Electron transfer driving-force dependence

Using the dyad shown in Figure 6.26, it has been possible to investigate the driving-force dependence of the rate constants for the electron-transfer processes. 

Study of the Driving Force Dependence of the Electron Transfer Rate... 

The reducing equivalents transferred can be considered either as hydrogen atoms or electrons. The driving force for the reaction, E, is the reduction/oxidation (redox) potential, and can be measured by electrochemistry it is often expressed in millivolts. The number of reducing equivalents transferred is n. The redox potential of a compound A depends on the concentrations of the oxidized and reduced species [Aqx] and [Area] according to the Nernst equation ... 

The photoinduced electron-transfer dynamics has also been examined for a series of porphyrin-fullerene-linked molecules with the same spacer employed for Fc-ZnP-H2P-C6o ZnP-Ceo (edge-to-edge distance Ree = 11-9 A), Fc-ZnP-Ceo (Ree = 30.3 A) and ZnP-H2P-Ceo (Ree = 30.3 A), shown in Chart 1 [53]. The driving force dependence of the electron-transfer rate constants ( et) of these dyad, triads, and tetrad molecules is shown in Fig. 3, where log et is plotted against the driving force (-AGet) [47]. 

A parabolic driving force dependence of logket is also observed for electron-transfer reduction of fullerenes in PhCN, as shown in Fig. 13.10 [18, 28-32]. 

The work that can be accomplished when electrons are transferred through a wire depends on the push (the thermodynamic driving force) behind the electrons. This driving force (the emf) is defined in terms of a potential difference (in volts) between two points in the circuit. Recall that a volt represents a joule of work per coulomb of charge transferred ... 

Figure 3. Driving force-dependence of intramolecular electron transfer rates in Ru-ammine-His33 modified Zn-substituted cytochrome c ( ), and Ru-bpy-His33 modified Fe-cytochrome c ( ). Solid lines were generated using Eq. 1 and the following parameters Ru-ammine,, i=1.15 eV, Hab = 0.10 cm Ru-bpy, X = 0.74 eV, Hab = 0.095 cm". ...

In the case of a redox reaction, the driving force for the reaction, and consequently for the rate constants, in particular depends on the potential dtfference at the interface. More precisely, this driving force depends on the difference between the potential at the surface of the metal and the potential in the electrolyte at the very point where the electroactive species is located when the electron transfer occurs. The kinetic models which reflect precisely these features are complex, and therefore we are kee ping ourselves confined to equations based on common and simplified descriptions for electrochemical kinetics for the E mechanism. In this context, any changes in the redox reaction rate constant can be described using the following two kinetic parameters ... 

Eugster, N., D.J. Fermin, and H.H. Girault (2002). Photoinduced electron transfer at hquid/hquid interfaces. Part VI. On the thermodynamic driving force dependence of the phenomenological electron transfer rate constant. J. Phys. Chem. B 106, 3428-3433. 

R= Ru(CN)6 -, Mo(CN)8 -, Fe(CN)6 -, and so forth (Table 2)) in an aqueous phase have been surveyed. At the probe microelectrode surface, ZnPor+ was oxidized to ZuFor" ". When the probe is positioned close to the benzene-water interface, ZnPor+ is reduced back to ZnPor by accepting an electron from R in the aqueous phase at the liquid-liquid interface. In the experiment, the driving force was controlled with two parameters the difference in standard potentials of the redox mediators in benzene and in water (AE ), and the interfacial potential drop (A ), which is controllable by varying the concentration ratio of a base electrolyte such as Cl04 in the two Kquids. The driving force dependence on the electron transfer rate at the liquid-liquid interface has been shown in the literature in the absence and presence of the monolayer. The existence of the monolayer lowers the electron transfer... 

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