4,447 research outputs found

    Aerobic Lineage of the Oxidative Stress Response Protein Rubrerythrin Emerged in an Ancient Microaerobic, (Hyper)Thermophilic Environment

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    Indexación: Web of Science; Scopus.Rubrerythrins (RBRs) are non-heme di-iron proteins belonging to the ferritin-like superfamily. They are involved in oxidative stress defense as peroxide scavengers in a wide range of organisms. The vast majority of RBRs, including classical forms of this protein, contain a C-terminal rubredoxin-like domain involved in electron transport that is used during catalysis in anaerobic conditions. Rubredoxin is an ancient and large protein family of short length (<100 residues) that contains a Fe-S center involved in electron transfer. However, functional forms of the enzyme lacking the rubredoxin-like domain have been reported (e.g., sulerythrin and ferriperoxin). In this study, phylogenomic evidence is presented that suggests that a complete lineage of rubrerythrins, lacking the rubredoxin-like domain, arose in an ancient microaerobic and (hyper)thermophilic environments in the ancestors of the Archaea Thermoproteales and Sulfolobales. This lineage (termed the "aerobic-type" lineage) subsequently evolved to become adapted to environments with progressively lower temperatures and higher oxygen concentrations via the acquisition of two co-localized genes, termed DUF3501 and RFO, encoding a conserved protein of unknown function and a predicted Fe-S oxidoreductase, respectively. Proposed Horizontal Gene Transfer events from these archaeal ancestors to Bacteria expanded the opportunities for further evolution of this RBR including adaption to lower temperatures. The second lineage (termed the cyanobacterial lineage) is proposed to have evolved in cyanobacterial ancestors, maybe in direct response to the production of oxygen via oxygenic photosynthesis during the Great Oxygen Event (GOE). It is hypothesized that both lineages of RBR emerged in a largely anaerobic world with "whiffs" of oxygen and that their subsequent independent evolutionary trajectories allowed microorganisms to transition from this anaerobic world to an aerobic one.http://journal.frontiersin.org/article/10.3389/fmicb.2016.01822/ful

    Testing a dissipative kinetic k-essence model

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    In this work, we present a study of a purely kinetic k-essence model, characterized basically by a parameter α\alpha in presence of a bulk dissipative term, whose relationship between viscous pressure Π\Pi and energy density ρ\rho of the background follows a polytropic type law Πρλ+1/2\Pi \propto \rho^{\lambda+1/2}, where λ\lambda, in principle, is a parameter without restrictions. Analytical solutions for the energy density of the k-essence field are found in two specific cases: λ=1/2\lambda=1/2 and λ=(1α)/2α\lambda=(1-\alpha)/2\alpha, and then we show that these solutions posses the same functional form than the non-viscous counterpart. Finally, both approach are contrasted with observational data from type Ia supernova, and the most recent Hubble parameter measurements, and therefore, the best values for the parameters of the theory are founds.Comment: 9 pages, 5 figures, accepted in EPJ

    Foreign in Their Own Country: A Critical Analysis of Puerto Ricans in the United States

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    Foreign in their own nation? The neglected United States territory? The 51st state that never was? Regardless of which of these questions one chooses to look through the prism of, they are all applicable when it comes to discussing Puerto Rico and its staggering relationship with the United States. These questions are all significant in some way because they are indicative of patterns of interaction and an overall story that has developed over the years between the two respective sides. These questions give a window into the contentious history that the island has had with the United States since being seized under its control in the late 19th century as a result of the Spanish-American war. Puerto Ricans have long been the source of marginalization because of the ambiguity surrounding their identity within their own nation, but in this paper the Puerto Rican experience is really brought to light in a cohesive and thoughtful manner. This is an exploration of how Puerto Ricans have been/currently are perceived and received by Americans in the U.S. This is an exploration of the question of how Puerto Ricans assimilate, but at the same time attempt to not lose their cultural identity in which they were brought up on. This is an exploration of what it means to be regarded as “foreign” in one’s own country and what the implications of that perceived foreignness are. This is an exploration of the Puerto Rican experience--analyzed through both the lens of society and themselves

    MECHANISTIC STUDY OF A RUTHENIUM HYDRIDE COMPLEX OF TYPE [RuH(CO)(N-N)(PR3)2]+ AS CATALYST PRECURSOR FOR THE HYDROFORMYLATION REACTION OF 1-HEXENE

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    Indexación: Web of Science; Scopus; Scielo.The catalytic activity of systems of type [RuH(CO)(N-N)(PR3)(2)](+) was evaluated in the hydroformylation reaction of 1-hexene. The observed activity is explained through a reaction mechanism on the basis of the quantum theory. The mechanism included total energy calculations for each of the intermediaries of the elemental steps considered in the catalytic cycle. The deactivation of the catalyst precursors takes place via dissociation of the polypyridine ligand and the subsequent formation of thermodynamically stable species, such as RuH(CO)(3)(PPh3)(2) and RuH3(CO)(PPh3)(2), which interrupt the catalytic cycle. In addition, the theoretical study allows to explain the observed regioselectivity which is defined in two steps: (a) the hydride migration reaction with an anti-Markovnikov orientation to produce the alkyl-linear-complex (3.1a), which is more stable by 19.4 kJ/mol than the Markovnikov orientation (alkyl-branched-complex) (3.1b); (b) the carbon monoxide insertion step generates the carbonyl alkyl-linear specie (4.1a) which is more stable by 9.5 kJ/mol than the alternative species (4.1b), determining the preferred formation of heptanal in the hydroformylation of 1-hexene. Palabras clavehttp://ref.scielo.org/db4yc

    Quinstant Dark Energy Predictions for Structure Formation

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    We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the non-linear one, for redshifts larger than one.Comment: 9 pages, 14 figures, "Accepted for publication in Astrophysics & Space Science
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