Bioinspired Dinuclear Copper Complexes for Small Molecule Activation

by Can-Jerome Spyra
Doctoral thesis
Date of Examination:2021-07-27
Date of issue:2021-09-06
Advisor:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Inke Siewert
Persistent Address: http://dx.doi.org/10.53846/goediss-8804

 

 

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Abstract

English

This thesis focuses on the activation of small molecules by dinuclear copper complexes. Initially, isolation of copper/oxygen intermediates on the basis of a non-symmetric pyrazolate/tacn scaffold was investigated. The employed ligand scaffold enforces a Cu-O-O-Cu torsion angle within the dinuclear peroxo complex close to 90°, making it a relevant model complex for the proposed intermediate along the trajectory of dioxygen binding at type III copper proteins. Further, interconversion of this non-symmetric peroxo complex to the hydroperoxo and superoxo intermediate was studied by UV/Vis spectroscopy. Elaboration of the respective binding motifs was done via Resonance Raman and EPR Spectroscopy as well as X-Ray diffraction. The determination of sought-after thermodynamic parameters, such as the pKa value of the Cu2OOH motif as well as the peroxo/superoxo redox potential could be determined by UV/Vis titration experiments and Cyclic Voltammetry measurements. On this basis the bond dissociation free energy of the hydroperoxo complex was derived and kinetic studies of the superoxo complex with TEMPO-H towards hydrogen atom transfer was investigated in detail. Thus, the isolated copper/oxygen complexes and their transformations completes the series of prior reported symmetrical pyrazolate/tacn copper/oxygen intermediates and demonstrates the gradual impact of ligand design on electronic properties of the respective complexes. Further isolation of a symmetric nitrosyl dicopper(II) complex on the basis of a pyrazolate/tacn scaffold was investigated, revealing fast conversion to the respective peroxo complex upon treatment with KO2. The nitrosyl complex further shows fast transformation to the respective dicopper(I) precursor upon chemical or electrochemical reduction.
Keywords: Small Molecule Activation; Bioinspired Model Complexes; Copper Complexes; Dioxygen Activation; UV/Vis Spectroscopy; Resonance Raman Spectroscopy; Hydrogen Atom Transfer; Bond Dissociation Free Energy; EPR Spectroscopy
 
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