ABP y tics adaptados a los laboratorios de prácticas de química física: su inserción e implementación

El trabajo que se presenta está basado en la experiencia docente llevada a cabo en los grupos de laboratorio de las asignaturas Termodinámica Química y Experimentación en Química Física, de primer y segundo curso de la Licenciatura en Química. El objetivo principal de este trabajo ha sido demostrar que el hecho de emplear e integrar el Aprendizaje Basado en Problemas (ABP) como estrategia didáctica con las Tecnologías de la Información y Comunicación (TICs), es válido y aplicable a cualquier asignatura universitaria de índole práctica que implique a la Química Física.This work presents the obtained results on the context of two experimental subjects entitled Thermodynamic Chemistry and Physical Chemistry Laboratory. The principal goal is to show that the Problem Based Learning (PBL) technique integrated with the new technologies of virtual-teaching works efficiently as new methodologies of teaching Physical Chemistry at the university

Steric Tuning of Sulfinamide/Sulfoxides as Chiral Ligands with C1, Pseudo-meso, and Pseudo‑C2 Symmetries: Application in Rhodium(I)-Mediated Arylation

A new family of sulfinamide/sulfoxide derivatives was synthesized as chiral bidentate ligands by stereoselective additions of methylsulfinyl carbanions to N-tert-butylsulfinylimines. The new ligands, with C1, pseudo-meso, and pseudo-C2 symmetries, were successfully assayed in Rh-catalyzed additions of arylboronic acids to activated ketones. The sterically dissymmetric C1 ligand (RS,SC,RS)-N-[1-(phenylsulfinyl)-3-methylbut-2-yl] tert-butylsulfinamide turned out to be the optimal one, allowing the 1,4-additions of diverse arylboronic acids, on different α,β-unsaturated cyclic ketones with high chemical yields and enantioselectivities up to >99% ee.Ministerio de Economía y Competitividad (Grant CTQ2016-78580-C2-2R

Tuning the structural, optical and photoluminescence properties of hybrid perovskite quantum dots by A-site doping

Hybrid organic-inorganic perovskites have been widely investigated in recent years due to their role as light absorbers in highly efficient solar cells and as emitters. Consequently, to control the emission properties of perovskite quantum dots (PQDs) is of great interest. In this study, Csx MA(1-x) PbI3 PQDs were synthesized. A shift in the emission peak from 670 to 740 nm was found for x≥0.2, and the quantum yield (QY) and recombination lifetime were affected when Cs was incorporated. The shift in the emission is observed to be due to the displacement of the valence band edge, but this is not because of an electronic effect resulting from the Cs incorporation, as observed from the PDOS analyses. It is likely due to the transition from tetragonal to orthorhombic phase of the PQDs when the Cs amount increased. Therefore, the emission properties of the PQDs synthesized can be regulated according to the amount of Cs incorporated in their network

Chitosan biofilms: Insights for the selective electromembrane extraction of fluoroquinolones from biological samples

A selective electromembrane extraction procedure for the extraction of Enrofloxacin, Marbofloxacin and Flumequine, usually employed as antibiotic in veterinarian use, is proposed by using a chitosan biofilm, composed by 60% (w/w) chitosan and 40% (w/w) Aliquat®336, as active biopolymeric support. The interaction mechanism occurring between the target drugs and the biopolymer has been deeply studied using the Quantum Theory of Atoms in Molecules. The obtained results show the interaction between the extracted fluoroquinolones and the biomembrane is stabilized by two hydrogen bonds formed between both the carboxyl and keto groups of the drugs with both the amine and hydroxyl groups of glucosamine in the biopolymer. The energetic results agree with the high extraction efficiency obtained for Marbofloxacin, Enrofloxacin and Flumequine in terms of enrichment factors (83, 82 and 58, respectively) in presence of other fluoroquinolones. Under optimum conditions, the proposed electromembrane extraction method exhibits wide linear ranges of 4.2e200 mg L1 , 5.6e200 mg L1 and 5.1e200 mg L1 , respectively; low limits of detection close to 1.3 mg L1 and appropriate repeatability (relative standard deviation values 4e7%).Fondos Europeos FEDER, Ministerio de Ciencia e Innovación y Agencia Estatal de Investigación, de España - PGC2018-096608- B-C22Ministerio de Ciencia, Innovación y Universidades de España - RED2018-102522-TJunta de Andalucía - 2019/FQM-106Premio Mensual Publicación Científica Destacada de la US. Facultad de Químic

The Role of the Interactions at the Tungsten Disulphide Surface in the Stability and Enhanced Thermal Properties of Nanofluids with Application in Solar Thermal Energy

Transition metal dichalcogenides (TMCs) exhibit unique properties that make them of interest for catalysis, sensing or energy storage applications. However, few studies have been performed into nanofluids based on TMCs for heat transfer applications. In this study, nanofluids based on 2D-WS2 are prepared by liquid phase exfoliation to analyze their potential usage in concentrating solar power plants. Periodic-Density Functional Theory (DFT) calculations were performed to rationalize the success of the exfoliation process. The hydrogen bond interaction between the hydroxyl group from PEG, which acts as a surfactant, and the S atoms of the WS2 surface stabilizes the nanosheets in the fluid. Electron localization function (ELF) analysis is indicative of the stability of the S-H interaction from WS2 with the molecules of surfactant due to the tendency to interact through weak intermolecular forces of van der Waals solids. Moreover, improvements in thermal properties were also found. Isobaric specific heat increased by up to 10% and thermal conductivity improved by up to 37.3%. The high stability of the nanofluids and the thermal improvements were associated with the high surface area of WS2 nanosheets. These results suggest that these nanofluids could be a promising heat transfer fluid in concentrating solar power plants

Revealing the role of Pb 2+ in the stability of organic–inorganic hybrid perovskite CH 3 NH 3 Pb 1− x Cd x I 3: an experimental and theoretical study

This paper presents the synthesis of organic–inorganic hybrid perovskite CH3NH3Pb1−xCdxI3. The effect of incorporating Cd2+ or Pb2+ on the stability of the perovskite structure was analysed from a theoretical and experimental viewpoint. The XRD results showed that the tetragonal perovskite structure was formed for x values of up to 0.5, which seems to indicate that the presence of a considerable amount of Pb2+ is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd2+ led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH3NH3Pb0.5Cd0.5I3 with regard to the MAPbI3 structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI3 perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb2+ ions in stabilizing this kind of hybrid perovskite structures. Finally, the DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy. The theoretical band gap values decreased as the concentration of Cd increased.Junta de Andalucía (P09- FQM-04938)Fondo Europeo de Desarrollo Regional (FEDER)Centro Informático Científico de Andalucía (CICA

Desarrollo de una barra de Hopkinson para generar aceleraciones de 50 Km/s2

Este trabajo presenta el diseño conceptual de un sistema de calibración por impacto para generar altas aceleraciones, llamado barra de Hopkinson. Hoy en día, se reportan aceleraciones hasta 35 km/s2 usando un sistema de impacto mediante cuerpos rígidos; el objetivo es bosquejar y analizar un sistema, para posterior producción, generando aceleraciones hasta 50 km/s2. Se aplicó una metodología de diseño fundamentada en procesos para explorar situaciones de diseño, técnicas de generación de ideas, lista de verificación, evaluación de alternativas con análisis FODA y registro de modos de falla mediante un AMEF de diseño; particularmente, los análisis de diseño mecánico se realizaron mediante MEF. La técnica aplicada en la experimentación fue por comparación, empleando un acelerómetro patrón y un dispositivo bajo prueba; la gestión de las señales se realizó programando en Labview. El 27.8% de ensayos fluctuaron en un intervalo de 35 a 50 km/s2 con población de cincuenta disparos atenuados

Investigation of enhanced thermal properties in NiO-based nanofluids for concentrating solar power applications: A molecular dynamics and experimental analysis

Nanofluids could be a promising alternative to the typical heat transfer fluids (HTF) used in concentrating solar power. This study analyses nanofluids based on a typical HTF for concentrating solar power (CSP) applications and NiO nanoparticles. The optimum nanoparticle concentration was determined by analysing the stability of the nanofluids. Some of their properties, such as density, viscosity, isobaric specific heat and thermal con- ductivity, were characterized to evaluate their performance. Their thermal conductivity increased by up to 96% and the heat transfer coefficient by 50%. Molecular dynamics calculations were performed to explain from a molecular perspective how the presence of equal proportions of two surfactants, benzalkonium chloride (BAC) and 1-Octadecanethiol (ODT), enhanced the thermal properties of the NiO nanofluid. The isobaric specific heat and thermal conductivity values followed the same experimental tendency. The analysis of the radial distribu- tion functions (RDFs) and spatial distribution functions (SDFs) revealed an inner layer of base fluid and sur- factant molecules around the NiO cell. This first layer contained BAC molecules at all the temperatures, while ODT was only incorporated at higher temperatures. The exchange of surfactant and base fluid molecules around the NiO as the temperature increases may play an important role in the enhancement of the thermal properties

Effect of hydrogen bonding and complexation with metal ions on the fluorescence of luotonin A

Fluorescence characteristics of a biologically active natural alkaloid, luotonin A (LuA), were studied by steady-state and time-resolved spectroscopic methods. The rate constant of the radiationless deactivation from the singlet-excited state diminished by more than one order of magnitude when the solvent polarity was changed from toluene to water. Dual emission was found in polyfluorinated alcohols of large hydrogen bond donating ability due to photoinitiated proton displacement along the hydrogen bond. In CH 2Cl2, LuA produced both 1:1 and 1:2 hydrogen-bonded complexes with hexafluoro-2-propanol (HFIP) in the ground state. Photoexcitation of the 1:2 complex led to protonated LuA, whose fluorescence appeared at a long wavelength. LuA served as a bidentate ligand forming 1:1 complexes with metal ions in acetonitrile. The stability of the complexes diminished in the series of Cd2+ > Zn2+ > Ag+, and upon competitive binding of water to the metal cations. The effect of chelate formation on the fluorescent properties was revealed. © 2013 The Royal Society of Chemistry and Owner Societies

MoS2 nanosheets vs nanowires: preparation and theoretical study of highly stable and efficient nanofluids for Concentrating Solar Power

The nano-colloidal suspension of nanomaterials in a base fluid, typically named a nanofluid, is a promising system that shows interesting properties, such as those related to heat transfer processes. Obtaining nanofluids with high stability is a priority challenge for this kind of system. So, a rationalization of the preparation of nanofluids is clearly needed. Thus, this study presents a methodology based on liquid phase exfoliation that makes it possible to prepare stable nanofluids and control the morphology of the nanostructures, which is defined by the surfactant used. Two stable nanofluids were prepared based on MoS2 nanosheets and MoS2 nanowires and a typical heat transfer fluid (HTF) used in high temperature applications. Periodic-Density Functional Theory (periodic-DFT) calculations were performed to rationalize why different nanostructures were obtained according to the surfactant used. Finally, enhancements in thermal properties were found, being up to 57% for thermal conductivity and up to 7.5% for isobaric specific heat. Therefore, these nanofluids are a promising alternative to the typical HTF used, which is a eutectic mixture of biphenyl and diphenyl oxide. Also, to our knowledge, controlling the nanostructures obtained and the rationalization of the methodology for the preparation of stable nanofluids is reported for the first time. This leads to highly stable nanofluids with improved thermal properties, promising for application in concentrating solar power