Electron self-exchange rate

In the present case, the electron hopping chemistry in the polymeric porphyrins is an especially rich topic because we can manipulate the axial coordination of the porphyrin, to learn how electron self exchange rates respond to axial coordination, and because we can compare the self exchange rates of the different redox couples of a given metallotetraphenylporphyrin polymer. To measure these chemical effects, and avoid potentially competing kinetic phenomena associated with mobilities of the electroneutrality-required counterions in the polymers, we chose a steady state measurement technique based on the sandwich electrode microstructure (19). 

Fig. 5. Plot of apparent electron self exchange rate constants kf P, derived from polymer De values for films containing the indicated metals, mixed valent states, and ligands, all in acetonitrile, using Equation 2, vs. literature heterogeneous electron transfer rate constants k° for the corresponding monomers in nitrile solvents. See Ref. 6 for details. (Reproduced from Ref. 6. Copyright 1987 American Chemical Society.)...

The electron self-exchange rate constants evaluated by the Marcus expressions (using cross-reaction data) and those determined experimentally differ in the following cases. Give possible reasons for these differences. 

The electron self-exchange rate constants (At) have been assessed for the following couples at 25 °C and x = 0.1 M ... 

Despite the lack of theoretical models for interfacial recombination processes in excitonic solar cells, it is obvious empirically that those cells which function efficiently must have a very slow rate of recombination. In DSSCs, this can be explained simply by the slow electron self-exchange rate of the I /I2 redox couple and the absence of field-driven recombination. However, in the case of solid-state, high-surface-area OPV cells, such as the conducting polymer/C60-derivative cells [36,39], the slow rate of interfacial recombination is an important problem that is not yet understood. 

The reversibility of the [Os(bpy)3]3+/2+ couple makes it useful for the determination of the electron self-exchange rates of other couples by application of the Marcus cross-reaction equation. Recently, this has been applied to the oxidation of S032- to S042- (622). The new rate constant for this reaction of 1.63 x 107 M-1 sec-1 is consistent with the... 

Table 10.2. Observed and calculated electron self-exchange rates of hexaamine cobalt(III/II) complexes11321.

Electron Self-Exchange Rate Constants kese (298K) for Blue Copper Proteins Retrieved from NMR Spectra... 

Since the metal ion is involved only for the acceptor part, the dependence of A-a on [M" ] should be responsible for the change in X.da with M"" concentration. The electron self-exchange between Fc NQ and the Fc—NQ /M" complex occurs via formation of the Fc NQ/M" complex as shown in Scheme 20. According to Scheme 20, the electron self- exchange rate constant (A ex) is given by Eq. 20, where Z is the frequency factor for the intermolecular ET reaction, (A,a )... 

An attempt was made to obtain the electron self-exchange rate constant for the [Fe(CN)2-(phen)2]" couple by an electrochemical method. Real space Laplace analysis was used for the chronoamperometric response of 7.05 x 10 4 M (M = mol dm 3) solutions of the iron(III) complex with 0.1 M tetra(/t-butyl)ammonium perchlorate as supporting electrolyte. A glassy carbon working electrode with 3 mm diameter was used for the measurements. The Butler-Volmer plot gave an excellent straight line, and the electrochemical self-exchange rate constant was obained to be 1.2 X lO cm s l from the In k value at the zero over-potential. From the... 

The much faster electron self-exchange rate observed for Rh than for Co reflects different localization of the corresponding redox couples, at the bpy ligand and the Co metal, respectively. 

Marcus theory of electron transfer (Eq. 4) [91] to the rate of electron transfer from ferrocyanide to HRP compound I (8 x 10 M s ) [105], An even larger reorganization energy (2 = 78.0 kcal mol ) [104] was derived from the electron self-exchange rate between HRP compound II and ferric HRP (4.9 x 10 m s ) [104], The extremely large 2 value (78.0 kcal mol ) for the metal-centered electron-exchange between HRP compound II (Fe ) and ferric HRP (Fe ) is consistent with the large... 

Table 1. Rate constants for electron self-exchange rates determined for different Co /Co systems in water at 25 C.

Electron self- exchange rate constants for macrobicychc cobalt complexes. 

An elegant example of the measurement of an electron self-exchange rate of a redox protein was reported by Dahlin et al. The copper ion of stellacyanin was removed and then replaced with either Cu or Cu. Oxidized [ Cu] stellacyanin was allowed to react with reduced [ Cu] stellacyanin for various times (10 ms to 7 min) at 20°C, after which the reaction was quenched by lowering the solution temperature to - 120°C using a rapid-freeze apparatus ... 

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