Doctoral theses
Current Record: 1994 of 2427
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| Identifier |
000315345 |
| Title |
Σχεδιασμός, σύνθεση και φυσικοχημικός χαρακτηρισμός ενώσεων-μοντέλων κυτοχρώματος c οξειδάσης |
| Alternative Title |
Design, synthesis and physicochemical characterization of model-compounds of cytochrome c oxidase |
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Author
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Χαραλαμπίδης, Γεώργιος Ηρακλή.
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Thesis advisor
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Κουτσολέλος, Αθανάσιος
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| Abstract |
Cytochrome c oxidase (CcO) is an important metalloenzyme of the respiratory chain in many aerobic organisms. It catalyses the four electron, four proton reduction,
of oxygen to water, without releasing toxic reactive intermediates (Η2Ο2), conserving the energy required for the biosynthesis of ATP. The catalytic active site of the enzyme consists of a heme (heme a3) and a copper atom (CuB) coordinated with three imidazoles from histidine residues. One of the copper-bound histidines is covalently
connected to a tyrosine residue. Despite all the above detailed information derived from the natural enzyme many issues of the catalytic reaction still remain controversial.
The synthesis and the study of biomimetic model compounds is an alternative method to elucidate the mechanism of O2 reduction. This method involves the
synthesis and detailed structural and electronic characterization of model molecules (synthetic analogues) that approach or achieve one or more significant properties of a
protein active site. The synthetic analogues are low molecular weight complexes and this fact makes easier the characterization and the study of these compounds.
The aim of this thesis was the construction and the study of functional
biomimetic model compounds that closely resemble the native enzyme active site. All complexes have a porphyrin base for the coordination of iron and a chelate with at least three nitrogen atoms for the coordination of copper ion. To adequately reproduce
the structure of the heme/Cu site, these ligands also contain a phenol ring or a tyrosine molecule in order to mimic the tyrosine of the native enzyme.
At first are described the synthetic routes that were followed for the
preparation of the synthetic analogues. In all the cases was initially synthesised the porphyrin ring which constitutes the place of iron coordination. Afterwards, the ligand in which will be attached the copper ion and the group which resembles the tyrosine of the native enzyme were covalently linked with the porphyrin ring,. The synthesis of
the model compounds is completed with the accomplishment of the metalation
reactions with iron and copper.
After the preparation of the biomimetic model compounds, it was examined by
proton NMR spectroscopy their conformation in solution. 1H NMR spectra is a
characteristic tool to probe the stereorelation between the porphyrin ring and appended substituents (copper ligand and the tyrosine molecule). This investigation consists of comparing the chemical shift of representative protons for the appended substituents before and after their attachment with the porphyrin ring. In all the cases
we found that the models adopt the desirable conformation as the copper ligand and the phenol ring are situated close to the porphyrin ring.
The synthetic analogues must not only adequately reproduce the immediate
coordination environment of both metals (iron and copper), but also mimic the catalytic activity of the native enzyme. For this reason in all the synthesised models it was examined their potential as catalysts for the electrochemical reduction of oxygen.
The technique that is especially suitable for studying catalytic behaviour of
biomimetic heme/Cu analogues is rotating ring-disk votammetry, wherein the electrode serves both as a source of electrons and as a catalyst support. From these studies it was defined the selectivity of the model compounds toward the four electron reduction of oxygen to water. The synthesized analogues are mixed catalysts, as the
average number of electrons by which one O2 molecule is reduced is ~3. Moreover the presence of a copper centre improves the catalysis in comparison with iron-only analogues. In contrast the catalytic activity of the model compounds is not affected by
the presence of the hydroxyl group.
Finally, at the synthesized biomimetic models it was examined their ability to
bind oxygen or carbon monoxide. Oxygen is the natural substrate of the enzyme while carbon monoxide is a biologically occurring inhibitor and a frequently employed biochemical probe for the study of cytochrome c oxidase and other hemes. The investigations of O2 and CO binding and the characterization of the products were performed by using optical spectroscopy and in some cases infrared spectroscopy. In
all the cases, upon exposure to diogygen a heme-superoxo complex (Fe–Ο2-) is
formed. The thermal stability of this product is remarkable as we can observe it at room temperature. Addition of carbon monoxide leads to the formation of a new adduct were the CO is bound only to the iron centre. Photolysis of the reduced hemebound
CO results in the dissociation of iron bound-bound CO followed by binding to
the copper ion. The natural enzyme exhibits similar behaviour.
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| Language |
Greek |
| Subject |
biomimetic models |
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cytochrome c oxidase |
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porhyrin complexes |
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Βιομιμητικά μοντέλα |
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κυτοχρωμικη c οξειδάση |
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πορφυρινικά σύμπλοκα |
| Issue date |
2007-12-07 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
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Type of Work--Doctoral theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/b/1/f/metadata-dlib-04585258de4eec5f8cfe742880de0789_1267080492.tkl
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| Views |
485 |
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