Iron-sulfur cluster electronic structural evolution and its contribution to diverse functionality

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This proposal builds upon the results that the applicants have obtained in the first funding period of the SPP 1927 and that have already led to five publications from our own groups and in collaboration with other SPP members. The project is centered around understanding the detailed electronic structure of complex iron-sulfur clusters in nature and in model systems. The ultimate goal is to develop insight into the unique reactivity of these systems, with special emphasis on nitrogenase and hydrogenase. The first funding period contained a spectroscopy- and a theory-oriented branch of research. In the spectroscopy-oriented part, 2p3d resonant inelastic x-ray scattering (RIXS) and X-ray magnetic circular dichroism (XMCD) have been developed as unique probes of the local electronic structure of Fe/S sites. The theoretical research was directed towards developing new model Hamiltonians on the basis of detailed first-principle wavefunction based calculations that will allow the calculation of spectroscopic observables for oligonuclear clusters, which are too complex to be rigorously treated by quantum chemistry. In the present proposal, both branches of research will be further extended and are expected to eventually converge into unique combined experimental and theoretical protocol for the elucidation of Fe/S site electronic structure. To this end, our 2p3d RIXS studies will focus on obtaining higher resolution data to further enhance the quantitative information. In addition, we will further explore XMCD as a complementary, powerful technique for the study of Fe/S sites and will apply it to the active sites of nitrogenase, as well hydrogenase. In parallel with the experimental developments, we will continue our studies on ab initio derived model Hamiltonians. Presently, these studies cover monomeric and dimeric Fe/S sites in detail. The major goal of the second funding period is to develop the necessary framework to treat higher nuclearities from trimers and tetramers, all the way to the FeMoco active sites of nitrogenase, the most complex active site in biology. We will also put major emphasis on developing the necessary framework to calculate magnetic and X-ray spectroscopic properties from the model Hamiltonian treatment. Eventually, we hope to utilize the developed protocols to obtain fundamental insights into the electronic structural consequences of nature’s evolved biosynthetic pathways in FeS cluster assembly. In addition to exploring these new research areas, we will continue and intensify our collaborative efforts in the SPP with the groups of Franc Meyer, Oliver Einsle and Matthias Boll, among others.