Spectroscopic studies on copper enzyme model complexes

  • Spektroskopische Untersuchungen an Modellkomplexen von Kupferenzymen

Teubner, Melissa-Miriam; Herres-Pawlis, Sonja (Thesis advisor); Rübhausen, Michael Alexander (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

For this thesis, modern spectroscopic techniques were applied to characterize model complexes of copper enzymes. Most importantly, a method was developed to observe the reaction pathway of a model complex with a substrate at low temperatures with Raman spectroscopy. The properties of enzymes, the natural catalysts that facilitate biochemical reactions at mild conditions, are of high interest since they can refine chemical processes tobe more environmentally friendly and more energy efficient. Therefore, it is of importance to improve the understanding of their structure and properties. This can be facilitated by utilizing enzyme model complexes, which are small molecules that try to mimic the active site of specific enzymes. In this work, model complexes of tyrosinase, particulate methane monooxygenase, and peptidylglycine alpha-hydroxylating monooxygenase are characterized. These copper-based enzymes are capable of oxidizing molecules after activating dioxygen by incorporation. The formed copper-oxygen core and its nuclearity are of special interest. Thus, the copper-oxygen motifs of several oxygenated model complexes were identified with Raman spectroscopy by assigning an oxygen-isotope-sensitive mode to a vibration characteristic for a specific copper-oxygen core. The oxidation states of the copper centers and their geometry were determined by X-ray absorption spectroscopy for a selection of these complexes at PETRA III. The findings were complemented by UV/Vis spectroscopy, density functional theory calculations, and other methods in cooperation with different research groups. Furthermore, a method was developed that allows the detailed observation of a reaction and to spectroscopically capture the formation of intermediates. This method was applied to an active tyrosinase model complex. The operando Raman method, where consecutive Raman spectra are recorded during the reaction at low temperatures, poses great challenges. However, through improvement of an existing cryostat, a method was developed that allows the observation of modifications of the structure during the reaction. This is possible by tracking the changes in vibrational modes, which can be attributed to molecular bonds, which in turn can be assigned to the complex or intermediates. Therefore, the operando Raman method is a promising tool to gain deeper insight into structural changes during a reaction.

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