Oxidation of Structural Ferrous Iron in Vermiculites: I. Oxidation by Fe3+

AbstractVermiculite prepared from biotite by interlayer cation exchange was reacted with solutions exhibiting redox potentials between 625 and 765 mV. The redox potential was controlled by the Fe2+/Fe3+ activity ratio, measured with a Pt electrode, and kept constant by addition of hydrogen peroxide to balance electron transfer from structural Fe2+ to Fe3+ in solution. Oxidation of structural Fe2+ was followed by Eh-stat titration and the rate of oxidation was shown to depend on the amount of Fe3+ penetrating into interlayer positions. Consequently, it was affected not only by the redox potential, but also by the activity between Fe3+ and all other cations present in solution or in an exchangeable state. Oxidation and cation exchange are coupled reactions. In contrast to the redox potential in solution, the effective redox potential controlling the oxidation of structural Fe2+ was increased by preferential sorption of the Fe3+ ion.

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The redox potentials of the two-iron plant algal ferredoxins. An electrostatic model

Biochemical Journal ◽

10.1042/bj1330283 ◽

1973 ◽

Vol 133 (2) ◽

pp. 283-287 ◽

Cited By ~ 4

Author(s):

R. J. Kassner ◽

W. Yang

Keyword(s):

Electron Transfer ◽

Free Energy ◽

Redox Potential ◽

Negative Charge ◽

Electrostatic Model ◽

Redox Potentials ◽

Electron Transfer Proteins ◽

Electrostatic Free Energy ◽

The One ◽

Charged Ions

The two-iron–sulphur co-ordination centre in plant and algal ferredoxins is considered as a collection of charged ions whose net negative charge is twice that of the one-iron–sulphur protein rubredoxin. Calculation of the electrostatic free-energy changes for reduction of the two types of proteins indicates that the redox potential of the two-iron–sulphur proteins should be more negative than that of the one-iron–sulphur protein and that in biological systems the ferredoxins should function as one-electron transfer proteins.

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

10.1101/2021.04.15.440034 ◽

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.

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Geothrix fermentans Secretes Two Different Redox-Active Compounds To Utilize Electron Acceptors across a Wide Range of Redox Potentials

Applied and Environmental Microbiology ◽

10.1128/aem.01460-12 ◽

2012 ◽

Vol 78 (19) ◽

pp. 6987-6995 ◽

Cited By ~ 44

Author(s):

Misha G. Mehta-Kolte ◽

Daniel R. Bond

Keyword(s):

Electron Transfer ◽

Redox Potential ◽

Electron Acceptor ◽

Extracellular Electron Transfer ◽

Redox Potentials ◽

Active Compounds ◽

Content Type ◽

Electron Shuttles ◽

Redox Active ◽

Geothrix Fermentans

ABSTRACTThe current understanding of dissimilatory metal reduction is based primarily on isolates from the proteobacterial generaGeobacterandShewanella. However, environments undergoing active Fe(III) reduction often harbor less-well-studied phyla that are equally abundant. In this work, electrochemical techniques were used to analyze respiratory electron transfer by the only known Fe(III)-reducing representative of theAcidobacteria,Geothrix fermentans. In contrast to previously characterized metal-reducing bacteria, which typically reach maximal rates of respiration at electron acceptor potentials of 0 V versus standard hydrogen electrode (SHE),G. fermentansrequired potentials as high as 0.55 V to respire at its maximum rate. In addition,G. fermentanssecreted two different soluble redox-active electron shuttles with separate redox potentials (−0.2 V and 0.3 V). The compound with the lower midpoint potential, responsible for 20 to 30% of electron transfer activity, was riboflavin. The behavior of the higher-potential compound was consistent with hydrophilic UV-fluorescent molecules previously found inG. fermentanssupernatants. Both electron shuttles were also produced when cultures were grown with Fe(III), but not when fumarate was the electron acceptor. This study reveals thatGeothrixis able to take advantage of higher-redox-potential environments, demonstrates that secretion of flavin-based shuttles is not confined toShewanella, and points to the existence of high-potential-redox-active compounds involved in extracellular electron transfer. Based on differences between the respiratory strategies ofGeothrixandGeobacter, these two groups of bacteria could exist in distinctive environmental niches defined by redox potential.

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Redox potentials along the redox-active low-barrier H-bonds in electron transfer pathways

Physical Chemistry Chemical Physics ◽

10.1039/d0cp04265j ◽

2020 ◽

Vol 22 (44) ◽

pp. 25467-25473 ◽

Cited By ~ 1

Author(s):

Keisuke Saito ◽

Manoj Mandal ◽

Hiroshi Ishikita

Keyword(s):

Electron Transfer ◽

Proton Transfer ◽

Redox Potential ◽

Driving Force ◽

Electronic Coupling ◽

Redox Potentials ◽

Redox Active ◽

Electron Transfer Pathways

Local proton transfer along redox-active low-barrier H-bonds can alter the driving force or electronic coupling for electron transfer, as the redox potential values depend on the H+ position in low-barrier H-bonds.

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Measurement of Redox Potential in Nanoecotoxicological Investigations

Journal of Toxicology ◽

10.1155/2012/270651 ◽

2012 ◽

Vol 2012 ◽

pp. 1-7 ◽

Cited By ~ 7

Author(s):

Ratna Tantra ◽

Alex Cackett ◽

Roger Peck ◽

Dipak Gohil ◽

Jacqueline Snowden

Keyword(s):

Redox Potential ◽

Reduction Potential ◽

Redox Potentials ◽

Dissolved Oxygen Concentration ◽

Liquid Media ◽

Pt Electrode ◽

Potential Value ◽

Oxidation Reduction ◽

Oxidation Reduction Potential ◽

Value Contribution

Redox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the redox potentials of six nanomaterials (either zinc oxide (ZnO) or cerium oxide (CeO2)) dispersions were measured using an oxidation-reduction potential (ORP) electrode probe. The particles under testing differed in terms of their particle size and dispersion stability in deionised water and in various ecotox media. The ORP values of the various dispersions and how they fluctuate relative to each other are discussed. Results show that the ORP values are mainly governed by the type of liquid media employed, with little contributions from the nanoparticles. Seawater was shown to have reduced the ORP value, which was attributed to an increase in the concentration of reducing agents such as sulphites or the reduction of dissolved oxygen concentration. The lack of redox potential value contribution from the particles themselves is thought to be due to insufficient interaction of the particles at the Pt electrode of the ORP probe.

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Tuning Redox Potential of Anthraquinone-2-Sulfonate (AQS) by Chemical Modification to Facilitate Electron Transfer From Electrodes in Shewanella oneidensis

Frontiers in Bioengineering and Biotechnology ◽

10.3389/fbioe.2021.705414 ◽

2021 ◽

Vol 9 ◽

Author(s):

Ning Xu ◽

Tai-Lin Wang ◽

Wen-Jie Li ◽

Yan Wang ◽

Jie-Jie Chen ◽

...

Keyword(s):

Electron Transfer ◽

Redox Potential ◽

Environmental Remediation ◽

Rational Design ◽

Coulombic Efficiency ◽

Shewanella Oneidensis ◽

Extracellular Electron Transfer ◽

Total Charge ◽

Redox Potentials ◽

Chemical Production

Bioelectrochemical systems (BESs) are emerging as attractive routes for sustainable energy generation, environmental remediation, bio-based chemical production and beyond. Electron shuttles (ESs) can be reversibly oxidized and reduced among multiple redox reactions, thereby assisting extracellular electron transfer (EET) process in BESs. Here, we explored the effects of 14 ESs on EET in Shewanella oneidensis MR-1, and found that anthraquinone-2-sulfonate (AQS) led to the highest cathodic current density, total charge production and reduction product formation. Subsequently, we showed that the introduction of -OH or -NH2 group into AQS at position one obviously affected redox potentials. The AQS-1-NH2 exhibited a lower redox potential and a higher Coulombic efficiency compared to AQS, revealing that the ESs with a more negative potential are conducive to minimize energy losses and improve the reduction of electron acceptor. Additionally, the cytochromes MtrA and MtrB were required for optimal AQS-mediated EET of S. oneidensis MR-1. This study will provide new clues for rational design of efficient ESs in microbial electrosynthesis.

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RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

RSC Advances ◽

10.1039/d1ra03293c ◽

2021 ◽

Vol 11 (35) ◽

pp. 21359-21366

Author(s):

Debabrata Chatterjee ◽

Marta Chrzanowska ◽

Anna Katafias ◽

Maria Oszajca ◽

Rudi van Eldik

Keyword(s):

Hydrogen Peroxide ◽

Electron Transfer ◽

Electrochemical Reduction ◽

Molecular Oxygen ◽

Outer Sphere ◽

Transfer Processes ◽

Edta Complexes ◽

Inner Sphere ◽

Electron Transfer Processes ◽

Sphere Mechanism

[RuII(edta)(L)]2–, where edta4– =ethylenediaminetetraacetate; L = pyrazine (pz) and H2O, can reduce molecular oxygen sequentially to hydrogen peroxide and further to water by involving both outer-sphere and inner-sphere electron transfer processes.

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Insight to Microbial Fe(III) Reduction Mediated by Redox-Active Humic Acids with Varied Redox Potentials

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18136807 ◽

2021 ◽

Vol 18 (13) ◽

pp. 6807

Author(s):

Jingtao Duan ◽

Zhiyuan Xu ◽

Zhen Yang ◽

Jie Jiang

Keyword(s):

Molecular Weight ◽

Electron Transfer ◽

Humic Acids ◽

Weight Fraction ◽

Electrochemical Analysis ◽

Microbial Reduction ◽

Redox Potentials ◽

Groundwater Environment ◽

Redox Active ◽

Different Molecular Weight

Redox-active humic acids (HA) are ubiquitous in terrestrial and aquatic systems and are involved in numerous electron transfer reactions affecting biogeochemical processes and fates of pollutants in soil environments. Redox-active contaminants are trapped in soil micropores (<2 nm) that have limited access to microbes and HA. Therefore, the contaminants whose molecular structure and properties are not damaged accumulate in the soil micropores and become potential pollution sources. Electron transfer capacities (ETC) of HA reflecting redox activities of low molecular weight fraction (LMWF, <2.5) HA can be detected by an electrochemical method, which is related to redox potentials (Eh) in soil and aquatic environments. Nevertheless, electron accepting capacities (EAC) and electron donating capacities (EDC) of these LMWF HA at different Eh are still unknown. EDC and EAC of different molecular weight HA at different Eh were analyzed using electrochemical methods. EAC of LMWF at −0.59 V was 12 times higher than that at −0.49 V, while EAC increased to 2.6 times when the Eh decreased from −0.59 V to −0.69 V. Afterward, LMWF can act as a shuttle to stimulate microbial Fe(III) reduction processes in microbial reduction experiments. Additionally, EAC by electrochemical analysis at a range of −0.49–−0.59 V was comparable to total calculated ETC of different molecular weight fractions of HA by microbial reduction. Therefore, it is indicated that redox-active functional groups that can be reduced at Eh range of −0.49–−0.59 are available to microbial reduction. This finding contributes to a novel perspective in the protection and remediation of the groundwater environment in the biogeochemistry process.

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Role of redox-inactive metals in controlling the redox potential of heterometallic manganese–oxido clusters

Photosynthesis Research ◽

10.1007/s11120-021-00846-y ◽

2021 ◽

Author(s):

Keisuke Saito ◽

Minesato Nakagawa ◽

Manoj Mandal ◽

Hiroshi Ishikita

Keyword(s):

Photosystem Ii ◽

Redox Potential ◽

Quantum Chemical Calculations ◽

Catalytic Reaction ◽

Quantum Chemical ◽

Ionic Radius ◽

Redox Potentials ◽

Oxygen Evolving ◽

Highest Occupied Molecular Orbitals

AbstractPhotosystem II (PSII) contains Ca2+, which is essential to the oxygen-evolving activity of the catalytic Mn4CaO5 complex. Replacement of Ca2+ with other redox-inactive metals results in a loss/decrease of oxygen-evolving activity. To investigate the role of Ca2+ in this catalytic reaction, we investigate artificial Mn3[M]O2 clusters redox-inactive metals [M] ([M] = Mg2+, Ca2+, Zn2+, Sr2+, and Y3+), which were synthesized by Tsui et al. (Nat Chem 5:293, 2013). The experimentally measured redox potentials (Em) of these clusters are best described by the energy of their highest occupied molecular orbitals. Quantum chemical calculations showed that the valence of metals predominantly affects Em(MnIII/IV), whereas the ionic radius of metals affects Em(MnIII/IV) only slightly.

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