Quinone Electrochemistry: From the Electron Transport Chain to Electron Mediators and Orientational Moieites

Quinones play a vital role in electron transport chains (ETC) in mitochondrial (eukaryotic) and bacterial (prokaryotic) cells. Within the mitochondrial ETC, ubiquinone (coenzyme Q) is responsible for transporting electrons and protons from complexes I and II to complex III, where the ETC ultimately produces adenosine triphosphate (ATP) from ATP synthase. Within bacterial cells, ubiquinone and menaquinone also act as electron and proton carriers between large membrane-bound complexes. Quinone functionality is also required for many oxidoreductase enzymes, which utilize a pyrroloquinoline quinone (PQQ) cofactor.

Naphthoquinone derivatives have been investigated for their suitability within enzymatic fuel cells (EFCs). At the bioanode, the electrochemical properties of naphthoquinone derivatives can be exploited to yield a bioanodic architecture that can mediate electron transfer between anodic enzymes and the electrode. In contrast, the chemical properties (not electrochemical redox properties) of the same naphthoquinone electrode architecture can be utilized at the biocathode of an EFC to efficiently orientate oxygen-reducing enzymes to undergo the direct bioelectrocatalytic reduction of oxygen.

The use of the same electrode architecture at the bioanode and biocathode of EFCs results in a simplified EFC design, which ultimately results in lower manufacturing costs of devices.