Mechanisms of electron transfer between a styrylquinolinium dye and yeast in biofuel cell

• Nanomolar concentrations of styrylquinolinium dye enhance biofuel cell outputs.
• Increased catalase and COX activities are established in the presence of the dye.
• Interaction of the dye with NADH and cytochrome c is proved in vitro.
• The dye acts as intracellular shuttle exchanging electrons and protons.

In the present study, the influence of the recently synthesized styrylquinolinium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide (DANSQI) on the intracellular processes as well as the electrical outputs of Candida melibiosica 2491 yeast-based biofuel cell was investigated. The addition of nanomolar quantities of DANSQI to the yeast suspension results in an increase of the current outputs right after the startup of the biofuel cells, associated with an electrooxidation of the dye on the anode. After that, the formed cation radical of the dye penetrates the yeast cells, provoking a set of intracellular changes. Studies of the subcellular anolyte fractions show that 1 μM dye increased the peroxisomal catalase activity 30-times (1.15 ± 0.06 Unit/mg protein) and over twice the mitochondrial cytochrome c oxidase activity (92 ± 5 Unit/mg protein). The results obtained by electrochemical and spectrophotometric analyses let to the supposition that the dye acts as subcellular shuttle, on account of its specific intramolecular charge transfer properties. The transition between its benzoid, quinolyl radical and ion forms and their putative role for the extracellular and intracellular charge transfer mechanisms are discussed.

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