Effects of kinetic coupling on experimentally determined electron transfer parameters

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Electron Transfer Theory

Background:

• Coupled electron transfer (ET) describes systems where a slow, non-adiabatic ET is preceded by a rapid, unfavorable adiabatic reaction.
• This preceding step activates the system for the subsequent electron transfer.
• The observed rate constant for coupled ET is an apparent value, influenced by the equilibrium of the initial reaction step.

Purpose of the Study:

• To investigate the impact of coupled reactions on the accurate determination of electron transfer parameters.
• To analyze how thermodynamic and entropic factors of the preceding step affect calculated reorganizational energy, electronic coupling, and distance.
• To highlight potential errors in electron transfer theory analysis due to coupled reaction complexities.

Main Methods:

• Theoretical analysis of coupled electron transfer reactions.
• Simulation of data sets for coupled ET reactions.
• Analysis of simulated data using established electron transfer theory.

Main Results:

• Analysis of DeltaG degrees dependence yields accurate reorganizational energy but underestimates electronic coupling and overestimates distance.
• Temperature dependence analysis overestimates reorganizational energy, with the error magnitude dependent on DeltaH degrees of the preceding step.
• Accuracy of electronic coupling and distance determination depends on the DeltaS degrees of the preceding reaction.

Conclusions:

• Coupled electron transfer reactions necessitate careful consideration of the preceding activation step in theoretical analysis.
• Misinterpretation of ET parameters can occur if the coupled nature of the reaction is not accounted for.
• Understanding the influence of thermodynamic and entropic factors is crucial for accurate modeling of complex electron transfer processes.