Two-electron couple

By plotting A p (as y ) against (as x ) for each pair of peaks, the intercepts are 24 mV for the first couple and 31 mV for the second. In both cases, therefore, the intercept is consistent with a value of about 59/n mV, provided that each couple is a two-electron transfer. We expect a two-electron couple, however, because the analyte is V2O5, so one electron is transferred per vanadium. 

Show that the two-electron coupling coefficients (3 21) have the symmetry properties given by (3 22). Use the results to deduce the symmetry properties of the second-order density matrix (3 23). 

This expression is often called the resolution of the identity . The expression (6.6) for the two-electron coupling coefficient can now be rewritten by introducing expression (7.6) between the generators of the unitary group. The result is,... 

The conductivity of salts in solvents of low dielectric constant, and of metals in liquid ammonia, exhibit minima which may be explained in terms of an equilibrium between ions and a coulombic compound of two ions, or "ion pairs." This equilibrium conforms to the law of mass action. At limiting conductance in solutions of sodium in liquid ammonia, part of the current is carried by metal ions, but seven-eighths is carried by electrions. Following the BLA model, it is assumed that when two ion pairs, consisting of a sodium ion and an electron, come together, the spins of the two electrons couple to form disodium spinide. Increase in conductivity past the minimum is assumed to be caused by dissociation of disodium spinide into sodium ions and spinions. 

There is reason to believe that an equilibrium of this type exists between the sodium ions and the electrion to form an ion pair as a result of coulombic interactions. If the conductance data for sodium are used to determine the equilibrium constant of sodium in liquid ammonia for computing the constant of the ion pair equilibrium, the experimental data do not conform to values required for such an equilibrium. This is because electrons in dilute solutions exhibit magnetic properties, from which we may conclude that, at very low concentrations, the electron has a spin of l/2 Bohr unit. It is, therefore, necessary to take into account the effect of the decreasing proportion of electrons that may be spin-coupled and interacting with the positive ions of the solvent. One of us (Evers) made the simplest possible assumption, following a model proposed by Becker, Lindquist, and Alder (BLA), namely that when two ion pairs, consisting of a sodium ion and an electron, come together the spins of the two electrons couple to form disodium spinide, and that this coulombic compound is not dissociated into ions at low concentrations. 

The light catalyzed oxidation of water by the PSII RC complex yields three products, O2, electrons, and protons (Fig. 1). Oxygen gas diffuses out of the cells while the protons accumulate in the lumenal space, since the latter cannot cross the lipophilic thylakoid membranes. During electron transfer from PSII to PSI, two electrons, coupled with two protons, are transported from the stromal side (outside) of the thylakoid membrane to the lumen (inside). This also contributes to the accumula tion of a proton gradient across the membrane. The proton gradient creates a proton... 

It is well known that superexchange theory provides useful relationships between one- and two-electron coupling elements (e.g., [28, 78, 138]). We consider the simple case of a monocation electron transfer system,... 

Some authors absorb the factor of 1/2 into the definition of the two-electron coupling coefficient and reduced density matrix. 

Figure 4-6. (A) A close-up view of the active site of yeast cytochrome c peroxidase showing the residues in the distal pocket at which hydrogen peroxide is reduced to water. Overlaid on the structure of the wild type enzyme are the positions of residues in the W51F mutant (tryptophan is replaced by phenylalanine). (B) Voltammograms of a film of wild type CcP on a PGE electrode, obtained in the absence and presence of H2O2 at ice temperature, pH 5.0. The electrode is rotating at 200 rpm, but the catalytic current in this case continues to increase as the rotation rate is increased therefore under these conditions the electrocatalysis is diffusion controlled and few facts are revealed about the enzyme s chemistry. For the W51F mutant, the signal due to the reversible two-electron couple and the catalytic wave are both shifted >100 mV more positive in potential compared to the wild-type enzyme. Reproduced from ref. 46 and 47 with permission.

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