Reorientation of Tetradecylmethylviologen on Gold Upon Co-Adsorption of Decanethiol and its Medition of Electron Transfer to Nitrate Reductase

Published

November 9, 1999

Author(s)

Vytautas Reipa, S L. Yeh, H G. Monbouquette, V L. Vilker

Abstract

Decanethiol was coadsorbed with tetradecylmethyl viologen (C₁₄MV; 1-Methyl-1 -tetradecyl-4,4 -bipyridinium chloride) on gold electrodes in order to improve stability of C₁₄MV as an electrochemical mediator for coupling to nitrate reductase enzymes. Surfaced-enhanced Raman spectroscopy (SERS) and in situ spectroscopic ellipsometry were used to monitor the structural properties of surface-confined C₁₄MV during its redox conversion.The potential range investigated was limited to that of the first electron transfer to give V^+., as the subsequent reduction to the neutral species is irreversible and could not be used for electron-transfer mediation to redox enzymes. When C₁₄MV was adsorbed by itself, in the absence of C₁₄MV solution species, the in situ optical studies showed the loss of initial electroactivity was due to the bipyridinium rings being oriented parallel to the electrode plane. This configuration is thought to be unfavorable for the anion (C1^-) transport in and out of the film, which is essential for the redox reaction. The electroactivity in the adsorbed film was restored by coadsorbed film was restored by coadsorbing decanethiol (C₁₀T) with C₁₄MV. This gave an intercalated film with the end-on, bipyridinium ring oriented vertically relative to the electrode surface. In this film, the smaller methyl group is positioned closer to the electrode surface, and the bipyridium electroactive groups are surrounded by longer decanethiol molecules. Both SERS and spectroscopic ellipsometry measurements show the presence of radical dimers in reduced surface films. Intercalated C₁₄MV is stable for several thousand voltammetry scans, and was found to be an efficient electron transfer mediator to soluble nitrate reductase despite being embedded in a decanethiolate layer.

Citation

Langmuir

Volume

15

Issue

23

Pub Type

Journals

Keywords

electron transfer, nitrate reductase, optics, viologen

Citation

Reipa, V. , Yeh, S. , Monbouquette, H. and Vilker, V. (1999), Reorientation of Tetradecylmethylviologen on Gold Upon Co-Adsorption of Decanethiol and its Medition of Electron Transfer to Nitrate Reductase, Langmuir (Accessed February 10, 2025)