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Title: A Hybrid Biological-Organic Photochemical Half-Cell for Generating Dihydrogen

Abstract

In this final report we describe our work on the fabrication of a hybrid biological/organic photochemical half-cell that couples Photosystem I, which produces electrons at a highly reducing redox potential, with a hydrogenase enzyme, which catalyzes H 2 evolution at high rates when provided with a source of electrons. We considered it far too ambitious at the present stage of knowledge to attempt to design a system that carries out the reaction 2H 2O + 8hv → 2H 2 + O 2 in a single photochemical step, hence, we focused our work on optimizing the half-cell reaction 2H + + 2e - + 2hv → H 2. The challenge has been to deliver low-potential electrons from PS I to H 2ase rapidly, at high quantum yield, and with high thermodynamic efficiency. To accomplish this, we engineered a molecular wire that connects the [4Fe-4S] clusters of PS I with those of the hydrogenase enzyme. In doing so, the highly reducing electrons generated by PS I are transferred by quantum mechanical tunneling to the enzyme. The core idea was to connect the terminal Fe/S cluster of Photosystem I to the distal Fe/S cluster of H 2ase through a covalently bonded “molecular wire”more » consisting of an 8-carbon hydrocarbon wire terminated on both ends with a sulfhydryl group. By providing a direct electron transfer pathway through signa bonds, diffusion chemistry is avoided, and, because the tether length and redox potentials were properly chosen, a rate of electron transfer between the two enzymes was achieved that twice exceeded the rate of electron transfer in natural photosynthesis. We also devised a way to utilize the FA and FB clusters of Photosystem I to serve as a reservoir so that electrons could be extracted from the quinone binding sites and passed through a similar molecular wire to the bound hydrogenase. The additional induction of the IsiA antenna pigments by iron starvation led to an optical cross section twice that of the naturally-occurring Photosystem I, thus further raising the rates of electron transfer to the enzyme. We were likewise able to re-engineer a naturally-occurring dicluster ferredoxin to replace the hydrocarbon molecular wire as the tether between Photosystem I and the hydrogenase enzyme. Finally, we developed techniques to place Photosystem I on electrodes and in block copolymer interfaces and we were able to measure photocurrents approaching 35.0 ± 3.5 mA cm -2 upon illumination of these assembled devices, which are among the highest reported so far for such systems on a per protein basis.« less

Authors:
 [1]
  1. Pennsylvania State Univ., University Park, PA (United States)
Publication Date:
Research Org.:
Pennsylvania State Univ., University Park, PA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1483277
Report Number(s):
DOE-PSU-46222-F
DOE Contract Number:  
FG02-05ER46222
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; Photosystem I; hydrogenase; molecular wire; hydrogen; light-induced hydrogen; solar energy; biofuels

Citation Formats

Golbeck, John. A Hybrid Biological-Organic Photochemical Half-Cell for Generating Dihydrogen. United States: N. p., 2018. Web. doi:10.2172/1483277.
Golbeck, John. A Hybrid Biological-Organic Photochemical Half-Cell for Generating Dihydrogen. United States. doi:10.2172/1483277.
Golbeck, John. Mon . "A Hybrid Biological-Organic Photochemical Half-Cell for Generating Dihydrogen". United States. doi:10.2172/1483277. https://www.osti.gov/servlets/purl/1483277.
@article{osti_1483277,
title = {A Hybrid Biological-Organic Photochemical Half-Cell for Generating Dihydrogen},
author = {Golbeck, John},
abstractNote = {In this final report we describe our work on the fabrication of a hybrid biological/organic photochemical half-cell that couples Photosystem I, which produces electrons at a highly reducing redox potential, with a hydrogenase enzyme, which catalyzes H2 evolution at high rates when provided with a source of electrons. We considered it far too ambitious at the present stage of knowledge to attempt to design a system that carries out the reaction 2H2O + 8hv → 2H2 + O2 in a single photochemical step, hence, we focused our work on optimizing the half-cell reaction 2H+ + 2e- + 2hv → H2. The challenge has been to deliver low-potential electrons from PS I to H2ase rapidly, at high quantum yield, and with high thermodynamic efficiency. To accomplish this, we engineered a molecular wire that connects the [4Fe-4S] clusters of PS I with those of the hydrogenase enzyme. In doing so, the highly reducing electrons generated by PS I are transferred by quantum mechanical tunneling to the enzyme. The core idea was to connect the terminal Fe/S cluster of Photosystem I to the distal Fe/S cluster of H2ase through a covalently bonded “molecular wire” consisting of an 8-carbon hydrocarbon wire terminated on both ends with a sulfhydryl group. By providing a direct electron transfer pathway through signa bonds, diffusion chemistry is avoided, and, because the tether length and redox potentials were properly chosen, a rate of electron transfer between the two enzymes was achieved that twice exceeded the rate of electron transfer in natural photosynthesis. We also devised a way to utilize the FA and FB clusters of Photosystem I to serve as a reservoir so that electrons could be extracted from the quinone binding sites and passed through a similar molecular wire to the bound hydrogenase. The additional induction of the IsiA antenna pigments by iron starvation led to an optical cross section twice that of the naturally-occurring Photosystem I, thus further raising the rates of electron transfer to the enzyme. We were likewise able to re-engineer a naturally-occurring dicluster ferredoxin to replace the hydrocarbon molecular wire as the tether between Photosystem I and the hydrogenase enzyme. Finally, we developed techniques to place Photosystem I on electrodes and in block copolymer interfaces and we were able to measure photocurrents approaching 35.0 ± 3.5 mA cm-2 upon illumination of these assembled devices, which are among the highest reported so far for such systems on a per protein basis.},
doi = {10.2172/1483277},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {11}
}