Fabrication of a Photoelectronic Device by Direct Chemical Binding of the Photosynthetic Reaction Center Protein to Metal Surfaces (original) (raw)

Photosystem I (PS I) is a transmembrane, multi-subunit protein-chlorophyll complex that mediates vectorial, light-induced electron transfer. The nanometer-sized dimensions, an energy yield of approximately 58 %, and the quantum effi-ciency of almost 1 make the reaction center a promising unit for applications in molecular nanoelectronics. PS I is located in the thylakoid membranes of chloroplasts and cyanobacteria. It mediates light-induced electron transfer from plastocyanin or cytochrome C 553 to ferredoxin. The crystalline structure of PS I from Synechococus elongatus and from plants' chloroplast was resolved to 2.5 and 4.4 Å, respectively. In cyanobacteria, the complex consists of at least 12 polypeptides, some of which bind 96 light-harvesting chlorophyll molecules. The electron-transport chain contains P700, A 0 , A 1 , F X , F A , and F B , representing a chlorophyll a dimer, a monomeric chlorophyll a, two phylloquinones, and three [4Fe-4S] iron-sulfur centers, respectively. The reaction-center core complex is made up of the heterodimeric PsaA and PsaB subunits, containing the primary electron donor, P700, which undergoes light-induced charge separation and transfers an electron through the sequential carriers A 0 , A 1 , and F X . The final acceptors, F A and F B , are located on another subunit, PsaC. The redox potential of the primary donor, P700, is +0.43 V and that of the final acceptor, F B , is -0.53 V, producing a redox difference of -1.0 V. The charge separation spans about 5 nm of the height of the protein, representing the center-tocenter distance between the primary donor and the final acceptor. The protein complex is 9 nm in height and has a diameter of 21 nm and 15 nm for the trimer and the monomer, respectively. The photoactivity and the nanometer-sized dimensions make this complex a promising unit for applications in molecular nanoelectronics. In earlier works, care was taken to indirectly attach plant PS I and bacterial reaction centers to solid surfaces in attempts avoid inactivation of selfassembled monolayers.