|Dipl.-Phys.||Free University Berlin (1998)|
|Dr. rer. nat.||Institut für Experimentalphysik, Free University Berlin (1999-2003)|
|Postdoc||Max Planck Institute for Bioinorganic Chemistry; today: MPI CEC (2004-2005)|
|Postdoc||Helmholtz Zentrum Berlin für Materialien und Energie (HZB) (2006-2013)|
|Staff Scientist||HZB's EPR lab (2013-2018)|
|Adjunct Professor||Monash University, Melbourne, Australia (since 2016)|
|Research group leader||MPI CEC (since 2018)|
The EPR Research Group at MPI CEC employs electron paramagnetic resonance (EPR) techniques to monitor and characterise paramagnetic states relevant to energy conversion and storage processes. Special focus is devoted to catalytically active transition metal ion complexes and proteins. We develop and utilise state-of-the-art EPR spectrometers ranging from GHz to THz frequencies. Our spectrometers are capable of a wide repertoire of CW/pulsed multi-resonance and multi-frequency EPR methods for powder, crystal, solution and in-situ experiments.
Currently we are working in the following fields of research:
An understanding of catalyst function enables rational modification and improvement, yet the most reactive, catalytically active states are typically only formed under operational conditions. This motivates our group to develop methodology for in situ / operando studies that allow EPR characterisation of catalysts for energy conversion reactions.
Reactions of interest presently include electrocatalytic water oxidation, with surface-confined or homogeneous transition metal catalysts. These studies require electrochemical measurements to be undertaken within the constraints of specific spectroscopic equipment, which we design and develop to ensure the conditions of analysis are truly relevant to operational catalytic conditions.
The applicability of EPR to any electrochemically derived/analysed species, is that single electron redox steps frequently involve EPR active states. The exceptional sensitivity of EPR to these states makes it powerful in examining the subtle, yet crucial, electronic effects that enable catalysis. EPR also allows selective analysis of paramagnetic oxidation states independent of diamagnetic species, thus providing selectivity that is unavailable with many other techniques - especially if the catalyst ground state is diamagnetic. In-situ EPR spectra are interpreted with extensive experiment-simulation comparisons and then correlated with catalytic measurements as well as with results from other techniques.
EPR characterization of high-spin (electron spin, S > 1/2) transition-metal ion states targets the determination of their spin coupling parameters. The latter are sensitive probes of the coordination environment and electronic structure of the metal ion. In the case of catalytically active ions, spin couplings can provide unique information on their structure-function relationship. Furthermore, spin couplings determine the magnetic properties of molecular nanomagnets (MNM), which are considered as core units of future spintronic devices. However, the highly desired spin couplings are oftentimes not accessible with standard EPR spectrometers. This is the case for many high spin states with large zero field splittings. To improve this situation we develop and apply advanced field and frequency domain EPR methods, covering the GHz to THz EPR-excitation energy range. For THz-EPR experiments the Schnegg group established the joint research lab EPR4Energy with the the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB).
Collaboration partners: Prof. Robert Bittl (FU Berlin), Dr. Karsten Holldack and Dr. Thomas Lohmiller (both HZB, Berlin).
Contact: Joscha Nehkorn
1. Nehrkorn, J.; Holldack, K.; Bittl, R.; Schnegg, A., J. Magn. Reson. 2017, 280, 10-19.
Paramagnetic states of metal proteins are studied by high-resolution multi-frequency and multi-resonance EPR techniques. Nuclear spins (e.g. 14/15N, 13C) of the first coordination sphere ligands (e.g. CN and CO) are used as reporters on the spin density distribution over a metal cluster. The latter can be probed by hyperfine spectroscopies (in our lab we use, ENDOR, HYSCORE and EDNMR), which allow determination of the hyperfine and quadrupole interactions. Optimum conditions for such experiments are achieved by single crystal EPR measurements. However, protein micro-crystals have typical sizes in the range 50 – 200 µm. Even at W-band, EPR investigation of these crystals is challenging. To lift this restriction, our group develops resonant structures adapted to the size and shape of nanoliter volume samples at X-, Q-, and W-band (9.5, 34, and 94 GHz respectively) up to the sub mm (244 GHz) and THz range. In order to significantly advance EPR spectroscopy for samples with nanolitre volumes, a novel sub-mm sized X-band self-resonant micro-helix resonator has been developed in collaboration with Prof. Lubitz (see Fig. 4). The sensitivity enhancement obtained with this resonator makes protein single crystals of dimensions typical for x-ray crystallography accessible to advanced EPR techniques.
Contact: Ed Reijerse
2. Sidabras, J. W.; Duan, J.; Winkler, M.; Happe, T.; Hussein, R.; Zouni, A.; Suter, D.; Schnegg, A.; Lubitz, W.; Reijerse, E. J., Science Advances 2019, 5 (10), eaay1394.
EPRoC are mm-sized sensors that incorporate a microwave source and detector on a surface array. This approach allows for a fundamental paradigm shift in EPR spectroscopy by facilitating in situ measurements of paramagnetic samples in environments which are difficult to access with conventional EPR setups in a cost-efficient way. We are developing EPR detection schemes that employ EPRoC sensors in a variety of different environments probing a wide range of sample morphologies in the scope of catalysis and battery research. We work on their integration in electrodes of electrochemistry experiments for the characterization of paramagnetic states in liquid solutions, e.g. in electrochemical cells, batteries or reactors. In addition, we are developing rotation-dependent EPRoC techniques for studies of microcrystals. The current generation of EPRoC sensors is capable of performing continuous wave and rapid scan EPR experiments. Partners: Prof. Dr. Klaus Lips (HZB), Prof. Jens Anders (Universität Stuttgart). Sponsored by the Federal Ministry of Education and Research (Grant reference number: 03SF0565A).
Contact: Markus Teucher