(401e) Electropolymerization of Polypyrrole By Photosystem I

The Photosystem I (PSI) protein complex found in all photosynthetic organisms is known for its impressive redox capabilities. PSI has two photoactive redox sites, the oxidizing P₇₀₀ chlorophyll pair and the reducing F_B iron-sulfur cluster with more than 1.1 V of potential difference between them. We are investigating the use of these active sites to perform photo-driven, nanomaterials chemistry directly at the protein donor site. The wide range of reduction potentials places PSI in a position to photooxidatively electropolymerize conductive polymers and photoreduce metal ions into nanoparticles. This presentation will focus on the preparation of PSI-polypyrrole conjugates. A reduction potential of 0.48 V vs. Ag/AgCl at the P₇₀₀ site makes PSI a promising candidate for oxidative polymerization of certain monomers. Because PSI is a renewable and vastly abundant bionanomaterial, electropolymerization via PSI is a sustainable and low-cost alternative to produce polypyrrole. Polymerization occurs with the addition of protein and pyrrole monomer in an acidic aqueous solution under light. Heterogeneous growth of the polymer is also demonstrated from a multilayer film of the PSI protein. The resulting product has been analyzed spectroscopically and electrochemically to confirm the presence of both PSI and electropolymerized polypyrrole. The growth of the polypyrrole alters the photovoltage and photocurrent response of the protein film. The combination of PSI with a conductive polymer can lead to photoactive polymer films that could be utilized in solar energy conversion systems.