Dr. Alexander Schnegg - EPR Research Group
|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)|
Selected MPI CEC publications
- Krzystek, J., Schnegg, A., Aliabadi, A., Holldack, K., Stoian, S.A., Ozarowski, A., Hicks, S.D., Abu Omar, M.M., Thomas, K.E., Ghosh, A., Caulfield, K.P., Tonzetich, Z.J., Telser, J. (2020). Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d4 Electron Count Inorganic Chemistry https://doi.org/10.1021/acs.inorgchem.9b02635
- Li, J., Chen, J., Sang, R., Ham, W.-S., Plutschack, M.B., Berger, F., Chabbra, S., Schnegg, A., Genicot, C., Ritter, T. (2020). Photoredox catalysis with aryl sulfonium salts enables site-selective late-stage fluorination Nature Chemistry 12, 56-62. https://doi.org/10.1038/s41557-019-0353-3
- Rams, M., Jochim, A., Böhme, M., Lohmiller, T., Ceglarska, M., Rams, M.M., Schnegg, A., Plass, W., Näther, C. (2019). Single‐Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain Chemistry – A European Journal https://doi.org/10.1002/chem.201903924
- Kutin, Y., Cox, N., Lubitz, W., Schnegg, A., Rüdiger, O. (2019). In Situ EPR Characterization of a Cobalt Oxide Water Oxidation Catalyst at Neutral pH Catalysts 9(11), 926. https://doi.org/10.3390/catal9110926
- Nehrkorn, J., Bonke, S.A., Aliabadi, A., Schwalbe, M., Schnegg, A. (2019). Examination of the Magneto-Structural Effects of Hangman Groups on Ferric Porphyrins by EPR Inorganic Chemistry 58(20), 14228-14237. https://doi.org/10.1021/acs.inorgchem.9b02348
- Sidabras, J., Duan, J., Winkler, M., Happe, T., Hussein, R., Zouni, A., Suter, D., Schnegg, A., Lubitz, W., Reijerse, E.J. (2019) Extending electron paramagnetic resonance to nanoliter volume protein single crystals using a self-resonant microhelix Science Advances 5(10), eaay1394. https://doi.org/10.1126/sciadv.aay1394
- Cheng, J., Liu, J., Leng, X., Lohmiller, T., Schnegg, A., Bill, E., Ye, S., Deng, L. (2019). A Two-Coordinate Iron(II) Imido Complex with NHC Ligation: Synthesis, Characterization, and Its Diversified Reactivity of Nitrene Transfer and C–H Bond Activation Inorganic Chemistry 58, 7634-6744. https://doi.org/10.1021/acs.inorgchem.9b01147
- Zhao, G., Busser, G.W., Froese, C., Hu, B., Bohnke, S.A., Schnegg, A., Ai, Y., Wei, D., Wang, X., Peng, B., Muhler, M. (2019). Anaerobic Alcohol Conversion to Carbonyl Compounds Over Nanoscaled Rh-doped SrTiO3 under Visible Light The Journal of Physical Chemistry Letters 10, 2075–2080. https://doi.org/10.1021/acs.jpclett.9b00621
- Nehrkorn, J., Veber, S.L., Zhukas, L.A., Novikov, V.N., Nelyubina, Y.V., Voloshin, Y.Z, Holldach, K., Stoll, S., Schnegg, A. (2018). Determination of Large Zero-Field Splitting in High-Spin Co(I) Clathrochelates Inorganic Chemistry 57(24), 15330-15340. https://doi.org/10.1021/acs.inorgchem.8b02670
EPR Research Group @ MPI CEC
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.
Ultimate EPR detection sensitivity
Laboratory-built spectrometers push the state-of-the-art in sensitivity and versatility, while application-specific resonator development focuses on maximising concentration sensitivity or, for single-crystal proteins, point sample sensitivity. Finite-element modelling of Maxwell's Equations guide the resonator design process and allows for experiment-tailored resonators, as opposed to general purpose cavities. These resonators provide higher sensitivity, more uniform excitation, and larger bandwidths than commercially provided cavities.
The combination of broadband resonators, versatile pulse capabilities at high frequencies, rapid-scan EPR and arbitrary-waveform generators open up new fields of EPR spectroscopy. Furthermore, we are designing and testing EPR probes or even miniaturised EPR spectrometers that can be attached to a sample or immersed into it. This high-risk/high-gain approach targets paramagnetic specimens in environments that are not yet accessible to EPR.
Collaboration partners: Prof. Dieter Suter (TU Dortmund) within Horizons 2020 Marie Skłodowska-Curie Fellowship 745702-Act-EPR, Dr. Aharon Blank (Technion Haifa) within GIF Project I-1352-302.5/2016, Prof. Dr. Klaus Lips (HZB, Berlin) and Prof. Jens Anders (Uni Stuttgart).
High-spin transition metal ion states
EPR characterisation of high-spin states (S > 1/2) in transition metal ions targets the determination of their spin coupling parameters. The latter are sensitive probes of the metal ion's coordination environment and electronic structure. In the case of a catalytically active ion, spin couplings can provide unique information on its structure-function relationship. Furthermore, spin couplings determine the magnetic properties of molecular nanomagnets (MNM), which are envisaged as core units of future spintronic devices. However, the highly desired spin couplings are oftentimes not accessible with standard 9.5 GHz EPR spectrometers in the case of high spin states. To bridge this gap we develop and apply advanced field and frequency domain EPR methods, covering the GHz to THz EPR-excitation energy range.
Collaboration partners: Prof. Robert Bittl (FU Berlin), Dr. Karsten Holldack and Dr. Thomas Lohmiller (both HZB, Berlin).
Paramagnetic states of metal proteins activating H2O or CO 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 pulsed ENDOR and HYSCORE experiments, 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 nl 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. High- resolution EPR is complemented by FTIR experiments, allowing for the characterisation of different oxidation states of a metal protein depending on the applied electrochemical potential. This complementary approach enables us to assign and characterise function determining protein metal cofactors hardly achievable with any other method.
 Cox, N., et al., Mol. Phys., 2013. 111(18-19): p. 2788-2808
 Sidabras, J.W., et al., Appl. Magn. Reson., 2017. 48: p. 1301-1314