Dr. Alexander Schnegg - EPR Research Group
|Dipl.-Phys.||Freie Universität Berlin (1998)|
|Dr. rer. nat.||Institut für Experimentalphysik, Freie Universität Berlin (1999-2003)|
|Postdoc||Max-Planck-Institut für Bioanorganische Chemie; heute: MPI CEC (2004-2005)|
|Postdoc||Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) (2006-2013)|
|Wiss. Mitarbeiter||Verantwortlicher Wissenschaftler im EPR-Labor am HZB (2013-2018)|
|Adjunct professor||Monash University, Melbourne, Australia (seit 2016)|
|Forschungsgruppenleiter||MPI CEC (seit 2018)|
- Kinauer, M.; Diefenbach, M.; Bamberger, H.; Demeshko, S.; Reijerse, E. J.; Volkmann, C.; Wurtele, C.; van Slageren, J.; de Bruin, B.; Holthausen, M. C.; Schneider, S., An iridium(iii/iv/v) redox series featuring a terminal imido complex with triplet ground state. Chemical Science 2018, 9, 4325.
- Suturina, E. A.; Nehrkorn, J.; Zadrozny, J. M.; Liu, J.; Atanasov, M.; Weyhermüller, T.; Maganas, D.; Hill, S.; Schnegg, A.; Bill, E.; Long, J. R.; Neese, F., Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)4]2- Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations. Inorganic Chemistry 2017, 56, 3102.
- Nehrkorn, J.; Holldack, K.; Bittl, R.; Schnegg, A., Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR. Journal of Magnetic Resonance 2017, 280, 10.
- Reijerse, E. J.; Pham, C. C.; Pelmenschikov, V.; Gilbert-Wilson, R.; Adamska-Venkatesh, A.; Siebel, J. F.; Gee, L. B.; Yoda, Y.; Tamasaku, K.; Lubitz, W.; Rauchfuss, T. B.; Cramer, S. P., Direct Observation of an Iron-Bound Terminal Hydride in FeFe -Hydrogenase by Nuclear Resonance Vibrational Spectroscopy. Journal of the American Chemical Society 2017, 139 (12), 4306.
- Bonke, S. A.; Bond, A. M.; Spiccia, L.; Simonov, A. N., Parameterization of Water Electrooxidation Catalyzed by Metal Oxides Using Fourier Transformed Alternating Current Voltammetry. Journal of the American Chemical Society, 2016, 138, 16095.
- Schnegg, A.; Nehrkorn, J.; Singh, A.; Calafell, I.; Bonke, S. A.; Hocking, R. K.; Lips, K; Spiccia, L., Probing the Fate of Mn Complexes in Nafion: A Combined Multifrequency EPR and XAS Stud. Journal of Physical Chemistry C, 2016, 120, 853.
- Bonke, S. A.; Wiechen, M.; D. W.; MacFarlane, D. R.; Spiccia, L. Renewable fuels from concentrated solar power: towards practical artificial photosynthesis. Energy & Environmental Science, 2015, 8, 2791.
- Nehrkorn, J.; Schnegg, A.; Holldack, K.; Stoll, S., General Magnetic Transition Dipole Moments for Electron Paramagnetic Resonance. Physical review letters 2015, 114, 010801.
- Fehr, M.; Schnegg, A.; Rech, B.; Astakhov, O.; Finger, F.; Bittl, R.; Teutloff, C.; Lips, K., Metastable Defect Formation at Microvoids Identified as a Source of Light-Induced Degradation in a− Si: H. Physical review letters 2014, 112, 066403.
- Schnegg, A.; Behrends, J.; Fehr, M.; Lips, K., Pulsed electrically detected magnetic resonance for thin film silicon and organic solar cells. Physical Chemistry Chemical Physics 2012, 14, 14418.
- Schnegg, A.; Behrends, J.; Lips, K.; Bittl, R.; Holldack, K., Frequency domain Fourier transform THz-EPR on single molecule magnets using coherent synchrotron radiation. Physical Chemistry Chemical Physics 2009, 11, 6820.
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.