauer and X-ray diffraction data it can be deduced that, under the combustion conditions used, new crystalline phases were formed, some of the substitutional Fe3+ ions existing in the cordierite lattice were reduced to Fe2+, and ferric oxides underwent a sintering process which results in hematite with higher particle size. All these findings were detected in the burner zone located in the proximity of the flame and were related to possible chemical reactions which might explain the observed deterioration of the burner material. © 2010 Elsevier Inc.

Kirkby O.M.,University College London | Sala M.,Laboratory Interdisciplinaire Carnot de Bourgogne | Balerdi G.,Unidad University | De Nalda R.,Institute Quimica Fisica Rocasolano | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Femtosecond time-resolved photoelectron spectroscopy experiments have been used to compare the electronic relaxation dynamics of aniline and d7-aniline following photoexcitation in the range 272-238 nm. Together with the results of recent theoretical investigations of the potential energy landscape [M. Sala, O. M. Kirkby, S. Guérin and H. H. Fielding, Phys. Chem. Chem. Phys., 2014, 16, 3122], these experiments allow us to resolve a number of unanswered questions surrounding the nonradiative relaxation mechanism. We find that tunnelling does not play a role in the electronic relaxation dynamics, which is surprising given that tunnelling plays an important role in the electronic relaxation of isoelectronic phenol and in pyrrole. We confirm the existence of two time constants associated with dynamics on the 11πσ∗ surface that we attribute to relaxation through a conical intersection between the 11πσ∗ and 11ππ∗ states and motion on the 11πσ∗ surface. We also present what we believe is the first report of an experimental signature of a 3-state conical intersection involving the 21ππ∗, 11πσ∗ and 11ππ∗ states. This journal is © the Owner Societies.

Cuesta A.,Institute Quimica Fisica Rocasolano | Cabello G.,Institute Quimica Fisica Rocasolano | Osawa M.,Hokkaido University | Gutierrez C.,Institute Quimica Fisica Rocasolano
ACS Catalysis | Year: 2012

We present a detailed spectrokinetic study of the electrocatalytic oxidation of formic acid on Au and Pt electrodes using ATR-SEIRAS that has allowed us to unveil the mechanisms of both the direct (in which adsorbed CO is not involved) and the indirect (through adsorbed CO) paths of the reaction with unprecedented detail. Au electrodes were used to study the mechanism of the direct path without the interference of the indirect path, and the observed quadratic dependence of the reaction rate on the formate coverage was then shown to apply also to Pt. The direct path consists of three steps, namely, (i) the electroadsorption of formate (corresponding to the first electron transfer), (ii) the purely chemical bimolecular decomposition of adsorbed formate, and (iii) the second electron transfer. The dehydration of HCOOH to adsorbed CO, that is then oxidized to CO 2 in the indirect path, was studied on Pt at E < 0.4 V vs the reversible hydrogen electrode (RHE), at which potentials the dehydration reaction is the only one taking place on the Pt surface. Our results show that adsorbed formate is also the intermediate in the dehydration of formic acid to adsorbed CO and is, hence, the key intermediate in the electrocatalytic oxidation of formic acid on metals. © 2012 American Chemical Society.

Oujja M.,Institute Quimica Fisica Rocasolano | Sanz M.,Institute Quimica Fisica Rocasolano | Agua F.,Institute Historia | Conde J.F.,Institute Historia | And 8 more authors.
Journal of Analytical Atomic Spectrometry | Year: 2015

In the present study, a historical set of Late Roman glasses from a recently unearthed graveyard located in the small city of Cubas de la Sagra, within the Madrid region (Spain) was compositionally analysed using different techniques such as ultraviolet-visible (UV-Vis) and laser induced fluorescence (LIF) spectroscopy, X-ray fluorescence (XRF) and laser induced breakdown spectroscopy (LIBS). LIBS results, recorded upon nanosecond (ns) and femtosecond (fs) laser irradiation, served for identification of major glass components (to classify them into main historical glass groups) and of minor components (e.g. chromophores, decolouring agents and degradation products). Quantitative information regarding these components was obtained on the basis of calibration curves obtained using glass certified standards and local standards. We have demonstrated that LIBS serves for the non-invasive/micro-destructive, quantitative chemical characterization of most of the analysed historical glasses. Furthermore, this work establishes a comparison between LIBS analysis of glasses in the ns and fs regimes on one hand, and on the other hand with the results obtained using XRF. The procedures and protocols here proposed can be applied for in situ study of historical glass collections, regardless of their size, provenance and chronology. This journal is © The Royal Society of Chemistry.

Zamora-Carreras H.,Institute Quimica Fisica Rocasolano | Torres M.,University ComplutenseMadrid | Bustamante N.,Institute Quimica Fisica Rocasolano | Macedo A.L.,New University of Lisbon | And 3 more authors.
Archives of Biochemistry and Biophysics | Year: 2015

Abstract Ole e 9 and Fra e 9 are two allergenic β-1,3-glucanases from olive and ash tree pollens, respectively. Both proteins present a modular structure with a catalytic N-terminal domain and a carbohydrate-binding module (CBM) at the C-terminus. Despite their significant sequence resemblance, they differ in some functional properties, such as their catalytic activity and the carbohydrate-binding ability. Here, we have studied the different capability of the recombinant C-terminal domain of both allergens to bind laminarin by NMR titrations, binding assays and ultracentrifugation. We show that rCtD-Ole e 9 has a higher affinity for laminarin than rCtD-Fra e 9. The complexes have different exchange regimes on the NMR time scale in agreement with the different affinity for laminarin observed in the biochemical experiments. Utilising NMR chemical shift perturbation data, we show that only one side of the protein surface is affected by the interaction and that the binding site is located in the inter-helical region between α1 and α2, which is buttressed by aromatic side chains. The binding surface is larger in rCtD-Ole e 9 which may account for its higher affinity for laminarin relative to rCtD-Fra e 9. © 2015 Elsevier Inc.

Becerra R.,Institute Quimica Fisica Rocasolano | Cannady J.P.,Dow Corning | Pfrang C.,University of Reading | Walsh R.,University of Reading
Journal of Physical Chemistry A | Year: 2015

Time-resolved kinetics studies of silylene, SiH2, generated by laser flash photolysis of phenylsilane, were performed to obtain rate coefficients for its bimolecular reaction with 2,5-dihydrofuran (2,5-DHF). The reaction was studied in the gas phase over the pressure range of 1-100 Torr in SF6 bath gas, at five temperatures in the range of 296-598 K. The reaction showed pressure dependences characteristic of a third body assisted association. The second-order rate coefficients obtained by Rice-Ramsperger-Kassel-Marcus (RRKM)-assisted extrapolation to the high-pressure limit at each temperature fitted the following Arrhenius equation where the error limits are single standard deviations: log(k/cm3 molecule-1 s-1) = (-9.96 ± 0.08) + (3.38 ± 0.62 kJ mol-1)/RT ln 10. End-product analysis revealed no GC-identifiable product. Quantum chemical (ab initio) calculations indicate that reaction of SiH2 with 2,5-DHF can occur at both the double bond (to form a silirane) and the O atom (to form a donor-acceptor, zwitterionic complex) via barrierless processes. Further possible reaction steps were explored, of which the only viable one appears to be decomposition of the O-complex to give 1,3-butadiene + silanone, although isomerization of the silirane cannot be completely ruled out. The potential energy surface for SiH2 + 2,5-DHF is consistent with that of SiH2 with Me2O, and with that of SiH2 with cis-but-2-ene, the simplest reference reactions. RRKM calculations incorporating reaction at both π- and O atom sites, can be made to fit the experimental rate coefficient pressure dependence curves at 296-476 K, giving values for k∞(π) and k∞(O) that indicate the latter is larger in magnitude at all temperatures, in contrast to values from individual model reactions. This unexpected result suggests that, in 2,5-DHF with its two different reaction sites, the O atom exerts the more pronounced electrophilic attraction on the approaching silylene. Arrhenius parameters for the individual pathways were obtained. The lack of a fit at 598 K is consistent with decomposition of the O-complex to give 1,3-butadiene + silanone. © 2015 American Chemical Society.

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