Artificial photosynthesis

Artificial photosynthesis for fuel production is a quite recent field. Our knowledge about photosynthesis and the natural H2 forming reactions increases rapidly and during the last 10 years the three-dimensional structures of the photosynthetic reaction centers Photosystem I and II and many Hydrogenases have been solved.

This sophisticated knowledge is provided by the photosynthesis group and is key for the biomimetic approach applied by the synthetic chemists in the Consortium for Artificial Photosynthesis. There have been many attempts to model crucial physical and chemical elementary steps in these enzymes by bio-mimetic chemistry. However, there have been few attempts to use the biomimetic approach to actually produce a fuel from solar energy similar to what is done in photosynthetic organisms. With the increased molecular understanding of natural photosynthesis and H2 production strong bio-inspired chemistry is more and more feasible. The research along this line, that is carried out by the Consortium for Artificial Photosynthesis, is one the largest attempts currently going on in the world.

Our general idea is to design multi-component molecules with many functions, based on principles from nature. Our strategy is to use principles from natural Photosystem II and to synthesize organic, stable compounds that can oxidize water using the energy in solar light. A class of complexes is synthesized around the central metal ion Ruthenium (II), which can be excited by light and is used instead of chlorophyll (Figure 1). These Ru-complexes are linked to multinuclear Manganese complexes that are built on principles from natural Photosystem II (Figure 2). We hope to develop chemistry where light oxidizes Ru(II) to Ru(III) which in its turn shall oxidize the Mn-ions. Our synthetic and spectroscopic groups stand on solid ground here and the Consortium has carried out pioneering, unique work in the last 10 years. The Consortium will also link photoactive Ru-centers to artificial, bio-mimetic molecules able to reduce protons to H2. This chemistry is new and will be developed in the project where we integrate groups with deep knowledge of the natural Hydrogenases with synthetic groups attempting to construct biomimetic metal centers able to form H2.
 

Figure 1. Analogies between natural photosynthesis (top) and artificial photosynthesis (bottom). In natural photosynthesis light is used to transfer electrons from water to valuable products in the form of carbohydrates etc. The solar energy is harvested by chlorophyll (green). In artificial photosynthesis, solar energy is harvested by a Rutenium center and is used to form a valuable product (in this case hydrogen) with electrons that originally come from water.
 

 

Figure 2. Project design showing a synthetic Ru-Mn complex and Photosystem II. The Figure high lights some principles that are followed in the project. In Photosystem II, chlorophylls harvest energy in light (green antenna and P680) and use this energy to drive photosynhesis. In particular a complex of 4 Mn-ions and a Tyrosine interact to oxidize water. In the Artificial molecules a Rutenium center is linked via a tyrosine analogue to a bi-nuclear Mn-center intended to accomplish water oxidation.
 

Figure 1 shows the principles for the Ru-Mn chemistry and how this is similar to the function of Photosystem II. Figure 2, shows the strong pillars, which link the two project lines and constitute the basis for our research. This is the combined effort from the biochemists in the Photosynthesis group with the other researchers in the Consortium for Artificial Photosynthesis.

A core agenda in the Consortium is that the synthetic group will advance their field in targeted basic research. They design and synthesize the complex multi-component molecules intended for light-driven water oxidation and H2 formation. The unique synergetic component in the Consortium will promote input from the biochemists and biophysicists focusing on questions relevant for artificial photosynthesis. The genetic, metabolic and bioreactor groups will all work in their particular field with our target in mind. The intention is that the findings from our basic research in biochemistry and biophysics quickly are implemented to improve the cyanobacteria that we use in the bioreactors. The continuous target is to improve the efficiency and yield of H2 from the photosynthetic microorganisms.

The synthesized complexes are studied by EPR spectroscopy in the Photosynthesis group and by fast optical spectroscopy and electrochemistry at Dept of Chemical Physics, Uppsala university. The synthetic work is carried out by the Synthesis Group.

_____________________

More information:

The Consortium for Artificial Photosynthesis

Last modified: 2021-09-30