My research focuses on biocatalysis, to learn from and mimic nature at the intersection of chemistry, biology and materials science. The overall goal is to establish fundamental chemical insight for supporting future renewable energy technologies, i.e. to develop efficient catalysts and new catalytic routes for energy conversion reactions based on abundant and cheap metals. Energy converting enzymes are capable of using earth-abundant metals in their active site to perform key chemical reactions (e.g. reduction of nitrogen to ammonia, oxidation/production of H2, and reduction of CO2 to CO and formate) in a very efficient manner. These reactions still represent big challenges for chemistry, and it is often difficult to synthesise catalysts with efficiencies similar to the natural enzymes for these energy conversion reactions.
My research combines the fields of biology, synthetic chemistry and physical chemistry to study energy converting metalloenzymes and understand the chemistry at their active site and the interplay between active site and protein matrix at the molecular level. Solutions to the energy problem require a fundamental understanding of how energy conversion processes happen in nature and of what it takes to make catalytic systems with performances and efficiencies as high as the systems existing in nature (i.e. energy converting metalloenzymes), while maintaining the relative simplicity of a molecular catalyst or catalytic material. Thus, my lines of research are dedicated to translating the understanding of complex biocatalytic processes into catalyst design for technological applications.
Study and exploitation of natural catalytic systems, i.e. metalloenzymes for energy conversion
This line of research focused mainly on hydrogenases ([FeFe] hydrogenases, but also [NiFe] hydrogenases) and CO dehydrogenases (CODHs). Hydrogenases are the most efficient H2 conversion catalysts in nature. They are able to reversibly interconvert H2 with protons and electrons at very high rates, under ambient conditions and without energy waste by utilising earth-abundant metals like Ni and/or Fe in their active site. On the other hand, CODHs catalyse the reversible interconversion of CO2 and CO in nature at very high rates, with minimal energy waste and using a Ni-Fe active site. To study the catalytic mechanism and the secondary-sphere interactions in these fascinating metalloenzymes, I apply complementary spectroscopic techniques alongside electrochemistry.
Figure 1. A) Structure of the [FeFe] hydrogenase from Clostridium pasteurianum (CpHydA1) artificially maturated with the active site mimic ADT (PDB ID 4XDC). The active site H-cluster and the redox cofactors in the enzyme (accessory iron-sulphur clusters, F-clusters) are shown together with the protein backbone illustrated as a cartoon. The H-domain harbouring the active site is coloured blue and the F-domain containing the accessory F-clusters is coloured pink. B) Homodimeric structure of the CODH-II from Carboxydothermus hydrogenoformans showing the Ni-Fe active site (at the right and left edge) and the iron-sulfphur cluster redox cofactors in the middle (PDB ID 3B51).
This second line of research combines synthetic chemistry with molecular biology. [FeFe] hydrogenases from various organism are recombinantly produced in E. coli as pro-enzymes in high yields (i.e. apo-enzyme lacking the active site). By using engineered affinity tags, high purity is achieved in just 1-purification step. The active holo-hydrogenase is then generated by mixing the pro-enzyme with synthetic active-site mimics. The high yield and purity in which these semi-synthetic enzymes can be produced facilitate advanced spectroscopic and spectroelectrochemical studies. I am interested in using new cofactor precursors to generate chemically altered active-site variants to fine-tune the active-site chemistry and the catalytic properties of the enzyme. This approach can be also used for rapid screening of mutant libraries to generate semi-synthetic hydrogenases with desirable features such as oxygen tolerance, enhanced catalytic performance, or enhanced temperature sensitivity.
Figure 2. Graphical scheme of the artificial maturation approach to generate semi-synthetic hydrogenases.
Collaborative institutes and universities
Diamond Light Source (UK), Max Planck Institute for Chemical Energy Conversion (Germany), Pacific Northwest National Laboratory (USA), SPring-8 (Japan), Bochum University (Germany), Uppsala University (Sweden), University of Nottingham (UK).