The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Donald J. Siegel - One of the best experts on this subject based on the ideXlab platform.
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Intrinsic Conductivity in Sodium–Air Battery Discharge Phases: Sodium Superoxide vs Sodium Peroxide
Chemistry of Materials, 2015Co-Authors: Sheng Yang, Donald J. SiegelAbstract:The primary discharge product in sodium–air batteries has been reported in some experiments to be sodium peroxide, Na2O2, while in others sodium Superoxide, NaO2, is observed. Importantly, cells that discharge to NaO2 exhibit low charging overpotentials, while those that discharge to Na2O2 do not. These differences could arise from a higher conductivity within the Superoxide; however, this explanation remains speculative given that charge transport in Superoxides is relatively unexplored. Here, density functional and quasi-particle GW methods are used to comparatively assess the conductivities of Na–O2 discharge phases by calculating the concentrations and mobilities of intrinsic charge carriers in Na2O2 and NaO2. Both compounds are predicted to be electrical insulators, with bandgaps in excess of 5 eV. In the case of sodium peroxide, the transport properties are similar to those reported previously for lithium peroxide, suggesting low bulk conductivity. Transport in the Superoxide has some features in co...
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intrinsic conductivity in sodium air battery discharge phases sodium Superoxide vs sodium peroxide
Chemistry of Materials, 2015Co-Authors: Sheng Yang, Donald J. SiegelAbstract:The primary discharge product in sodium–air batteries has been reported in some experiments to be sodium peroxide, Na2O2, while in others sodium Superoxide, NaO2, is observed. Importantly, cells that discharge to NaO2 exhibit low charging overpotentials, while those that discharge to Na2O2 do not. These differences could arise from a higher conductivity within the Superoxide; however, this explanation remains speculative given that charge transport in Superoxides is relatively unexplored. Here, density functional and quasi-particle GW methods are used to comparatively assess the conductivities of Na–O2 discharge phases by calculating the concentrations and mobilities of intrinsic charge carriers in Na2O2 and NaO2. Both compounds are predicted to be electrical insulators, with bandgaps in excess of 5 eV. In the case of sodium peroxide, the transport properties are similar to those reported previously for lithium peroxide, suggesting low bulk conductivity. Transport in the Superoxide has some features in co...
Holly Van Remmen - One of the best experts on this subject based on the ideXlab platform.
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complex i generated mitochondrial matrix directed Superoxide is released from the mitochondria through voltage dependent anion channels
Biochemical and Biophysical Research Communications, 2012Co-Authors: Michael S Lustgarten, Arunabh Bhattacharya, Florian L Muller, Youngmok C Jang, Takahiko Shimizu, Takuji Shirasawa, Arlan Richardson, Holly Van RemmenAbstract:Mitochondrial complex I has previously been shown to release Superoxide exclusively towards the mitochondrial matrix, whereas complex III releases Superoxide to both the matrix and the cytosol. Superoxide produced at complex III has been shown to exit the mitochondria through voltage dependent anion channels (VDAC). To test whether complex I-derived, mitochondrial matrix-directed Superoxide can be released to the cytosol, we measured Superoxide generation in mitochondria isolated from wild type and from mice genetically altered to be deficient in MnSOD activity (TnIFastCreSod2(fl/fl)). Under experimental conditions that produce Superoxide primarily by complex I (glutamate/malate plus rotenone, GM+R), MnSOD-deficient mitochondria release ∼4-fold more Superoxide than mitochondria isolated from wild type mice. Exogenous CuZnSOD completely abolished the EPR-derived GM+R signal in mitochondria isolated from both genotypes, evidence that confirms mitochondrial Superoxide release. Addition of the VDAC inhibitor DIDS significantly reduced mitochondrial Superoxide release (∼75%) in mitochondria from either genotype respiring on GM+R. Conversely, inhibition of potential inner membrane sites of Superoxide exit, including the matrix face of the mitochondrial permeability transition pore and the inner membrane anion channel did not reduce mitochondrial Superoxide release in the presence of GM+R in mitochondria isolated from either genotype. These data support the concept that complex I-derived mitochondrial Superoxide release does indeed occur and that the majority of this release occurs through VDACs.
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complex iii releases Superoxide to both sides of the inner mitochondrial membrane
Journal of Biological Chemistry, 2004Co-Authors: Florian L Muller, Yuhong Liu, Holly Van RemmenAbstract:Mechanisms of mitochondrial Superoxide formation remain poorly understood despite considerable medical interest in oxidative stress. Superoxide is produced from both Complexes I and III of the electron transport chain, and once in its anionic form it is too strongly charged to readily cross the inner mitochondrial membrane. Thus, Superoxide production exhibits a distinct membrane sidedness or "topology." In the present work, using measurements of hydrogen peroxide (Amplex red) as well as Superoxide (modified Cypridina luciferin analog and aconitase), we demonstrate that Complex I-dependent Superoxide is exclusively released into the matrix and that no detectable levels escape from intact mitochondria. This finding fits well with the proposed site of electron leak at Complex I, namely the iron-sulfur clusters of the (matrix-protruding) hydrophilic arm. Our data on Complex III show direct extramitochondrial release of Superoxide, but measurements of hydrogen peroxide production revealed that this could only account for ∼50% of the total electron leak even in mitochondria lacking CuZn-Superoxide dismutase. We posit that the remaining ∼50% of the electron leak must be due to Superoxide released to the matrix. Measurements of (mitochondrial matrix) aconitase inhibition, performed in the presence of exogenous Superoxide dismutase and catalase, confirmed this hypothesis. Our data indicate that Complex III can release Superoxide to both sides of the inner mitochondrial membrane. The locus of Superoxide production in Complex III, the ubiquinol oxidation site, is situated immediately next to the intermembrane space. This explains extramitochondrial release of Superoxide but raises the question of how Superoxide could reach the matrix. We discuss two models explaining this result.
Sheng Yang - One of the best experts on this subject based on the ideXlab platform.
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Intrinsic Conductivity in Sodium–Air Battery Discharge Phases: Sodium Superoxide vs Sodium Peroxide
Chemistry of Materials, 2015Co-Authors: Sheng Yang, Donald J. SiegelAbstract:The primary discharge product in sodium–air batteries has been reported in some experiments to be sodium peroxide, Na2O2, while in others sodium Superoxide, NaO2, is observed. Importantly, cells that discharge to NaO2 exhibit low charging overpotentials, while those that discharge to Na2O2 do not. These differences could arise from a higher conductivity within the Superoxide; however, this explanation remains speculative given that charge transport in Superoxides is relatively unexplored. Here, density functional and quasi-particle GW methods are used to comparatively assess the conductivities of Na–O2 discharge phases by calculating the concentrations and mobilities of intrinsic charge carriers in Na2O2 and NaO2. Both compounds are predicted to be electrical insulators, with bandgaps in excess of 5 eV. In the case of sodium peroxide, the transport properties are similar to those reported previously for lithium peroxide, suggesting low bulk conductivity. Transport in the Superoxide has some features in co...
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intrinsic conductivity in sodium air battery discharge phases sodium Superoxide vs sodium peroxide
Chemistry of Materials, 2015Co-Authors: Sheng Yang, Donald J. SiegelAbstract:The primary discharge product in sodium–air batteries has been reported in some experiments to be sodium peroxide, Na2O2, while in others sodium Superoxide, NaO2, is observed. Importantly, cells that discharge to NaO2 exhibit low charging overpotentials, while those that discharge to Na2O2 do not. These differences could arise from a higher conductivity within the Superoxide; however, this explanation remains speculative given that charge transport in Superoxides is relatively unexplored. Here, density functional and quasi-particle GW methods are used to comparatively assess the conductivities of Na–O2 discharge phases by calculating the concentrations and mobilities of intrinsic charge carriers in Na2O2 and NaO2. Both compounds are predicted to be electrical insulators, with bandgaps in excess of 5 eV. In the case of sodium peroxide, the transport properties are similar to those reported previously for lithium peroxide, suggesting low bulk conductivity. Transport in the Superoxide has some features in co...
Irwin Fridovich - One of the best experts on this subject based on the ideXlab platform.
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Copper- and Zinc-containing Superoxide Dismutase Can Act as a Superoxide Reductase and a Superoxide Oxidase
The Journal of biological chemistry, 2000Co-Authors: Stefan I. Liochev, Irwin FridovichAbstract:Abstract The copper- and zinc-containing Superoxide dismutase can catalyze the oxidation of ferrocyanide by O⨪2 as well as the reduction of ferricyanide by O⨪2. Thus, it can act as a Superoxide dismutase (SOD), a Superoxide reductase (SOR), and a Superoxide oxidase (SOO). The human manganese-containing SOD does not exert SOR or SOO activities with ferrocyanide or ferricyanide as the redox partners. It is possible that some biological reductants can take the place of ferrocyanide and can also interact with human manganese-containing Superoxide dismutase, thus making the SOR activity a reality for both SODs. The consequences of this possibility vis a visH2O2 production, the overproduction of SODs, and the role of copper- and zinc-containing Superoxide dismutase mutations in causing familial amyotrophic lateral sclerosis are discussed, as well as the likelihood that the biologically effective SOD mimics, as described to date, actually function as SORs.
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Superoxide Radical and Superoxide Dismutases
Annual review of biochemistry, 1995Co-Authors: Irwin FridovichAbstract:The metalloenzymes that have been named Superoxide dismutases have several attributes. They are abundant, widely distributed, essential as a defense against oxygen toxicity; they are also unique among enzymes in that their natural substrate is an unstable free radical. They are evolution’s answer to the biological production of the Superoxide radical (O 2 − ). This free radical, previously considered only in connection with the high energy irradiation of oxygenated aqueous media, is also produced under ordinary circumstances within respiring cells. The Superoxide radical is intrinsically reactive and can furthermore engender other enormously reactive radicals and excited states which are potentially capable of destroying the delicate chemical architecture of the cell. The intermediates of oxygen reduction, i.e., O 2 − , H2O2, and OH·, are the primary cause of oxygen toxicity; the enzymes, which catalytically scavenge them or prevent their production, are the foremost defenses which limit that toxicity. H2O2 and the catalases and peroxidases, which scavenge it, are discussed in other chapters of this volume. We shall devote ourselves to Superoxide and the Superoxide dismutases.
B Kalyanaraman - One of the best experts on this subject based on the ideXlab platform.
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Superoxide anion formation from lucigenin an electron spin resonance spin trapping study
FEBS Letters, 1997Co-Authors: Jeannette Vasquezvivar, Neil Hogg, Kirkwood A Pritchard, Pavel Martasek, B KalyanaramanAbstract:Lucigenin (LC2+) is frequently used as a Superoxide probe. To detect Superoxide, lucigenin must be reduced to the lucigenin cation radical (LC.+). We show, using the phosphorylated spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), that lucigenin stimulates NADPH-dependent Superoxide production by endothelial nitric oxide synthase (eNOS). The formation of the DEPMPO-Superoxide adduct is calcium/calmodulin independent. DEPMPO-Superoxide adduct formation is inhibited by diphenyleneiodonium and is abolished by Superoxide dismutase. It is likely that eNOS/NADPH can reduce lucigenin to LC.+ which reduces oxygen to Superoxide. Consequently, lucigenin cannot be used to measure Superoxide formation.
