Redox reference

Let us choose, as an arbitrary reference level, the energy of an electron at rest in vacuum, e ) (cf. Section 3.1.2). This reference energy is obvious in studies of the solid phase, but for the liquid phase, the Trasatti s conception of absolute electrode potentials (Section 3.1.5) has to be adopted. The formal energy levels of the electrolyte redox systems, REDox, referred to o, are given by the relationship ... 

There are three types of reference electrodes discussed reference electrodes of the first kind, reference electrodes of the second kind, and redox reference electrodes. The first two are used with potentiometric chemical sensors, whereas the last one helps us to get around the difficult problem of comparing potentials in different solvents. There is also a pseudo-reference electrode that does not have a stable, defined, reproducible potential. It serves only as the signal return to satisfy the condition of closing the electrical circuit (see Section 5.2). Because the liquid junction always causes some leakage of the internal solution, electrodes of the first kind are particularly affected. 

Another form of redox reference electrode is similar to the electrode of the first kind. In this case the inert metal (e.g., Pt, Au, or C) is used as the inner electrode and a stable and soluble redox couple is placed inside the inner reference electrode compartment. A normal liquid junction is used in this type of reference electrode. Unlike the electrode of the first kind, the redox reference electrode is relatively immune to changes in concentration inside the reference electrode compartment because it is the ratio of the reduced/oxidized form of redox couple that determines the potential and not the absolute concentrations. However, redox reference electrodes are sensitive to changes of concentration of oxygen and other redox species. 

Pseudo-reference Electrodes and Internal Redox Reference Couples... 

Protein Oxidation State Change Edge Shift (eV) Ligand vs. Metal Redox References... 

The basis of both anabolic and catabolic pathways is the reactions of reduction and oxidation. Oxidation refers to the combination of an atom or molecule with oxygen, or the loss from it of hydrogen or of one or more electrons. Reduction, the opposite of oxidation, is the gain of one or more electrons by an atom or molecule. The nature of these reactions requires them to occur together i.e., oxidation always occurs in conjunction with reduction. The term redox refers to this coupling of reduction and oxidation. 

The one-electron reduction potential of interest is then calculated from the equilibrium constant and the one-electron reduction potential of the redox reference couple using Nemst s equation (AE° = 0.0591 log K). While electrochemical techniques often yield irreversible oxidation potentials, pulse radiolysis usually yields thermodynamically correct one-electron reduction potenticils, provided the reactions are fast... 

In biology, pH and redox are inextricably linked. However, given the range of effects that redox has on the chemistiy of mfps, a separate treatment is presented here. Redox refers to the electron transfer between different components, and redox potentials reflect the ease or difficulty of electron transfer. For example, there are about 2.5 pmoles O2 permL of seawater at 20 °C. The reduction of O2 to water requires the transfer of 2e and 2 H from somewhere to each o)ygen atom to produce one molecule of water. As a half-reaction, the favorability of this reaction is indicated by the positive Ej at standard conditions (pH 7,1 atm, 1 M concentration, 25 °C, SHE) ... 

Also known as the standard hydrogen electrode (SHE), it is a redox reference electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. The potential of the NHE is defined as zero and based oti equilibrium of the following redox half-cell reaction, typically on a Pt surface 2H+(aq) + 2e H2(g). The activities of both the reduced form and the oxidized form are maintained at unity. That implies that the pressure of hydrogen gas is 1 atm and the concentration of hydrogen ions in the solution is 1 M. 

Redox An abbreviation for reduction/oxidation, redox refers to simultaneous reactions in which one agent is oxidized (loss of an electron) and one is reduced (gain of an electron). 

An alternate redox reference compound to metallocenes has been proposed by Compton and co-workers [25]. The redox chemistry of A,iV,iV, A/ -tetramethyl-p-phenylenediamine (TMPD) is two electron transfer processes as shown below ... 

As can be seen from Table 7.9, the potential difference between the CcICc" couple and the TMPD first redox process is constant for the ILs tested. The approximate 20 mV shifts observed are most likely due to experimental uncertainties. Thus, the TMPD complex offers an alternative to the ferrocene or cobaltocene couples for reference potential calibration. If the potential of the TMPD couple is close to that of the electroactive species, then use of the bis (phenyl)chromium(l) tetraphenylborate (BCr) redox couple with ILs has also been proposed by Lewandowski et al. [49]. Studies of this redox reference compound in [EMIm][BF4] show that it has a stable potential at +0.236 to +0.248 V vs. CcICc" (range dependent on electrode material) [49]. 

De Vreese P, Haerens K, Matthijs E, Binnemans K (2012) Redox reference systems in ionic liquids. Electrochim Acta 76 242-248. doi 10.1016/j.electacta.2012.04.108... 

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