Electrochemically Gated Long Distance Charge Transport in Photosystem I

Abstract

The transport of electrons along photosynthetic and respiratory chains involves aseries of enzymatic reactions that are coupled through redoxm ediators,i ncluding proteins and small molecules.The use of native and synthetic redoxprobes is key to understanding charge transport mechanisms and to the design of bioelectronic sensors and solar energy conversion devices.H owever,r edoxp robes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites.H erein, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I( PSI) complexes.C urrent-distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redoxp otential of P700, with current extending farther under hole injection conditions. Photosynthesis is an essential process for plants,a lgae,a nd bacteria since it converts light energy,C O 2 ,a nd water into carbohydrate molecules.A lthough the identity and structure of the main proteins and complexes involved in photosynthesis have been extensively characterized, [1] the underlying electron transport pathways,their mechanisms and regulation are not fully understood at the nanometer scale.P rogress in this direction would enable the rational design of bioelectronic nanodevices based on photosynthetic complexes for solar energy applications like hydrogen production [2] and photocurrent generation in photovoltaic cells. [3]

Printable logic circuits comprising self-assembled protein complexes

“…It is a trimeric membrane protein complex that converts photon energy into separated electron/hole pairs to generate chemical reduction potential as part of natural photosynthesis 14 . Due to the difference in hydrophobicity between the sides and the top/bottom (which is common for membrane proteins), PSI can be induced to self-assemble on surfaces with a preferred orientation [15][16][17][18][19] ; in particular, linkers with hydrophilic terminal groups (e.g., hydroxyl group and carboxylic acid) form strong hydrogen bonds with the hydrophilic luminal or stromal surface of PSI trimers, positioning either the P700 reaction center or the F B iron-sulfur complex next to the substrate. We have used self-assembled monolayers (SAMs) of thiols on Au and peptides engineered by phage display on tindoped indium oxide (ITO) to orient PSI with near-perfect selectivity 20 .…”