153 research outputs found

    Microscopic mechanism of water diffusion in glucose glasses

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    The preservation of biomaterials depends critically on the mobility of water in the glassy state, manifested as a secondary beta relaxation and diffusion. We use coarse grain simulations to elucidate the molecular mechanism underlying the relaxations for water-glucose glass, finding two pathways for water diffusion: (i) water jumps into neighbor water positions (linking to water structure), and (ii) water jumps into glucose positions (coupling to glucose rotation). This work suggests strategies for enhancing preservation by stiffening the segmental motions of the carbohydrates

    Tuning of tetrahedrality in a silicon potential yields a series of monatomic (metal-like) glassformers of very high fragility

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    We obtain monatomic glass formers in simulations by modifying the tetrahedral character in a silicon potential to explore a triple point zone between potentials favoring diamond (dc) and bcc crystals. dc crystallization is always preceded by a polyamorphic transformation of the liquid, and is frustrated when the Kauzmann temperature of the high temperature liquid intersects the liquid-liquid coexistence line. The glass forming liquids are extraordinarily fragile. Our results suggest that Si and Ge liquids may be vitrified at a pressure close to the diamond-beta-tin-liquid triple point.Comment: 12 pages, including 3 figures. This revised version covers the same as the original submission plus a discussion of the effect of the polyamorphic transformation on the glass formation ability of the tetrahedral liquids studie

    M3B: A Coarse Grain Force Field for Molecular Simulations of Malto-Oligosaccharides and Their Water Mixtures

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    We derive a chemically realistic coarse grain model and force field for the simulation of malto-oligosaccharides (α(1→4) d-glucans) and their aqueous mixtures. This coarse grain model for carbohydrates (denoted M3B) represents each glucose monomer by three beads while describing the water molecule as a single particle. M3B includes no charges or hydrogen-bonding terms, using only two-body Morse functions to describe long-range forces. The configurations obtained with the M3B model map uniquely and quickly back to a full atomistic description. M3B was parametrized to fit the results from atomistic simulations for the gas phase and amorphous bulk phase of sugars over a wide range of pressures. In particular, we required that the M3B force field provide an accurate representation of such quantities as excluded volume interactions and the distribution of torsional configurations about the intermonomer bonds. We find that M3B leads to a helical structure for polysaccharide chains and predicts left-handed helices to be more stable than right-handed ones, in agreement with the experiments. We find that parallel and antiparallel double-helical bulk structures of malto-oligosaccharides are feasible and of similar energy. The M3B model leads to a glass transition temperature (T_g) for glucose of 296 K in good agreement with experiment (304 K) and a T_g for 12 wt % water−glucose mixtures of 239 K in good agreement with experiment (240 K). These results suggest that these characteristic physical properties of carbohydrates can be described well without the use of explicit hydrogen bonds or electrostatics and also without introducing explicit directional forces in the nonbonded interactions. Molecular dynamics (MD) simulations with M3B are ∌7000 times faster than fully flexible atomistic simulations, making it practical to study large systems for long times. We expect that M3B will be of use for the study of the structure and dynamics of complex syrups and supercooled carbohydrates solutions

    Fluorinated Imidazoles as Proton Carriers for Water-Free Fuel Cell Membranes

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    We propose an alternative new material (2,4,5-trifluoroimidazole impregnated Nafion) for use as a high-temperature, water-free membrane for proton-exchange membrane fuel cells. This material has been tested computationally using molecular dynamics and quantum mechanics techniques, leading to an estimated conductivity of ∌0.06 S/cm at 177 °C. This material overcomes the weakness of the imidazole-impregnated membranes, i.e., the poisoning of the Pt electrode. We find that 2,4,5-trifluoroimidazole binds weakly to platinum surfaces, so poisoning is not expected

    Long-term changes in phytoplankton phenology and community structure in the BahĂ­a Blanca Estuary, Argentina

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    The phytoplankton of the Bahía Blanca Estuary, Argentina, has been surveyed since 1978. Chlorophyll a, phytoplankton abundance, species composition and physico-chemical variables have been fortnightly recorded. From 1978 to 2002, a single winter–early spring diatom bloom has dominated the main pattern of phytoplankton interannual variability. Such pattern showed noticeable changes since 2006: the absence of the typical winter bloom and changes in phenology, together with the replacement of the dominant blooming species, i.e. Thalassiosira curviseriata, and the appearance of different blooming species, i.e. Cyclotella sp. and Thalassiosira minima. The new pattern showed relatively short-lived diatom blooms that spread throughout the year. In addition, shifts in the phytoplankton size structure toward small-sized diatoms, including the replacement of relatively large Thalassiosira spp. by small Cyclotella species and Chaetoceros species have been noticed. The changes in the phenology and composition of the phytoplankton are mainly attributed to warmer winters and the extremely dry weather conditions evidenced in recent years in the Bahía Blanca area. Changing climate has modified the hydrological features in the inner part of the estuary (i.e. higher temperatures and salinities) and potentially triggered the reorganization of the phytoplankton community. This long-term study provides evidence on species-specific and structural changes at the bottom of the pelagic food web likely related to the recent hydroclimatic conditions in a temperature estuary of the southwestern Atlantic

    Characterization of egg yolk immunoglobulin (IgY) against enterotoxigenic Escherichia coli and evaluation of its effects on bovine intestinal cells

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    Escherichia coli (ETEC) infection is common in calves. Egg yolk antibodies (IgY) have been used to treat gastrointestinal infectious diseases. This study aimed to characterize IgY against bovine ETEC and to evaluate its effects on bovine intestinal cell culture challenged with a bovine ETEC strain. IgY was isolated from the egg yolks of hens immunized with ETEC. The characteristics of IgY were determined by Bradford, ELISA, gel electrophoresis and immunoblotting. Significant differences in anti-ETEC activity between anti-ETEC IgY and non-specific IgY were found in lyophilized fractions. In the bacterial growth assay, anti-ETEC IgY (40 mg/mL) showed growth inhibition of ETEC after 2 h of incubation (p<0.05). The difference in bacterial growth between anti-ETEC IgY and non-specific IgY groups was 0.51 log CFU/ml after an 8 h incubation (p<0.05). The bacterial adhesion assay indicated that anti-ETEC IgY (40 mg/ml) significantly decreased the adhesion of ETEC to bovine intestinal epithelial cells within 4 h (about 1.36 log units compared with the control group; p<0.05). This study demonstrates that anti-ETEC IgY inhibits the growth and adherence of ETEC to bovine intestinal cells and is a potential alternative to traditional treatments of infections.Fil: Bellingeri, Romina Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal; ArgentinaFil: Busso, Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal; ArgentinaFil: Alustiza, Fabrisio Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Picco, Natalia Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal; ArgentinaFil: Molinero, Daniela Paola. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Genética y Mutagenesis Ambiental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Grosso, Maria Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal. Laboratorio de Radioisótopos; ArgentinaFil: Motta, Carlos. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Vivas, Adriana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Anatomía Animal; Argentin

    Electrochemically Generated Nanobubbles: Invariance of the Current with Respect to Electrode Size and Potential

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    Gas-producing electrochemical reactions are key to energy conversion and generation technologies. Bubble formation dramatically decreases gas-production rates on nanoelectrodes, by confining the reaction to the electrode boundary. This results in the collapse of the current to a stationary value independent of the potential. Startlingly, these residual currents also appear to be insensitive to the nanoelectrode diameter in the 5 to 500 nm range. These results are counterintuitive, as it may be expected that the current be proportional to the circumference of the electrode, i.e., the length of the three-phase line where the reaction occurs. Here, we use molecular simulations and a kinetic model to elucidate the origin of current insensitivity with respect to the potential and establish its relationship to the size of nanoelectrodes. We provide critical insights for the design and operation of nanoscale electrochemical devices and demonstrate that nanoelectrode arrays maximize conversion rates compared to macroscopic electrodes with same total area.Fil: Gadea, Esteban David. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a; ArgentinaFil: PĂ©rez Sirkin, Yamila AnahĂ­. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a; ArgentinaFil: Molinero, Valeria. University of Utah; Estados UnidosFil: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de QuĂ­mica, FĂ­sica de los Materiales, Medioambiente y EnergĂ­a; Argentin
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