Selección de “indicadores microbiológicos de calidad del suelo” como tópico generativo para la enseñanza de Microbiología Agrícola en la FCAyF

Se presenta una innovación en el área de Microbiología Agrícola de las Carreras de Ingeniería Agronómica y Forestal, propiciando el “uso de indicadores microbiológicos de calidad del suelo” como “tópico generativo” en el marco de “la enseñanza para la comprensión”. Con la aplicación de esta metodología, se busca concientizar a los alumnos sobre la importancia de la conservación del recurso suelo y su biodiversidad, así como ponerlos en contacto con problemáticas hipotéticas de su futura actividad laboral. Se definieron las Metas de Comprensión, seleccionando los indicadores microbiológicos: determinación del recuento de flora total y grupos funcionales (celulolíticos, amonificadores, nitrificadores), actividad global del suelo empleando técnicas como la evaluación de la respiración y la deshidrogenasa. En base a los datos analizados se observa que la selección de este tópico generativo resultó adecuada para el desarrollo e integración de los contenidos del curso y permitió fomentar en los alumnos una actitud participativa en el proceso de enseñanza-aprendizaje.Eje temático 2: Los cambios e innovaciones en los procesos de formación\na - Alternativas didácticas y experiencias de renovación de la enseñanz

Photochemical reaction mechanisms and kinetics with molecular nanocrystals: surface quenching of triplet benzophenone nanocrystals

Organic molecular nanocrystals suspended in water are useful when studying reactions that occur in the solid state because they retain not only the reactive and supramolecular properties of bulk crystals, but are also amenable to transmission spectroscopy. Having previously studied the triplet state of benzophenone nanocrystals by laser flash photolysis transmission spectroscopy, we now report nanosecond experiments in the presence of several possible quenchers: anionic and cationic surfactants, dissolved oxygen, and as a function of solvent deuteration (H2O and D2O). After finding these to have no effect, several anionic quenchers (IS, BrS, and NS3) were tested by Stern-Volmer analysis. Significant correlation between the quenching rates in solution and in nanocrystals suggests that the electronic excitation is accessible to quenchers at the surface. © 2010 John Wiley & Sons, Ltd.Fil: Simoncelli, Sabrina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of California at Los Angeles; Estados Unidos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Kuzmanich, Gregory. University of California at Los Angeles; Estados UnidosFil: Gard, Matthew N.. University of California at Los Angeles; Estados UnidosFil: Garcia Garibay, Miguel A.. University of California at Los Angeles; Estados Unido

Excited state kinetics in crystalline solids: Self-quenching in nanocrystals of 4,4′-disubstituted benzophenone triplets occurs by a reductive quenching mechanism

We report an efficient triplet state self-quenching mechanism in crystals of eight benzophenones, which included the parent structure (1), six 4,4′-disubstituted compounds with NH 2 (2), NMe 2 (3), OH (4), OMe (5), COOH (6), and COOMe (7), and benzophenone-3,3′,4, 4′-tetracarboxylic dianhydride (8). Self-quenching effects were determined by measuring their triplet-triplet lifetimes and spectra using femtosecond and nanosecond transient absorption measurements with nanocrystalline suspensions. When possible, triplet lifetimes were confirmed by measuring the phosphorescence lifetimes and with the help of diffusion-limited quenching with iodide ions. We were surprised to discover that the triplet lifetimes of substituted benzophenones in crystals vary over 9 orders of magnitude from ca. 62 ps to 1 ms. In contrast to nanocrystalline suspensions, the lifetimes in solution only vary over 3 orders of magnitude (1-1000 μs). Analysis of the rate constants of quenching show that the more electron-rich benzophenones are the most efficiently deactivated such that there is an excellent correlation, ρ = -2.85, between the triplet quenching rate constants and the Hammet θ + values for the 4,4′ substituents. Several crystal structures indicate the existence of near-neighbor arrangements that deviate from the proposed ideal for "n-type" quenching, suggesting that charge transfer quenching is mediated by a relatively loose arrangement. © 2011 American Chemical Society.Fil: Kuzmanich, Gregory. University of California at Los Angeles; Estados UnidosFil: Simoncelli, Sabrina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Gard, Matthew N.. University of California at Los Angeles; Estados UnidosFil: Spänig, Fabian. Friedrich Alexander Universität Erlangen; AlemaniaFil: Henderson, Bryana L.. University of California at Los Angeles; Estados UnidosFil: Guldi, Dirk M.. Friedrich Alexander Universität Erlangen; AlemaniaFil: Garcia Garibay, Miguel A.. University of California at Los Angeles; Estados Unido

Excited State Kinetics in Crystalline Solids: Self-Quenching in Nanocrystals of 4,4′-Disubstituted Benzophenone Triplets Occurs by a Reductive Quenching Mechanism

We report an efficient triplet state self-quenching mechanism in crystals of eight benzophenones, which included the parent structure (<b>1</b>), six 4,4′-disubstituted compounds with NH₂ (<b>2</b>), NMe₂ (<b>3</b>), OH (<b>4</b>), OMe (<b>5</b>), COOH (<b>6</b>), and COOMe (<b>7</b>), and benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (<b>8</b>). Self-quenching effects were determined by measuring their triplet–triplet lifetimes and spectra using femtosecond and nanosecond transient absorption measurements with nanocrystalline suspensions. When possible, triplet lifetimes were confirmed by measuring the phosphorescence lifetimes and with the help of diffusion-limited quenching with iodide ions. We were surprised to discover that the triplet lifetimes of substituted benzophenones in crystals vary over 9 orders of magnitude from ca. 62 ps to 1 ms. In contrast to nanocrystalline suspensions, the lifetimes in solution only vary over 3 orders of magnitude (1–1000 μs). Analysis of the rate constants of quenching show that the more electron-rich benzophenones are the most efficiently deactivated such that there is an excellent correlation, ρ = −2.85, between the triplet quenching rate constants and the Hammet σ⁺ values for the 4,4′ substituents. Several crystal structures indicate the existence of near-neighbor arrangements that deviate from the proposed ideal for “n-type” quenching, suggesting that charge transfer quenching is mediated by a relatively loose arrangement

Cruciforms’ Polarized Emission Confirms Disjoint Molecular Orbitals and Excited States

Steady-state and time-resolved polarized spectroscopy studies reveal that electronic excitation to the third excited state of 1,4-distyryl-2,5-bis(arylethynyl)benzene cruciforms results in fluorescence emission that is shifted an angle of ca. 60°. This result is consistent with quantum chemical calculations of the lowest electronic excited states and their transition dipole moments. The shift originates from the disjointed nature of the occupied molecular orbitals being localized on the different branches of the cruciforms