Estudio de estabilidad de complejos atómicos en semiconductores del grupo IV mediante el modelo de Keating Anarmónico

Se presenta un estudio de energías de configuración de pequeños clusters de átomos de C, Ge y Sn en Si para posiciones sustitucionales, mediante el modelo de Keating anarmónico. Los resultados muestran en general tendencia a la nucleación excepto Cx en Si y una posible formación de estructuras complejas de 4 átomos en Si 158 - xGe C

Reductive activation and structural rearrangement in superoxide reductase: a combined infrared spectroscopic and computational study

Superoxide reductases (SOR) are a family of non-heme iron enzymes that limit oxidative stress by catalysing the reduction of superoxide to hydrogen peroxide and, thus, represent model systems for the detoxification of reactive oxygen species. In several enzymes of this type, reductive activation of the active site involves the reversible dissociation of a glutamate from the proposed substrate binding site at the iron. In this study we have employed IR spectroscopic and theoretical methods to gain insights into redox-linked structural changes of 1Fe-type superoxide reductases, focusing on the enzyme from the archaeon Ignicoccus hospitalis. Guided by crystal structure data and complemented by spectra calculation for an active site model, the main IR difference signals could be assigned. These signals reflect redox-induced structural changes in the first coordination sphere of the iron centre, adjacent loop and helical regions, and more remote β-sheets. By comparison with the spectra obtained for the E23A mutant of Ignicoccus hospitalis SOR, it is shown that glutamate E23 dissociates reversibly from the ferrous iron during reductive activation of the wild type enzyme. Moreover, this process is found to trigger a global conformational transition of the protein that is strictly dependent on the presence of E23. Similar concerted structural changes can be inferred from the IR spectra of related SORs such as that from Archaeoglobus fulgidus, indicating a widespread mechanism. A possible functional role of this process in terms of synergistic effects during reductive activation of the homotetrameric enzyme is proposed.DFG, EXC 314, Unifying Concepts in Catalysi

Reflectividad, transmisión y actividad fotoinducida del RNiO3 (r=Pr,Sm) en el infrarrojo

Con el fin de esclarecer el mecanismo responsable de la transición metal-aislador que experimentan RNiO₃, (R - Pr, Sm) a Tm.a ∼135K y ∼403K respectivamente, se ha estudiado con espectroscopia infrarroja la evolución con la temperatura de los espectros de reflectividad, transmisión y la actividad fotoinducida. Los espectros de reflectividad se ajustaron por medio de una simulación de la función dieléctrica mediante un modelo clásico de osciladores de Lorentz amortiguados a los que se agregó un término de Drude para describir el comportamiento del plasma. La conductividad óptica experimental así determinada ha sido analizada empleando la teoría de pequeños polarones de Heese v Reik. El análisis de los espectros de reflectividad y el excelente acuerdo hallado entre la teoría de pequeños polarones y los resultados experimentales nos ha permitido verificar la intensidad de la interacción electrón-fonón y así confirmar la participación determinante de fonones en las propiedades de transporte de RNi0₃ (R=Pr, Sm). De esta manera, la transición metal-aislador esta directamente relacionada con la localización a TM.A de electrones auto atrapados en entornos polarónicos.Centro de Química Inorgánic

A cryopreservation protocol for immature zygotic embryos of species of Ilex (Aquifoliaceae)

ABSTRACT: Tropical Ilex species have recalcitrant seeds. This work describes experiments demonstrating the feasibility of long-term conservation of Ilex brasiliensis, I. brevicuspis, I. dumosa, I. intergerrima, I. paraguariensis, I. pseudoboxus, I. taubertiana, and I. theezans through cryopreservation of zygotic rudimentary embryos at the heart developmental stage. The embryos were aseptically removed from the seeds and precultured (7 days) in the dark, at 27± 2ºC on solidified (0.8% agar) 1/4MS medium, [consisting of quarterstrength salts and vitamins o

Evolución del banco in vitro de germoplasma de mandioca (Manihot esculenta, Euphorbiaceae) de la Facultad de Ciencias Agrarias de la UNNE y del Instituto de Botánica del Nordeste (CONICET-UNNE) en tiempos prepandémicos y pandémicos por COVID-19

El funcionamiento normal de laboratorios de conservación de germoplasma vegetal involucra la realización de actividades numerosas y diversas, las cuales fueron afectadas por la pandemia causada por coronavirus de 2019 (COVID-19). El objetivo de esta comunicación es realizar una reseña de la evolución del banco de germoplasma in vitro de mandioca presente en la FCA-UNNE e IBONE (CONICET-UNNE) y dar a conocer las prácticas de manejo habituales y los procedimientos realizados para preservar con vida el material vegetal protegiendo la salud del personal involucrado antes y durante la pandemia por COVID-19. Docentes, investigadores, alumnos de grado y posgrado llevaron adelante, durante casi 40 años, la conservación in vitro de 56 cultivares de mandioca provenientes de diferentes países. Previamente a marzo del año 2020, el manejo del banco estaba centrado principalmente en la ejecución de actividades científico-tecnológicas para la conservación del material y la búsqueda de parámetros para establecer un orden de subcultivos. Decretado el Aislamiento Social, Preventivo y Obligatorio en Argentina, se continuó con las actividades de conservación aplicando las prácticas usuales y siguiendo las medidas sanitarias de orden político-institucionales implementadas. Para afrontar los nuevos escenarios sanitarios, se deberán ajustar metodologías que sean eficaces para mantener la viabilidad del material vegetal y prolongar el tiempo de conservación

Structural basis for the Pr-Pfr long-range signaling mechanism of a full-length bacterial phytochrome at the atomic level.

Phytochromes constitute a widespread photoreceptor family that typically interconverts between two photostates called Pr (red light–absorbing) and Pfr (far-red light–absorbing). The lack of full-length structures solved at the (near-)atomic level in both pure Pr and Pfr states leaves gaps in the structural mechanisms involved in the signal transmission pathways during the photoconversion. Here, we present the crystallographic structures of three versions from the plant pathogen Xanthomonas campestris virulence regulator XccBphP bacteriophytochrome, including two full-length proteins, in the Pr and Pfr states. The structures show a reorganization of the interaction networks within and around the chromophore-binding pocket, an α-helix/β-sheet tongue transition, and specific domain reorientations, along with interchanging kinks and breaks at the helical spine as a result of the photoswitching, which subsequently affect the quaternary assembly. These structural findings, combined with multidisciplinary studies, allow us to describe the signaling mechanism of a full-length bacterial phytochrome at the atomic level

Structural basis for the Pr-Pfr long-range signaling mechanism of a full-length bacterial phytochrome at the atomic level

Phytochromes constitute a widespread photoreceptor family that typically interconverts between two photostates called Pr (red light–absorbing) and Pfr (far-red light–absorbing). The lack of full-length structures solved at the (near-)atomic level in both pure Pr and Pfr states leaves gaps in the structural mechanisms involved in the signal transmission pathways during the photoconversion. Here, we present the crystallographic structures of three versions from the plant pathogen Xanthomonas campestris virulence regulator XccBphP bacteriophytochrome, including two full-length proteins, in the Pr and Pfr states. The structures show a reorganization of the interaction networks within and around the chromophore-binding pocket, an α-helix/β-sheet tongue transition, and specific domain reorientations, along with interchanging kinks and breaks at the helical spine as a result of the photoswitching, which subsequently affect the quaternary assembly. These structural findings, combined with multidisciplinary studies, allow us to describe the signaling mechanism of a full-length bacterial phytochrome at the atomic level.DFG, 221545957, SFB 1078: Proteinfunktion durch ProtonierungsdynamikEC/H2020/664726/EU/EMBL Interdisciplinary, International and Intersectorial Postdocs/EI3PO

Radical-SAM dependent nucleotide dehydratase (SAND), rectification of the names of an ancient iron-sulfur enzyme using NC-IUBMB recommendations

In 1789, the influential French chemist Antoine-Laurent Lavoisier described his view of science and its langague in his book Traité élémentaire de chimie. According to the Robert Kerr’s translation it states (Lavoisier, 1790): “As ideas are preserved and communicated by means of words, it necessarily follows that we cannot improve the language of any science without at the same time improving the science itself; neither can we, on the other hand, improve a science without improving the language or nomenclature which belongs to it.” This view reminds us of Confucius’s earlier doctrine, the rectification of names (Steinkraus, 1980; Lau, 2000). Confucius believed that rectification of names is imperative. He explained (Steinkraus, 1980; Lau, 2000): “If language is incorrect, then what is said does not concord with what was meant, what is to be done cannot be affected. If what is to be done cannot be affected, then rites and music will not flourish. If rites and music do not flourish, then mutilations and lesser punishments will go astray. And if mutilations and lesser punishments go astray, then the people have nowhere to put hand or foot. Therefore the gentleman uses only such language as is proper for speech, and only speaks of what it would be proper to carry into effect. The gentleman in what he says leaves nothing to mere chance.” Inspired by these views, we make the analogy that the progress of science and the language used to describe it are two entangled electrons. This entanglement highlights the importance of introducing systemic names for enzymes using EC classification and the ever-growing problem of protein names (McDonald and Tipton, 2021). Here, we tackle one specific case of iron-sulfur ([FeS]) enzymes. We show that the language used to describe a conserved [FeS] enzyme of the innate immune system, i.e., viperin or RSAD2, is now inadequate and disentangled from its science. We discuss that the enzyme has cellular functions beyond its antiviral activity and that eukaryotic and prokaryotic enzymes catalyse the same chemical reactions. To prevent bias towards antiviral activity while studying various biochemical activities of the enzyme and using scientifically incorrect terms like “prokaryotic viperins,” we rectify the language describing the enzyme. Based on NC-IUBMB recommendations, we introduce the nomenclature S-adenosylmethionine (SAM) dependent Nucleotide Dehydratase (SAND)