Visualizing Redox Chemistry: Probing Environmental Oxidation–Reduction Reactions with Indicator Dyes

Tratnyek, Paul G.; Reilkoff, Thea E.; Lemon, Anthony W.; Scherer, Michelle M.; Balko, Barbara A.; Feik, Linda M.; Henegar, Brad D.

doi:10.1007/s00897010471a

Cited by 71 publications

(68 citation statements)

References 28 publications

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“…4). Relative populations of [DFsc-Zn( ii ) 2 ]–SQ • (λ max = 740 nm) and oxidized ITS (λ max = 594 nm, E mid,7 = −46 mV) 41 under steady-state conditions were determined, and fit in the Nernst equation to yield the midpoint potential E mid,7 = −21 mV versus NHE for the reduction of [DFsc-Zn( ii ) 2 ]–SQ • at neutral pH, a value that is ~400 mV less than the reported reduction potential of free SQ • in aqueous solution 39 . This finding indicates that [DFsc-Zn( ii ) 2 ]–SQ • is strongly stabilized in the protein environment (by 9 kcal mol −1 ).…”

Section: Resultsmentioning

confidence: 99%

Designed metalloprotein stabilizes a semiquinone radical

Ulas

Lemmin

et al. 2016

Nature Chem

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Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(ii) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal–ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol−1). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry.

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Section: Resultsmentioning

confidence: 99%

Designed metalloprotein stabilizes a semiquinone radical

Ulas

Lemmin

et al. 2016

Nature Chem

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“…The oxidized quinoid form of I2S (I2S ox ) is bright blue (λ max = 610 nm), and the reduced dihydro form (I2S red ) is pale yellow (λ max = 407 nm) at circum-neutral pH. 38 At the concentrations used in this study (∼140 μM), the reduction of I2S is easily detected by the visible change of solution color from blue to yellow. We have shown previously that the sulfonated indigo redox indicators do not adsorb significantly to most relevant, environmental materials (ZVI, iron oxides, sediments, etc.)…”

Section: ■ Experimental Sectionmentioning

confidence: 98%

Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron

Fan

Chen

Johnson

et al. 2015

Environ. Sci. Technol.

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Nano zerovalent iron synthesized with carboxymethylcelluose (CMC-nZVI) is among the leading formulations of nZVI currently used for in situ groundwater remediation. The main advantage of CMC-nZVI is that it forms stable suspensions, which are relatively mobile in porous media. Rapid contaminant reduction by CMC-nZVI is well documented, but the fate of the CMC-nZVI (including "aging" and "reductant demand") is not well characterized. Improved understanding of CMC-nZVI fate requires methods with greater specificity for Fe(0), less vulnerability to sampling/recovery artifacts, and more practical application in the field. These criteria can be met with a simple and specific colorimetric approach using indigo-5,5'-disulfonate (I2S) as a chemical redox probe (CRP). The measured stoichiometric ratio for reaction between I2S and nZVI is 1.45 ± 0.03, suggesting complete oxidation of nZVI to Fe(III) species. However, near pH 7, reduction of I2S is diagnostic for Fe(0), because aqueous Fe(II) reduces I2S much more slowly than Fe(0). At that pH, adding Fe(II) increased I2S reduction rates by Fe(0), consistent with depassivation of nZVI, but did not affect the stoichiometry. Using the I2S assay to quantify changes in the Fe(0) content of CMC-nZVI, the rate of Fe(0) oxidation by water was found to be orders of magnitude faster than previously reported values for other types of nZVI.

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“…Resazurin (purple at alkaline pH) is reduced irreversibly to resorufin (pink) and then reduced reversibly to dihydroresorufin (colorless) (Tratnyek et al 2001). Resazurin produced a color change of purple to pink for the saltstone sample, yet the slag-free sample remained purple implying a reduced solution with saltstone and an oxidized solution with the no slag sample.…”

Section: Resultsmentioning

confidence: 99%

“…Redox indicators have been used as chemical probes to study the redox behavior of environmental systems (Tratnyek et al 2001). They are an approved method for use by soil surveyors interested in delineating wetlands.…”

Section: Chemical Redox Indicatorsmentioning

confidence: 99%

“…Identification of distinct spectroscopic features indicative of reduced or oxidized species within saltstone was targeted for this method. Chemical redox indicators have been used as chemical probes to study the redox behavior of environmental systems (Tratnyek et al 2001). They are an approved method for use by soil surveyors interested in delineating wetlands where "redox features" can be tested with a redox indicator to determine whether the feature is oxidized or reduced.…”

Section: Introductionmentioning

confidence: 99%

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