Iron centers in [FeFe] hydrogenase and biomimetic coordination complexes studied by XAS/XES and DFT: hydrogen catalysis and oxygen inhibition
Final Report Abstract
Hydrogenase enzymes are nature´s blueprints for efficient hydrogen conversion catalysts. Intermediates of their metal cofactors in the reaction cycles need to be characterized for understanding the chemical mechanism. Advanced X-ray absorption, emission, and nuclear resonance spectroscopy methods at synchrotron radiation sources in combination with density functional theory and molecular mechanics calculations were developed and employed to study the active site H-cluster in [FeFe]-hydrogenase and biomimetic model compounds. These methods facilitate site-selective determination of molecular structures, electronic configurations, and vibrational dynamics of individual metal sites in the complex cofactors. In a highly collaborative approach involving national and international partners, complete data sets including high-resolution K-edge XAS and Kß-XES spectra were collected in technically demanding experiments for various states of the H-cluster in wildtype and mutated [FeFe]-hydrogenase protein variants for the first time and for numerous synthetic compounds. Quantitative simulation and analysis of spectral features using quantum chemical calculations was achieved. This work has revealed the sensitivity of the methods towards ligand binding, redox, and spins state changes at the metal centers and established standard routines for highresolution X-ray spectroscopy studies on cofactors in molecules under functional conditions. Model structures for relevant intermediates of the H-cluster in active and impaired [FeFe]- hydrogenase were formulated, a state with a metal-bridging hydride bound to the catalytic diiron site was detected, structural differences between O2-sensitive and O2-tolerant enzymes were described, further insight into oxygen inhibition reactions was obtained, and relations between redox and protonation changes were implied. Our results seem to suggest a catalytic cycle of hydrogen conversion in [FeFe]-hydrogenase, which deviates from previously proposed schemes, and emphasize the importance of coordination dynamics at the active site during the H2 and O2 reactions. These relations are further explored in ongoing research. Complete understanding of the reaction cycle of hydrogen conversion in [FeFe]-hydrogenase still has not been reached. Novel in vitro reconstitution methods for obtaining selectively isotope labeled and functional H-cluster species in [FeFe]-hydrogenase have become available. They facilitate dedicated methods such as 57Fe nuclear resonance vibrational spectroscopy, as explored already in this project. Further research along this line is highly appealing to study functional cofactor dynamics. We have shown that the combination of XAS/XES/NRVS and QM/MM approaches leads to significant progress in the understanding of the cofactor function in hydrogenases. This strategy is expected to strongly contribute to unraveling of the relevant intermediates in biological and synthetic hydrogen chemistry.
Publications
- Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT. Dalton Trans. 42, 7539-7554 (2013)
N. Leidel, C.-H. Hsieh, P. Chernev, K. G. V. Sigfridsson, M. Y. Darensbourg, M. Haumann
(See online at https://doi.org/10.1039/c3dt33042g) - Electronic and molecular structures of the active-site H-cluster in [FeFe]-hydrogenase determined by site-selective X-ray spectroscopy and quantum chemical calculations. Chem. Sci. 5, 1187-1203 (2014)
C. Lambertz, P. Chernev, K. Klingan, N. Leidel, K. Sigfridsson, T. Happe, M. Haumann
(See online at https://doi.org/10.1039/c3sc52703d) - Hydride binding to the active site of [FeFe]-hydrogenase. Inorg. Chem. 53, 12164-12177 (2014)
P. Chernev, C. Lambertz, K. Sigfridsson, N. Leidel, R. Kositzki, C. Hsieh, R. Schiwon, S. Yao, C. Limberg, M. Driess, T. Happe, M. Haumann
(See online at https://doi.org/10.1021/ic502047q) - Lyophilization protects [FeFe]-hydrogenases against O2-induced H-cluster degradation. Nat. Sci. Rep. 5, 13978/1- 10 (2015)
J. Noth, R. Kositzki, K. Klein, M. Winkler, M. Haumann, T. Happe
(See online at https://doi.org/10.1038/srep13978) - Unprecedented biomimetic [2Fe−2S] clusters with extensively delocalized mixed-valence iron centers. Angew. Chem. Int. Ed. 54, 12506-12510 (2015)
S. Yao, F. Meier, N. Lindenmaier, R. Rudolph, B. Blom, M. Adelhardt, J. Sutter, S. Mebs, M. Haumann, K. Meyer, M. Kaupp, M. Driess
(See online at https://doi.org/10.1002/anie.201506788) - Stepwise isotope editing of [FeFe]-hydrogenases exposes cofactor dynamics. Proc. Natl. Acad. Sci. USA
M. Senger, S. Mebs, J. Duan, F. Wittkamp, U.-P. Apfel, J. Heberle, M. Haumann, S. Stripp
(See online at https://doi.org/10.1073/pnas.1606178113)
