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Bettina Basel presents experimental conditions which allow to extract the three-spin contribution precisely from experimental multi-spin double electron-electron resonance (DEER) signals. The theory and concepts behind the used techniques, which are among others broadband chirp pump pulses, over coupling of microwave resonators and echo reduction measurements, are discussed and explained in detail. Moreover the setup and results of DEER experiments with newly introduced double chirp pump pulses consisting of two separate chirps are shown. Particular attention is paid to the phenomenon of orientation selection and the concept of orthogonal spin labeling.

Inhaltsverzeichnis

Frontmatter

1. A General Introduction

Molecular absorption spectra are obtained by measuring the attenuation versus frequency of a beam of electromagnetic radiation as it passes through a sample of matter. In such kinds of spectroscopy, the electric field component of the radiation interacts with the electric dipole moment of the molecule. In magnetic resonance spectroscopy, however, the interaction of magnetic dipole moments with the oscillating magnetic component of electromagnetic radiation is measured. Molecular magnetic moments may either arise from the nuclei (nuclear magnetic resonance, NMR) or the electrons (electron paramagnetic resonance, EPR) of a system.
Bettina Basel

2. Theory

To describe the EPR experiment in a classical way, the interaction of the macroscopic bulk magnetization with the applied microwave frequency has to be regarded.
Bettina Basel

3. Scope of the Thesis

As discussed in chapter 2.3.3.5 the three-spin contribution depends on the angle between the two inter-spin vectors \(\overrightarrow{KL}\) and \(\overrightarrow{KM}\), while the two-spin contribution is independent from this angle.It should thus be possible to extract the angular information from the three-spin contribution. The goal of this thesis is to find an experimental method with which this is in principal possible. Therefore, various approaches were tested, which shall be briefly introduced in this section.
Bettina Basel

4. Materials and Methods

All commercially available chemicals were used as received. Perdeuterated glycerol (98%, d8) was purchased from Isotec. Perdeuterated o-terphenyl was synthesized by Herbert Zimmermann, MPI for Medical Research, Heidelberg, Germany.
Bettina Basel

5. Results and Discussion

In 2009 Jeschke, G. et al. proved that it is, in principle, possible to extract inter-spin angles of small triradicals with not too complex structures by fitting a geometry model to the experimental two-spin and three-spin contribution [1]. For more complex molecules, e.g. proteins, however it might not be possible to fit the experimental data with a simple geometry model. Therefore, a way of extracting the angular information from the higher-order terms of the experimental DEER signal has to be found.
Bettina Basel

6. Summary and Outlook

The aim of this thesis was to find experimental conditions under which the three-spin contribution can be extracted precisely from the DEER signal for a system with three spins.
As a starting point, simulations of the two-spin and three-spin contribution were performed for nitroxide triradicals. These investigations showed that the changes in the three-spin contribution, which are directly related to variations in the angle, have about the same magnitude as those changes in the three- and two-spin contribution that are caused by variations in the third side length.
Bettina Basel

Backmatter

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