Voltammetric and spectroelectrochemical characterization of a water-soluble viologen polymer and its application to electron-transfer mediator for enzyme-free regeneration of NADH

A water-soluble polyxylylviologen (PXV2+) was characterized with a view to making use of it as a redox electron-transfer (ET) mediator. Cyclic voltammetric and spectropotentiometric studies showed (i) that PXV2+ gives two redox waves centering at −0.40 and −0.83 V (vs. Ag/AgCl (3.3 mol dm−3 KCl)) and (ii) that the lifetime of its monocation radical (PXV+·) is two orders of magnitude greater than that of the well-utilized dimethyl viologen monocation radical. Subsequently, the reaction of the PXV2+/+· couple with NAD+ was evaluated in the similar manners as above. On the basis of this evaluation and the bioluminescence assay using bacterial NADH/FMN oxidoreductase and luciferase, it was shown (i) that the PXV2+/+· couple functions as a useful electron-transfer mediator and (ii) that PXV+· reacts with NAD+, leading to generation of the enzymatically active NADH, in the absence of any reductases.