scholarly journals Species-Specific, pH-Independent, Standard Redox Potential of Selenocysteine and Selenocysteamine

Antioxidants ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 465
Author(s):  
Tamás Pálla ◽  
Arash Mirzahosseini ◽  
Béla Noszál
Keyword(s):  
Redox Potential ◽  
Equilibrium Constants ◽  
Biological Significance ◽  
Redox Potentials ◽  
Acid Base ◽  
Redox Equilibrium ◽  
Standard Redox Potential ◽  
Ph Dependent ◽  
Species Specific ◽  
Redox Equilibria

Microscopic redox equilibrium constants and standard redox potential values were determined to quantify selenolate-diselenide equilibria of biological significance. The highly composite, codependent acid-base and redox equilibria of selenolates could so far be converted into pH-dependent, apparent parameters (equilibrium constants, redox potentials) only. In this work, the selenolate-diselenide redox equilibria of selenocysteamine and selenocysteine against dithiothreitol were analyzed by quantitative nuclear magnetic resonance (NMR) methods to characterize the interfering acid-base and redox equilibria. The directly obtained, pH-dependent, conditional redox equilibrium constants were then decomposed by our method into pH-independent, microscopic constants, which characterize the two-electron redox transitions of selenocysteamine and selenocysteine. The 12 different, species-specific parameter values show close correlation with the respective selenolate basicities, providing a tool to estimate otherwise inaccessible site-specific selenolate-diselenide redox potentials of related moieties in large peptides and proteins.

Some Physicochemical Peculiarities of Poplar Plastocyanins a and b

2009 ◽  
Vol 64 (5-6) ◽  
pp. 399-404 ◽  
Author(s):  
Petya K. Christova ◽  
Anthony A. Donchev ◽  
Alexandra C. Shosheva ◽  
Vladimir I. Getov ◽  
Mitko I. Dimitrov
Keyword(s):  
Plant Species ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
The Other ◽  
Redox Potentials ◽  
Extinction Coefficients ◽  
Structural Differences ◽  
Ph Dependent ◽  
Ph Range ◽  
Reduced Forms

The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectro photometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients ε597, equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron potentials E0′: PCa: ε597 = (4.72 ± 0.08) mM-1 cm-1, Keq = 0.133 ± 0.009, E0′ = (354 ± 11) mV; PCb: ε597 = (5.23 ± 0.16) mM-1 cm-1, Keq = 0.175 ± 0.010, E0′ = (363 ± 12) mV. The pH dependence of the redox potential of PCb was studied too. It was found, that the value of E0′ for PCb is constant in the pH range 6.5 - 9.5, but decreases in the range 4.8 - 6.5. On the whole, the dependence resembles that of PC from some well-known plant species, including poplar PCa. The changes of E0′ in the pH-dependent region for poplar PCb, however, are smaller and are 13 mV per pH unit, whereas in the other well-known plant species the changes are about 50 - 60 mV per pH unit. It has been assumed that the weaker pH dependence of E0′ of PCb accounts for some structural differences between PCa and PCb

Species-specific thiol-disulfide equilibrium constants of ovothiol A and penicillamine with glutathione

RSC Advances ◽  
2016 ◽  
Vol 6 (32) ◽  
pp. 26757-26764 ◽  
Author(s):  
Arash Mirzahosseini ◽  
Béla Noszál
Keyword(s):  
Equilibrium Constants ◽  
Protonation Constants ◽  
Glutathione System ◽  
Redox Equilibrium ◽  
System P ◽  
The Difference ◽  
Species Specific

The correlation between species-specific redox equilibrium constants and the difference of thiolate protonation constants was determined for the ovothiol–glutathione system.

Electrochemical Description of Redox Equilibria in Nuclear Glass

2009 ◽  
Vol 1193 ◽  
Author(s):  
O. Pinet ◽  
S. Mure
Keyword(s):  
Wide Spectrum ◽  
Equilibrium Constants ◽  
Electrochemical Techniques ◽  
Fission Products ◽  
Redox Equilibrium ◽  
Redox Species ◽  
Dissolved Species ◽  
Single Matrix ◽  
Glass Matrices ◽  
Redox Equilibria

AbstractGlass matrices were selected to immobilize fission products because glass is capable of chemically incorporating a wide spectrum of elements within a single matrix. Some of these elements can be found at different oxidation states. The redox equilibrium constants of multivalent species can be used to develop thermodynamic models for a better description of nuclear glasses. Some of the multivalent species loaded in nuclear glass, such as iron and sulfur, have already been a subject of investigation by conventional glassmakers or geochemists in the earth sciences. Other redox species more specifically related to nuclear glass, including cerium and ruthenium, have also been investigated. These studies have demonstrated the advantages of using electrochemical techniques, voltammetry and potentiometry, to determine the equilibrium constants. Oxygen potential measurements are also particularly suitable for characterizing the redox state of the multivalent dissolved species in molten glass.

Spectrophotometric study of the acid-base and optical properties of the 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-(diethylamino)phenol (BrPADAP, ClPADAP) and their complexation equilibria with zinc(II) ions

1982 ◽  
Vol 47 (10) ◽  
pp. 2676-2691 ◽  
Author(s):  
Miroslav Macka ◽  
Vlastimil Kubáň
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Alkaline Media ◽  
Acid Base ◽  
Ethanol Medium ◽  
Triton X ◽  
Mixed Water ◽  
Derivatives Of

The optical and acid-base characteristics of BrPADAP and ClPADAP were studied in mixed water-ethanol and water-DMF media and in 10% ethanol medium in the presence of cationic, anionic and nonionic tensides. The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the ML and ML2 complexes with zinc(II) ions were found by graphical analysis and numerical interpretation of the absorbance curves by the modified SQUAD-G program. Optimal conditions were found for the spectrophotometric determination of Zn(II) in the presence of 0.1% Triton X-100 or 1% Brij 35 in alkaline media with pH = 6.5-10. BrPADAP and ClPADAP are the most sensitive reagents (ε = 1.3-1.6 . 105 mmol-1 cm2 at 557 and 560 nm, respectively) for the determination of zinc with high colour contrast of the reaction (Δλ = 104 nm) and selectivity similar to that for the other N-heterocyclic azodyes (PAN, PAR, etc.).

Total weak acid concentration and effective dissociation constant of nonvolatile buffers in human plasma

2001 ◽  
Vol 91 (3) ◽  
pp. 1364-1371 ◽  
Author(s):  
Peter D. Constable
Keyword(s):  
Dissociation Constant ◽  
Human Plasma ◽  
Total Concentration ◽  
Weak Acid ◽  
Strong Ion Difference ◽  
Acid Base ◽  
Horse Plasma ◽  
Using Data ◽  
Species Specific

The strong ion approach provides a quantitative physicochemical method for describing the mechanism for an acid-base disturbance. The approach requires species-specific values for the total concentration of plasma nonvolatile buffers (Atot) and the effective dissociation constant for plasma nonvolatile buffers ( K a), but these values have not been determined for human plasma. Accordingly, the purpose of this study was to calculate accurate Atot and K a values using data obtained from in vitro strong ion titration and CO2tonometry. The calculated values for Atot (24.1 mmol/l) and K a (1.05 × 10−7) were significantly ( P < 0.05) different from the experimentally determined values for horse plasma and differed from the empirically assumed values for human plasma (Atot = 19.0 meq/l and K a = 3.0 × 10−7). The derivatives of pH with respect to the three independent variables [strong ion difference (SID), Pco 2, and Atot] of the strong ion approach were calculated as follows: [Formula: see text] [Formula: see text], [Formula: see text]where S is solubility of CO2 in plasma. The derivatives provide a useful method for calculating the effect of independent changes in SID+, Pco 2, and Atot on plasma pH. The calculated values for Atot and K a should facilitate application of the strong ion approach to acid-base disturbances in humans.

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

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.

scholarly journals Dithienylpyrrole Electrografting on a Surface through the Electroreduction of Diazonium Salts

Electrochem ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 20-31
Author(s):  
Thi Huong Le ◽  
Van Quyen Nguyen ◽  
Gaelle Trippe-Allard ◽  
Jean-Christophe Lacroix ◽  
Pascal Martin
Keyword(s):  
Electron Transfer ◽  
Redox Potential ◽  
Diazonium Salts ◽  
Organic Thin Film ◽  
Organic Film ◽  
Aniline Derivative ◽  
Standard Redox Potential ◽  
Key Issues ◽  
Adhesion Process

The control of the interface and the adhesion process are key issues for the development of new application based on electrochromic materials. In this work the functionalization of an electrode’s surface through electroreduction of diazonium generated in situ from 4-(2,5-di-thiophen-2-yl-pyrrol-1-yl)-phenylamine (SNS-An) has been proposed. The synthesis of the aniline derivative SNS-An was performed and the electrografting was investigated by cyclic voltammetry on various electrodes. Then the organic thin film was fully characterized by several techniques and XPS analysis confirms the presence of an organic film based on the chemical composition of the starting monomer and allows an estimation of its thickness confirmed by AFM scratching measurements. Depending on the number of electrodeposition cycles, the thickness varies from 2 nm to 10 nm, which corresponds to a few grafted oligomers. In addition, the grafted film showed a good electrochemical stability depending on the scan rates up to 400 V/s and the electrochemical response of the modified electrode towards several redox probes showed that the attached layer acts as a conductive switch. Therefore, the electrode behaves as a barrier to electron transfer when the standard redox potential of the probe is below the layer switching potential, whereas the layer can be considered as transparent towards the electron transfer for redox probes with a redox potential above it.

scholarly journals Electrochemically Induced Metal- vs. Ligand-Based Redox Changes in Mackinawite: Identification of a Fe3+- and Polysulfide-Containing Intermediate

2021 ◽  
Author(s):  
Sebastian Sanden ◽  
Robert Szilagyi ◽  
Yamei Li ◽  
Norio Kitadai ◽  
Samuel M Webb ◽  
...  
Keyword(s):  
Redox Potential ◽  
Ferrous Iron ◽  
Maturation Process ◽  
Anaerobic Conditions ◽  
Ph Dependent

Under anaerobic conditions, ferrous iron reacts with sulfide producing FeS, which can then undergo a temperature, redox potential, and pH dependent maturation process resulting in the formation of oxidized mineral...

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