OXIGÊNIO NO CONTEXTO DA COVID-19: O QUE SABEMOS SOBRE A MOLÉCULA QUE RESPIRAMOS E O PAPEL CENTRAL DA QUÍMICA

OXYGEN IN THE COVID-19 CONTEXT: WHAT WE KNOW ABOUT THE MOLECULE WE BREATHE AND THE CENTRAL ROLE OF CHEMISTRY. In this work, the role of chemistry in the coronavirus disease 2019 (COVID-19) pandemic is highlighted through the medical oxygen supply crises in Brazil, as an example of oxygen utility in health. Starting from oxygen chemical characterization, the oxygen cycle in nature is discussed to show how oxygen is formed through photosynthesis, followed by the description of the industrial oxygen production from atmospheric air, including physical-chemical aspects. The use of medical oxygen concentrator is presented and how this device works from the chemical point of view. Besides, the noninvasive and painless oximetry is described in terms of how oxygen saturation level in blood is measured using LED - light emitting diode.

Obtaining a Fibrous Polymeric Material from a Mixture of Polyvinylidene Fluoride and Polystyrene by Capillary-free Electrospinning for a Sealed Lead-Acid Accumulator Separator

The paper considers the most significant properties of moulding solutions based on a mixture of polyvinylidene fluoride and polystyrene for the process of capillary-free electrospinning nonwoven materials. It has been shown that the material obtained from the mixed solution of polyvinylidene fluoride and polystyrene in the ratio of components 0.75 : 0.25 is the largest porous, the diameter of the fibers is in the widest range from 0.14 to 2.8 µm, and branching of the fibers is observed. The use of an absorptive glass matrix separator and this material improved the oxygen cycle efficiency.

The impact of composition choices on solar evolution: age, helio- and asteroseismology, and neutrinos

ABSTRACT The Sun is the most studied and well-known star, and as such, solar fundamental parameters are often used to bridge gaps in the knowledge of other stars, when these are required for modelling. However, the two most powerful and precise independent methodologies currently available to infer the internal solar structure are in disagreement. We aim to show the potential impact of composition choices in the overall evolution of a star, using the Sun as example. To this effect, we create two Standard Solar Models and a comparison model using different combinations of metallicity and relative element abundances and compare evolutionary, helioseismic, and neutrino-related properties for each. We report differences in age for models calibrated to the same point on the HR diagram, in red giant branch, of more than 1 Gyr, and found that the current precision level of asteroseismic measurements is enough to differentiate these models, which would exhibit differences in period spacing of 1.30–2.58 per cent. Additionally, we show that the measurement of neutrino fluxes from the carbon–nitrogen–oxygen cycle with a precision of around 17 per cent, which could be achieved by the next generation of solar neutrino experiments, could help resolve the stellar abundance problem.

Planktic foraminiferal I/Ca from Holocene sediments of the Pacific and Indian Ocean

<p>Current climatic trends are expected to lead to expansion of oxygen minimum zones and an overall decrease in oxygen concentration [O<sub>2</sub>] in the oceans. In order to improve predictions of future trends we need to create a better understanding of the natural oxygen cycle. The iodine to calcium ratio (I/Ca) of planktonic foraminifera is an increasingly popular proxy to assess upper water column oxygenation. Recent studies suggest that this ratio is mainly controlled by subsurface water dissolved oxygen concentrations. A thorough assessment of the proxy has been carried out for the South Atlantic, but is currently lacking for the Indian and Pacific Oceans, which contain the worlds’ most intense and large oxygen minimum zones. Here we present results of recent (Holocene) planktonic foraminifera (mixed layer and deep dwelling species) I/Ca measurements across a range of oceanographic conditions ([O<sub>2</sub>] varies between < 10 µmol/kg to > 200 µmol/kg) from the Indian and Pacific Ocean to further refine the proxy, using sample material provided by Lamont-Doherty Core Repository.</p>

Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen

The balance between sources and sinks of molecular oxygen in the oceans has greatly impacted the composition of Earth’s atmosphere since the evolution of oxygenic photosynthesis, thereby exerting key influence on Earth’s climate and the redox state of (sub)surface Earth. The canonical source and sink terms of the marine oxygen budget include photosynthesis, respiration, photorespiration, the Mehler reaction, and other smaller terms. However, recent advances in understanding cryptic oxygen cycling, namely the ubiquitous one-electron reduction of O2 to superoxide by microorganisms outside the cell, remains unexplored as a potential player in global oxygen dynamics. Here we show that dark extracellular superoxide production by marine microbes represents a previously unconsidered global oxygen flux and sink comparable in magnitude to other key terms. We estimate that extracellular superoxide production represents a gross oxygen sink comprising about a third of marine gross oxygen production, and a net oxygen sink amounting to 15 to 50% of that. We further demonstrate that this total marine dark extracellular superoxide flux is consistent with concentrations of superoxide in marine environments. These findings underscore prolific marine sources of reactive oxygen species and a complex and dynamic oxygen cycle in which oxygen consumption and corresponding carbon oxidation are not necessarily confined to cell membranes or exclusively related to respiration. This revised model of the marine oxygen cycle will ultimately allow for greater reconciliation among estimates of primary production and respiration and a greater mechanistic understanding of redox cycling in the ocean.