Recently discovered metallic-like conductance within the pilus protein filaments produced by the microbe Geobacter sulfurreducens indicates these materials serve as strong candidates for bioelectronic applications such as artificial photosynthesis. Microbial synthesis of fuels from carbon dioxide and electricity has the potential to become a more efficient and sustainable method of solar energy harvesting than current technologies that rely on biological photosynthesis. Indeed, direct electron transfer from electrode to microbial biofilms (e.g., via conducting protein filaments) results in carbon dioxide reduction and cellular excretion of desired organic compounds, which produces minimal waste without requiring additional energy. The high level of conductance observed in G. sulfurreducens pili filaments, which suggests these proteins serve as efficient nanowires, is currently thought to arise from π-stacking interactions between aromatic amino acid residues. However, a more detailed atomistic description is required to obtain a fundamental understanding of the structure-function relationships in G. sulfurreducens pili filaments. We apply density functional theory and electron transport calculations based on the NEGF formalism to provide a molecular-level description of conductance in G. sulfurreducens pili filaments. We examine the role of surrounding residues in modulating energy level alignment and transport properties within the chain of π-stacked aromatic residues that constitute the protein nanowires. We compare our analysis with experimental conductance measurements, thus providing insights into the pH-dependent conductance observed in these protein filaments.

DFT-NEGF study of conducting protein filaments for solar energy harvesting

251st National Meeting (2016)

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