Production Of Molecular Oxygen Research Articles

Lithium isotopic constraints on the evolution of continental clay mineral factory and marine oxygenation in the earliest Paleozoic Era.

The evolution of oxygen cycles on Earth's surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic-Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organic carbon production and burial respond to global environmental changes and whether these feedbacks trigger global oxygenation during this interval. Here, we report a large lithium isotopic and elemental dataset from marine mudstones spanning the upper Neoproterozoic to middle Cambrian [~660 million years ago (Ma) to 500 Ma]. These data indicate a dramatic increase in continental clay formation after ~525 Ma, likely linked to secular changes in global climate and compositions of the continental crust. Using a global biogeochemical model, we suggest that intensified continental weathering and clay delivery to the oceans could have notably increased the burial efficiency of organic carbon and facilitated greater oxygen accumulation in the earliest Paleozoic oceans.

Electrocatalytic Water Oxidation by Mononuclear Copper Complexes of Bis-amide Ligands with N4 Donor: Experimental and Theoretical Investigation.

The present work describes electrocatalytic water oxidation of three monomeric copper complexes [CuII(L1)] (1), [CuII(L2)(H2O)] (2), and [CuII(L3)] (3) with bis-amide tetradentate ligands: L1 = N,N'-(1,2-phenylene)dipicolinamide, L2 = N,N'-(4,5-dimethyl-1,2-phenylene)bis(pyrazine-2-carboxamide), L3 = N,N'-(1,2-phenylene)bis(pyrazine-2-carboxamide), for the production of molecular oxygen by the oxidation of water at pH 13.0. Ligands and all complexes have been synthesized and characterized by single crystal XRD, analytical, and spectroscopic techniques. X-ray crystallographic data show that the ligand coordinates to copper in a dianionic fashion through deprotonation of two -NH protons. Cyclic voltammetry study shows a reversible copper-centered redox couple with one ligand-based oxidation event. The electrocatalytic water oxidation occurs at an onset potential of 1.16 (overpotential, η ≈ 697 mV), 1.2 (η ≈ 737 mV), and 1.23 V (η ≈ 767 mV) for 1, 2, and 3 respectively. A systematic variation of the ligand scaffold has been found to display a profound effect on the rate of electrocatalytic oxygen evolution. The results of the theoretical (density functional theory) studies show the stepwise ligand-centered oxidation process and the formation of the O-O bond during water oxidation passes through the water nucleophilic attack for all the copper complexes. At pH = 13, the turnover frequencies have been experimentally obtained as 88, 1462, and 10 s-1 (peak current measurements) for complexes 1, 2, and 3, respectively. Production of oxygen gas during controlled potential electrolysis was detected by gas chromatography.

Direct production of molecular oxygen from carbon dioxide and helium ion collisions

The prebiotic mechanism to produce molecular oxygen (O2) in carbon dioxide (CO2)-rich planetary atmospheres is of great importance in understanding astrochemical reactions and is potentially relevant to the origin of life on Earth. Here, we demonstrate that, aside from the direct productions of O2 by photodissociation and dissociative electron attachment, the low-energy ion-molecule reaction between cationic helium in solar winds and molecular CO2 is a noticeable mechanism. Branching ratios of the reaction channels are determined, and their absolute cross-sections are estimated accordingly. The present findings represent a further, indispensable step towards fully understanding the origins of atmospheric O2.

A genetically encoded system for oxygen generation in living cells

Oxygen plays a key role in supporting life on our planet. It is particularly important in higher eukaryotes where it boosts bioenergetics as a thermodynamically favorable terminal electron acceptor and has important roles in cell signaling and development. Many human diseases stem from either insufficient or excessive oxygen. Despite its fundamental importance, we lack methods with which to manipulate the supply of oxygen with high spatiotemporal resolution in cells and in organisms. Here, we introduce a genetic system, SupplemeNtal Oxygen Released from ChLorite (SNORCL), for on-demand local generation of molecular oxygen in living cells, by harnessing prokaryotic chlorite O2-lyase (Cld) enzymes that convert chlorite (ClO2-) into molecular oxygen (O2) and chloride (Cl-). We show that active Cld enzymes can be targeted to either the cytosol or mitochondria of human cells, and that coexpressing a chlorite transporter results in molecular oxygen production inside cells in response to externally added chlorite. This first-generation system allows fine temporal and spatial control of oxygen production, with immediate research applications. In the future, we anticipate that technologies based on SNORCL will have additional widespread applications in research, biotechnology, and medicine.

Photosynthetic Production of Molecular Oxygen by Water Oxidation

This review deals with the production of oxygen by photo-oxidation of water, which is a topic fitting a journal devoted to oxygen. Most of the present biosphere, including mankind, depends on oxygen. Elucidating the mechanism is of importance for solving the present energy crisis. Photosynthesis evolved in bacteria, first in a form that did not produce oxygen. The oxygen-producing version arose with the advent of cyanobacteria about three billion years ago. The production of oxygen by photo-oxidation of water requires the co-operative action of four photons. These are harvested from daylight by chlorophyll and other pigments (e.g., phycobiliproteins) and are channeled to photosystem II and photosystem I. The oxygen-evolving complex resides in photosystem II, surrounded by protein subunits, and contains one ion of calcium, four ions of manganese, and a number of oxygen atoms. For each quantum of energy it receives from absorbed light, it proceeds one step through a cycle of states known as the Kok–Joliot cycle. For each turn of the cycle, one molecule of oxygen (O2) is produced.

Abiotic molecular oxygen production-Ionic pathway from sulfur dioxide.

Molecular oxygen, O2, is vital to life on Earth and possibly also on exoplanets. Although the biogenic processes leading to its accumulation in Earth’s atmosphere are well understood, its abiotic origin is still not fully established. Here, we report combined experimental and theoretical evidence for electronic state–selective production of O2 from SO2, a chemical constituent of many planetary atmospheres and one that played an important part on Earth in the Great Oxidation Event. The O2 production involves dissociative double ionization of SO2 leading to efficient formation of the ion, which can be converted to abiotic O2 by electron neutralization or by charge exchange. This formation process may contribute substantially to the abundance of O2 and related ions in planetary atmospheres, such as the Jovian moons Io, Europa, and Ganymede. We suggest that this sort of ionic pathway for the formation of abiotic O2 involving multiply charged molecular ion decomposition may also exist for other atmospheric and planetary molecules.

Oxygen production and rapid iron oxidation in stromatolites immediately predating the Great Oxidation Event

Earth's surface became permanently oxygenated during the Great Oxidation Episode, a geochemical transition between ∼2.43 and 2.22 billion years ago, but shallow-water cyanobacterial oases with molecular oxygen production likely existed for hundreds of millions of years before, in the otherwise anoxic and iron-rich oceans. Despite abundant geochemical evidence for elevated ambient oxygen in the Archean upper ocean, sites of active microbial oxygen production have not been geochemically characterized. We report geochemical and iron isotopic data for a horizon of iron-rich stromatolites in the 2.46–2.43 Ga Griquatown Iron Formation in South Africa deposited on the margin of an anoxic ferruginous basin. Bulk-rock and micro-sampled iron isotope data for the stromatolites indicate quantitative oxidation of iron delivered by deep upwelling currents, which is most readily explained by cyanobacterial communities inhabiting the stromatolites and producing local oxygen enrichments near the fair-weather wave-base. Modest enrichments in Mn and Ce indicate high oxidation potential in this stromatolitic setting. The iron-rich nature of the stromatolites indicates that upwelling iron sources in the early Paleoproterozoic oceans overwhelmed established iron-precipitation mechanisms in deeper basins that had generally maintained iron-poor conditions in shallow-marine peritidal zone during the Neoarchean.

Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange.

A new strategy to incorporate the Sn(II) cation and its stereoactive lone pair into the structure of a photocatalytic oxide has been achieved by leveraging the asymmetric coordination environments within the (111)-oriented perovskite-type layers of Ba5Nb4O15. This layered perovskite represents one of the few known photocatalysts capable of efficiently splitting water, but its activity is restricted to ultraviolet radiation owing to its large band gap. By reacting this layered niobate at 350 °C for 24 h within a low-melting SnCl2/SnF2 salt, the new (Ba1-xSnx)Nb4O15 (x = 0-0.5; P3̅m1; a = 5.79650(5) Å, c = 11.79288(8) Å; Z = 2) has been prepared in high purity with up to ∼50% Sn(II) cations. Statistical disordering of the Sn(II) cations was probed by neutron diffraction Rietveld refinements and found to occur predominantly over the asymmetric cation sites, Ba2 and Ba3, for the 40% Sn(II) composition of x = 0.4. An increasing Sn(II) amount significantly red-shifts the band gap (Eg) from 0% Sn for x = 0 (3.78 eV; ultraviolet, indirect) to 40% Sn for x = 0.4 (Eg = 2.35 eV; visible, indirect), as found by UV-vis diffuse reflectance. Density functional theory calculations show an increasing metastability, i.e., a thermodynamic instability toward decomposition to the simpler oxides SnO, Nb2O5, and SnNb2O6. A synthetic limit of ∼50% Sn(II) cations can be kinetically stabilized under these reaction conditions. For the highest Sn(II) amounts, photocatalytic rates are observed for the production of molecular oxygen from water of up to ∼77 μmol O2 h-1 g-1 (visible irradiation) and ∼159 μmol O2 h-1 g-1 (UV-vis irradiation), with apparent quantum yields of ∼0.35 and 0.52%, respectively. By comparison, pure Ba5Nb4O15 exhibits no measurable photocatalytic activity under visible-light irradiation. Electronic structure calculations show that the decreased band gap stems from the introduction of the Sn(II) cations and the formation of a higher-energy valence band arising from the filled 5s2 valence orbitals. Thus, visible-light bandgap excitation occurs from electronic transitions predominantly involving the Sn(II) (5s2) to Nb(V) (4d0) cations. This study demonstrates the new and powerful utility of low-temperature Sn(II)-exchange reactions to sensitize layer-type oxide photocatalysts to the visible region of the solar spectrum, which is facilitated by exploiting their asymmetric cation environments.

Synthesizability and Properties of Metastable Semiconductors for Solar Energy Conversion

Metastable semiconductors in many chemical systems have been discovered that have desirable semiconductor properties for driving fuel-producing redox reactions from water and sunlight, such as strong visible light absorption, optimal band-edge energies, extreme defect tolerance, and enhanced carrier mobilities and charge separation. These properties are intimately related to their metastable nature, i.e., their crystalline structures and compositions lead to thermodynamic instabilities. New results will be presented that demonstrate flux-mediated synthetic routes to new metastable n-type Sn(II)-titanates and p-type Cu(I)-niobates. These semiconductors possess some the smallest known visible-light band gaps that also maintain suitable conduction and valence band energies for the photocatalytic reduction and oxidation of water to molecular hydrogen and oxygen, respectively. Their electronic structures also show advantageous features for solar energy conversion, such as small bandgaps, high band dispersion and defect tolerance. These characteristics are intimately related to their metastability and kinetic stabilization, which can be achieved via solid solutions that inhibit phase segregation. Thus, the solid-solution semiconductors Cu5(Ta1-x Nb x )11O30 and (Ba1-x Sn x )(Zr1-yTi y )O3 have been prepared using flux-mediated synthesis methods. Their band gaps, band edge energies and photocatalytic activities for the production of molecular hydrogen and molecular oxygen are found to be a sensitive function of their chemical compositions.

Reconciling evidence of oxidative weathering and atmospheric anoxia on Archean Earth.

Evidence continues to emerge for the production and low-level accumulation of molecular oxygen (O2) at Earth’s surface before the Great Oxidation Event. Quantifying this early O2 has proven difficult. Here, we use the distribution and isotopic composition of molybdenum in the ancient sedimentary record to quantify Archean Mo cycling, which allows us to calculate lower limits for atmospheric O2 partial pressures (PO2) and O2 production fluxes during the Archean. We consider two end-member scenarios. First, if O2 was evenly distributed throughout the atmosphere, then PO2 > 10–6.9 present atmospheric level was required for large periods of time during the Archean eon. Alternatively, if O2 accumulation was instead spatially restricted (e.g., occurring only near the sites of O2 production), then O2 production fluxes >0.01 Tmol O2/year were required. Archean O2 levels were vanishingly low according to our calculations but substantially above those predicted for an abiotic Earth system.

The Impact of Ligand Carboxylates on Electrocatalyzed Water Oxidation.

ConspectusFossil fuel shortage and severe climate changes due to global warming have prompted extensive research on carbon-neutral and renewable energy resources. Hydrogen gas (H2), a clean and high energy density fuel, has emerged as a potential solution for both fulfilling energy demands and diminishing the emission of greenhouse gases. Currently, water oxidation (WO) constitutes the bottleneck in the overall process of producing H2 from water. As a result, the design of efficient catalysts for WO has become an intensively pursued area of research in recent years. Among all the molecular catalysts reported to date, ruthenium-based catalysts have attracted particular attention due to their robust nature and higher activity compared to catalysts based on other transition metals.Over the past two decades, we and others have studied a wide range of ruthenium complexes displaying impressive catalytic performance for WO in terms of turnover number (TON) and turnover frequency (TOF). However, to produce practically applicable electrochemical, photochemical, or photo-electrochemical WO reactors, further improvement of the catalysts’ structure to decrease the overpotential and increase the WO rate is of utmost importance. WO reaction, that is, the production of molecular oxygen and protons from water, requires the formation of an O–O bond through the orchestration of multiple proton and electron transfers. Promotion of these processes using redox noninnocent ligand frameworks that can accept and transfer electrons has therefore attracted substantial attention. The strategic modifications of the ligand structure in ruthenium complexes to enable proton-coupled electron transfer (PCET) and atom proton transfer (APT; in the context of WO, it is the oxygen atom (metal oxo) transfer to the oxygen atom of a water molecule in concert with proton transfer to another water molecule) to facilitate the O–O bond formation have played a central role in these efforts.In particular, promising results have been obtained with ligand frameworks containing carboxylic acid groups that either are directly bonded to the metal center or reside in the close vicinity. The improvement of redox and chemical properties of the catalysts by introduction of carboxylate groups in the ligands has proven to be quite general as demonstrated for a range of mono- and dinuclear ruthenium complexes featuring ligand scaffolds based on pyridine, imidazole, and pyridazine cores. In the first coordination sphere, the carboxylate groups are firmly coordinated to the metal center as negatively charged ligands, improving the stability of the complexes and preventing metal leaching during catalysis. Another important phenomenon is the reduction of the potentials required for the formation of higher valent intermediates, especially metal-oxo species, which take active part in the key O–O bond formation step. Furthermore, the free carboxylic acid/carboxylate units in the proximity to the active center have shown exciting proton donor/acceptor properties (through PCET or APT, chemically noninnocent) that can dramatically improve the rate as well as the overpotential of the WO reaction.

Photophysical properties of heavy atom containing tetrasulfonyl phthalocyanines as possible photosensitizers in photodynamic therapy.

The excitation energies, singlet-triplet energy gap and spin-orbit coupling constants for Zn-, GaCl-, Pd-, and Pt- tetrasulfonyl phthalocyanines complexes (ZnPc, GaClPc, PdPc, and PtPc) have been computed by using the density functional theory and employing the M06 exchange-correlation functional. Results show that these systems possess interesting photophysical properties, which make them possible photosensitizers to be proposed in photodynamic therapy (PDT). Absorption energies of all the complexes examined have been found falling inside the so-called therapeutic window (550-800 nm). Singlet-triplet energy gap values are higher than those required for the production of cytotoxic molecular oxygen and the spin-orbit coupling constants are such as to ensure an efficient spin orbit intersystem crossing. The obtained data are consistent with the experimental oxygen singlet quantum yields. The platinum complex appears to be the most effective candidate to propose for PDT.

Effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) aggregation on its spectral and kinetic characteristics and singlet oxygen production

The present work reports the effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) aggregation on its excited states absorption spectra, triplet states quenching by molecular oxygen and singlet oxygen production. Experimental techniques such as optical absorption, Z-scan with a white light continuum source and the Laser Flash Photolysis were used to fulfil the study. J-aggregates possess reverse saturable absorption in the 505–660 nm spectral range with a peak centered close to 540 nm. These facts together with their fast relaxation time suggest that they can be employed as material for ultrafast optical limiting and switching. Even though aggregation reduces the porphyrin excited-state lifetimes and quantum yields, it does not reduce the probability of the contact between the quencher and the excited aggregate. Aggregation does not change the contribution of energy transfer mechanisms to triplet state quenching by molecular oxygen. The production of singlet oxygen, the intense absorption in the phototherapeutic window and the high efficiency of conversion of light energy into heat, allow consider J-aggregates as a theranostic agent for photomedicine. It is proposed to use J-aggregates for diagnostics by photoacoustic images and in combination with a near-infrared photodynamic/photothermal dual mode therapy, thus improving synergistically the therapeutic response.

Solid-Solution Photocatalysts: New Insights Via Percolation Theory

Solid-solution semiconductors in many metal-oxynitride and metal-chalcogenide systems have been demonstrated to efficiently drive water oxidation and/or reduction under visible-light irradiation as suspended powders or thin films, respectively. This occurs despite the high level of inherent atomic-level disorder that would normally be expected to decrease charge mobility and increase charge recombination in these systems. Within the mixed-metal oxides, current results will be presented on the syntheses, structures and photoelectrochemical properties of the solid solutions Cu5(Ta1-x Nb x )11O30 and (Ba1-x Sn x )(Zr1-yTi y )O3 with band gaps that span the visible light energies from ~1.9 to 3.1 eV. Their band gaps, band edge energies and photocatalytic activities for the production of molecular hydrogen and molecular oxygen are found to be a sensitive function of their Ta-to-Nb or Zr-to-Ti and Ba-to-Sn molar ratios, as shown in the Figure for the (Ba1-x Sn x )(Zr1-yTi y )O3 solid-solution semiconductor. Notably, electronic structure calculations reveal that the highest photocatalytic activities should occur at the percolation thresholds of the mixed transition-metal frameworks, wherein extended diffusion pathways for the minority carriers start to form across the surfaces. In the semiconductors that will be described, the extended diffusion pathways constitute the lowest energies of the conduction bands and/or highest energies of the valence bands, and thus revealing an underlying driving force for achieving efficient charge separation in solid-solution systems. Figure 1

Mineralization of Melanoidin by H₂O₂ Producing Enzymes from Marine Cyanobacteria Oscillatoria boryana BDU 92181

Intracellular enzymes of Oscillatoria boryana BDU 92181 exhibited mineralizing activity on melanoidin, a recalcitrant pigment present in the distillery wastewater. Melanoidin decolourization was postulated to be due to the production of hydrogen peroxide and molecular oxygen released by the cyanobacterium during photosynthesis. The present study was aimed to find out the efficacy of the marine cyanobacterium O. boryana BDU 92181 in producing H2O2 and enzymes involved in hydrogen peroxide production with a view to utilize its potential for decolorization of melanoidin pigment in the distillery effluent. The enzymes involved in the melanoidin degradation have not so far been attempted with cyanobacteria.
 The results obtained in the present work suggested the activity of the glucose oxidase and Manganese peroxidase enzymes in a marine cyanobacterium Oscillatoria boryana BDU 92181 and whose activity was found to be enhanced in the presence of melanoidin.

The evolution of oxygen-utilizing enzymes suggests early biosphere oxygenation.

Production of molecular oxygen was a turning point in the Earth's history. The geological record indicates the Great Oxidation Event, which marked a permanent transition to an oxidizing atmosphere around 2.4 Ga. However, the degree to which oxygen was available to life before oxygenation of the atmosphere remains unknown. Here, phylogenetic analysis of all known oxygen-utilizing and -producing enzymes (O2-enzymes) indicates that oxygen became widely available to living organisms well before the Great Oxidation Event. About 60% of the O2-enzyme families whose birth can be dated appear to have emerged at the separation of terrestrial and marine bacteria (22 families, compared to two families assigned to the last universal common ancestor). This node, dubbed the last universal oxygen ancestor, coincides with a burst of emergence of both oxygenases and other oxidoreductases, thus suggesting a wider availability of oxygen around 3.1 Ga.

Quantification of RuBisCO Expression and Photosynthetic Oxygen Evolution in Cyanobacteria.

Phototrophic microorganisms are frequently engineered to regulate the expression and the activity of targeted enzymes of interest for specific biotechnological and agricultural applications. This protocol describes a method to evaluate the expression of RuBisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase) in the model cyanobacterium Synechococcus elongatus PCC 7942, at both the transcript and protein levels by quantitative PCR and Western blot, respectively. We further describe an experimental method to determine photosynthetic activity using an oxygen electrode that measures the rate of molecular oxygen production by cyanobacterial cultures. Our protocol can be utilized to assess the effects of RuBisCO engineering at the metabolic and physiological levels.

Dissociative electron attachment to carbon dioxide

Our experimental progresses on the reaction dynamics of dissociative electron attachment (DEA) to carbon dioxide (CO2) are summarized in this review. First, we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2. Second, the experimental technique developments are described, in particular, on the high-resolution velocity map imaging apparatus in which we put a lot of efforts during the past two years. Third, our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’ work. At last, we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.

S- and N-doped graphene-based catalysts for the oxygen evolution reaction

In-situ Raman spectroscopy, rotating ring-disk electrode (RRDE), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) techniques were used to determine the catalytic activity of graphite and heteroatom-doped graphene catalysts toward the oxygen evolution reaction (OER) in alkaline media. Main results indicate that the OER is strongly influenced by the nature and amount of the doping agent in addition to the interaction with the electrolyte media, which also conditioned the AreaD/AreaG (AD/AG) ratio and the position of the D- and G-bands. Additionally, an exhaustive Raman characterization of powder materials and catalyst inks in the presence of air, water and sodium hydroxide is reported. Finally, the percentage of molecular oxygen production is estimated by a novel procedure. This work is not intended to reveal the best catalysts toward the OER, but to show novel techniques to study the OER at graphene-based catalysts.

Metal-free highly efficient photocatalysts for overall water splitting: C3N5 multilayers.

As a promising means of renewable energy storage, the production of molecular hydrogen and oxygen from photocatalytic water splitting has gained increasing interest. The optimal photocatalyst for water splitting should have high solar energy conversion efficiency and strong photocatalytic redox ability to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few photocatalysts have been reported to fulfil these two contradictive requirements. Here, we demonstrated from first-principles calculations that the recently synthesized two-dimensional carbon nitride (C3N5) multilayers can serve as promising candidates to reach this goal. The intrinsic electric field which is more pronounced in the multilayers alters the band alignment of the photocatalysts, making the HER and OER be driven solely by the photogenerated carriers. The thickness-dependent electronic band gap (2.95-2.16 eV) along with the high carrier mobility broadens the energy range of light absorption and promotes carrier separation and transfer, leading to high solar energy conversion efficiency. Our computational results offer not only low-cost, Earth-abundant and environmentally friendly photocatalysts but also a promising strategy for the design of photocatalysts for highly efficient overall water splitting without using sacrificial reagents.