<p>The quantum chemical investigations presented in this thesis use hybrid density functional theory to shed light on the catalytic mechanisms of mononuclear non-heme iron oxygenases, accommodating a ferrous ion in their active sites. More specifically, the dioxygen activation process and the subsequent oxidative reactions in the following enzymes were studied: tetrahydrobiopterin-dependent hydroxylases, naphthalene 1,2-dioxygenase and α-ketoglutarate-dependent enzymes. In light of many experimental efforts devoted to the functional mimics of non-heme iron oxygenases, the reactivity of functional analogues was also examined.</p><p>The computed energetics and the available experimental data served to assess the feasibility of the reaction mechanisms investigated. Dioxygen activation in tetrahydrobiopterin- and α-ketoglutarate-dependent enzymes were found to involve a high-valent iron-oxo species, which was then capable of substrate hydroxylation. In the case of naphthalene 1,2-dioxygenase, the reactivity of an iron(III)-hydroxperoxo species toward the substrate was investigated and compared to the biomimetic counterpart.</p>

The quantum chemical investigations presented in this thesis use hybrid density functional theory to shed light on the catalytic mechanisms of mononuclear non-heme iron oxygenases, accommodating a ferrous ion in their active sites. More specifically, the dioxygen activation process and the subsequent oxidative reactions in the following enzymes were studied: tetrahydrobiopterin-dependent hydroxylases, naphthalene 1,2-dioxygenase and α-ketoglutarate-dependent enzymes. In light of many experimental efforts devoted to the functional mimics of non-heme iron oxygenases, the reactivity of functional analogues was also examined. The computed energetics and the available experimental data served to assess the feasibility of the reaction mechanisms investigated. Dioxygen activation in tetrahydrobiopterin- and α-ketoglutarate-dependent enzymes were found to involve a high-valent iron-oxo species, which was then capable of substrate hydroxylation. In the case of naphthalene 1,2-dioxygenase, the reactivity of an iron(III)-hydroxperoxo species toward the substrate was investigated and compared to the biomimetic counterpart.

In der vorliegenden Arbeit werden unter Verwendung von Hydrotris(pyrazolyl)-boraten (Tp) als tripodale Zuschauerliganden Modellsysteme für unterschiedliche Nicht-Häm-Eisenenzyme entwickelt und untersucht. Dabei steht im ersten Schritt die Syntheseoptimierung und Implementierung der noch nicht für biomimetische Studien verwendeten TpMes und TpMes* Liganden im Vordergrund. Darauffolgend werden geeignete Metall-Chloro-Vorläuferkomplexe [TpMesMCl] synthetisiert. Das Koordinationsverhalten des TpMes*-Liganden gegenüber zweiwertigen Übergangsmetallionen wird systematisch untersucht und eine Reihe von heteroleptischen [TpMes*MCl] und homoleptischen [(TpMes*)2M] Komplexen synthetisiert und charakterisiert. Die Modellverbindungen [TpMesFeCysOEt] und [TpMesFeCysAm], welche Cysteinatethylester und Cysteaminat als Substratliganden tragen, dienen jeweils als strukturelles sowie funktionelles Modell für die Cystein- und die Cysteamindioxygenase. Die Mesitylreste des TpMes-Liganden bilden eine schützende, becherartige Struktur um das Eisenzentrum. Die Reaktionsprodukte können so unter anderem erstmalig kristallografisch charakterisiert werden. Zudem wird ein Intermediat in der Reaktion von [TpMes*FeCysAm] mit O2 beobachtet und eingehend untersucht. Die Eisen(II)komplexe [TpMesFeOBzR], die neben dem Tp-Liganden unterschiedlich substituierte Benzoate tragen, zeigen bemerkenswerte Ähnlichkeit zum Ruhezustand von Lipoxygenasen. Mit tert-Butylhydroperoxid (tBuOOH) können temperaturempfindliche Spezies beobachtet werden, die den mononuklearen [TpMesFe(OOtBu)(OBzR)] Alkylperoxiden zugeordnet werden. Im letzten Teil dieser Arbeit wird [TpMesFeACC] als Modell für die 1-Aminocyclopropansäureoxidase dargestellt. Es ist möglich, reaktive Spezies mit tBuOOH und meta-Chlorperbenzoesäure (mCPBA) zu beobachten. Zudem liefert die elektrochemische in-situ-Aktivierung von Sauerstoff in Folge Hinweise auf (Hydro-)-peroxidkomplexe bei der Reaktion von [TpMesFeACC] mit dem Superoxidradikalanion. / In the present work model systems for different non-heme iron enzymes are developed and investigated with the help of hydrotris(pyrazolyl) borates (Tp) as tripodal spectator ligands. The first part focusses on the optimization of the synthesis and implementation of the TpMes and TpMes* ligands for biomimetic studies. Following this, suitable precursor complexes [TpMesMCl] are prepared. The coordination behavior of the so far rarely used TpMes* ligand towards divalent transition metal ions is systematically investigated and several heteroleptic [TpMes*MCl] and homoleptic [(TpMes*)2M] complexes are synthesized and characterized. The model complexes [TpMesFeCysOEt] and [TpMesFeCysAm], which carry cysteinate ethylester and cysteaminate as substrate ligands, serve as structural and functional models for the cysteine and cysteamine dioxygenase, respectively. The mesityl residues of the TpMes ligand form a protective, cup-like structure around the iron center. The reaction products could be characterized crystallographically for the first time. An intermediate in the reaction of [TpMes*FeCysAm] with O2 is intensively studied. The iron(II) complexes [TpMesFeOBzR], which in addition to the Tp ligand carry substituted benzoates, show remarkable similarities to the resting state of lipoxygenases. With tert-butyl hydroperoxide (tBuOOH) temperature-sensitive species are observed, which are assigned to the mononuclear [TpMesFe(OOtBu)(OBzR)] alkylperoxides. In the last part of this work, [TpMesFeACC] is presented as a model for 1-aminocyclopropan-1-carboxylic acid oxidase. It is possible to observe reactive species with tBuOOH and meta-chloroperbenzoic acid (mCPBA). In addition, the electrochemical in-situ activation of oxygen provides evidence for (hydro-)peroxide complexes in the reaction of [TpMesFeACC] with the superoxide radical anion.