Topic
Oxygen
About: Oxygen is a research topic. Over the lifetime, 48149 publications have been published within this topic receiving 1113788 citations. The topic is also known as: O & Oxygen.
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TL;DR: It was this oxygen that enabled oxygenic life to evolve and that led to the current diverse and complex life on earth by dramatically increasing the metabolic energy that became available from aerobic respiration.
Abstract: Oxygen, which supports all aerobic life, is produced by photosynthetic water oxidation in plants, algae, and cyanobacteria. The water-oxidation reaction probably first appeared in nature ∼3 billion years ago in the precursors to present-day cyanobacteria, although the exact timing is not yet entirely clear.1−5 A key component in the appearance of oxygenic photosynthesis was a metal complex that could store oxidizing equivalents to facilitate the four-electron oxidation of two water molecules to dioxygen, meanwhile making the electrons available for the reductive carbon-fixing reactions required for sustaining life.6−8 This metal complex involved in oxygenic photosynthesis, the oxygen-evolving complex (OEC), consists of an oxo-bridged structure with four Mn atoms and one Ca atom. No variations have been observed so far among oxygenic photosynthetic organisms through higher plants and algae back to cyanobacteria, which represents the earliest oxygenic photosynthetic organisms. Oxygen itself is the byproduct of the photosynthetic water oxidation reaction shown in eq 1:
1
However, it was this oxygen that enabled oxygenic life to evolve and that led to the current diverse and complex life on earth by dramatically increasing the metabolic energy that became available from aerobic respiration. Oxygen produced by this process was also key for the development of the protective ozone layer, which allowed life to transition from marine forms to terrestrial life.
524 citations
TL;DR: During stepwise restoration of oxygen flow, the phosphorescence images showed marked heterogeneous patterns of tissue reoxygenation, which indicated that there were regional inequalities in oxygen delivery.
Abstract: The imaging of phosphorescence provides a method for monitoring oxygen distribution within the vascular system of intact tissues. Isolated rat lives were perfused through the portal vein with media containing palladium coproporphyrin, which phosphoresced and was used to image the liver at various perfusion rates. Because oxygen is a powerful quenching agent for phosphors, the transition from well-perfused liver to anoxia (no flow of oxygen) resulted in large increases of phosphorescence. During stepwise restoration of oxygen flow, the phosphorescence images showed marked heterogeneous patterns of tissue reoxygenation, which indicated that there were regional inequalities in oxygen delivery.
524 citations
TL;DR: Advances have been made in elucidating possible oxygen-sensing systems and regulatory components that are involved in these responses, which lead to the induction of a plant-specific and energy-conserving pathway of sucrose degradation, which decreases oxygen consumption and improves plant performance.
522 citations
TL;DR: In this paper, the authors studied the reaction of carbon monoxide catalyzed by Pt(111) using reactive molecular beam-surface scattering and showed that at low coverage, the reaction proceeds with an activation energy E*LH =24.1 kcal/mole and a pre-exponential υ4 =0.11 cm2 particles−1
Abstract: The oxidation of carbon monoxide catalyzed by Pt(111) was studied in ultrahigh vacuum using reactive molecular beam–surface scattering. Under all conditions studied, the reaction follows a Langmuir–Hinshelwood mechanism: the combination of a chemisorbed CO molecule and an oxygen adatom. When both reactants are at low coverage, the reaction proceeds with an activation energy E*LH =24.1 kcal/mole and a pre‐exponential υ4 =0.11 cm2 particles−1 sec−1. At very high oxygen coverage, E*LH decreases to about 11.7 kcal/mole and υ4 to about 2×10−6 cm2 particles−1 sec−1. This is largely attributed to the corresponding increase in the energy of the adsorbed reactants. When a CO molecule incident from the gas phase strikes the surface presaturated with oxygen, it enters a weakly held precursor state to chemisorption. Desorption from this state causes a decrease in chemisorption probability with temperature. Once chemisorbed, the CO molecule then has almost unit probability of reacting to produce CO2 below 540 K. The CO2 product angular distribution varies from cosγ to cos4γ depending sensitively upon the adsorbed reactant concentrations.
522 citations
TL;DR: In this article, a series of activated carbons with different degrees of activation was treated with HNO 3, H 2 O 2, and (NH 4 ) 2 S 2 O 8 in order to introduce oxygen surface complexes.
Abstract: A series of activated carbons with different degrees of activation was treated with HNO 3 , H 2 O 2 , and (NH 4 ) 2 S 2 O 8 in order to introduce oxygen surface complexes. The effects of the oxidizing treatments on the surface area, the pore texture, and the surface chemical nature were analyzed by means of N 2 and CO 2 adsorption, mercury porosimetry, FTIR, TPD, electrophoretic, and mass titration measurements. Results obtained show that the HNO 3 treatment affects the surface area and the porosity of the samples to a greater extent than the other treatments. Carboxyl groups were essentially fixed after the three treatments, although ketone and ether groups, as detected by FTIR, were also fixed after the treatments with peroxides. The most important conclusion was that the stronger acid groups were fixed after the (NH4) 2 S 2 O 5 treatment rather than after the HNO 3 treatment, in spite of the fact that this latter treatment fixed the largest number of oxygen complexes that evolved as CO 2 .
521 citations