Side-Selective Modification of Photosystem I Protein and Preparation of Oriented Photo-Electrochemical Films

Abstract

The directional orientation of photoreactive protein complexes extracted from plants, algae, and cyanobacteria is of crucial importance to the performance of biologically-modified, photo-active electrodes. The photo-electrochemical response of such protein complexes is inherently directional and achieving uniform orientation is necessary to mitigate problems such as electron-hole recombination, low net charge transfer due to competing electrochemical reactions, and loss of direct electron transfer to the electrode. [1] Previous efforts to control orientation have explored bio-conjugation [2] and electrostatic interactions with self-assembled monolayers (SAMs) [3] to improve photocurrent generation. However, the ability to efficiently modify, deposit, and characterize the orientation of such bio-electrode films has not been demonstrated. To achieve controlled orientation, an extraction-modification procedure has been developed based on side-selective functionalization of photosystem I (PSI), a photo-active protein complex derived from spinach. Reactive amine groups on the surface of PSI can be leveraged to incorporate a variety of new functional groups through solution-based modification reactions. The functional group chosen for modification can be tailored to achieve oriented deposition on the substrate electrode. Herein we explore modification strategies utilizing the thiol-gold affinity and polyethylene glycol (PEG) “capping”. The deposition kinetics, monolayer structure, and electrochemical reactivity of the modified PSI monolayers have been studied to better understand the ability to control PSI orientation on gold electrodes. Controlled orientation will allow for the future development of oriented PSI based devices such as biohybrid photovoltaics or electrochemical photocatalysis membranes, and this facile modification procedure may be implemented with other membrane bound proteins and protein complexes. [1] G. LeBlanc, et al, Langmuir, 30 (37), 10990–11001, 2014. [2] R. F. Simmerman, et al, Bioconjugate Chem, 26 (10), 2097–2105, 2015. [3] K. A. Manocchi, et al, Langmuir, 29 (7), 2412–2419, 2013.