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MatEnSAP Report Summary

Project ID: 682833
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - MatEnSAP (Semi-Artificial Photosynthesis with Wired Enzymes)

Reporting period: 2016-10-01 to 2018-03-31

Summary of the context and overall objectives of the project

The motivation of this research is to develop new toolsets for driving endergonic reactions via a new interdisciplinary approach: semi-artificial photosynthesis. Focus would be placed firstly to study 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 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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We can report that substantial progress has been made in the first two parts of the project, and we are on track to deliver several novel solar fuel generation pathways, for aim 3, in the upcoming years.
Specifically, in relation to aim 1, which aims to establish the toolbox needed to interface the biotic with the abiotic components:

i) We have expanded current state-of-the-art indium tin oxide electrode design to allow for the incorporation of larger/more complex biocatalysts (live cells and components). This led to the publication Zhang et al. (2018), J. Am. Chem. Soc., 140, 6-9, which utilised the new electrodes to immobilise biofilms of live cyanobacterial cells, allowing their photoelectrochemistry to be studied. As a result, it was revealed that the unique photocatalytic activity of photosystem II can be accessed in vivo, albeit at the sacrifice of electron transfer efficiency.

ii) We have successfully integrated a state-of-the-art photosensitiser, p-Si, with a titanium dioxide electrode scaffold that can host enzymes such as hydrogenase. We showed that the integrated photoelectrode can transfer the photoexcited electrons to the hydrogenase, resulting in sustained light-driven hydrogen production. This led to the publication of Leung et al. (2017), Chemical Science, 8, 5172-5180. This work established the basis of how photosensitisers can be wired to enzymes to drive endergonic reactions.

iii) We have developed new inverse opal graphene-based electrodes, and tested it for integrating photosystem II. We performed a full comparison study with the indium tin oxide analogous electrodes found that the latter performs significantly better for photoelectrochemistry. The full characterisation is in preparation for publication.


In relations to aim 2, which aims to develop new approaches to understand the biotic-abiotic interface in order to provide mechanistic understanding of the enzymes and also provide design guidance for optimising the ‘wiring’ at the interface:

i) A Mo-containing formate dehydrogenase enzyme, which can be used to selectively catalyse CO2 reduction to formate, was characterised using a combination of inhibition studies, electrochemical output, and modelling. The approach gave new insights into the oxidation states of the Mo active site during CO2 reduction and inhibition, which was previously poorly characterised, and led to the publication by Robinson et al. (2017), J. Am. Chem. Soc., 139, 29, 9927-9936. This adds new mechanistic understanding of the CO2 reduction enzyme that will be used soon in semi-artificial photosynthetic systems.

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. Although this represents an unexpected result, it is in line with aim 2, and led to the publication by Reuillard et al. (2017), J. Am. Chem. Soc., 139, 9, 3324-3327. This work established Raman spectroscopy as a powerful technique for studying protein films in situ, and will be employed to characterise subsequent systems.

iii) The development of the rotating ring disk electrode (RRDE) as a means to study photo-induced charge conversion events by protein-films was recently successful, with a manuscript on the characterisation of additional energy transfer pathways in photosystem II in the production of H2O2 being in preparation. This work established RRDE as a new powerful method to probe the catalytic dynamics of photosynthetic films on electrodes.

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, in line with aim 2, is also being prepared for publication. This work is fundamental is future rational integration of protein films into the customised electrode scaffolds arising from the proj

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Work is in progress to produce complete water splitting systems using semi-artificial photosynthetic approaches, in line with objective three. Towards reaching bias-free photo-induced water splitting systems and progress beyond the state of the art, photosystem II is currently being wired to hydrogenase via complementary light absorbers such as p-Si, organic dyes and perovskites. Understanding and tuning the interface between the biotic and abiotic components are important challenges to overcome to reach the most efficient pathways possible for energy storage.

The use of the quartz crystal microbalance with dissipation is also currently being developed as a new means to understand protein film integration and the changes in biotic-abiotic interface during light illumination and electrochemical regimes.

Transient absorption spectroscopy is being pursued as a new means of understanding how the simple process of interfacing photosystems with conductive nanoparticles can influence the photo-to charge conversion life-times within the protein.

IR spectroscopy is also being developed as a means of monitoring enzyme adsorption and catalysis in protein film systems.

Atomic Force Microscopy (AFM) and Scanning Electrochemical Microscopy (SECM) will be pursued in collaboration.

Our efficient progress in establishing electrode-enzyme interfaces in aim 1 has allowed us to progress faster and to a larger extent in photoelectrchemical and photocatalytic studies with our semiconductor-enzyme systems (aim 3). This required the setting up of a new workstation for this purpose that consists of a potentiostat, solar light simulator and gas chromatograph as our existing facilities were already running at full capacity. It is therefore expected that several unbiased semi-artificial photosynthetic water-splitting systems will be produced by the end of the project and we are hopeful that these systems will be extended to perform unbiased CO2 reduction.
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