Fourier-Transform ESR-Spektrometer
Final Report Abstract
The Fourier Transform ESR spectrometer has been an essential instrument in the Collaborative Research Center CRC813 „Chemistry at spin centers“. The CRC projects in which the spectrometer has been used span a wide range of inorganic, organic and biological systems all having the presence of unpaired electrons in common. Below a brief overview of some projects is given: In particular, the EPR spectrometer has been successfully used in the CRC project of the AG van Gastel to establish that the bioluminescent proteins, responsible for the emission of light in fireflies, beetles and bugs, operate by a catalytic mechanism in which radicals play a role. Secondly, the spectrometer has been used to provide new insight in the exact structure of the solvated electron in solid and liquid ammonia at low concentrations. Interestingly, two species have been observed. For one of them, an isotropic g-shift has been observed for the first time, indicating that this solvated electron is indeed a molecular entity. The spectrometer has been employed in the CRC projects with the group of Prof. Dr. A. Gansäuer to investigate the catalytic mechanism of titanocenes in epoxide ring opening. By using EPR spectroscopy in combination with spin-trapping (a technique to trap shortlived radicals and convert them into stable radicals) and quantum chemistry, the complete mechanism, which indeed involves a radical intermediate could be solved. Together with the group of Prof. S. Höger, radical species in light-harvesting donoracceptor polymers were investigated. The EPR investigation focused on the photoexcited triplet state, which could be attained by optically exciting either the donor or the acceptor moiety. In collaboration with the AG Filippou, new compounds with triple bonds between a transition metal and an element of the group (IV) have been characterized. These unique paramagnetic molecules displayed a rich EPR spectrum from which the electronic structure of the molecule could be elucidated. Furthermore, a bissilylene radical cation and a ferracyclobutadien has been characterized with respect to their geometric and electronic structure using cw/pulsed X- and Q-band methods. The AG Streubel has its research focus on phosphor chemistry. Though chemistry with other main group elements is well known, phosphor chemistry is much less explored. In analogy to the epoxide opening reactions studied in the Gansäuer group, the oxaphosphirane analogues and phosphinidenoid derivatives have been investigated by EPR spectroscopy. In a further project, the reactivity of nitroxides bound to metal complexes of phosphorous is being followed by cw X-band EPR. Within the CRC, the AG Schiemann uses the spectrometer for EPR based trilateration of metal centers in model complexes and biological systems. The focus is hereby on high spin metal centers as hemin and manganese(II). A second project involves the EPR based geometric and electronic characterization of hemines transiently bound to peptides and proteins. The goal in this project is to answer the question whether hemin can regulate proteins. Additionally, EPR experiments have been performed on samples from the group of Prof. U. B. Kaupp (Institut Caesar der Max Planck Gesellschaft, Bonn) to verify the successful labeling of proteins by nitroxide moieties.
Publications
- Insights into the Chemistry of Transient P-Chlorophosphanyl Complexes. Angew. Chem. Int. Ed. 49 (2010) 6894
A. Özbolat-Schön, M. Bode,G. Schnakenburg, A. Anoop. M. van Gastel, F. Neese, R. Streubel
(See online at https://doi.org/10.1002/anie.201002885|) - EPR and ENDOR Study of the Frozen Ammoniated Electron at Low Alkali-metal Concentrations. J. Phys. Chem. A. 115 (2011) 1939
A. Meyer, M. van Gastel
(See online at https://dx.doi.org/10.1021/jp200600r) - Photoinduced Charge Separation in an Organic Donor-Acceptor Hybrid Molecule. J. Phys. Chem. B. 115 (2011) 13526
A. Marchanka, S.K. Maier, S. Höger, M. van Gastel
(See online at https://doi.org/10.1021/jp208334y) - An Unusal Case of Facile Non-Degenerate P-C Bond Making and Breaking. Chem. Asian J. 7 (2012) 1708
V. Nesterov, A. Özbolat-Schön, G. Schnakenburg, L. Shi, A. Cangönül, M. van Gastel, F. Neese, R. Streubel
(See online at https://doi.org/10.1002/asia.201200161) - Deoxygenation of Coordinated Oxaphosphiranes: A New Route to P=C Double-Bond Systems. Chem.-Eur. J 18 (2012) 9780
C. Albrecht, L. Shi, J.-M. Perez, M. van Gastel, S. Schwieger, F. Neese, R. Streubel
(See online at https://doi.org/10.1002/chem.201201405) - Electronic structure of the lowest triplet state of flavin mononucleotide. J. Phys. Chem. A 116 (2012) 10090
L. Kammler, M. van Gastel
(See online at https://doi.org/10.1021/jp305778v) - H2O Activation for Hydrogen-Atom Transfer: Correct Structures and Revised Mechanisms. Angew. Chem. Int. Ed. 51 (2012) 3266
A. Gansäuer, M. Behlendorf, A. Cangönül, C. Kube, J.M.Cuerva, J. Friedrich, M. van Gastel
(See online at https://doi.org/10.1002/anie.201107556) - Open-Shell Complexes Containing Metal-Germanium Triple Bonds. Angew. Chem. Int. Ed. 51 (2012) 789
A.C. Filippou, A. Barandov, G. Schnakenburg, B. Lewall, M. van Gastel, A. Marchanka
(See online at https://doi.org/10.1002/anie.201107120|) - Radical 4-exo Cyclizations via Template Catalysis. Chem.-Eur. J 18 (2012) 2591
A. Gansäuer, K. Knebel, C. Kube, M. van Gastel, A. Cangönül, K. Djaasberg, T. Hängele, M. Hülsen, M. Dolg, J. Friedrich
(See online at https://doi.org/10.1002/chem.201102959) - Reversed Freeze Quench Method near the Solvent Phase Transition. J. Phys. Chem. A 116 (2012) 3899
A. Marchanka, M. van Gastel
(See online at https://doi.org/10.1021/jp300555x)
