Absolute Potential of the Standard Hydrogen Electrode and the Problem of Interconversion of Potentials in Different Solvents

2010 ◽  
Vol 114 (23) ◽  
pp. 7894-7899 ◽  
Author(s):  
Abdirisak A. Isse ◽  
Armando Gennaro
Keyword(s):  
Standard Hydrogen Electrode ◽  
Hydrogen Electrode ◽  
Absolute Potential

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.

Synthesis and Biological Evaluation of 7α,7α,7α,8α,8α,8α- Hexafluororiboflavin and 7α,7α,7α,8α,8α,8α-Hexafluoro-FMN

1983 ◽  
Vol 38 (9-10) ◽  
pp. 701-707 ◽  
Author(s):  
Peter Nielsen ◽  
Adelbert Bacher ◽  
Diana Darling ◽  
Mark Cushman
Keyword(s):  
Lactobacillus Casei ◽  
Reduction Potential ◽  
Biological Evaluation ◽  
Standard Hydrogen Electrode ◽  
Significant Extent ◽  
Hydrogen Electrode ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Order Of Magnitude ◽  
Synthesis And Biological Evaluation

7α,7α,7α,8α,8α,8α-Hexafluororiboflavin (4) has been prepared and its oxidation-reduction potential determined polarographically to be + 0.02 V with respect to the standard hydrogen electrode. Compound 4 does not by itself promote the growth of Lactobacillus casei. However, in the presence of low riboflavin (1) concentrations, the hexafluoro analog 4 has some growth enhancing activity. The FMN analog 7α,7α,7α,8α,8α,8α-hexafluororiboflavin 5′-phosphate (10) was also synthesized and found to bind tightly to apoflavodoxin from Megasphaera elsdenii. The dissociation constant (3.2 × 10-9m) is about one order of magnitude larger than that of FMN (1.1 × 10-10м). However, apoflavodoxin reconstituted with hexafluororiboflavin 5′-phosphate (10) has no coenzyme activity. Hexafluoro-FMN (10) was also unable to act as a coenzyme for luciferase from Photobacterium fisheri. Hexafluororiboflavin 4 did not inhibit the light riboflavin synthase from Bacillus subtilis to a significant extent {Ki> 10-4 м).

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
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