|
|||||
|
|
Pulsed EPR Dipolar Spectroscopy under the Breakdown of the High-Field Approximation: The High-Spin Iron(III) Case |
|
| Authors: | Dr Dinar Abdullin Dr Hideto Matsuoka Dr Maxim Yulikov Nico Fleck Dr Christoph Klein Dr Sebastian Spicher Dr Gregor Hagelueken Prof Dr Stefan Grimme Prof Dr Arne Lützen Prof Dr Olav Schiemann |
| Institution: | 1. Institute of Physical and Theoretical Chemistry, University of Bonn, Bonn, Germany;2. Institute of Physical and Theoretical Chemistry, University of Bonn, Bonn, Germany
Current address: Graduate School of Science, Osaka City University, Osaka, Japan;3. Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland;4. Institute of Physical and Theoretical Chemistry, University of Bonn, Bonn, Germany Kekulé Institute of Organic Chemistry and Biochemistry, University of Bonn, Bonn, Germany;5. Mulliken Center for Theoretical Chemistry, University of Bonn, Bonn, Germany;6. Kekulé Institute of Organic Chemistry and Biochemistry, University of Bonn, Bonn, Germany |
| Abstract: | Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe3+/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe3+ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe3+ heme proteins. |
| Keywords: | biophysics DEER spectroscopy EPR spectroscopy nitroxide pulsed dipolar spectroscopy |