New Synthetic Approaches and Structural Models of the Oxygen-Evolving Complex in Photosystem II from the Use of Oximato-Based Ligands
Notice bibliographique
Résumé
The employment of the chelating/bridging ligands salicylhydroxime (shiH3), quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH2) in heterometallic Mn‒Ca chemistry has afforded various compounds with diverse topologies, metal stoichiometries and Mn oxidation state descriptions. \n\tChapter 1 provides a general introduction to the oxygen-evolving complex (OEC) of Photosystem II (PSII) including discussions of fundamental aspects such as composition, structural proposals, mechanism of O‒O bond formation and synthetic approaches. My research results are reported in Chapter 2, 3 and 4. In the first project (Chapter 2), one-pot reactions between Mn(ClO4)2∙6H2O, Ca(ClO4)2∙4H2O and the potentially tetradentate chelating/bridging ligand salicylhydroxime (shiH3), resulting from the in situ metal ion-assisted amide-iminol tautomerism of salicylhydroxamic acid (shaH2), in the presence of various fluorescence carboxylate groups (2-naphthoic acid = L1-H; 9-anthracenecarboxylic acid = L2-H; 1-pyrenecarboxylic acid = L3-H) and base NEt3 has led to a family of structurally similar {MnIII4Ca} clusters (1‒4¬) with distorted square pyramidal topologies. The combined results demonstrate the ability of shiH3 and fluorescence carboxylates to yield new heterometallic Mn‒Ca clusters with (i) the same Mn‒Ca ratio as the OEC of PSII, (ii) structural stability in solution, (iii) a pronounced redox and optical activity and (iv) predominant antiferromagnetic exchange interactions with S = 0 spin ground states. These complexes may be relevant to lower oxidation level species of the catalytic cycle of the OEC. \n\tThe second project of this thesis, discussed in Chapter 3, involved one-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0 triangular precursors and either CaBr2∙xH2O or CaCl2∙6H2O in the presence of shaH2. This afforded the heterometallic complexes [MnIII4Ca2(O2CPh)4(shi)4(H2O)3(Me2CO)] (5) and (pyH)[MnII2MnIII4Ca2Cl2(O2CPh)7(shi)4(py)4] (6), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO3)2∙4H2O/Ca(NO3)2∙4H2O and Mn(O2CPh)2∙2H2O/Ca(ClO4)2∙4H2O “metal blends” and shaH2 in the presence of external base NEt3, led to the new complexes (NHEt3)[MnIII4MnIV4Ca2(OEt)2(shi)10(EtOH)2] (7) and (NHEt3)4[MnIII8Ca2(CO3)4(shi)8] (8), respectively. Solid-state dc magnetic susceptibility studies of 5‒8 revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground state values. From a bioinorganic chemistry perspective, these compounds may demonstrate some relevance to both the high-valent scheme (7) and lower oxidation level species (5, 6 and 8) of the catalytic cycle of the OEC. \n\tIn the last chapter of this thesis (Chapter 4), the ligands quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH2) were introduced for a first time in heterometallic Mn‒Ca chemistry. This afforded a mixed-valence {MnII/III22Ca2} (9) cluster containing several {Mn4CaOx} subunits and a butterfly-like {MnIV2Ca2} (10) complex, respectively. These compounds demonstrate structural and magnetic relevance to both the low- and high-valent states of the OEC. \n\tAll research-based Chapters (Chapter 2‒4) are divided into subsections in order to facilitate the understanding of the research concepts by the familiar and non-familiar readers and contextualize the messages, goals and conclusions of each individual project. I felt it was appropriate to begin each Chapter with a short preface of the work that summarizes the most important aspects of the specific project, followed by the complete experimental work and discussion of the results, and end with conclusions and some future perspectives.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».