Periodic Reporting for period 3 - MatEnSAP (Semi-Artificial Photosynthesis with Wired Enzymes)
Berichtszeitraum: 2019-10-01 bis 2021-03-31
The motivation of this research is to develop new toolsets for driving energy demanding (endergonic) reactions with sunlight via a new interdisciplinary approach: semi-artificial photosynthesis. We focus on the study of solar-to-fuel conversion reactions since they form the basis of renewable fuel generation, which is urgently needed to reduce greenhouse gas emissions and provide a practical route of storing solar energy.
Currently, solar fuel conversion is studied via ‘artificial photosynthesis’, which utilises solely synthetic, often biomimetic, components to convert and store solar energy, but is often constrained by inefficient catalysis as well as costly and toxic materials. Nature, on the other hand has already produced many bio-catalysts that can efficiently and selectively perform thermodynamically and kinetically demanding multi-electron transformations, which drive life-sustaining reactions such as photosynthesis. Semi-artificial photosynthesis bridges the rapidly developing fields of synthetic biology and artificial photosynthesis, and is an unexplored platform for understanding solar fuel generation.
The objectives of this research are to: 1) develop the toolbox (in the form of for example: electrodes, redox connections, and complementary photosensitisers) needed for bridging artificial and biological photosynthesis; 2) modify and develop techniques that can be used in a complementary manner to provide a holistic picture of the biotic-abiotic interface, and thus aid rational design in semi-artificial photosynthesis; and 3) produce novel and efficient proof-of-concept solar fuel generation pathways that cannot be accessed via artificial or natural photosynthesis alone.
Currently, solar fuel conversion is studied via ‘artificial photosynthesis’, which utilises solely synthetic, often biomimetic, components to convert and store solar energy, but is often constrained by inefficient catalysis as well as costly and toxic materials. Nature, on the other hand has already produced many bio-catalysts that can efficiently and selectively perform thermodynamically and kinetically demanding multi-electron transformations, which drive life-sustaining reactions such as photosynthesis. Semi-artificial photosynthesis bridges the rapidly developing fields of synthetic biology and artificial photosynthesis, and is an unexplored platform for understanding solar fuel generation.
The objectives of this research are to: 1) develop the toolbox (in the form of for example: electrodes, redox connections, and complementary photosensitisers) needed for bridging artificial and biological photosynthesis; 2) modify and develop techniques that can be used in a complementary manner to provide a holistic picture of the biotic-abiotic interface, and thus aid rational design in semi-artificial photosynthesis; and 3) produce novel and efficient proof-of-concept solar fuel generation pathways that cannot be accessed via artificial or natural photosynthesis alone.
Aim 1 aims to establish the toolbox needed to interface the biotic with the abiotic components:
i) We expanded current state-of-the-art indium tin oxide electrode design to allow for the incorporation of live cells [J. Am. Chem. Soc., 2018, 140, 6-9; Proc. Natl. Acad. Sci, 2020, 117, 5074-5080].
ii) We integrated state-of-the-art photovoltaic componements, p-Si and lead halide perovskites, with a titanium dioxide electrode scaffold that can host enzymes such as hydrogenase and formate dehydrogenase for sustained light-driven fuel production [Angew. Chem. Int. Ed., 2018, 57, 10595-10599; ACS Energy Lett., 2020, 12, 8176-8282; ACS Catal., 2021, 11, 1868-1876].
iii) We developed new inverse opal graphene-based electrodes and performed a full comparison study with the indium tin oxide analogous electrodes [Nano Lett., 2019, 19, 1844-1850]. We also explored porous titanium dioxide electrodes [Angew. Chem. Int. Ed., 2019, 58, 4601-1605].
iv) A review has been published [Nature Nanotechn., 2018, 13, 890-899].
Aim 2 develops new approaches to understand the biotic-abiotic interface:
i) A Mo-containing formate dehydrogenase, which can be used to selectively catalyse CO2 reduction to formate, was characterised using a combination of inhibition studies, electrochemical output, and modelling [J. Am. Chem. Soc., 2017, 139, 29, 9927-9936; J. Am. Chem. Soc., 2020, 142, 12226-12236].
ii) The discovery that a protein conduit, MtrC, is a high performance H2O2 reductant was made when developing Raman spectroscopy as a means to monitor protein electrochemistry in vitro [J. Am. Chem. Soc., 2017, 139, 9, 3324-3327].
iii) We employed the rotating ring disk electrode technique as a means to study photo-induced charge conversion events by protein-films and reported the characterisation of additional energy transfer pathways in photosystem II in the production of H2O2 [J. Am. Chem. Soc., 2018, 140, 17923-17931].
iv) Comprehensive work to systematically study how electrode morphology and surface chemistry influence photosystem II loading and photoactivity, employing a range of techniques including fluorescence microscopy, photoelectrochemistry and ATR-IR, has been reported [Nano Lett., 2019, 19, 1844-1850].
v) Reversible electrochemistry for a formate dehydrogenase on a metal oxide electrode has been demonstrated and the enzyme-electrode interface been characterised by QCM and ATR-IR spectroscopy [Angew. Chem. Int. Ed., 2019, 58, 4601-1605].
vi) We have extended the use of our interface characterisation techniques to studying the whole cell-electrode interface and suggested plausible mechanisms for extracellular electron transfer [J. Am. Chem. Soc., 2020, 142, 5194-5203]
vii) We have contributed to the development of protein film electrochemical EPR spectroscopy [2019, 55, 8840-8843]
viii) Two reviews have been published [Acc. Chem. Res., 2019, 52, 1439-1448; Nat. Rev. Chem., 2020, 4, 6-21].
Aim 3 establishes novel proof-of-concept solar fuel generation pathways via semi-artificial photosynthesis:
i) We have accomplished the wiring of enzymes for solar-driven overall water splitting without external bias [Nature Energy, 2018, 3, 944-951].
ii) Solar-driven CO2 reduction to water oxidation has been achieved by wiring Photosystem II to formate dehydrogenase [J. Am. Chem. Soc., 2018, 140, 16418-16422].
iii) Reversible interconversion of formate into H2/CO2 has been accomplished with a pair of wired redox enzymes (J. Am. Chem. Soc., 2019, 141, 17498-17502]
iv) A review has been published [Chem. Soc. Rev., 2020, 49, 4926-4952].
i) We expanded current state-of-the-art indium tin oxide electrode design to allow for the incorporation of live cells [J. Am. Chem. Soc., 2018, 140, 6-9; Proc. Natl. Acad. Sci, 2020, 117, 5074-5080].
ii) We integrated state-of-the-art photovoltaic componements, p-Si and lead halide perovskites, with a titanium dioxide electrode scaffold that can host enzymes such as hydrogenase and formate dehydrogenase for sustained light-driven fuel production [Angew. Chem. Int. Ed., 2018, 57, 10595-10599; ACS Energy Lett., 2020, 12, 8176-8282; ACS Catal., 2021, 11, 1868-1876].
iii) We developed new inverse opal graphene-based electrodes and performed a full comparison study with the indium tin oxide analogous electrodes [Nano Lett., 2019, 19, 1844-1850]. We also explored porous titanium dioxide electrodes [Angew. Chem. Int. Ed., 2019, 58, 4601-1605].
iv) A review has been published [Nature Nanotechn., 2018, 13, 890-899].
Aim 2 develops new approaches to understand the biotic-abiotic interface:
i) A Mo-containing formate dehydrogenase, which can be used to selectively catalyse CO2 reduction to formate, was characterised using a combination of inhibition studies, electrochemical output, and modelling [J. Am. Chem. Soc., 2017, 139, 29, 9927-9936; J. Am. Chem. Soc., 2020, 142, 12226-12236].
ii) The discovery that a protein conduit, MtrC, is a high performance H2O2 reductant was made when developing Raman spectroscopy as a means to monitor protein electrochemistry in vitro [J. Am. Chem. Soc., 2017, 139, 9, 3324-3327].
iii) We employed the rotating ring disk electrode technique as a means to study photo-induced charge conversion events by protein-films and reported the characterisation of additional energy transfer pathways in photosystem II in the production of H2O2 [J. Am. Chem. Soc., 2018, 140, 17923-17931].
iv) Comprehensive work to systematically study how electrode morphology and surface chemistry influence photosystem II loading and photoactivity, employing a range of techniques including fluorescence microscopy, photoelectrochemistry and ATR-IR, has been reported [Nano Lett., 2019, 19, 1844-1850].
v) Reversible electrochemistry for a formate dehydrogenase on a metal oxide electrode has been demonstrated and the enzyme-electrode interface been characterised by QCM and ATR-IR spectroscopy [Angew. Chem. Int. Ed., 2019, 58, 4601-1605].
vi) We have extended the use of our interface characterisation techniques to studying the whole cell-electrode interface and suggested plausible mechanisms for extracellular electron transfer [J. Am. Chem. Soc., 2020, 142, 5194-5203]
vii) We have contributed to the development of protein film electrochemical EPR spectroscopy [2019, 55, 8840-8843]
viii) Two reviews have been published [Acc. Chem. Res., 2019, 52, 1439-1448; Nat. Rev. Chem., 2020, 4, 6-21].
Aim 3 establishes novel proof-of-concept solar fuel generation pathways via semi-artificial photosynthesis:
i) We have accomplished the wiring of enzymes for solar-driven overall water splitting without external bias [Nature Energy, 2018, 3, 944-951].
ii) Solar-driven CO2 reduction to water oxidation has been achieved by wiring Photosystem II to formate dehydrogenase [J. Am. Chem. Soc., 2018, 140, 16418-16422].
iii) Reversible interconversion of formate into H2/CO2 has been accomplished with a pair of wired redox enzymes (J. Am. Chem. Soc., 2019, 141, 17498-17502]
iv) A review has been published [Chem. Soc. Rev., 2020, 49, 4926-4952].
Progress has been made with respect to all three goals of the project. As for the combination of biological catalysts with synthetic materials (aim 1), we have already integrated isolated enzymes with semiconductors, conducting metal oxides, 3D electrode architectures, polymers and synthetic dyes as proposed. We have also recently shown the possibility to use state-of-the-art light absorbers from the photovoltaics field such as silicon and perovskites for semi-artificial photosynthesis and combine live (photosynthetic and non-photosynthetic) bacteria with metal oxide electrodes, allowing potentially the more efficient synthesis of more complex organic products with improved stability in the future.
As for the development of techniques to investigate the enzyme-electrode interface (aim 2), we have already successfully demonstrated the usefulness of advanced electrochemistry (e.g. rotating ring disk electrochemistry; photoelectrochemistry), advanced vibrational spectroscopy (IR and Resonance Raman spectroscopy) and quartz crystal microbalance with dissipation. An ongoing focus is the investigation of the local environment and its influence on the performance of our hybrid electrodes. We have also explored AFM-SECM, but the use of this technique for porous electrodes is not possible and single-enzyme analysis is extremely challenging even using state of the art instrumentation. Nevertheless, we have started to advance other imaging techniques on our systems with external collaborators. In addition, we have also explored other techniques that have not been listed in the proposal such as protein film electron paramagnetic resonance spectroscopy and are looking into transient absorption spectroscopy as a means to gain insights into the electron transfer dynamics for interfaced enzymes with semiconductors in collaboration.
Following the demonstration of bias-free solar H2 synthesis using semi-artificial photosynthesis (aim 3), the focus will be on the development of bias-free CO2 reduction to formate and more complex products using enzyme cascades or live cells.
As for the development of techniques to investigate the enzyme-electrode interface (aim 2), we have already successfully demonstrated the usefulness of advanced electrochemistry (e.g. rotating ring disk electrochemistry; photoelectrochemistry), advanced vibrational spectroscopy (IR and Resonance Raman spectroscopy) and quartz crystal microbalance with dissipation. An ongoing focus is the investigation of the local environment and its influence on the performance of our hybrid electrodes. We have also explored AFM-SECM, but the use of this technique for porous electrodes is not possible and single-enzyme analysis is extremely challenging even using state of the art instrumentation. Nevertheless, we have started to advance other imaging techniques on our systems with external collaborators. In addition, we have also explored other techniques that have not been listed in the proposal such as protein film electron paramagnetic resonance spectroscopy and are looking into transient absorption spectroscopy as a means to gain insights into the electron transfer dynamics for interfaced enzymes with semiconductors in collaboration.
Following the demonstration of bias-free solar H2 synthesis using semi-artificial photosynthesis (aim 3), the focus will be on the development of bias-free CO2 reduction to formate and more complex products using enzyme cascades or live cells.