M redox potential

Cheng, J., Sulpizi, M., Sprik, M. Redox potentials and pKa for benzoquinone from density functional theory based molecular dynamics. J. Chem. Phys. 2009,131,154504. 

The FeMoco has been observed in three redox states. When the enzyme is isolated in the presence of dithionite, the FeMoco is in the M ( native ) form. Most c stallographic studies have taken place on enzyme in which the FeMoco is in the M state. M° can be generated by one-electron oxidation of M with dyes, and can be reactivated by reduction. The M° /M redox potential is dependent on the organism from which the nitrogenase is derived, lying in the range OmV to — 180mV. " The X-ray crystal structure of MoFe protein with the FeMoco in the M° state shows no major differences from M is the turnover state of the enzyme,... 

The standard redox potentials of inorganic oxidants used in organic synthesis are generally around or above + 1.0 V. Organic substrates do not have such high potentials. The values for the CH4/CH3OH and CjHj/CjHjOH couples are at +0,59 V and 0.52 V, respectively. The oxidation of alcohols and aldehydes corresponds to values around 0.0 V (W.M. 

A metallic electrode whose potential is a function of the concentration of M"+ in an M"+/M redox half-reaction. 

Electrodes of the Second Kind An electrode of the first kind involving an M"+/M redox couple will respond to the concentration of another species if that species is in equilibrium with M"+. For example, the potential of a silver electrode in a solution of Ag+ is given by... 

AK Churg, A Warshel. Control of the redox potential of cytochrome c and microscopic dielectric effects m proteins. Biochemistry 25 1675, 1986. 

J-M Mouesca, JL Chen, F Noodleman, D Bashford, DA Case. Density functional/Poisson-Boltzmann calculations of redox potentials for iron-sulfur clusters. J Am Chem Soc 116 11898-11914, 1994. 

VS Shenoy. Contribution of Protein Environment to Redox Potentials of Rubredoxm and Cytochrome c. M.S. Thesis. Pullman, WA Washington State University, 1992. 

PD Swartz, BW Beck, T Ichiye. Stiaictural origins of redox potential m iron-sulfur proteins Electrostatic potentials of crystal structures. Biophys 1 71 2958-2969, 1996. 

BW Beck, Q Xie, T Ichiye. Computational study of S—H S hydrogen bonds m [4Ee-4S]-type ferredoxm x-ray and NMR structures Characterization and implications for redox potentials. Protein Sci, submitted. 

MK Eidsness, AK Burden, KA Richie, DMJ Kurtz, RA Scott, ET Smith, T Ichiye, C Kang. Modulation of the redox potential of the Ee(SCys)4 site m rubredoxm by the orientation of a peptide dipole. Biochemistry 38 14803-14809, 1999. 

As a result, the electromotive force (EMF) of the cell is zero In the presence of fluoride ions, cerium(IV) forms a complex with fluoride ions that lowers the cerium(IV)-cerium(IIl) redox potential The inner half-cell is smaller, and so only 5 mL of cerium(IV)-cenum (III) solution is added To the external half-cell, 50 mL of the solution is added, but the EMF of the cell is still zero When 10 mL of the unknown fluonde solution is added to the inner half-cell, 100 mL of distilled water IS added to the external half-cell The solution in the external half-cell is mixed thoroughly by turning on the stirrer, and 0 5 M sodium fluonde solution is added from the microburet until the null point is reached The quantity of known fluonde m the titrant will be 10 times the quantity of the unknown fluoride sample, and so the microburet readings must be corrected prior to actual calculations... 

It follows from the electrochemical mechanism of corrosion that the rates of the anodic and cathodic reactions are interdependent, and that either or both may control the rate of the corrosion reaction. It is also evident from thermodynamic considerations (Tables 1.9 and 1.10) that for a species in solution to act as an electron acceptor its redox potential must be more positive than that of the M /M equilibrium or of any other equilibrium involving an oxidised form of the metal. 

Environment (aqueous) Lower the redox potential of the solution, i.e. lower Increase the potential of the M /M equilibrium, i.e. increase, Lower a by raising pH, remove dissolved O2 or other oxidising species Increase / + by removing complexants (e.g. CN ions) from solution... 

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

It has been shown (Section 10.89) that the potential at the equivalence point is the mean of the two standard redox potentials. In Fig. 10.14, the curve shows the variation of the potential during the titration of 0.1 M iron(II) ion with... 

M cerium(IV) solution, and the equivalence point is at 1.10 volts. Ferroin changes from deep red to pale blue at a redox potential of 1.12 volts the indicator will therefore be present in the red form. After the addition of, say, a 0.1 per cent excess of cerium(IV) sulphate solution the potential rises to 1.27 volts, and the indicator is oxidised to the pale blue form. It is evident that the titration error is negligibly small. 

The absolute rate constants for attack of carbon-centered radicals on p-benzoquinone (38) and other quinones have been determined to be in the range I0M08 M 1 s 1.1 -04 This rate shows a strong dependence on the electrophilicity of the attacking radical and there is some correlation between the efficiency of various quinones as inhibitors of polymerization and the redox potential of the quinone. The complexity of the mechanism means that the stoichiometry of inhibition by these compounds is often not straightforward. Measurements of moles of inhibitor consumed for each chain terminated for common inhibitors of this class give values in the range 0.05-2.0.176... 

NMR studies on graphite-phosphoric acid showed simultaneous, motional narrowing of both H and resonances above 225 K, indicating high mobility of phosphoric acid in the compound (FS). Chloro-sulfonic acid is inserted alone into graphite in the presence of many inorganic chlorides. The reaction temperature and stage seem to be related to the redox potential of the M"+-M couple (M3). 

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