Consistent scheme for computing standard hydrogen electrode and redox potentials

2012 ◽  
Vol 34 (1) ◽  
pp. 21-26 ◽  
Author(s):  
Toru Matsui ◽  
Yasutaka Kitagawa ◽  
Mitsutaka Okumura ◽  
Yasuteru Shigeta ◽  
Shigeyoshi Sakaki
Keyword(s):  
Standard Hydrogen Electrode ◽  
Redox Potentials ◽  
Hydrogen Electrode

Accurate Standard Hydrogen Electrode Potential and Applications to the Redox Potentials of Vitamin C and NAD/NADH

2015 ◽  
Vol 119 (2) ◽  
pp. 369-376 ◽  
Author(s):  
Toru Matsui ◽  
Yasutaka Kitagawa ◽  
Mitsutaka Okumura ◽  
Yasuteru Shigeta
Keyword(s):  
Vitamin C ◽  
Electrode Potential ◽  
Standard Hydrogen Electrode ◽  
Redox Potentials ◽  
Hydrogen Electrode

Redox properties of MX-80 and Montigel bentonite-water systems

2002 ◽  
Vol 757 ◽  
Author(s):  
Cecilia Lazo ◽  
Ola Karnland ◽  
Eva-Lena Tullborg ◽  
Ignasi Puigdomenech
Keyword(s):  
Dissolved Oxygen ◽  
Pyrite Oxidation ◽  
Water Systems ◽  
Redox Properties ◽  
Membrane Electrode ◽  
Main Process ◽  
Standard Hydrogen Electrode ◽  
Redox Potentials ◽  
Hydrogen Electrode ◽  
Similar Time

ABSTRACTThe uptake of dissolved oxygen (O2) has been studied in bentonite suspensions in 0.1 M NaCl media at (25±2)°C. MX-80 and Montigel bentonites were used in concentrations varying from 18 to 73 g/L. The experiments were performed in a magnetically stirred closed glass vessel, in an N2-glove box. Redox potentials where measured with Pt-wires, and dissolved O2 was measured both with a membrane electrode and with an optode. The experiments with MX-80 show that dissolved O2 disappears in ∼5 days under these conditions. Redox potentials decreased from ∼ +500 to ∼ +125 mVSHE (versus Standard Hydrogen Electrode). The data for the Montigel bentonite show similar time scales for O2 uptake but lower redox potentials at the end of the experiments ∼ −175 mVSHE. Pyrite oxidation is perhaps not the main process for O2 uptake, as MX-80 contains 0.3% FeS2 while Montigel bentonite only has a negligible amount.

scholarly journals Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 437 ◽  
Author(s):  
Peter Cook ◽  
YoungJae Kim ◽  
Ke Yuan ◽  
Maria C. Marcano ◽  
Udo Becker
Keyword(s):  
Photoelectron Spectroscopy ◽  
Redox Reactions ◽  
Redox Potentials ◽  
Free Energies ◽  
Cathodic Peak ◽  
Redox Transformation ◽  
Hydrogen Electrode ◽  
Midpoint Potential ◽  
Ph Conditions ◽  
Cv Measurements

Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh and pH conditions (+0.3 to −0.6 V vs. standard hydrogen electrode, SHE; pH 4.6) using a combination of electrochemical, spectroscopic, and computational approaches. Cyclic voltammetry (CV) measurements reveal one anodic/cathodic peak pair at a midpoint potential of +30 mV (vs. SHE) that represents reduction and oxidation between HSeO3− and H2Se/HSe−. Two peak pairs with midpoint potentials of −400 and −520 mV represent the redox transformation from Se(0) to HSe− and H2Se species, respectively. The changes in Gibbs free energies of adsorption of Se species on galena surfaces as a function of Se oxidation state were modeled using quantum-mechanical calculations and the resulting electrochemical peak shifts are (−0.17 eV for HSeO3−/H2Se, −0.07 eV for HSeO3−/HSe−, 0.15 eV for Se(0)/HSe−, and −0.15 eV for Se(0)/H2Se). These shifts explain deviation between Nernstian equilibrium redox potentials and observed midpoint potentials. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of Se(0) potentials below −100 mV and Se(0) and Se(−II) species at potentials below −400 mV.

scholarly journals Tactic Response ofShewanella oneidensisMR-1 toward Insoluble Electron Acceptors

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Joseph Oram ◽  
Lars J. C. Jeuken
Keyword(s):  
Average Velocity ◽  
Cell Tracking ◽  
Reduction Potential ◽  
Electron Acceptors ◽  
Electrochemical Potential ◽  
Electrochemical Cells ◽  
Standard Hydrogen Electrode ◽  
Hydrogen Electrode ◽  
Exoelectrogenic Bacteria ◽  
Insoluble Electron Acceptors

ABSTRACTExoelectrogenic bacteria are defined by their ability to respire on extracellular and insoluble electron acceptors and have applications in bioremediation and microbial electrochemical systems (MESs), while playing important roles in biogeochemical cycling.Shewanella oneidensisMR-1, which has become a model organism for the study of extracellular respiration, is known to display taxis toward insoluble electron acceptors, including electrodes. Multiple mechanisms have been proposed for MR-1’s tactic behavior, and, here, we report on the role of electrochemical potential by video microscopy cell tracking experiments in three-electrode electrochemical cells. MR-1 trajectories were determined using a particle tracking algorithm and validated with Shannon’s entropy method. Tactic response by MR-1 in the electrochemical cell was observed to depend on the applied potential, as indicated by the average velocity and density of motile (>4 µm/s) MR-1 close to the electrode (<50 µm). Tactic behavior was observed at oxidative potentials, with a strong switch between the potentials −0.15 to −0.25 V versus the standard hydrogen electrode (SHE), which coincides with the reduction potential of flavins. The average velocity and density of motile MR-1 close to the electrode increased when riboflavin was added (2 µM), but were completely absent in a ΔmtrC/ΔomcAmutant of MR-1. Besides flavin’s function as an electron mediator to support anaerobic respiration on insoluble electron acceptors, we propose that riboflavin is excreted by MR-1 to sense redox gradients in its environment, aiding taxis toward insoluble electron acceptors, including electrodes in MESs.IMPORTANCEPrevious hypotheses of tactic behavior of exoelectrogenic bacteria are based on techniques that do not accurately control the electrochemical potential, such as chemical-in-plug assays or microscopy tracking experiments in two-electrode cells. Here, we have revisited previous experiments and, for the first time, performed microscopy cell-tracking experiments in three-electrode electrochemical cells, with defined electrode potentials. Based on these experiments, taxis toward electrodes is observed to switch at about −0.2 V versus standard hydrogen electrode (SHE), coinciding with the reduction potential of flavins.

scholarly journals Electrochemical and spectroscopic characterization of the 7Fe form of ferredoxin III from Desulfovibrio africanus

1989 ◽  
Vol 264 (1) ◽  
pp. 265-273 ◽  
Author(s):  
F A Armstrong ◽  
S J George ◽  
R Cammack ◽  
E C Hatchikian ◽  
A J Thomson
Keyword(s):  
Low Temperature ◽  
Pyrolytic Graphite ◽  
Spectroscopic Characterization ◽  
Carbon Electrode ◽  
Standard Hydrogen Electrode ◽  
Hydrogen Electrode ◽  
Iron Cluster ◽  
Desulfovibrio Gigas ◽  
Acid Labile

Desulfovibrio africanus ferredoxin III is a monomeric protein (Mr 6585) containing seven cysteine residues and 7-8 iron atoms and 6-8 atoms of acid-labile sulphur. It is shown that reversible unmediated electrochemistry of the two iron-sulphur clusters can be obtained by using a pyrolytic-graphite-‘edge’ carbon electrode in the presence of an appropriate aminoglycoside, neomycin or tobramycin, as promoter. Cyclic voltammetry reveals two well-defined reversible waves with E0′ = -140 +/- 10 mV and -410 +/- 5 mV (standard hydrogen electrode) at 2 degrees C. Bulk reduction confirms that each of these corresponds to a one-electron process. Low-temperature e.p.r. and magnetic-c.d. spectroscopy identify the higher-potential redox couple with a cluster of core [3Fe-4S]1+.0 and the lower with a [4Fe-4S]2+.1+ centre. The low-temperature magnetic-c.d. spectra and magnetization properties of the three-iron cluster show that it is essentially identical with that in Desulfovibrio gigas ferredoxin II. We assign cysteine-11, -17 and -51 as ligands of the [3Fe-4S] core and cysteine-21, -41, -44 and -47 to the [4Fe-4S] centre.

scholarly journals Geobacter sulfurreducens inner membrane cytochrome CbcBA controls electron transfer and growth yield near the energetic limit of respiration

2021 ◽  
Author(s):  
Komal Joshi ◽  
Chi Ho Chan ◽  
Daniel R. Bond
Keyword(s):  
Electron Transfer ◽  
Redox Potential ◽  
Growth Yield ◽  
Growth Efficiency ◽  
Geobacter Sulfurreducens ◽  
Redox Potentials ◽  
Hydrogen Electrode ◽  
Highly Expressed Genes ◽  
Reducing Bacteria ◽  
Transfer Chain

AbstractGeobacter sulfurreducens utilizes extracellular electron acceptors such as Mn(IV), Fe(III), syntrophic partners, and electrodes that vary from +0.4 to −0.3 V vs. Standard Hydrogen Electrode (SHE), representing a potential energy span that should require a highly branched electron transfer chain. Here we describe CbcBA, a bc-type cytochrome essential near the thermodynamic limit of respiration when acetate is the electron donor. Mutants lacking cbcBA ceased Fe(III) reduction at −0.21 V vs. SHE, could not transfer electrons to electrodes between −0.21 and −0.28 V, and could not reduce the final 10% – 35% of Fe(III) minerals. As redox potential decreased during Fe(III) reduction, cbcBA was induced with the aid of the regulator BccR to become one of the most highly expressed genes in G. sulfurreducens. Growth yield (CFU/mM Fe(II)) was 112% of WT in ΔcbcBA, and deletion of cbcL (a different bc-cytochrome essential near −0.15 V) in ΔcbcBA increased yield to 220%. Together with ImcH, which is required at high redox potentials, CbcBA represents a third cytoplasmic membrane oxidoreductase in G. sulfurreducens. This expanding list shows how these important metal-reducing bacteria may constantly sense redox potential to adjust growth efficiency in changing environments.

scholarly journals Redox potential as a master variable controlling pathways of metal reduction byGeobacter sulfurreducens

2016 ◽  
Author(s):  
Caleb E. Levar ◽  
Colleen L. Hoffman ◽  
Aubrey J. Dunshee ◽  
Brandy M. Toner ◽  
Daniel R. Bond
Keyword(s):  
Redox Potential ◽  
Geobacter Sulfurreducens ◽  
High Potential ◽  
Growth Yields ◽  
Redox Potentials ◽  
Hydrogen Electrode ◽  
Additional Energy ◽  
Single Organism ◽  
Wide Range ◽  
Dependent Pathway

AbstractGeobacter sulfurreducensuses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of −0.10 V vs. the Standard Hydrogen Electrode (SHE), while the ImcH-dependent pathway operates only above this value. Here, we provide evidence thatG. sulfurreducensalso requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)- (oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.

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