Estudio de rotación interna Aplicación a derivados de benceno

Tesis inédita de la Universidad de Madrid, Facultad de Ciencias, Sección de Químicas, leída el 18 de diciembre de 1974.Universidad de MadridTRUEProQuestpu

Effect of Iron Isomorphic Substitution in Mg:Al and Zn:Al-Layered Double-Hydroxide Structures by Means of First Principle Calculations

Layered double hydroxides (LDHs) are important components in terrestrial and extra-terrestrial environments. The presence of iron in these minerals provides them a wide potential application in environmental and materials sciences. In this work, the role of Fe in the crystallographic properties of LDHs M2+:M3+ 2:1 with Mg:(Fe,Al), Mg:Fe, Zn:(Fe,Al), and Zn:Fe is investigated by means of quantum mechanical calculations based on the density functional theory (DFT). Several relative proportions of Fe are studied. The cation ordering of these LDHs has been explored, finding useful insights for experimental synthetic paths of these minerals. The a and b cell parameters increase with the iron concentration. Some diffraction lines at high angle decrease in angle and increase in intensity with the increasing iron concentration. All of them agree with the experimental results. The iron substitutions tend to aggregate.EU Framework Programme Horizon 2020 CA17120Spanish Andalusian project P18-RT-3786Consejo Superior de Investigaciones CientificasMinistry of Science and Innovation, Spain (MICINN) Spanish Government FJC2018-035820-

Compressional behavior of the aragonite-structure carbonates to 6 GPa

Supplementary Information The online version contains supplemen- tary material available at https://doi.org/10.1007/s00269-023-01237-6.The behaviors of aragonite (CaCO3 ), strontianite (SrCO3 ), cerussite (PbCO3 ), and witherite (BaCO3 ) at increasing pressure have been studied up to 6 GPa using density functional theory with plane waves. A parallelism of the orthorhombic carbonates with the closed-packed AsNi structure is considered in our analysis, being the CO2−3 groups not centered in the interstice of the octahedron. The decomposition of the unit-cell volume into atomic contributions using the Quantum Theory of Atoms in Molecules has allowed the analysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distances, and atomic compressibilities are calculated. The largest compression is on the c crystallographic axis, and the c linear modulus has a linear function with the mineral bulk modulus (K0 ). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) only gives linear functions when K0 is related either with the CC distances modulus or the modulus of the distances of the C to the faces of the octahedron perpendicular to c. These last distances are the projections of the Metal–Oxygen (MO) distances to the center of the octahedron. K0AE carbonates also show linear functions with the atomic moduli of their cations. However, the whole series show a linear relation with the atomic modulus of C atoms. Therefore, the whole series highlight the importance of the C atoms and their interactions in the mechanism of compression of the orthorhombic carbonate series.Spanish MCINN and European FEDER Grants FIS2016-77692-C2. 2PCIN-2017-098Junta de Andalucía for the RNM-264-363 and RNM-264-1897 PAI-Grant

Illitización hidrotermal de esmectita en el sitema (NH4)O-Al2O3-SiO2-H2O: influencia de la presencia de amonio

Durante la diagénesis se producen reacciones que afectan a filosilicatos y a la materia orgánica, ligadas a la generación de hidrocarburos, esto lleva a la fijación de NH4 en las illitas y a la disolución por ácidos orgánicos. Además, las esmectitas sufren un aumento de carga tetraédrica y la fijación de NH4+, que lleva a la formación de interestratificados I/S e illita. El amonio contribuye a la disolución de la esmectita. El papel del amonio, como dador de protones, es completamente novedoso. Para estudiar la influencia de NH4+ en la illitización de la esmectita, se ha llevado a cabo la síntesis de filosilicatos en condiciones hidrotermales, en presencia de amonio. Como material de partida se ha utilizado una bentonita natural (Cabo de Gata, Almería). Los experimentos se han realizado en el sistema químico (NH4+)-Al2O3-SiO2-H2O, a 100, 150 y 200 ºC, la presión del vapor de agua a esas temperaturas (0.101, 0.476 y 1.554 MPa), entre 15 y 90 días y 2 concentraciones de amonio (0.1 y 0.2 M). Los sólidos se caracterizaron por DRX, FTIR y TEM/AEM. El estudio mediante DRX revela que: - la esmectita incorpora amonio en la estructura, esto es corroborado también por FTIR. - algunas láminas de esmectita se transforman en láminas de illita - la presencia de un pico a 10 Å, sugiere la formación de illita, esto sólo es a 200, 150ºC. - Como subproductos se forma clinoptilolita, buddigtonita y cuarzo. El estudio mediante TEM/AEM muestra partículas delgadas con bajo contenido en Si y alto en AlIV, similares a fases illíticas y paquetes de partículas similares a la esmectita de partida, pero con amonio en la interlámina. El progreso de la illitization necesita protones, en nuestro caso estos H+ provienen del NH4. El aumento de la carga tetraédrica se interpreta como la disolución de la esmectita y la transformación a beidellita y a illita. El amonio puede actuar como un catalizador de la disolución y de laillitización de esmectita durante la diagénesis.Universidad de Málaga.Campus de Excelencia Internacional Andalucía Tech

2M1 phlogopite–muscovite series minerals at increasing pressure to 9 GPa. I Atomic volumes and compressibilities

Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Authors are thankful to Andalusian project P18-RT-3786 for financial support, and to the Computational Centers of the University of Granada and CSIC for computational facilities.Muscovite (Ms) and phlogopite (Phl) series mineral is studied in the 2M1 polytype and modeled by the substitution of three Mg2+ cations in the three octahedral sites of Phl [KMg3(Si3Al)O10(OH)2] by two Al3+ and one vacancy, increasing the substitution up to reach the Ms [KAl2□(Si3Al)O10(OH)2]. The series was computationally examined at DFT using Quantum ESPRESSO, as a function of pressure from − 3 to 9 GPa. Crystal structure is calculated, and cell parameters, and geometry of atomic groups agree with experimental values. OH in the Mg2+ octahedrons are approximately perpendicular to the (001) plane, meanwhile when they are in Al3+, octahedral groups are approximately parallel to this plane. From Quantum Theory of Atoms in Molecules, the atomic basins are calculated as a function of the pressure, K+ and basal O show the largest volumes. The bulk excess volume (Vxs) and the excess atomic volumes are analyzed as a function of the composition and the pressure. K+, basal and apical O Vxs show a behavior similar to the bulk Vxs as a function of the composition, keeping qualitatively this behavior as a function of pressure; substituent atoms do not show a Vxs behavior similar to the bulk and their effect consequently is mostly translated to atoms in the interlayer space. Atomic compressibilities are also calculated. Atomic compressibilities are separated in the different sheets of the crystal cell. Atomic moduli of K and basal O are the lowest and the ones behaving as the bulk modulus of the series. The atomic bulk modulus of the H’s is different depending of their position with respect to the (001) plane.CRUE-CSICAndalusian project P18-RT-378

Effects of the cation ordering in Mg:Al and Zn:Al layered double hydroxides on crystallographic and spectroscopical properties by means of first principles calculations

The authors would like to acknowledge the contribution of the European COST Action CA17120 supported by the EU Framework Programme Horizon 2020, and thank the Computational Center of CSIC and Supercomputing Center Alhambra of UGR for the high-performance computing services, and Spanish funding projects FIS2016-77692-C22-P and PCIN-2017-098, and the Andalusian funding project P18-RT3786 for financial support. C.P. acknowledges a Juan de la Cierva-Formacion postdoctoral contract (ref. FJC2018-035820-I) from the Spanish Ministry of Science. A.P.L. thanks to Secretaria de Educacion, Ciencia, Tecnologia e Innovacion (SECTEI) of the Mexico City for the scholarship for the postdoctoral stay.Layered double hydroxides (LDH) are interesting materials due to their high absorption and catalytic properties. Their applications in environment, agriculture and pharmaceutical fields are becoming widely important. The interlayer and intralayer cation ordering on layered double hydroxides of Mg:Al 2:1 and Zn:Al 2:1 are studied by means of different ordering models at Density Functional Theory level. The cation ordering in LDH is interesting for monitoring the synthesis of these solids and for the applications of LDH, however it is difficult to determine experimentally. We have explored several ordering arrangements of the cation distribution in Mg:Al 2:1 and Zn: Al 2:1 LDH and the effect of these cation arrangements on some crystallographic and spectroscopic properties.EU Framework Programme Horizon 2020 CA17120Spanish funding projects FIS2016-77692-C22-P PCIN-2017-098Andalusian funding project P18-RT3786Juan de la Cierva-Formacion postdoctoral contract from the Spanish Ministry of Science FJC2018-035820-ISecretaria de Educacion, Ciencia, Tecnologia e Innovacion (SECTEI) of the Mexico Cit

DFT Research on the Dehydroxylation Reaction of Pyrophyllite 1. First-Principle Molecular Dynamics Simulations

The dehydroxylation of pyrophyllite involves the reaction of OH groups and elimination of water molecules through two possible mechanisms, one involving the bridging hydroxyl groups of an octahedral Al3+ pair and the other two hydroxyl groups reacting across the dioctahedral vacancy. First-principles molecular dynamics simulations at the density functional theory level are used together with the metadynamics algorithm to explore the free-energy surface (FES) of the initial step of the dehydroxylation. We observe that the two possible dehydroxylation mechanisms yield similar activation energies at 0 K, but at high temperatures, the cross mechanism has lower free energy than that of the on-site one. The dehydroxylation process produces different semidehydroxylated intermediates that should be taken into account. The role of the temperature in favoring a dehydroxylation nonconcerted chain mechanism over another is here elucidated, and a novel competitive mechanism, which is assisted by the structural apical oxygens in the high-temperature regime, is proposed.IAC

Morphology alteration of nickel microstructures for glycerol electrooxidation

Shape-controlled microstructures (triangles and urchin-like) of Ni were synthesized using polyol synthesis in the presence/absence of capping agent (polyvinilpyrrolidone, PVP). Direct visualization of crystal structure and morphology before/after electrochemical tests in KOH were characterized using electron microscopy techniques. Electrochemical characterizations illustrated that urchin-Ni-PVP has highest catalytic activity among all investigated electrocatalysts for glycerol electrooxidation reaction (GEOR). Improved activity was attributed to the surface area and the highly porous structure as identified by electron tomography analysis. All Ni shapes showed similar selectivity. DFT calculations on low-index β-NiOOH and β-Ni(OH) planes were performed as possible surfaces present during electrochemical processes. The (0 0 1) surface is the most thermodynamically stable in both systems and has different possible terminations. For O, Ni and mixed Ni-O atoms terminations the β-NiOOH(0 0 1) present metallic behavior. DFT results show that either Ni or Ni-O exposed β-NiOOH(0 0 1) surfaces are possible scenarios for glycerol adsorption on different catalytic charged surface sites.This paper was partially supported by grants of CONICET (Argentina National Research Council), Universidad Nacional del Sur (UNS) and by ANPCyT through PICT 4085, and PIP-CONICET Nos. 11220130100436 research grant, as well as by SGCyT- UNS., E. A. G., P. V. J., M. G. S. and A. J. are members of CONICET., F. E and F. G. are fellow researchers at this institution. The authors acknowledge Ni Electro Can project administered from Queen's University and supported by “Grant No. RGPNM 477963-2015 under the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Frontiers Program. The support by MinCyT and UOttawa research grant is also acknowledged for travel funds to Universidad Nacional del Sur. M. G. S., A. H.-L. and C. I. S.-D. do thank to Dr. Santiago Melchor Ferrer from the University of Granada for important assistances to the DFT calculations; and A. H.-L. and C. I. S.-D. acknowledge the Spanish MINCINN project grants FIS2016-77692-C2-2P and PCIN-2017-098, along with FEDER European funds; we also thank to the Alhambra Computing Center (University of Granada, Spain) for important CPU time

Adiciones y correcciones a la orquidoflora valenciana

Some data about rare orchid taxa at the Valencian Community (Spain) or expansions of their distribution area to new shires are shown; The confirmed presence of Ophrys × chobautii for the Valencian Community and Neottia nidus-avis in Alicante province must be emphasized

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality