- Titel
- Spectro-electrochemical investigation of iron-porphyrin based synthetic Cytochrome c oxidase mimics
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-999542
- Übersetzter Titel (DE)
- Spektro-elektrochemische Untersuchung von synthetischen Cytochrom c Oxidase Mimetika auf Eisenporphyrinbasis
- Erstveröffentlichung
- 2025
- Datum der Einreichung
- 27.06.2025
- Datum der Verteidigung
- 29.09.2025
- Abstract (EN)
- Two iron-porphyrin based catalysts for the oxygen reduction reaction (ORR) were designed based on the catalytic bi-nuclear centre (BNC) of Cytochrome c oxidase (CcO). For this, two pendant pyridine groups were covalently bound to the porphyrin ring, using a rigid xanthene linker for positioning at a fixed distance. Investigations started with this Hangman complex called Py2XPFe, employing different methods of immobilization. Finally, the catalyst was immobilized onto roughened silver electrodes via incubation casting and investigated using surface-enhanced resonance Raman spectroscopy (SERRs) and electrochemical measurements in a rotating ring-disk electrode (RRDE) setup. The influence of the protonatable hanging groups was surveyed in dependence on bulk-pH (8.5 – 6.0) and applied potential (+0.2 – (-0.4) V vs. Ag/AgCl). Paired with DFT calculations on a truncated molecule Py2XBr, lacking the porphyrin subunit, several modes of protonation of the pyridine hanging groups were elucidated. After mostly unprotonated hanging groups in the basic regime, a single proton shared by both pyridines in a Zundel-like fashion dominates the regime at and above neutral pH. At a pH of 7.0, the single protonation changes from a shared to a localized manner. While being thermodynamically less stable it may exist transiently as a potential induced intermediate. Lowering the pH further, leads to the protonation of both hanging groups. While each of these stages influences the SERR spectra, especially the general visibility/intensity, only the local single and double protonation influence the catalytic behaviour. In the basic regime, no reasonable performance of the catalyst could be detected. In the acidic regime on the other hand, selectivity towards 4-electron reduction of oxygen reaches nearly 98 %. The second catalyst examined demonstrates a greater similarity to its natural counterpart CcO, in that copper is bound to the hanging pyridine groups as a second metal ion, resulting in the designation Py2CuXPFe or Pacman complex. Investigations were performed analogously to those of the Hangman complex and did show better ORR performance, especially in the basic regime. The SERR spectra indicated the presence of significant amounts of low spin (LS) iron species for the Pacman complex, which was observed for the Hangman only in small fractions. In both cases, LS formation was linked to OH -ligation and thought to undergo an early reduction, compared to the HS variant. Yet, only for the Pacman complex, this translates into an earlier onset potential for ORR and likely requires pH-values above pH = 8.5, the upper limit of the investigated range. By comparison it was also elucidated that the porphyrin ring of the Hangman complex is significantly distorted upon hydroxy ligation. The resulting LS species was not or hardly visible in the SERR spectra and likely the cause for the various, unexpected intensity changes observed during the investigation of the Hangman complex, combined with the protonation events. The ligation of copper seemingly allows for a more planar structure of the porphyrin ring, both with OH -ligation and during ORR turnover. Lastly, some experiments concerning the actual enzyme CcO and its immobilization are presented.
- Verweis
- Erste Veröffentlichung über Ergebnisse der Untersuchung des Hangmankomplexes aus Kapitel 4.1
Link: https://doi.org/10.1021/acs.jpcc.4c01357
Protonation of Pendant Pyridine Substituents in an Iron Porphyrin Hangman Complex: Influence on Spectral Visibility and Electrocatalysis
DOI: 10.1021/acs.jpcc.4c01357 - Freie Schlagwörter (EN)
- Iron porphyrin, Cytochrome c Oxidase, Raman spectroscopy, Electrochemistry, Oxygen reduction reation
- Klassifikation (DDC)
- 540
- Klassifikation (RVK)
- VK 8207
- GutachterIn
- Prof. Dr. Inez Marita Weidinger
- Jun.-Prof. Dr. Patrycja Kielb
- BetreuerIn Hochschule / Universität
- Prof. Dr. Inez Marita Weidinger
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Förder- / Projektangaben
- Deutsche Forschungsgemeinschaft SFB 1078
Protonation dynamics in protein function
(ProtDyn) - Deutsche Forschungsgemeinschaft SFB 1415
Chemie der synthetischen zweidimensionalen Materialien
(2DMs) - Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-999542
- Veröffentlichungsdatum Qucosa
- 27.10.2025
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC-SA 4.0- Inhaltsverzeichnis
Abstract i Danksagung iii Table of contents iv List of figures ix List of tables xx Abbreviations and acronyms xxi 1. Introduction 1 2. Theory 6 2.1. Objects of investigation 6 2.1.1. Porphyrins and Haems 6 2.1.2. Cytochrome c oxidase 7 2.1.3. The Hangman complex Py2XPFe 10 2.1.4. The Pacman complex Py2CuXPFe 12 2.1.5. The truncated catalyst Py2XBr 12 2.2. Reactions of interest 13 2.2.1. The Oxygen reduction reaction 13 2.2.2. The catalytic cycle of Cytochrome c Oxidase 14 2.3. Electrochemistry 16 2.3.1. General 3-electrode setup 16 2.3.2. Electrochemistry in solution 18 2.3.3. Voltammetry methods 20 2.3.4. The rotating ring-disk electrode 26 2.3.5. Chronoamperometry at the R(R)DE 29 2.3.6. Local effects of applied potential 30 2.4. Spectroscopy 32 2.4.1. UV-Vis spectroscopy 32 2.4.2. RAMAN spectroscopy 33 2.4.2.1. The RAMAN effect 33 2.4.2.2. Molecular vibrations 35 2.4.2.2.1. Diatomic molecules as harmonic oscillator 35 2.4.2.2.2. Triatomic considerations and normal modes 39 2.4.2.2.3. Complex molecules and symmetry 42 2.4.2.2.4. Porphyrin vibrations and RAMAN bands 46 2.4.2.2.5. Electron orbitals and orbital splitting 49 2.4.2.2.6. Porphyrin distortions 51 2.4.2.3. RAMAN intensities and selection rules 53 2.4.2.4. Resonance RAMAN spectroscopy 58 2.4.2.5. Surface-enhanced RAMAN spectroscopy 61 2.4.3. The (confocal) RAMAN microscope 63 2.5. Immobilization: dry cast, incubation and self-assembled Monolayers 64 3. Materials and methods 68 3.1. Materials 68 3.2. Electrode preparation 68 3.2.1. Polishing 68 3.2.2. Roughening 68 3.2.3. Self-assembly of monolayers 70 3.2.4. Immobilization of target molecules 71 3.3. Electrochemical methods 72 3.4. Spectroscopical methods 73 3.4.1. UV-Vis spectroscopy 73 3.4.2. RAMAN spectroscopy 73 3.5. Synthesis 74 3.6. DFT-calculations 74 3.7. Expression, purification and mutation of Cytochrome c oxidase 74 4. Results 75 4.1. Hangman, Py2XPFe investigation 75 4.1.1. Preface 75 4.1.2. Py2XPFeCl or Py2XPFe? A necessary disclaimer 75 4.1.3. Solution-based spectroscopy 76 4.1.3.1. UV-Vis spectroscopy of Py2XPFe 76 4.1.3.2. Resonance RAMAN spectroscopy 78 4.1.4. Immobilization by dry casting 80 4.1.4.1. SERRs on dry casted Py2XPFe 80 4.1.4.2. Potential titration 81 4.1.5. Immobilization on a SAM 84 4.1.5.1. SERRs on the SAM 84 4.1.5.2. SERRs in ambient atmosphere 86 4.1.5.1. SERRs in inert atmosphere 87 4.1.6. Immobilization by incubation casting 89 4.1.6.1. Potential dependent SERRs 89 4.1.6.1.1. SERRs in ambient atmosphere 89 4.1.6.1.2. SERRs in inert atmosphere 91 4.1.7. pH-dependency of incubation cast Py2XPFe 94 4.1.7.1. pH-titration at constant potential 94 4.1.7.1.1. SERRs in ambient atmosphere 94 4.1.7.1.2. SERRs in inert atmosphere 96 4.1.8. Investigation of Py2XBr 97 4.1.8.1. SERs of immobilized Py2XBr 97 4.1.8.2. DFT calculations on Py2XBr 99 4.1.8.3. Comparing theory and practice 101 4.1.8.4. Calculation of the pH-based spectra from pure state ones 104 4.1.9. Combined potential- and pH-titration 105 4.1.9.1. SERRs of Py2XPFe in inert atmosphere 105 4.1.9.2. SERRs of Py2XPFe in ambient atmosphere 109 4.1.10. Electrochemical ORR 112 4.1.10.1. pH-dependent ORR of Py2XPFe 112 4.1.10.2. Ruling out platinum as an interference 113 4.1.10.3. Comparing Hangman and the blank 114 4.1.10.4. Catalytic activity and selectivity of Py2XPFe 116 4.1.11. Buffer ions as possible ligands 118 4.1.12. Discussion 118 4.2. Pacman, Py2CuXPFe investigation 125 4.2.1. Potential-dependent titration in inert atmosphere 125 4.2.2. Combined potential- and pH-titration 129 4.2.3. Titration in ambient environment 134 4.2.4. Electrochemical ORR 139 4.2.5. Catalytic activity and selectivity of Py2CuXPFe 141 4.2.6. Discussion 143 4.3. Summary – comparing Hangman and Pacman 145 4.4. Investigation of Cytochrome c Oxidase 149 4.4.1. Preface 149 4.4.2. UV-Vis spectroscopy of CcO 149 4.4.3. Immobilization procedures 151 4.4.3.1. By the book – mixed -OH and -NH3 SAM 151 4.4.3.2. Hydrophobic -CH3 SAM 153 4.4.3.3. Incorporation in polypyrrole 156 4.4.3.1. By mutation 158 4.4.4. Summary 163 5. Appendix 165 6. References 175 Publications 191 Versicherung 192