Physical activation of graphene: An effective, simple and clean procedure for obtaining microporous graphene for high-performance Li/S batteries

Graphene nanosheets are a promising scaffold to accommodate S for achieving high performanceLi/S battery. Nanosheet activation is used as a viable strategy to induce a micropore system and further improve the battery performance. Accordingly, chemical activation methods dominate despite the need of multiple stages, which slow down the process in addition to making them tiresome. Here, a three-dimensional (3D)N-doped graphene specimen was physically activated with CO2, a clean and single step process, and used for the preparation of a sulfur composite (A-3DNG/S). The A-3DNG/S composite exhibited outstanding electrochemical properties such as an excellent rate capability (1,000 mAh·g─1at 2C), high reversible capacity and cycling stability (average capacity ~ 800 mAh·g─1at 1C after 200cycles), values which exceed those measured in chemically activated graphene. Therefore, these results support the use of physical activation as a simple and efficient alternative to improve the performance of carbons as an S host for high-performance Li-S batteries

Highly graphitized carbon nanosheets with embedded Ni nanocrystals as anode for Li-ion batteries

A C/Ni composite was prepared via thermal decomposition of a nickel oleate complex at 700 °C, yielding disperse Ni nanocrystals with an average size of 20 nm, encapsulated by carbon nanosheets as deduced from transmission electron microscopy (TEM) images and confirmed from X-ray photoelectron spectroscopy (XPS). Furthermore, the X-ray diffraction pattern revealed a good ordering of the carbon layers, forced by the Ni encapsulation to adopt a bending structure. Considering the close interaction between the graphitized framework and the metallic nanoparticles we have studied the properties of the composite as an anode for Li-ion batteries. Compared with other nanostructured synthetic carbons, this carbon composite has a low voltage hysteresis and a modest irreversible capacity value, properties that play a significant role in its behaviour as electrodes in full cell configuration. At moderate rate values, 0.25 C, the electrode delivers an average capacity value around 723 mAh·g−1 on cycling, among the highest values so far reported for this carbon type. At higher rate values, 1 C, the average capacity values delivered by the cell on cycling decrease, around 205 mAh·g−1, but it maintains good capacity retention, a coulombic efficiency close to 100% after the first cycles and recovery of the capacity values when the rate is restored from 3 to 0.1 C

Virtual Design in Organic Electronics: Screening of a Large Set of 1,4-Bis(phenylethynyl)benzene Derivatives as Molecular Semiconductors

In this work, we have theoretically studied the electronic properties of a large series of 1,4-bis(phenylethynyl)benzene derivatives, with the chemical formula Y–C≡C–X–C≡C–Y, with X and Y being aromatic rings and chosen to act as donor and acceptor moieties. Employing state-of-the-art DFT calculations, we analyzed a set of relevant electronic properties related to the optoelectronic and semiconductor character of these systems, namely, molecular and energy levels, electron affinity, ionization potential, reorganization energy, and electronic coupling between neighboring molecules forming dimers, obtained after evaluation of binding energy landscapes. The latter energy magnitude is needed to disclose first the favored intermolecular interactions (i.e., the lowest binding energy) to concomitantly estimate next the charge transport rates. The systematic screening performed allowed us to anticipate the possible use of some of these derivatives as p-type, n-type, or even ambipolar organic molecular semiconductors.M.M. thanks the E2TP CYTEMA-SANTANDER program for financial support. Likewise, the authors are grateful for the project DIPUAB-16-GARZONRUIZ financed jointly by the “Diputación de Albacete” and the “Universidad de Castilla-La Mancha”

Pilas de combustible de Membrana polimérica

En este trabajo revisamos brevemente las pilas de combustible poliméricas (PEM) basadas en membranas de intercambio protónico y que constituyen la tecnología idónea de pilas de combustible de baja temperatura, y por tanto las más adecuadas para aplicación en transporte. Revisaremos los materiales que las componen pero tambíen los desarrollos necesarios para su implantación definitiva en un mercado inclemente con las tecnologías caras, por límpias que sean

The characterization of Escherichia coli CpdB as a recombinantpProtein reveals that, besides having the expected 3´-nucleotidase and 2´,3´-cyclic mononucleotide phosphodiesterase activities, it is also active as cyclic dinucleotide phosphodiesterase

Endogenous cyclic diadenylate phosphodiesterase activity was accidentally detected in lysates of Escherichia coli BL21. Since this kind of activity is uncommon in Gram-negative bacteria, its identification was undertaken. After partial purification and analysis by denaturing gel electrophoresis, renatured activity correlated with a protein identified by fingerprinting as CpdB (cpdB gene product), which is annotated as 3´-nucleotidase / 2´,3´- cyclicmononucleotide phosphodiesterase, and it is synthesized as a precursor protein with a signal sequence removable upon export to the periplasm. It has never been studied as a recombinant protein. The coding sequence of mature CpdB was cloned and expressed as a GST fusion protein. The study of the purified recombinant protein, separated from GST, confirmed CpdB annotation. The assay of catalytic efficiencies (kcat/Km) for a large substrate set revealed novel CpdB features, including very high efficiencies for 3´-AMP and 2´,3´- cyclic mononucleotides, and previously unknown activities on cyclic and linear dinucleotides. The catalytic efficiencies of the latter activities, though low in relative terms when compared to the major ones, are far from negligible. Actually, they are perfectly comparable to those of the ‘average’ enzyme and the known, bona fide cyclic dinucleotide phosphodiesterases. On the other hand, CpdB differs from these enzymes in its extracytoplasmic location and in the absence of EAL, HD and DHH domains. Instead, it contains the domains of the 5´-nucleotidase family pertaining to the metallophosphoesterase superfamily, although CpdB lacks 5´-nucleotidase activity. The possibility that the extracytoplasmic activity of CpdB on cyclic dinucleotides could have physiological meaning is discussed.Trabajo financiado por: Junta de Extremadura y Fondos FEDER. Ayudas GR10133 y GR15143 Donación privada para María Jesús Costas Vázquez. Contrato 2015/00481/001peerReviewe

Application of crosslinked polybenzimidazole-poly(Vinyl benzyl chloride) anion exchange membranes in direct ethanol fuel cells

Crosslinked membranes have been synthesized by a casting process using polybenzimidazole (PBI) and poly(vinyl benzyl chloride) (PVBC). The membranes were quaternized with 1,4-diazabicyclo[2.2.2]octane (DABCO) to obtain fixed positive quaternary ammonium groups. XPS analysis has showed insights into the changes from crosslinked to quaternized membranes, demonstrating that the crosslinking reaction and the incorporation of DABCO have occurred, while the13C-NMR corroborates the reaction of DABCO with PVBC only by one nitrogen atom. Mechanical properties were evaluated, obtaining maximum stress values around 72 MPa and 40 MPa for crosslinked and quaternized membranes, respectively. Resistance to oxidative media was also satisfactory and the membranes were evaluated in single direct ethanol fuel cell. PBI-c-PVBC/OH 1:2 membrane obtained 66 mW cm−2 peak power density, 25% higher than commercial PBI membranes, using 0.5 bar backpressure of pure O2 in the cathode and 1 mL min−1 KOH 2M EtOH 2 M aqueous solution in the anode. When the pressure was increased, the best performance was obtained by the same membrane, reaching 70 mW cm−2 peak power density at 2 bar O2 backpressure. Based on the characterization and single cell performance, PBI-c-PVBC/OH membranes are considered promising candidates as anion exchange electrolytes for direct ethanol fuel cells.Fil: Herranz, Daniel. Universidad Autónoma de Madrid; EspañaFil: Coppola, Roxana Elisabeth. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Escudero Cid, Ricardo. Universidad Autónoma de Madrid; EspañaFil: Ochoa Romero, Kerly. Universidad Autónoma de Madrid; EspañaFil: D'accorso, Norma Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Pérez Flores, Juan Carlos. Universidad de Castilla-La Mancha; EspañaFil: Canales Vázquez, Jesús. Universidad de Castilla-La Mancha; EspañaFil: Palacio, Carlos. Universidad Autónoma de Madrid; EspañaFil: Abuin, Graciela Carmen. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Ocón, Pilar. Universidad Autónoma de Madrid; Españ

Molecular bases of catalysis and ADP-ribose preference of human Mn2+-dependent ADP-ribose/CDP-alcohol diphosphatase and conversion by mutagenesis to a preferential cyclic ADP-ribose phosphohydrolase

Entre las fosfatasas métalo-dependientes, ADP-ribosa/CDP-alcohol diphosphatases forman una familia de proteínas (ADPRibase-Mn-like) principalmente restringida, en eucariotas, vertebrados y plantas, con expresión preferencial, al menos en roedores, en células inmunológicas. La rata y el pez cebra, el único Ribase-Mn ADP bioquímicamente estudiados, son ADP-ribosa phosphohydrolases y algo menos eficiente, de CDP-alcoholes y 2',3'-cAMP. Además, la rata, pero no el pez cebra, muestra una única enzima con actividad ADP-ribosa phosphohydrolytic cíclica. La base molecular de tal especificidad es desconocida. Las ADPRibase-Mn de humanos mostraron actividades similares, incluyendo ADP-ribosa phosphohydrolase cíclica, lo que parece común a los mamíferos Ribase-Mn ADP. Acoplamiento del sustrato en un modelo de homología de ADPRibase-Mn de humanos sugiere posibles interacciones de ADP-ribosa con siete residuos ubicado, con una sola excepción (Cys253), ya sea dentro de la metalo-fosfatasas dependientes de la firma (Gln27, Asn110, Su111), o en regiones estructurales exclusivos de la familia ADPRibase-Mn: s2s3 (PHE37 y Arg43) y h7h8 (Phe210), alrededor de la entrada del sitio activo. Se construyeron mutantes y parámetros cinéticos para ADP-ribosa, CDP-colina, 2',3'-cAMP y cíclica de ADP-ribosa fueron determinadas. Phe37 fue necesaria para ADP-ribosa preferencia sin efecto catalítico, según lo indicado por el aumento de la ADP-ribosa Km y kcat invariable de F37A-ADPRibase-Mn Km, mientras que los valores para los otros sustratos apenas se vieron afectadas. Arg43 era esencial para la catálisis como indicado por la drástica pérdida de eficacia demostrada por R43A-ADPRibase-Mn. Inesperadamente, Cys253 obstaculizaba para cADPR phosphohydrolase, según lo indicado por las diez veces la ganancia de eficiencia de C253A-ADPRibase-Mn con ADP-ribosa cíclica. Esto permitió el diseño de un mutante triple (F37A L196F C253A) para que ADP-ribosa cíclica era el mejor sustrato, con una eficiencia catalítica de 3,5'104 M-1s-1 versus 4'103 M-1s-1 del tipo salvaje.Among metallo-dependent phosphatases, ADP-ribose/CDP-alcohol diphosphatases form a protein family (ADPRibase-Mn-like) mainly restricted, in eukaryotes, to vertebrates and plants, with preferential expression, at least in rodents, in immune cells. Rat and zebrafish ADPRibase-Mn, the only biochemically studied, are phosphohydrolases of ADP-ribose and, somewhat less efficiently, of CDP-alcohols and 2´,3´-cAMP. Furthermore, the rat but not the zebrafish enzyme displays a unique phosphohydrolytic activity on cyclic ADP-ribose. The molecular basis of such specificity is unknown. Human ADPRibase-Mn showed similar activities, including cyclic ADP-ribose phosphohydrolase, which seems thus common to mammalian ADPRibase-Mn. Substrate docking on a homology model of human ADPRibase-Mn suggested possible interactions of ADP-ribose with seven residues located, with one exception (Cys253), either within the metallo-dependent phosphatases signature (Gln27, Asn110, His111), or in unique structural regions of the ADPRibase-Mn family: s2s3 (Phe37 and Arg43) and h7h8 (Phe210), around the active site entrance. Mutants were constructed, and kinetic parameters for ADP-ribose, CDP-choline, 2´,3´-cAMP and cyclic ADP-ribose were determined. Phe37 was needed for ADP-ribose preference without catalytic effect, as indicated by the increased ADP-ribose Km and unchanged kcat of F37A-ADPRibase-Mn, while the Km values for the other substrates were little affected. Arg43 was essential for catalysis as indicated by the drastic efficiency loss shown by R43A-ADPRibase-Mn. Unexpectedly, Cys253 was hindering for cADPR phosphohydrolase, as indicated by the specific tenfold gain of efficiency of C253A-ADPRibase-Mn with cyclic ADP-ribose. This allowed the design of a triple mutant (F37A+L196F+C253A) for which cyclic ADP-ribose was the best substrate, with a catalytic efficiency of 3.5´104 M-1s-1 versus 4´103 M-1s-1 of the wild type.Trabajo patrocinado por: Ministerio de Ciencia e Innovación. Proyecto BFU2009-07296 (I+D+i) Junta de Extremadura. Proyecto GRU09135 y GR10133 Cofinanciación por el Fondo Europeo de Desarrollo Regional y Fondo Social EuropeopeerReviewe

Exchange Bias Optimization by Controlled Oxidation of Cobalt Nanoparticle Films Prepared by Sputter Gas Aggregation

Porous films of cobalt nanoparticles have been obtained by sputter gas aggregation and controllably oxidized by air annealing at 100 C for progressively longer times (up to more than 1400 h). The magnetic properties of the samples were monitored during the process, with a focus on the exchange bias field. Air annealing proves to be a convenient way to control the Co/CoO ratio in the samples, allowing the optimization of the exchange bias field to a value above 6 kOe at 5 K. The occurrence of the maximum in the exchange bias field is understood in terms of the density of CoO uncompensated spins and their degree of pinning, with the former reducing and the latter increasing upon the growth of a progressively thicker CoO shell. Vertical shifts exhibited in the magnetization loops are found to correlate qualitatively with the peak in the exchange bias field, while an increase in vertical shift observed for longer oxidation times may be explained by a growing fraction of almost completely oxidized particles. The presence of a hummingbird-like form in magnetization loops can be understood in terms of a combination of hard (biased) and soft (unbiased) components; however, the precise origin of the soft phase is as yet unresolved

Understanding the Driving Mechanisms of Enhanced Luminescence Emission of Oligo(styryl)benzenes and Tri(styryl)-s-triazine

This work is focused on unraveling the mechanisms responsible for the aggregation-induced enhanced emission and solid-state luminescence enhancement effects observed in star-shaped molecules based on 1,3,5-tris(styryl)- benzene and tri(styryl)-s-triazine cores. To achieve this, the photophysical properties of this set of molecules were analyzed in three states: free molecules, molecular aggregates in solution, and the solid state. Different spectroscopy and microscopy experiments and DFT calculations were conducted to scrutinize the causative mechanisms of the luminescence enhancement phenomenon observed in some experimental conditions. Enhanced luminescence emission was interpreted in the context of short- and long-range excitonic coupling mechanisms and the restriction of intramolecular vibrations. Additionally, we found that the formation of pstacking aggregates could block E/Z photoisomerization through torsional motions between phenylene rings in the excited state, and hence, enhancing the luminescence of the syste