Ls. Wong et al., CHARACTERIZATION OF MERCAPTOETHYLAMINE-MODIFIED GOLD ELECTRODE SURFACE AND ANALYSES OF DIRECT ELECTRON-TRANSFER TO PUTIDAREDOXIN, Langmuir, 11(12), 1995, pp. 4818-4822
Direct electron transfer to putidaredoxin (Pdx) in solution from bare
gold and mercaptoethylamine-modified gold electrodes was studied by cy
clic voltammetry. The current response of Pdx at a bare gold electrode
was irreversible and highly unstable. The modified electrode offered
improved, but still impersistent, quasi-reversible current response. S
urface-enhanced Raman spectroscopy revealed that mercaptoethylamine ad
sorbed on gold was in mixed trans and gauche conformations at 0.0 V (A
g/AgCl) initially. As the potential was changed anodically or cathodic
ally over the range of +0.4 to -0.8 V, the adsorbate population became
largely gauche in conformation. A link between the conformation chang
e and deterioration of Pdx current response at the electrode was sugge
sted. Simulations of the electrochemical system yielded an estimated P
dx diffusion coefficient D = 1.4 x 10(-7) cm(2)/s and the apparent het
erogeneous electron transfer rate constant k degrees = 1.0 x 10(-4) cm
/s.