Rotating disk electrode voltammetric determination of the heterogeneous electron transfer kinetics of soluble spinach ferredoxin

Abstract

The heterogeneous electron transfer kinetics of soluble spinach ferredoxin reacting at modified gold electrodes have been characterized by both steady state and transient electrochemical methods. The steady state analysis was conducted at a methyl viologen modified gold disk electrode using rotating disk hydrodynamic voltammetry. The results presented are the first reported steady state kinetic parameters observed for the unmediated reduction of ferredoxin at this surface. Single potential step chronoabsorptometry was utilized to observe the transient kinetic behavior of ferredoxin at modified gold minigrid electrodes. The kinetic parameters reported herein were evaluated using a recetly advanced, generalized analysis that is applicable to heterogeneous electron transfer systems that exhibit any degree of reversibility. Both analyses yield a formal heterogeneous electron transfer rate constant, k s,h 0' , and electrochemical transfer coefficient, α, in the following ranges: 1×10 −4 cm/s< k s,h 0' <6×10 −4 cm/s and 0.4<α<0.5 for the experimental conditions employed. These results indicated that ferredoxin exhibits quasi-reversible heterogeneous electron transfer kinetics at this electrode surface. Moreover, agreement between the methods utilized to characterize this reaction points to a direct one-electron transfer process between the modified gold electrode surface and ferredoxin as the rate determining step.