Source Of O2 Research Articles

Nonclassical B‐Hb⋯π interaction in diborane⋯localized‐π sandwiches: A DFT‐D3 study

AbstractThe study presents a quantitative estimation of B‐Hb⋯π interaction in diborane‐localized‐π half sandwiches and sandwiches. DFT‐D3 method is used for geometry optimization and estimating the stability of the complexes (in terms of stabilization energies). The diborane molecule is the source of bridging hydrogen and O2, C2H4, and C2H2 molecules are considered as the localized π‐systems. MP2 and CCSD(T) calculations are also performed to measure the stability of the chosen complexes. Results indicate that the complexes are feebly stable in gas phase with stabilization energies <5.0 kcal mol−1. Compared to DFT‐D3 functionals, MP2 calculations are found to be more suitable in predicting the stability of the complexes. Dispersive interaction is the primary mode of interaction in stabilizing the complexes. Presence of substituents either on diborane or on the considered π‐systems play key role in stabilizing the complexes. Thermochemical analysis demonstrates the exothermic nature of complexation. 1H and 13B NMR analysis are also performed.

Enhanced NOX-2 derived oxidative stress in offspring of patients with early myocardial infarction

BackgroundOffspring of patients with early myocardial infarction have a higher risk to develop cardiovascular events; the underlying physiopathology is still unclear. Several lines of evidence support a role for oxidative stress in atherogenesis and NADPH oxidase-2 (NOX-2) is considered a major source of O2– in human. Furthermore, oxidative stress regulates arachidonic acid metabolism via activation of platelet phospholipase-A2.The aim of this study was to address NOX-2 activity as well as serum thromboxane B2 (TXB2) and 8-isoPGF2-alpha in offspring of patients with premature myocardial infarction. MethodsNinety-two consecutive subjects, including 46 offspring of patients with premature myocardial infarction and 46 healthy subjects (HS) matched for age and gender, were recruited.A cross sectional study was performed to compare serum activity of soluble NOX-2-dp (sNOX-2-dp), blood levels of isoprostanes and serum TXB2 in these two groups. ResultsCompared with HS, offspring of patients with early myocardial infarction had higher values of serum TxB2, isoprostanes and sNOX-2-dp. Bivariate analysis in the overall population showed that serum sNOX-2-dp levels were significantly associated with serum isoprostanes and TXB2. A multiple linear regression analysis was performed to define the independent predictors of sNOX-2-dp. Serum isoprostanes (SE: 0.07; standardized coefficient β: 0.579; P < 0.001) and TXB2 levels (SE: 0.06; standardized coefficient β: 0.211; P < 0.001) were significantly associated to sNOX-2-dp (R2: 0.42). ConclusionThis study shows that Nox-2 activation is a key determinant of oxidative stress and platelet activation in offspring of patients with premature myocardial infarction.

Effects of Oxide Ions on the Electrodeposition Process of Silicon in Molten Fluorides

We studied the effects of O2− ions on the coordination structure of Si ions and the electrodeposition process of Si films in molten fluorides using SiO2 powder (as a source of Si) and Li2O (as a source of O2−). High-temperature Raman spectroscopic data revealed that the dissolution of SiO2 in molten KF, LiF-KF, and LiF-NaF-KF without Li2O was proceeded by the formation of silicate ions, with the [Si2O5]2− ion acting as the dominant species. On the other hand, when 3.0 mol% Li2O was added to molten LiF-KF and LiF-NaF-KF, the intensity of Raman band due to [SiO3F]3− ion was increased compared to that without Li2O system, which indicated that the O2− ions could cause breakage of Si-O-Si bonds of SiO2 or [Si2O5]2− ions. Furthermore, the reduction currents, attributed to the reduction of Si ions, increased significantly by the addition of Li2O; moreover, the thickness and current efficiency of the electrodeposited polycrystalline Si layer prepared by potentiostatic electrolysis was improved. These results indicated that the O2− ions can change the coordination structure of Si ions in molten fluorides and that the design of the molten salts bath is a key technology for fabricating high-quality Si layers with high current efficiency.

Electrochemical Deoxidation of Titanium Scrap in MgCl2-HoCl3 System

A novel electrochemical deoxidation process for Ti in the magnesium chloride−holmium chloride (MgCl2−HoCl3) system was developed. The reaction mechanism was proposed on the basis of the E-pO2− diagram constructed in this study and the experimental results. Metallic Mg was electrodeposited on a Ti cathode to remove O in the form of O2− from Ti via electrolysis conducted in molten MgCl2−HoCl3, with C and Ti as the anode and cathode, respectively. The activity of the generated O2− (i.e., aO2−) in the system was effectively maintained at a very low value by the generation of holmium oxychloride (HoOCl) and/or the effusion of COx gas from the anode. By applying a voltage ranging from 2.1 to 3.0 V between the cathode and anode at 1173 K, the O concentration in Ti was effectively deoxidized to below 1000 mass ppm O. The deoxidation capability of this process was maintained even after the addition of MgO into the system as an additional source of O2−. This novel deoxidation method can be used to recycle large quantities of Ti scrap with high O concentration.

Subcellular accumulation and source of O2[rad]− and H2O2 in submerged plant Hydrilla verticillata (L.f.) Royle under NH4+-N stress condition

In this study, the effects of excess NH4+-N on the subcellular accumulation of O2− and H2O2 in submerged plant Hydrilla verticillata (L.f.) Royle were investigated using both histochemical and cytochemical methods. Treatments with ≥ 2.00 and ≥ 5.00 mg L−1 NH4+-N for 5 d significantly increased production of O2− and H2O2, respectively. The activities of plasma membrane-bound NADPH (nicotinamide adenine dinucleotide phosphate) oxidases and antioxidant enzymes (superoxide dismutase, peroxidase, ascorbate peroxidase, catalase, dehydroascorbate reductase and glutathione reductase) were also increased correspondingly. This study also provides the first cytochemical evidence of subcellular accumulation of O2− and H2O2 in the submerged plants. In the leaves of H. verticillata treated with 20.0 mg L−1 NH4+-N, O2− dependent DAB precipitates were found primarily on the inner side of the plasma membrane, extracellular space and chloroplasts. H2O2-CeCl3 precipitates were mainly localized on the inner side of the plasma membrane and extracellular space of the mesophyll cells. Treatments with the inhibitors of NADPH oxidase (diphenylene iodonium and imidazole) indicate that NH4+-N-induced production of O2− and H2O2 in H. verticillata leaves may involve plasma membrane-bound NADPH oxidase. Moreover, low-light treatment decreased NH4+-induced O2− production, suggesting that alterations in the photosynthetic electron transfer chain due to NH4+ toxicity could lead to O2− production.

145 - Imbalance between nitric oxide and superoxide anion induced by uncoupled nitric oxide synthase contributes to human metastatic melanoma development

Melanoma is the most aggressive type of cutaneous tumors due to its metastatic potential and high mortality. Increased levels of reactive oxygen species, including superoxide anion (O2–), and the consequent installation of a pro-oxidant environment are associated with melanoma development. The enzyme nitric oxide synthase (NOS), responsible for the production of nitric oxide (NO), when uncoupled is as a source of O2–, for example by the absence of its cofactor tetrahydrobiopterin (BH4). The present work shows that BH4 synthesis is compromised in melanoma cell lines. Analysis through qPCR showed that the expression of the transcripts for proteins involved in the de novo, salvage and recycling BH4 pathways are altered in melanoma cells when compared to melanocytes, resulting in decreased BH4:BH2 ratio. Western blot analysis showed increased expression of endothelial and inducible NOS in human melanoma cells, altering the stoichiometry between NOS levels and BH4 concentration and contributing to NOS uncoupling. The treatment of melanoma cells with exogenous BH4 increased NO concentration and decreased O2– levels, leading to NOS coupling, which in turn reduced the cell viability, cell proliferation and the ability of melanoma cells to form tumorspheres. Moreover, BH4 level restoration rendered melanoma cells more sensitive to apoptosis, demonstrating the role of dysfunctional NOS in melanoma genesis.

Petrogenic organic carbon retention in terrestrial basins: A case study from perialpine Lake Constance

Inland waters play a major role in the global carbon cycle, with particulate organic carbon (POC) burial in terrestrial wetlands surpassing that in ocean sediments. Lake Constance, the second largest lake at the periphery of the European Alps, receives POC sourced from both aquatic and terrestrial productivity as well as petrogenic OC (OCpetro) from bedrock erosion. Distinguishing POC inputs to lake sediments is key to assessing carbon flux and fate as reworked OCpetro represents neither a net sink of atmospheric CO2 nor source of O2. New stable and radiocarbon isotopic data indicate that 11 (9–12) Gg/yr of OCpetro is buried in Lake Constance with underlying sediments on average containing 0.3 (0.25–0.33) wt% OCpetro. Extrapolation of these results suggests that 27 TgOCpetro/yr (12–54 TgOC/yr) could be subject to temporary geological storage in lakes globally, which is comparable to estimates of 43−25+61 TgOCpetro/yr delivered to the ocean by rivers (Galy et al., 2015). More studies are needed to quantify OCpetro burial in inland sedimentary reservoirs in order to accurately account for atmospheric carbon sequestration in terrestrial basins.

Laboratory Studies of Vibrational Excitation in O2(a1Δg, v) Involving O2, N2, and CO2

Collisional removal of electronic energy from O2 in the low-lying a1Δg state is typically an extremely slow process for the v = 0 level. In this study, we report results on the deactivation of O2( a1Δg, v = 1-3) in collisions with O2 and CO2. Ozone photodissociation in the 200-310 nm Hartley band is the source of O2( a, v), and resonance-enhanced multiphoton ionization is used to probe the vibrational-level populations. Deactivation of the a( v = 1-3) levels in collisions with O2 at 300 K is fast, with rate coefficients of (5.6 ± 1.1) × 10-11, (3.6 ± 0.4) × 10-11, and (1.9 ± 0.4) × 10-11 cm3 s-1 (2σ) for v = 1, 2, and 3, respectively. The relaxation process appears to involve a near-resonant electronic energy transfer pathway analogous to that observed in vibrationally excited O2( b1Σg+). With CO2 collider gas, the removal rate coefficient at 300 K is (1.8 ± 0.4) × 10-14 and (4.4 ± 0.6) × 10-14 cm3 s-1 (2σ) for v = 1 and 2, respectively. Despite the small mole fraction of O2 in the atmospheres of Mars and Venus, O2 is at least as important as CO2 in the final stages of collisional relaxation within the O2 vibrational-level manifold.

CaO2 based Fenton-like reaction at neutral pH: Accelerated reduction of ferric species and production of superoxide radicals

One challenge in H2O2 based Fenton-like reaction is to break through the limitation of slow reduction of ferric species (FeIII). Present work describes a dramatic acceleration of Fenton-like reaction at neutral pH by using calcium peroxide (CaO2) as a source of hydrogen peroxide (H2O2) and EDTA as a chelating agent of ferric ions. In an optimized condition, phenol degradation in the H2O2 system displayed an initial latent time of 60 min, while phenol can be degraded immediately and removed completely in 30 min in the CaO2 system. Visual MINTEQ analyses indicated Fe-EDTA− was the active species in the reaction. The contribution of 1O2 in CaO2 system was excluded by the poor selectivity in phenol conversion and the comparable 1O2-TEMP EPR signals in both CaO2 and H2O2 systems. Kinetic analyses using chloroform as the probe of O2·− suggested the high production rate of O2·−, which is four orders of magnitude higher than that in H2O2 system. The mechanism of the accelerated CaO2 based Fenton-like reactions was featured by that two electrons coming from CaO2 can be utilized to promote reduction of FeIII: an inner sphere electron transfer takes place to reduce FeIII-EDTA and produce O2·−, and subsequently O2·− provides an electron to reduce another FeIII-EDTA. The revealed intrinsic reducibility in CaO2 based Fenton-like reaction represents a new strategy to break through the well-known rate limiting step of FeIII reduction in Fenton-like reaction and facilitate the removal of organic pollutants at neutral pHs, and also indicates a promising source of O2·− for diverse applications.

A Mesoarchean shift in uranium isotope systematics

Oxygenic photosynthesis fundamentally transformed all major biogeochemical cycles and increased the size and complexity of Earth's biosphere. However, there is still debate about when this metabolism evolved. As oxygenic photosynthesis is the only significant source of O2 at Earth’s surface, O2-sensitive trace element enrichments and isotopic signatures in Archean sedimentary rocks can potentially be used to determine the onset of oxygenic photosynthesis by tracking shifts in the oxidative capacity of Earth’s surface environment. Here, we present an extensive new Archean U isotope record from iron formations, organic-rich shales, and paleosols. Variability in δ238U values gradually increased from Archean to Phanerozoic, consistent with current view of gradual oxidation of Earth’s surface. In addition, statistical analysis on available δ238U data indicates a turning point of δ238U variability at roughly 3.0 billon years ago. We suggest that such a turning point in δ238U variability indicates the initiation of relatively large-scale oxidative weathering of U(IV)-bearing minerals, implying that oxygenic photosynthesis may have evolved before 3.0 billion years ago.

Highly Productive Oxidative Biocatalysis in Continuous Flow by Enhancing the Aqueous Equilibrium Solubility of Oxygen

AbstractWe report a simple, mild, and synthetically clean approach to accelerate the rate of enzymatic oxidation reactions by a factor of up to 100 when compared to conventional batch gas/liquid systems. Biocatalytic decomposition of H2O2 is used to produce a soluble source of O2 directly in reaction media, thereby enabling the concentration of aqueous O2 to be increased beyond equilibrium solubility under safe and practical conditions. To best exploit this method, a novel flow reactor was developed to maximize productivity (g product L−1 h−1). This scalable benchtop method provides a distinct advantage over conventional bio‐oxidation in that no pressurized gas or specialist equipment is employed. The method is general across different oxidase enzymes and compatible with a variety of functional groups. These results culminate in record space‐time yields for bio‐oxidation.

Highly Productive Oxidative Biocatalysis in Continuous Flow by Enhancing the Aqueous Equilibrium Solubility of Oxygen

We report a simple, mild, and synthetically clean approach to accelerate the rate of enzymatic oxidation reactions by a factor of up to 100 when compared to conventional batch gas/liquid systems. Biocatalytic decomposition of H2 O2 is used to produce a soluble source of O2 directly in reaction media, thereby enabling the concentration of aqueous O2 to be increased beyond equilibrium solubility under safe and practical conditions. To best exploit this method, a novel flow reactor was developed to maximize productivity (g product L-1 h-1 ). This scalable benchtop method provides a distinct advantage over conventional bio-oxidation in that no pressurized gas or specialist equipment is employed. The method is general across different oxidase enzymes and compatible with a variety of functional groups. These results culminate in record space-time yields for bio-oxidation.

Origin of molecular oxygen formation in irradiated borosilicate glasses studied by molecular dynamics simulation

AbstractFormation of molecular oxygen was observed in borosilicate glasses irradiated with energetic ions and electrons, which has significant effects on mechanical properties of glasses and evaluation of High Level nuclear Waste (HLW) immobilization. Though O2 was considered from the broken of X‐O‐Na (X is Si or B) in borosilicate glass, what was X species remained unclear. To find out the original source of molecular oxygen O2 in irradiated borosilicate glasses, several oxygen atoms were artificial randomly removed from the pristine glasses by molecular dynamics simulation (MD). The simulation results suggested that the formation of O2 firstly came from [BO4] units by the conversion of [BO4] to [BO3] units. When the conversion reached saturation, the [SiO4] units acted as the secondary source. Sodium phase separation was also derived after oxygen atoms reduced, which was well‐agreed with electron irradiated glasses. After the oxygen was removed, average Si‐O‐Si angle decreased and the small size rings increased. These simulation results were in good agreement with experiments.

Linking the rise of atmospheric oxygen to growth in the continental phosphorus inventory

The concentration of atmospheric oxygen (pO2) is thought to have increased throughout Earth history, punctuated by rapid increases ca. 2.4 and 0.8 billion years ago near the beginning and end of the Proterozoic Eon. As photosynthesis is the largest source of free O2, the reigning paradigm of rising O2 levels centres around biologic metabolism. Here we show that the phosphorus content of igneous rocks correlates, in a first-order sense, with secular increases in O2 through time, suggesting that rising O2 levels are affected by long-term mantle cooling and its effect on the continental phosphorus inventory. Because phosphorus is the limiting nutrient for primary productivity, its availability has fundamental control over the efficiency of oxygenic photosynthesis, pointing to a previously unrecognized role of the solid Earth in biologic and atmospheric evolution. Furthermore, as many bio-essential elements are effectively incompatible in the mantle, this relationship has implications for any terrestrial planet. All planets will cool, and those with efficient plate tectonic convection will cool more rapidly. We are left concluding that the speed of such cooling may affect pattern of biological evolution on any habitable planet.

Natively oxidized amino acid residues in the spinach cytochrome b 6 f complex.

The cytochrome b 6 f complex of oxygenic photosynthesis produces substantial levels of reactive oxygen species (ROS). It has been observed that the ROS production rate by b 6 f is 10-20 fold higher than that observed for the analogous respiratory cytochrome bc1 complex. The types of ROS produced (O2•-, 1O2, and, possibly, H2O2) and the site(s) of ROS production within the b 6 f complex have been the subject of some debate. Proposed sources of ROS have included the heme b p , PQ p•- (possible sources for O2•-), the Rieske iron-sulfur cluster (possible source of O2•- and/or 1O2), Chl a (possible source of 1O2), and heme c n (possible source of O2•- and/or H2O2). Our working hypothesis is that amino acid residues proximal to the ROS production sites will be more susceptible to oxidative modification than distant residues. In the current study, we have identified natively oxidized amino acid residues in the subunits of the spinach cytochrome b 6 f complex. The oxidized residues were identified by tandem mass spectrometry using the MassMatrix Program. Our results indicate that numerous residues, principally localized near p-side cofactors and Chl a, were oxidatively modified. We hypothesize that these sites are sources for ROS generation in the spinach cytochrome b 6 f complex.

127 - The Role of Uncoupled Nitric Oxide Synthase in Melanoma Development

Cancer is one of the leading causes of death in the world. Increased levels of reactive oxygen species, including superoxide anion (O2•‒), and the consequent installation of a pro-oxidant environment, contribute to the development of this disorder. The enzyme nitric oxide synthase (NOS), responsible for the production of nitric oxide, becomes the source of O2•‒ when it is in a state referred as uncoupled. The presence of tetrahydrobiopterin cofactor (BH4) is critical to keeping the enzyme coupled. The objective of this study was to evaluate the uncoupling of nitric oxide synthase and its contribution to carcinogenesis in human melanoma cells. The data obtained suggest that BH4 synthesis is compromised in melanoma lineages. Through qPCR we show that the expression levels of the transcripts from via de novo, salvage and recycling pathways are altered in tumors when compared to melanocytes, suggesting low levels of BH4 and uncoupling of NOS in tumor cells. When treated with BH4, cells from the SK-MEL-28 melanoma cell line showed decreased superoxide anion levels. Treatment with BH4 decreased the cell viability of SK-MEL-28 cells. These same cells when treated with BH4 showed reduced ability to form colonies and tumorspheres. It has been shown that treatment with BH4 rendered SK-MEL-28 cells more sensitive to apoptosis. This work contributed to evaluate the importance of BH4, as a cofactor of nitric oxide synthase, in the progression of melanoma.

Reflections on O2 as a Biosignature in Exoplanetary Atmospheres.

Oxygenic photosynthesis is Earth's dominant metabolism, having evolved to harvest the largest expected energy source at the surface of most terrestrial habitable zone planets. Using CO2 and H2O—molecules that are expected to be abundant and widespread on habitable terrestrial planets—oxygenic photosynthesis is plausible as a significant planetary process with a global impact. Photosynthetic O2 has long been considered particularly robust as a sign of life on a habitable exoplanet, due to the lack of known “false positives”—geological or photochemical processes that could also produce large quantities of stable O2. O2 has other advantages as a biosignature, including its high abundance and uniform distribution throughout the atmospheric column and its distinct, strong absorption in the visible and near-infrared. However, recent modeling work has shown that false positives for abundant oxygen or ozone could be produced by abiotic mechanisms, including photochemistry and atmospheric escape. Environmental factors for abiotic O2 have been identified and will improve our ability to choose optimal targets and measurements to guard against false positives. Most of these false-positive mechanisms are dependent on properties of the host star and are often strongest for planets orbiting M dwarfs. In particular, selecting planets found within the conservative habitable zone and those orbiting host stars more massive than 0.4 M⊙ (M3V and earlier) may help avoid planets with abundant abiotic O2 generated by water loss. Searching for O4 or CO in the planetary spectrum, or the lack of H2O or CH4, could help discriminate between abiotic and biological sources of O2 or O3. In advance of the next generation of telescopes, thorough evaluation of potential biosignatures—including likely environmental context and factors that could produce false positives—ultimately works to increase our confidence in life detection. Key Words: Biosignatures—Exoplanets—Oxygen—Photosynthesis—Planetary spectra. Astrobiology 17, 1022–1052.

Molecular-Orbital-Based Verification of Effective Water Photo Splitting to HOOH As a Precursor of Oxygen and Hydrogen on Pt-Loaded TiO2

Density functional theory based molecular modeling (DFT/MM) (B3LYP/6-31G*) of molecular complexes that are induced by van der Waals and Coulomb interaction lead us to theoretical understandings of physical and chemical phenomena especially when they are effective and efficient in electronic function. Recently, DFT/MM verified that in efficient water splitting in photoelectrochemical TiO2-based cells, electron-transfer oxidation of water yields HOOH on UV-light irradiated and biased-TiO2 anode.1) With regards to water photo splitting using Pt-loaded anatase TiO2 (Pt/TiO2), Arakawa and Sayama reported that efficient Pt/TiO2-catalyzed water photo splitting occurs in carbonate solution, giving stoichiometric amounts of O2 and H2.2) On careful examination of their data, concentration of hydroxide ion (HO-) as source of O2 and of water molecules as source of H2 seem to balance by using slightly alkali solution (pH=11) that is buffered by carbonate ion. In addition, they proposed two photolysis mechanisms via HOOH or peroxocarbonate for oxygen formation. However, it is not cleared how HOOH forms initially. Successive two-electron transfer oxidation is hardly conceivable on Pt/TiO2 because of very low energy potential of HOMO of one-electron-oxidized water molecule. We now verify and predict that, in Arakawa and Sayama’s photocatalytic water splitting, one-electron-transfer water oxidation leads to formation of OH radical (HO.) and then its coupling reaction to HOOH, and that exothermic platinum-mediated H2 evolution is driving force for the effective photo splitting of water. Hydrated hydroxyl ions, e.g., HO-/H2O and HO-/(H2O)2 are considered to undergo one-electron-oxidization on TiO2. We verified on the basis of DFT/MM of their electron transfer oxidations that, all oxidations will occur endothermically, and the two-electron transfer oxidations will be hardly occurred because more energy is necessary to withdraw electron on HOMO (E=-7.2 and -8.2 eV) of respective one-electron-oxidized specie, [HO-/H2O].- and [HO-/(H2O)2].-. The DFT/MM also rationalizes larger endothermic energy as much as 5 times of those of one-electron-oxidation (Figure 1). We extended DFT/MM to one-electron oxidation of [HO-/H2O] on anatase TiO2 model, [HO-/H2O/OHTi9O18H] (Figure 2). [HO-/H2O] interacts with [OHTi9O18H] exothermically (DE= -32.35 kcal/mol), and HOMO energy becomes lowered to HOMO=-2.23eV compared to HOMO=1.06eV of [HO-/H2O]. DFT/MM of one-electron-oxidized [HO-/H2O/OHTi9O18H].- reveals that spin (radical) locates on hydrated [HO./H2O/OH] site on Ti9O18H. Accumulation of hydroxyl radical (HO.) will yield hydrogen peroxide by coupling of HO. on photo-irradiated TiO2 surface. It is known that sodium percarbonate is an adduct of sodium carbonate and hydrogen peroxide with formula 2Na2CO3•3H2O2.3) Carbonate-stabilized hydrogen peroxide (HOOH) undergoes disproportionation reaction to yield triplet oxygen, 3O2 and H2O via auto-electron transfer and proton transfer at hydrogen-bonded HOOH dimer, [(H2O2) 2] as depicted in Figure 3. DFT/MM is extended to understand photo-reductive formation of H2 on Pt of Pt/TiO2. Platinum metal may prefer to less polar H2O species rather than polar ones. As shown in Figure 4, symmetrical nonpolar cyclic H2O trimer [np(H2O)3] is molecular-modeled for feasibility study of successive electron transfer reduction. All of intermediary [np(H2O)3].- and [np(H2O)3]..--, which have no hydrogen bonding, are shown with electron density. As LUMO configuration and spin density are also informative for electron-transfer reduction, LUMO configuration is shown for the starting [np(H2O)3] and spin density for others. Figure 4 shows that reductive electron transfer to LUMO orbital, and spin density is delocalized at center of [np(H2O)3].- and [np(H2O)3]..--. Interestingly, the elongated O-H bond in SPE[np(H2O)3]..--, where oxygen atoms are fixed and calculated, is suggestive as transient state of coupling of hydrogen radical to H2. Large endothermic energy, DE=+45.94 kcal/mol and DE=+178.27 makes us understand difficulty of successive photo-reduction of water under UV light irradiance in the absence of any catalysts. We succeeded in molecular modeling of platinum cluster as Pt6. DFT/MM is then farther extended to van der Waals complex of [np(H2O)3] with Pt6 (Figure 5). Molecular orbital-driven alignment of np(H2O)3 with Pt6 occurs exothermically (DE=-43.06 kcal/mol) and LUMO energy, -3.65eV is low enough to accept electron effectively for reduction. One-electron accepted [np(H2O)3/Pt6].- and two-electron accepted [np(H2O)3/Pt6]..-- are both calculated to form exothermically, giving DE=-77.21 and DE=-65.63 kcal/mol, respectively. Close examination of [np(H2O)3/Pt6]..-- suggests that, although spin density locates exclusively at Pt6, all hydrogen of water orients to Pt6 and HOMO energy is very positive, HOMO(1.66eV). We now understand that Pt clusters work as mediator for effective exothermic and efficient successive electron transfer for H2 evolution, and simultaneously, accelerate photocatalytic water splitting to HO. and HOOH. References 1) S.Yanagida, S.Yanagisawa, K. Yamashita, R. Jono and H. Segawa, Molecules 2015, 20(6), 9732-9744; doi:10.3390/molecules20069732. 2) K. Sayama and H. Arakawa, J. Chem. Soc., Faraday Trans., 1997, 93(8), 1647È1654 3) Wikipedia, search “Sodium percarbonate” Figure 1

Pt Electrodes Enable the Formation of μ4-O Centers in MOF-5 from Multiple Oxygen Sources.

The μ4-O2- ions in the Zn4O(O2C-)6 secondary building units of Zn4O(1,4-benzenedicarboxylate)3 (MOF-5) electrodeposited under cathodic bias can be sourced from nitrate, water, and molecular oxygen when using platinum gauze as working electrodes. The use of Zn(ClO4)2·6H2O, anhydrous Zn(NO3)2, or anhydrous Zn(CF3SO3)2 as Zn2+ sources under rigorous control of other sources of oxygen, including water and O2, confirm that the source of the μ4-O2- ions can be promiscuous. Although this finding reveals a relatively complicated manifold of electrochemical processes responsible for the crystallization of MOF-5 under cathodic bias, it further highlights the importance of hydroxide intermediates in the formation of the Zn4O(O2C-R) secondary building units in this iconic material and is illustrative of the complicated crystallization mechanisms of metal-organic frameworks in general.

Mitochondrial Superoxide Signaling Contributes to Norepinephrine-Mediated T-Lymphocyte Cytokine Profiles.

Norepinephrine (NE) produces multifaceted regulatory patterns in T-lymphocytes. Recently, we have shown that NE utilizes redox signaling as evidenced by increased superoxide (O2●-) causally linked to the observed changes in these cells; however, the source of this reactive oxygen species (ROS) remains elusive. Herein, we hypothesized that the source of increased O2●- in NE-stimulated T-lymphocytes is due to disruption of mitochondrial bioenergetics. To address this hypothesis, we utilized purified mouse splenic CD4+ and CD8+ T-lymphocytes stimulated with NE and assessed O2●- levels, mitochondrial metabolism, cellular proliferation, and cytokine profiles. We demonstrate that the increase in O2●- levels in response to NE is time-dependent and occurs at later points of T-lymphocyte activation. Moreover, the source of O2●- was indeed the mitochondria as evidenced by enhanced MitoSOX Red oxidation as well as abrogation of this signal by the addition of the mitochondrial-targeted O2●--scavenging antioxidant MitoTempol. NE-stimulated T-lymphocytes also demonstrated decreased mitochondrial respiratory capacity, which suggests disruption of mitochondrial metabolism and the potential source of increased mitochondrial O2●-. The effects of NE in regards to redox signaling appear to be adrenergic receptor-dependent as specific receptor antagonists could reverse the increase in O2●-; however, differential receptors regulating these processes were observed in CD4+ versus CD8+ T-lymphocytes. Finally, mitochondrial O2●- was shown to be mechanistic to the NE-mediated T-lymphocyte phenotype as supplementation of MitoTempol could reverse specific changes in cytokine expression observed with NE treatment. Overall, these studies indicate that mitochondrial metabolism and O2●--mediated redox signaling play a regulatory role in the T-lymphocyte response to NE.