Electron Transfer in a Bio-Photoelectrode Based on Photosystem I Multilayer Immobilized on the Conducting Glass

Abstract

A film of ~40 layers of partially oriented photosystem I (PSI) complexes isolated from the red alga Cyanidioschyzon merolae formed on the conducting glass through electrodeposition was investigated by time-resolved absorption spectroscopy and chronoamperometry. The experiments were performed at a range of electric potentials applied to the film and at different compositions of electrolyte solution being in contact with the film. The amount of immobilized proteins supporting light-induced charge separation (active PSI) ranged from ~10%, in the absence of any reducing agents (redox compounds or low potential), to ~20% when ascorbate and 2,6-dichlorophenolindophenol were added, and to ~35% when the high negative potential was additionally applied. The origin of the large fraction of permanently inactive PSI (65–90%) was unclear. Both reducing agents increased the subpopulation of active PSI complexes, with the neutral P700 primary electron donor, by reducing significant fractions of the photo-oxidized P700 species. The efficiencies of light-induced charge separation in the PSI film (10–35%) did not translate into an equally effective generation of photocurrent, whose internal quantum efficiency reached the maximal value of 0.47% at the lowest potentials. This mismatch indicates that the vast majority of the charge-separated states in multilayered PSI complexes underwent charge recombination.

Photoactive and conductive biohybrid films by polymerization of pyrrole through voids in photosystem I multilayer films

“…Second, while PPy provides a high interfacial area with the electrolyte, the polymer can hinder redox mediator transport to limit access to the active sites of PSI within the composite film. Thus, the rate that the mediator can remove holes from the P 700 sites is reduced in the presence of the polymer, which can amplify charge recombination events 19 within PSI clusters and decrease the cathodic current. Third, the large pseudo-capacitance of the film may slow redox-mediated charge transfer.…”

“…The photoresponsive oxidation and reduction capabilities of PSI, as well as its rapid charge separation, are leading factors that attest to its suitability for photoelectrochemical applications, 19 similar to those shown by other nanomaterials in arti-cial photosynthesis. [20][21][22] On the stromal side of the protein, the iron-sulfur cluster known as the F B site attains one of the most negative reduction potentials (−590 mV vs. SHE) in nature.…”

In situ Time-Resolved Spectroelectrochemistry Reveals Limitations of Biohybrid Photoelectrode Performance

“…15,16 Additionally, extensive transient absorption measurements have been applied RCs suspended in solution, revealing the mechanisms of charge separation and stabilization of the charge separated state that underpin high quantum efficiencies (see supplemental information for details). 7,[17][18][19][20][21] However, only a few spectroscopic studies on biohybrid systems have managed to investigate RC operation at the electrode surface in a biohybrid system, an environment in which mediator-electrode interactions and substrate depletion can drastically shift limiting processes during operation. 21 Furthermore, no study to date has provided a comprehensive method that empirically deconvolutes all electron transfer pathways and loss processes in a biophotoelectrode exposed to continuous illumination and under operating conditions of an applied potential.…”

“…7,[17][18][19][20][21] However, only a few spectroscopic studies on biohybrid systems have managed to investigate RC operation at the electrode surface in a biohybrid system, an environment in which mediator-electrode interactions and substrate depletion can drastically shift limiting processes during operation. 21 Furthermore, no study to date has provided a comprehensive method that empirically deconvolutes all electron transfer pathways and loss processes in a biophotoelectrode exposed to continuous illumination and under operating conditions of an applied potential. Investigations in situ and in operandum are crucial for the rational design of high-performing biohybrids, particularly in the context of recent and more complex benchmark architectures that drive large photocurrent densities but encounter multiple loss channels from short circuits, electron transfer bottlenecks, and excitation quenching.…”

Biomolecular and Biohybrid Systems for Solar Energy Conversion

“…Whilst the structure and function of photosynthetic macromolecular machines have been optimized through billions of years of evolution, their optimal implementation as efficient biocatalysts remains to be realized. This challenge was addressed by the comprehensive and rational nano-engineering of the biophotocatalyst and the catalyst/electrolyte interface described in the paper by Szewczyk et al [1]. By combining photocurrent measurements with transient absorption spectroscopy analyses, the authors provided an in-depth dissection of the electron transfer process limitations that occur within the model biophotocatalyst, Photosystem I (PSI), upon its partially oriented immobilization on conductive glass (fluorine-dopped tin oxide, FTO).…”