Electrocatalytic oxidation of NADH by ferrocene derivatives and the influence of cyclodextrin complexation

The electrocatalytic oxidation of NADH by ferrocene derivatives and the influence of the complexation reaction of β-cyclodextrin (β-CD) were investigated in a buffered solution (pH 7.0). From the cyclic voltammetric behaviour, the electron-transfer rate constants from NADH to the ferricinium species were determined. The relationship between the rate constant and the half-wave potential demonstrated that the one-electron reaction of the NADH/NADH^.+ couple is 1.02 V (vs. SHE). The deprotonation rate constant of NADH^.+ was also estimated to be 6×10⁶ s^-1. The addition of β-CD accelerated the apparent reaction rate. However, analysis of the behaviour with ferrocenecarboxylic acid (FCA) suggested that the electron-transfer rate from NADH to the oxidized FCA in β-CD was three-tenths of that expected from the fully diffusion-controlled reaction.