Transport properties of chemically synthesized polypyrrole thin films

The electronic transport in polypyrrole thin films synthesized chemically from the vapor phase is studied as a function of temperature as well as of electric and magnetic fields. We find distinct differences in comparison to the behavior of both polypyrrole films prepared by electrochemical growth as well as of the bulk films obtained from conventional chemical synthesis. For small electric fields F, a transition from Efros-Shklovskii variable range hopping to Arrhenius activated transport is observed at 30 K. High electric fields induce short range hopping. The characteristic hopping distance is found to be proportional to F^(-1/2). The magnetoresistance R(B) is independent of F below a critical magnetic field, above which F counteracts the magnetic field induced localization.Comment: 6 pages, 5 figure

Towards deterministically controlled InGaAs/GaAs lateral quantum dot molecules

We report on the fabrication, detailed characterization and modeling of lateral InGaAs quantum dot molecules (QDMs) embedded in a GaAs matrix and we discuss strategies to fully control their spatial configuration and electronic properties. The three-dimensional morphology of encapsulated QDMs was revealed by selective wet chemical etching of the GaAs top capping layer and subsequent imaging by atomic force microscopy (AFM). The AFM investigation showed that different overgrowth procedures have a profound consequence on the QDM height and shape. QDMs partially capped and annealed in situ for micro- photoluminescence spectroscopy consist of shallow but well-defined quantum dots (QDs) in contrast to misleading results usually provided by surface morphology measurements when they are buried by a thin GaAs layer. This uncapping approach is crucial for determining the QDM structural parameters, which are required for modeling the system. A single-band effective-mass approximation is employed to calculate the confined electron and heavy-hole energy levels, taking the geometry and structural information extracted from the uncapping experiments as inputs. The calculated transition energy of the single QDM shows good agreement with the experimentally observed values. By decreasing the edge-to-edge distance between the two QDs within a QDM, a splitting of the electron (hole) wavefunction into symmetric and antisymmetric states is observed, indicating the presence of lateral coupling. Site control of such lateral QDMs obtained by growth on a pre-patterned substrate, combined with a technology to fabricate gate structures at well-defined positions with respect to the QDMs, could lead to deterministically controlled devices based on QDMs. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Conservación de alimentos orgánicos de alto contenido lipídico mediante tecnologías de biomateriales nano y microestructurados

El presente proyecto intentó reunir conocimientos científicos que permitan el desarrollo de tecnologías basadas en biomateriales para preservar la calidad e inocuidad de alimentos orgánicos de alto contenido lipídico de la región de Entre Ríos, por ejemplo, nuez pecán. Dichas tecnologías implicaron la obtención de nano y microestructuras capaces de vehiculizar compuestos bioactivos provenientes de aceites esenciales y su incorporación en matrices alimenticias por espolvoreo. Los objetivos específicos que se plantearon fueron los siguientes: Obtención de nano y microestructuras biopoliméricas. Caracterización y obtención de polvos de nano y microestructuras biopoliméricas. Evaluación del impacto de la aplicación de nano y microestructuras por espolvoreo sobre la oxidación lipídica de nuez pecán.      El conocimiento adquirido podria promover el desarrollo de tecnologías innovadoras para la conservación de alimentos orgánicos de alto contenido lipídico y su extensión para la conservación de otros alimentos. Al mismo tiempo, se espera favorecer al sector agroindustrial implicado mediante la valorización de sus productos y su empleo en aplicaciones de creciente interés a nivel nacional e internacional.                                                                                                                                                                  ARK/CAICYT: http://id.caicyt.gov.ar/ark:/s22504559/vwu2gmaf

Establishing broad generality of DNA catalysts for site-specific hydrolysis of single-stranded DNA

We recently reported that a DNA catalyst (deoxyribozyme) can site-specifically hydrolyze DNA on the minutes time scale. Sequence specificity is provided by Watson-Crick base pairing between the DNA substrate and two oligonucleotide binding arms that flank the 40-nt catalytic region of the deoxyribozyme. The DNA catalyst from our recent in vitro selection effort, 10MD5, can cleave a single-stranded DNA substrate sequence with the aid of Zn2+ and Mn2+ cofactors, as long as the substrate cleavage site encompasses the four particular nucleotides ATG^T. Thus, 10MD5 can cleave only 1 out of every 256 (44) arbitrarily chosen DNA sites, which is rather poor substrate sequence tolerance. In this study, we demonstrated substantially broader generality of deoxyribozymes for site-specific DNA hydrolysis. New selection experiments were performed, revealing the optimality of presenting only one or two unpaired DNA substrate nucleotides to the N40 DNA catalytic region. Comprehensive selections were then performed, including in some cases a key selection pressure to cleave the substrate at a predetermined site. These efforts led to identification of numerous new DNA-hydrolyzing deoxyribozymes, many of which require merely two particular nucleotide identities at the cleavage site (e.g. T^G), while retaining Watson-Crick sequence generality beyond those nucleotides along with useful cleavage rates. These findings establish experimentally that broadly sequence-tolerant and site-specific deoxyribozymes are readily identified for hydrolysis of single-stranded DNA

Acrylamide formation and quality properties of chitosan based batter formulations

[EN] The potential of chitosan to mitigate acrylamide formation has been already demonstrated. The two main objectives of this study were: 1) to select the most adequate degree of deacetylation (DD) and molecular weight (Mw) of chitosan based on acrylamide mitigation criteria and 2) to evaluate the influence of including chitosan in batter formulations on some important technological parameters of raw batters (flow behavior and water retention capacity) and on some quality properties of fried batters (oil uptake, color and texture). Results in model systems showed that chitosans with higher deacetylation degree (86.5 and 92.8%) achieved a decrease of acrylamide between 44 and 81%, depending on reaction time, compared to the control (without chitosan). Furthermore, acid hydrolysis process of chitosan was found to negatively affect its inhibitory effect on acrylamide formation independently of the molecular weight. Raw chitosan based batter formulations presented higher consistency and water retention capacity than the control; chitosan addition to batters reduced the hardening of the fried samples during the post-frying cooling period. No significant differences in water loss were observed between batters with or without added chitosan; however, chitosan-batter formulations showed lower oil uptake during frying as compared to control samples.The authors thank the gs1:Universitat Politecnica de Valencia for the PhD scholarship given to Mariola Sansano Tomas.Sansano Tomás, M.; Castelló Gómez, ML.; Heredia Gutiérrez, AB.; Andrés Grau, AM. (2016). Acrylamide formation and quality properties of chitosan based batter formulations. Food Hydrocolloids. 66:1-7. doi:10.1016/j.foodhyd.2016.10.019S176