Electron transfer kinetics, parameters

FIGURE 4.1 3. a RDEV response of a monolayer catalytic coating for the reaction scheme in Figure 4.10 with a slow P/Q electron transfer. Kinetic parameter [equation (4.5)] kr°8/DA = 5. The same electrode transfer MHL law as in Figure 1.18. Dotted line Nemstian limiting case. Solid lines from left to right, e (5r0DAC = 1, 0.1, 0.01. h Derivation of the catalytic rate constant, c Derivation of the kinetic law. 

Morris studied the aqueous solution voltammetric behavior of some uranyl coordination complexes to learn how changes in the ligand environment influence the redox potentials and heterogeneous electron-transfer kinetic parameters for the single-electron transfer... 

When the electrolysis process is irreversible (in a thermodynamic sense) but still limited by linear diffusion, the potential-time relationship takes a form that includes the heterogeneous electron-transfer kinetic parameters. For a cathodic process the relation is... 

Heterogeneous Electron Transfer Kinetic Parameters of Redox Proteins by Single Potential Step Chronoabsorptometry... 

E. E. Bancroft, H. N. Blount, and F. M. Hawkridge, in Spectroelectrochemical Determination of Heterogeneous Electron Transfer Kinetic Parameters (K. M. Kadish, ed.). Advances in Chemistry Series No. 201, Chap. 2, American Chemical Society, Washington,... 

References in italics cite heterogeneous electron transfer kinetic parameters. 

The single potential step chronoabsorptometry technique has been employed to determine the heterogeneous electron transfer kinetic parameters of myoglobin [36], horse heart cytochrome c [37] and soluble spinach ferredoxin [38]. In every case, the chronoabsorptometric data were analysed according to the irreversible model (the reverse reaction is ignored). The error associated with the use of this model for the kinetic analysis of these systems is most pronounced at low overpotentials, long transient times, and large reaction rates. 

The oxidation of thiosulphate by [AuONHa) is also thought to proceed by substitution, giving [Au(Sa03)(NH3)3]+, and subsequent electron transfer. Kinetic parameters were determined for the initial substitution step. ... 

Edmund E. Bowden conducted potential step chronoabsorptometry experiments on the reaction of myoglobin at modified gold minigrid electrodes [40]. Although these experiments were very reproducible, the heterogeneous electron transfer kinetic parameters raised concerns, namely, the rate constant was very low (k° = 3.9 X 10-11 cm/s) and alpha was high (a = 0.88). These issues became muted as the work progressed, as will be discussed below. 

As with the other reaction schemes involving the coupling of electron transfer with a follow-up homogeneous reaction, the kinetics of electron transfer may interfere in the rate control of the overall process, similar to what was described earlier for the EC mechanism. Under these conditions a convenient way of obtaining the rate constant for the follow-up reaction with no interference from the electron transfer kinetics is to use double potential chronoamperometry in place of cyclic voltammetry. The variations of normalized anodic-to-cathodic current ratio with the dimensionless rate parameter are summarized in Figure 2.15 for all four electrodimerization mechanisms. 

The most important operational parameter is the scan rate. Increasing this parameter results in increasing interference of the electron transfer kinetics and in the passage from peak- to plateau-shaped responses. 

General Discussion—Parameters of Electron-Transfer Kinetics... 

Experimental data for the interligand electron transfer kinetics following photoexcitation of [Os(bpy)3] " " are in agreement with a reaction/diffusion model measurements were made in a range of solvents. The variable parameters in the model are interligand electronic coupling and solvent polarization barrier height. 

Electron transfer kinetics from the triplet excited state of TMPD to PA in polystyrene has been monitored by phosphorescence emission decay in ref. 85. The rate constant has been found to be invariant over the temperature interval 77-143 K. Parameters ae and ve calculated from the phosphorescence decay using eqn. (12) were found to be ae = 3.46 A and vc = 104 s 1. 

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