Die vorliegende Arbeit befaßt sich mit neuartigen ein- und zweikernigen Komplexen basierend auf dem Phosphanbaustein P(C6H4CH2NMe2-2)3. Im Vordergrund steht dabei die Synthese sowie die Untersuchung des elektrochemischen Verhaltens dieser Verbindungen. Einkernige Verbindungen des Typs [P(C6H4CH2NMe2-2)3]MX (M = Cu, Ag; X = nicht-koordinierter, anorganischer Rest) dienen dabei als Ausgangsverbindungen zur Darstellung ein- und zweikerniger Komplexe mit s-Donorliganden. Die Verknüpfung zweier [P(C6H4CH2NMe2-2)3]M-Fragmente (M = Cu, Ag) erfolgt über bis(s-Donor)liganden. Mittels cyclovoltammetrischer Experimente wird die elektrochemische Beeinflussung der Metallzentren untereinander untersucht. Weiterhin befaßt sich diese Arbeit mit der Synthese sowie der Untersuchung der thermischen Eigenschaften Lewis-Basen-stabilisierter Kupfer(I)-b-Diketonate bzw. -Carboxylate. Durch die Wahl der Lewis-Base sowie des b-Diketonato- bzw. Carboxylato-Fragmentes ist es möglich, Einfluß auf die Eigenschaften der erhaltenen Komplexe zu nehmen. Thermogravimetrische Untersuchungen bzw. OMCVD-Versuche lassen Rückschlüsse auf die Eignung solcher Systeme zur Abscheidung elementaren Kupfers zu.

Treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2, 1) with 5/6 equivalent of MeNH2 in abs. EtOH results in the exclusive formation of the ethyl ester of o-phenylene(N′-methyl oxamide)(oxamic acid) (opooH3EtMe, 2) in ca. 50% yield. Treatment of 2 with four equivalents of [Me4N]OH followed by the addition of Cu(ClO4)2·6H2O gave [Me4N]2[Cu(opooMe)]·H2O (3A) in ca. 80% yield. As 3A appears to be a hygroscopic solid, the related [nBu4N]+ salts [nBu4N]2[M(opooMe)]·H2O (M = Cu (3B), Ni (4)) have been synthesized. By addition of two equivalents of [Cu(pmdta)(NO3)2] to a MeCN solution of 3B the novel asymmetric trinuclear complex [Cu3(opooMe)(pmdta)2](NO3)2 (5) could be obtained in ca. 90% yield. Compounds 2, 3A, 3B, 4 and 5 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 3A in the form of [Me4N]2[Cu(opooMe)]·MeOH (3A′), 3B in the form of [nBu4N]2[Cu(opooMe)] (3B′), 4 in the form of [nBu4N]2[Ni(opooMe)]·1.25H2O (4′) and 5 in the form of [Cu3(opooMe)(pmdta)2] (NO3)2·3MeCN (5′), respectively, have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 3B (1%) in the host lattice of 4 (99%) in the form of single crystals have been made available, allowing single crystal EPR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine interaction. Out of these studies the spin density distribution of the [Cu(opooMe)]2− complex fragment could be determined. The magnetic properties of 5 were studied by susceptibility measurements versus temperature. An intramolecular J parameter of −65 cm−1 has been obtained, unexpectedly, as 5 should possess two different J values due to its two different spacers between the adjacent CuII ions, namely an oxamate (C2NO3) and an oxamidate (C2N2O2) fragment. This unexpected result is explained by a summarizing discussion of the experimentally obtained EPR results (spin density distribution) of 3B, the geometries of the terminal [Cu(pmdta)]2+ fragments of 5 determined by X-ray crystallographic studies and accompanying quantum chemical calculations of the spin density distribution of the mononuclear [Cu(opooMe)]2− and of the magnetic exchange interactions of trinuclear [Cu3(opooMe)(pmdta)2]2+ complex fragments. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Im Rahmen dieser Arbeit wurden Siliciumkomplexe mit dianionischen Pyrrol-2-carbaldimin-funktionalisierten N,N,O- und N,N,N,N-Chelatliganden synthetisiert und kristallografisch, NMR- und UV/Vis-spektroskopisch und mittels quantenchemischer Berechnungen charakterisiert. Die pentakoordinierten Si-Komplexe mit N,N,O-Ligandrückgraten wiesen in Abhängigkeit von den weiteren Si-gebundenen Substituenten unterschiedlich konfigurierte verzerrt trigonal-bipyramidale Si-Koordinationssphären auf. Die Ursache der Farbigkeit dieser Verbindungen konnte mittels quantenchemischer Berechnungen detailliert erklärt werden. – Die Si-Komplexe mit N,N,N,N-Ligandrückgraten liegen in Abhängigkeit von den weiteren Si-gebundenen Substituenten als 5-fach koordinierte kationische oder neutrale 6-fach koordinierte Si-Komplexe vor. Deren Farbigkeit wurde mittels UV/VIS-Spektroskopie untersucht. Von ausgewählten Komplexen wurden die Tensoren der 29Si-NMR-Verschiebung rechnerisch und CP/MAS-NMR-spektroskopisch bestimmt.

Self-assembly processes were used to construct supramolecular architectures based on metal-ligand interactions. The structures formed strongly depend on the used metal ion, the ligand type, the chosen counter ion and solvent as well as on the experimental conditions. The focus of the studies was the design of multifunctional N-donor ligands and the characterization of their complexing and structural properties. This work was divided into three distinct main parts: The bis(2-pyridylimine), the bis(2-hydroxyaryl) imine and the tripodal imine / amine ligand approach. In the first part a series of bis(2-pyridylimine) derivatives having different linking elements were employed as building blocks for novel supramolecular architectures. Reaction of individual d-block metal salts with these ligands has led to the isolation of coordination polymers, a metallamacrocycle, double-stranded helicates, triple-stranded helicates as well as of circular meso-helicates. The nature of the spacer in the Schiff base ligands, the noncovalent weak interactions, such as hydrogen bond, face-to-face π-π and edge-to-face CH-π interactions, are all important factors influencing the architecture of the final products. Topological control of the assembly process of the hexanuclear meso-helicates is clearly associated with the bidentate coordination of the sulfate anion which directs the formation of a double- rather than a triple-stranded helicate around the octahedrally coordinated Cu(II). Surprisingly, the variation of the linker function in the ligands, which significantly changes the linking angle of the pyridylimine strands, has only a little influence of the resulting structure. Also the use of a mixture of ligands does not influence the meso-helicate topology; the result is the symmetrically mixed meso-helicate. The new iron(II) triple helicate [Fe2(L5)3](PF6)4 14 {L5 = bis[4-(2-pyridylmethyleneimino)phenyl]-1,1-cyclohexane} in its chloride form binds strongly to DNA as confirmed by induced circular dichroism signals in both the metal-to-ligand charge transfer (MLCT) and in-ligand bands of the helicate. The induced CD spectrum gives some evidence that [Fe2(L5)3]4+ interacts with the DNA in a single binding mode, which is consistent with major groove binding. The cytotoxicity of the new iron(II) triple helicate 14 was evaluated on human lung cancer A549 cells and compared with that of cisplatin and that of the previously reported iron(II) triple helicate [Fe2(L1)3]4+{L1 = bis[4-(2-pyridylmethyleneimino)phenyl]methane}. The first results show some distinguishing features for 14 obviously caused by the existing structural differences of the complexes. In the second part of the thesis, novel uranyl complexes of the bis(2-hydroxyaryl) imine ligands have been synthesized and characterized. 1D coordination polymers and mononuclear structures were formed. In all complexes a distorted hexagonal bipyramidal coordination geometry around the uranyl centre is observed. The imine nitrogen atoms of the ligands do not bind to the metal centre but interact strongly with the hydroxy group via H-bonding. DFT calculations made with L8 ( α,α’-Bis(salicylimino)-m-xylene) are in good agreement with the X-ray crystal structure data. Liquid-liquid extraction studies involving selected ligands and Eu(III) or U(VI) indicate remarkably high selectivity for U(VI) over Eu(III) at weak acidic pH conditions. We believe that the study made opens up new possibilities for uranyl ion extraction which could be interesting in view of the treatment of nuclear waste. In the third part of the thesis, a series of multifunctional tripodal ligands with different N-donor centres were used for U(VI) and lanthanide, Nd(III), Eu(III) and Yb(III), binding and extraction. Reaction of these metal ions with selected tripodal ligands afforded complexes which were characterized by ESI mass spectroscopy. The complex composition was found to be 1:1 in all cases. The extraction behaviour of the tripodal ligands towards Eu(III) and U(VI) was studied both in the absence and presence of octanoic acid as co-ligand using the extraction system Eu(NO3)3 or UO2(NO3)2–buffer–H2O/ ligand–CHCl3. These separation systems show a remarkably high selectivity for U(VI) over Eu(III). It is interesting to note that the addition of the octanoic acid to the extraction system leads to high synergistic effects. A series of Eu(III) extraction experiments were done to clarify the composition of the extracted complexes. The results clearly point to the formation of various species with changing composition.

The present dissertation focuses on the synthesis of iron(II) complexes and the study of their SCO behavior. The equilibrium between the HS and the LS states gives to the SCO systems large potential applications for molecular electronics. However, today there is not a single molecular device from SCO compounds in the market. This is due to the fact that the SCO systems discovered up to now were unable (e.g. TLIESST « 300 K) for these applications. The aim of this thesis is to synthesize new SCO compounds with sustainable properties for applications. In the beginning of the thesis, [Fe(rac-22a))]2+∙2[BF4]- and [Fe(rac-22b)]2+∙2[BF4]- employing rigid hexadentate ligands were described. In contrast to the expectation, the N-methylation of the amines shifts the equilibrium towards the LS state. [Fe(rac-22b)2+∙2[BF4]- shows a T1/2 higher at 74 K and 52 K than the non methylated [Fe(rac-22a)2+∙2[BF4]- respectively in nitrobenzene and acetonitrile. The T1/2 are solvent-dependent for these complexes. After that, ligand series 9-R2-2-(6-R1-pyridin-2-yl)-1,10-phenanthroline 25b (R2 = Me), 25f (R2 = Ph), 25d (R2 = C(O)H), 25c (R1 = Ph), 25l (R1 = oxylphenyl-4-oxymethylene), 25m (R1 = oxymesitylene) and 25j (R1 = pyrol-1-yl) were synthesized. It was observed that the size of the substituent influences the SCO properties (T1/2). In addition, the influence of the counterion was shown with [Fe(25c)2]2+∙2[BF4]- and [Fe(25c)2]2+∙2[B(Ph)4]-. The B(Ph)4- conterions bring π∙∙∙π interactions in the molecular cell which shift the T1/2 parameter to a high temperature (200 K) compared to the complex with BF4- ions (175 K). Moreover the substituents R1 on the terminal position of the pyridine effect on T1/2 more than the substituents R2 on the terminal position of the phenanthroline. For example, [Fe(25f)]2+∙2[BF4]- (R1 = Ph) is a pure HS complex while the complex [Fe(25c)]2+∙2[BF4]- (R2 = Ph) is a SCO system (T1/2 = 175 K). The expansion of the coordination mode from N6 to N8 was investigated by the synthesis of the tetradentate ligands. This expansion shows an unexpected coordination mode, [Fe(25i)2]2+∙2[BF4]- (R2 = pyrazol-1-yl) forms a distorted square antiprism coordination geometry (HS iron(II)-complex) and does not show any Fe-N bond breaking over the application of the temperature as expected. / Die vorliegende Dissertation behandelt die Synthese von Eisen(II)-Komplexen und ihr spin crossover (SCO)-Verhalten. Das Gleichgewicht zwischen high-spin (HS)- und low-spin (LS)-Zustand verleiht den SCO-Systemen eine großes Anwendungspotential im Bereich der molekularen Elektronik. Dennoch existiert bis heute kein SCO-basiertes molekulares Bauteil auf dem Markt. Hauptgrund hierfür ist, dass die bislang bekannten SCO-Systeme keine hinreichenden Eigenschaften (z.B. TLIESST « 300 K) aufweisen. Das Ziel der vorliegenden Arbeit ist die Synthese neuer SCO-Verbindungen mit geeigneten Eigenschaften für die Anwendung. Zu Beginn der Arbeit werden die Komplexe [Fe(rac-22a)]2+∙2[BF4]– und [Fe(rac-22b)]2+ ∙2[BF4]– mit starren hexadentaten Liganden beschrieben. Entgegen der Erwartung verschiebt die N-Methylierung der Amine das Gleichgewicht in Richtung des LS-Zustandes. Verglichen mit dem nicht-methylierten Komplex Fe(rac-22b)]2+∙2[BF4]– zeigt Fe(rac-22a)]2+∙2[BF4]– eine höhere Übergangstemperatur T1/2, welche in Nitrobenzen 74 K und in Acetonitril 52 K beträgt. Für die Komplexe ist T1/2 lösungsmittelabhängig. Im Folgenden wurde die Ligandenserie 9-R2-2-(6-R1-pyridin-2-yl)-1,10-phenanthrolin mit den Vertretern 25b (R2= Me), 25f (R2 = Ph), 25d (R2 = C(O)H, 25c (R1 = Ph), 25l (R1 = oxyphenyl-4-oxymethylen), 25m (R1 = oxymesitylen) und 25j (R1 = pyrol-1-yl) hergestellt. Es wurde beobachtet, dass die Größe des Substituenten das SCO-Verhalten (T1/2) beeinflusst. Ergänzend wurde der Einfluss des Gegenions anhand der Komplexe [Fe(25c)]2+∙2[BF4]– und [Fe(25c)]2+∙2[B(Ph)4]– untersucht. Das Gegenion B(Ph)4– ermöglicht intra- und intermolekulare π···π-Wechselwirkungen in der Zelle, welche die Übergangstemperature T1/2 (200 K) gegenüber dem BF4–-Komplex (175 K) erhöhen. Des Weiteren beeinflussen die Substituenten R1 an der Pyridin-Einheit die ubergangskomplexes T1/2 stärker als die Substituenten R2 an der Phenanthrolin-Einheit. So ist [Fe(25f)]2+∙2[BF4]– (R1 = Ph) ein reiner HS-Komplex, während der Komplex [Fe(25c)]2+∙2[BF4]– (R2 = Ph) ein SCO-System ist (T1/2 = 175 K). Die Erhöhung der Koordinationszahl von N6 auf N8 wurde über die Synthese von tetradentaten Liganden untersucht. Diese Erhöhung führt zu einem unerwarteten Koordinationsmodus. So bildet [Fe(25i)]2+∙2[BF4]– (R2 = pyrazol-1-yl) eine quadratisch-antiprismatische Koordinationssphäre (HS Eisen(II)-Komplex) und zeigt, wie erwartet, über den untersuchten Temperaturbereich keine Fe–N-Bindungsspaltung.

The assembly of nanostructures into “multi”-dimensional materials is one of the main topics occurring in nanoscience today. It is now possible to produce high quality nanostructures reproducibly but for their further application larger structures that are easier to handle are required. Nevertheless during their assembly their nanometer size and accompanying properties must be maintained. This challenge was addressed in this work. Lead chalcogenides have been chosen as an example system because they are expected to offer great opportunities as thermoelectric materials. Three different ways to achieve assemblies of lead chalcogenide nanostructures were used and the resulting structures characterized with respect to their potential application as thermoelectric material. The first means by which a “multi”-dimensional assembly of lead chalcogenide quantum dots can be produced is the formation of porous structures such as aerogels and xerogels. A procedure, where the addition of an initiator such as oxidizers or incident radiation is unnecessary, is introduced and the formation process studied by absorption spectroscopy. The time-consuming aggregation step could be significantly reduced by employing a slightly elevated temperature during gelation that does not lead to any observable differences within the resulting gel structures. After either supercritical or subcritical drying, highly porous monolithic gel structures can be achieved. During the gel formation the size and the shape of the particles changed and they were directly linked together. Nevertheless the resulting porous structures remain crystalline and size dependent effects of the optical properties could be shown. Gels produced from a mixture of PbS and PbSe QDs show a homogenous distribution of both materials but it is not clear to what extent they form an alloy. Although the particles are directly linked together the resulting porous structures possess a very high resistivity and so it was not possible to characterize the semiconductor aerogels with regard to their thermoelectric properties. To achieve an enhanced conductivity porous structures containing PbS and Au nanoparticles have been produced. As has been seen for the pure semiconductor gels the size of the PbS quantum dots has increased and elongated particles were formed. In contrast to the PbS QDs the Au nanoparticles did not change their size and shape and are unevenly distributed within the PbS network. Through the use of the gold nanoparticles the conductivity could be increased and although the conductivity is still quite small, it was possible to determine Seebeck coefficients near room temperature for a mixed semiconductor-metal gel. The second means by which QD solids could be formed was by the compaction of the QD building blocks into a material that is still nanostructured. Therefore the synthesis of PbS was optimized to achieve sufficient amounts of PbS quantum dots. The ligands used in the synthesis of the QDs unfortunately act as an insulating layer resulting in QD solids with resistivities as high as 2 Gigaohm. For this reason different surface modification strategies were introduced to minimize the interparticle distance and to increase the coupling between the QDs so as to increase the conductivity of the resulting quantum dot solids. One very promising method was the exchange of the initial ligands by shorter ones that can be destroyed at lower temperatures. By such heat treatments the resistivity could be decreased by up to six orders of magnitude. For the pressing of the quantum dots two different compaction methods (SPS and hydraulic pressing) were compared. While the grain growth within the SPS pressed samples is significantly higher the same densification can be achieved by a cold hydraulic pressing as well as by SPS. The densification could be further increased through the use of preheated PbS QDs due to the destruction of the ligands. Samples which had been surface modified with MPA and subsequently thermally treated show the best results with respect to their thermopower and resistivities. Nevertheless the conductivity of the QD solids is still too high for them to be used as efficient thermoelectric materials. The final assembly method does not involve QDs but instead with one dimensional nanowires. Therefore a synthesis was developed that enables the formation of PbS nanowires of different diameters and one that is easy up-scalable. By the use of a less reactive sulfur precursor and an additional surfactant the formation of nuclei is significantly retarded and within an annealing time of two hours nanowires can be formed presumably by an oriented attachment mechanism. Single crystalline nanowires with a diameter of 65-105 nm could be achieved with the longest axes of the nanowires being parallel to [100]. The resulting nanowires were used as building blocks for film formation on glass substrates by an easily implemented method that requires no special equipment. To characterize the films with a view to their possible application as a thermoelectric material, surface modifications of the films were performed to improve the charge transfer in the films and the Seebeck coefficients of the resulting films measured. Therefore the previous approach of using MPA was applied and a subsequent thermal treatment demonstrated very promising results. In addition an crosslinking ligand was used for surface treatment that leads to similar results as was observed for the thermally treated MPA approach. Both approaches lead to an order of magnitude decrease in the resistivity and due to the fewer grain boundaries present in the films composed of nanowires as compared to the QD assemblies the conductivity is significantly higher. The Seebeck coefficient measurements show that the thermal treatment only slightly affects the Seebeck coefficients. Therefore a significantly higher power factor could be achieved for the nanowire films than for the QD solids.

Featuring size-tunable electrical and optical properties, semiconductor nanocrystals (NCs) attract intensive interest in developing promising functional materials for optoelectronic appli-cations. The surface ligands not only play an important role in the synthesis and colloidal sta-bility of NCs, but also significantly affect their photophysical and electrochemical properties. In this dissertation, I am dealing with the surface ligand engineering of NCs (including both perovskite and metal chalcogenide families) for optical and photocatalytic applications. Polymer ligands are regarded to enable better colloidal stability, durability and processability of fluorescent NCs, which is especially important for perovskite NCs. However, the current wide-used polymer ligands fail to provide sufficient surface passivation for the NCs, which is unfavorable for their luminescence. To address this issue, a dual-ligand system based on par-tially hydrolyzed poly(methyl methacrylate) (h-PMMA) and highly branched polyethyl-enimine (PEI) was designed to stabilize perovskite NCs. The hydrophobic polymer of h-PMMA imparts excellent film-forming properties and durability to the resulting NC-polymer composite. The PEI forms an amino-rich, strongly binding ligand layer on the surface of the NCs being responsible for the significant improvement of the photoluminescence quantum yield and the stability of the resulting material. These superior properties allowed us to fabri-cate a proof-of-concept thin film organic light-emitting diode (OLED) with h-PMMA/PEI-stabilized perovskite NCs. A further insight into the roles of double polymer ligands (h-PMMA and PEI) during the mechanosynthesis of perovskites nanoparticles (NPs) was pro-vided. The h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of NPs. The PEI with large amounts of amino groups induced enrichment of PbBr2 in the reaction mixture, which in turn caused the formation of heterostructured CsPbBr3-CsPb2Br5-mPbBr2 and CsPbBr3-Cs4PbBr6-nCsBr NPs. Not only polymer, but also inorganic ligands can be extremely attractive for capping of NCs. In the frame of this thesis, a two-step surface modification strategy was developed to control-lably destabilize the colloidal NCs, which in turn facilitated their 3D assembly into aerogels. Specifically, the long-chain oleic acid ligands were exchanged to the ultra-short-chain inorganic (NH4)2S ligands. These new ligands were further protonated by changing the dispersing solvent, which caused desired colloidal destabilization. The as-prepared CdSe NC aerogels with highly porous and self-supporting structure were found to be attractive for solid-state photocatalysis in a gas phase. Indeed, the (NH4)2S ligand is favourable for the adsorption and activation of substrate molecules (i.e., H2O and CO2) on the large open surface of NC gel, thereby promoting the progress of CO2 photoreduction. As a result, the photocatalytic activity for CO2 reduction of CdSe NC aerogels created in this work is 12-fold higher than that of the pristine non-assembled NC-precipitates.:Abstract 1 Contents 3 Abbreviations 6 List of Figures and Tables 8 1. Colloidal Semiconductor Nanocrystals and their Ligand Shell 13 1.1. Colloidal Semiconductor Nanocrystals 14 1.1.1. Inorganic Core of NCs 15 1.1.1.1. Metal Chalcogenide NCs 16 1.1.1.2. Metal Pnictide NCs 16 1.1.1.3. Halide Perovskites NCs 17 1.1.2. The Surface Ligands for NCs 18 1.1.2.1. The Classification of Surface Ligands based on Head-Groups 18 1.1.2.2. The Classification of Surface Ligands based on Tail-Groups 19 1.2. The Role of Ligands 20 1.2.1. The Role of Ligands in the Synthesis of NCs 20 1.2.2. The Role of Ligand in Colloidal NCs Dispersion and Stability 22 1.2.3. The Role of Ligand in the Light-Matter Interactions as Applied to NCs 24 1.3. The Surface Ligand Engineering of NCs 26 1.3.1. Introducing Ligands during the Synthesis 26 1.3.2. Introducing the Ligands during Post-Synthesis Process 27 1.4. Challenges to be Addressed in this Dissertation 29 2. Polymer Ligands Enhance the Stability and Fluorescence of Perovskite for Optical Application 31 2.1. Background and Motivation 32 2.2. Results and Discussion 34 2.2.1. Spectral Characterization 34 2.2.2. Morphological Characterization 40 2.2.3. Surface Composition 41 2.2.4. Processability, Stability and Durability 43 2.2.5. Green-LED 46 2.3. Conclusions 48 3. Polymer Ligands Assist Mechanosynthesis of Perovskite Nanoparticles 49 3.1. Background and Motivation 50 3.2. Results and Discussion 50 3.2.1 Morphology and Composition 51 3.2.2 Formation and Phase Conversion of the Nanoparticles 53 3.2.3. Spectral Characterization 58 3.3. Conclusions 60 4. Ligand Protonation Promote 3D Assembly of CdSe Nanocrystals for CO2 Photoreduction 62 4.1. Background and Motivation 63 4.2. Results and Discussion 64 4.2.1. The Gelation Method 64 4.2.2. Surface Composition of the NC Aerogels 67 4.2.3. Performance of CdSe-S Aerogels in Photoreduction of CO2 68 4.2.4. Photocatalytic Mechanism of the CdSe-S/Ni Aerogel 70 4.3. Conclusion 73 5. Conclusions and Perspectives 75 Appendix. Experimental Section 78 A.1. Reagents 78 A.2. NCs synthesis 78 A.2.1 Mechanosynthesis of Polymer-Coordinated Perovskite NCs 78 A.2.2 Oil Phase Synthesis of Colloidal CdSe NCs 79 A.2.3 Ligand Protonation-Promoted Assembly of CdSe-S NCs into Gel 79 A.3. Optical and Photocatalytic Applications of NCs 80 A.3.1 Optical Applications of Polymer-Stabilized Perovskite NCs 80 A.3.2 Photocatalytic Applications of CdSe-S Aerogels 80 A.4. Characterization Methods 81 A.4.1 Morphology Characterization 81 A.4.2.Element Characterization 81 A.4.3 Diffraction Characterization 82 A.4.4 Spectroscopy Characterization 82 A.4.5 Gas adsorption Measurement 82 A.4.6 Electrochemical Measurements 83 A.4.7 Other Characterizations 83 A.5. Additional Data 84 Bibliography 87 List of Publications 96 Acknowledgements 98 Erklärung 100

The objective of this project was to study the influence of increased salinities on interaction processes in the system radionuclide – organics – clay – aquifer. For this purpose, complexation, redox, sorption, and diffusion studies were performed under variation of the ionic strength (up to 4 mol/kg) and the background electrolyte. The U(VI) complexation by propionate was studied in dependence on ionic strength (up to 4 mol/kg NaClO4) by TRLFS, ATR FT-IR spectroscopy, and DFT calculations. An influence of ionic strength on stability constants was detected, depending on the charge of the respective complexes. The conditional stability constants, determined for 1:1, 1:2, and 1:3 complexes at specific ionic strengths, were extrapolated to zero ionic strength. The interaction of the bacteria Sporomusa sp. MT-2.99 and Paenibacillus sp. MT-2.2 cells, isolated from Opalinus Clay, with Pu was studied. The experiments can be divided into such without an electron donor where biosorption is favored and such with addition of Na-pyruvate as an electron donor stimulating also bioreduction processes. Moreover, experiments were performed to study the interactions of the halophilic archaeon Halobacterium noricense DSM-15987 with U(VI), Eu(III), and Cm(III) in 3 M NaCl solutions. Research for improving process understanding with respect to the mobility of multivalent metals in systems containing humic matter was focused on the reversibility of elementary processes and on their interaction. Kinetic stabilization processes in the dynamics of humate complexation equilibria were quantified in isotope exchange studies. The influence of high salinity on the mobilizing potential of humic-like clay organics was systematically investigated and was described by modeling. The sorption of Tc(VII)/Tc(IV) onto the iron(II)-containing minerals magnetite and siderite was studied by means of batch sorption experiments, ATR FT-IR and X-ray absorption spectroscopy. The strong Tc retention at these minerals could be attributed to surface-mediated reduction of Tc(VII) to Tc(IV). An influence of ionic strength was not observed. The influence of ionic strength (up to 3 mol/kg) and background electrolyte (NaCl, CaCl2, MgCl2) on U(VI) sorption onto montmorillonite was studied. The U(VI) sorption is influenced by the background electrolyte, the influence of ionic strength is small. Surface complexation modeling was performed applying the 2SPNE SC/CE model. Surface complexation constants were determined for the NaCl and CaCl2 system and were extrapolated to zero ionic strength. Surface complexation in mixed electrolytes can be modeled applying surface complexation constants derived for pure electrolytes. The influence of citrate on U(VI) diffusion in Opalinus Clay was studied using Opalinus Clay pore water as background electrolyte. The diffusion parameter values obtained for the HTO through-diffusion and the U(VI) in-diffusion in the absence of citric acid were in agreement with literature data. In the presence of citric acid, U(VI) diffusion was significantly retarded, which was attributed to a change in speciation, probably U(VI) was reduced to U(IV). Larger-scale heterogeneous material effects on diffusive transport were investigated with PET. Diffusion parameters were derived by optimum fit of a FEM-model to the measurement. These parameters are in accordance with the results from 1D-through-diffusion experiments. Deviations from the simple transversal-isotropic behavior, which are identified as residuals from the model, are indications for heterogeneous transport on the mm-scale. PET measurements were also conducted in order to display the improvement of the EDZ with waterglass injections. These experiments enable to draw conclusions on the complex reactive transport process and thus an estimation of the achieved improvement of the barrier function. The image reconstruction procedure was largely improved, mainly with the aid of Monte-Carlo simulations, and now allows quantitative analysis and error estimation.

Hydrogenasen sind komplexe Enzyme, die die reversible Oxidation von molekularem Wasserstoff zu Protonen und Elektronen katalysieren. Diese Enzyme erlauben ihrem Wirtsorganismus das Wachstum unter chemolithoautotrophen Bedingungen. Der Modellorganismus Ralstonia eutropha besitzt drei gut charakterisierte Hydrogenasen der [NiFe]-Klasse, die sich durch ihre Sauerstofftoleranz auszeichnen. Ihr aktives Zentrum besteht aus einer komplexen prosthetischen Gruppe, welche aus einem Nickel- und einem Eisenatom besteht. Letzteres koordiniert drei diatomare Liganden, zwei Cyanide und ein CO. Die Synthese der gesamten Ni(SR)2(µ-SR)2Fe(CN)2(CO)-Gruppe ist ein komplexer Prozess. Die sogenannte Maturation benötigt wenigstens sechs akzessorische Proteine, die sogenannten Hyp-Proteine. Das umfassende Verständnis dieser Maturationsprozesse ermöglicht eine Vielzahl von biotechnologischen Anwendungen. Die vorliegende Arbeit untersucht die Maturation unter verschiedenen Gesichtspunkten. Zentrale, offene Fragen sind die Herkunft des Carbonylliganden sowie die Prozesse, die zur Ligandierung des katalytischen Eisens führen. Dazu wurden molekularbiologische, biochemische und spektroskopische Methoden in Verbindung mit Isotopenmarkierung eingesetzt. Unter anderem konnte dabei gezeigt werden, dass das katalytische Eisen alle seine Liganden bereits im HypCD-Komplex, dem zentralen Element der Maturation, erhält. Ferner konnte in dieser Arbeit, erstmalig für [NiFe]-Hydrogenasen, eine konkrete Biosynthese des seltenen und toxischen diatomaren CO-Liganden beschrieben werden. Ausgehend vom Alpha-Kohlenstoff von Glycin wird der Tetrahydrofolat (THF)-abhängige C1-Metabolismus mit C1-Einheiten versorgt. Durch die enzymatische Aktivität von HypX wird die Formylgruppe von N10-Formyl-THF zu CO umgesetzt. / Hydrogenases are complex enzymes that catalyze the reversible oxidation of molecular hydrogen into protons and electrons. These enzymes allow their host organism to grow under chemolithoautotrophic conditions. The model organism Ralstonia eutropha has three well-characterized [NiFe]-hydrogenases, which exhibit an extraordinary high oxygen tolerance. Its active center is a complex prosthetic group which consists of a nickel and iron atom. The latter coordinates three diatomic ligands, two cyanides and one CO. The biosynthesis of the whole Ni(SR)2(μ-SR)2Fe(CN)2(CO)-group is a complex process. This so-called maturation process needs the activity of at least six accessory proteins, the Hyp-proteins. Understanding the maturation allows a variety of biotechnological applications. The present study examines the maturation of [NiFe]-hydrogenases under different aspects. The major questions concern the origin of the carbonyl ligand as well as the processes that lead to ligandation of the designated catalytic iron. To adress these tasks, molecular biological, biochemical and spectroscopic methods in combination with isotopic labeling were employed. Inter alia, it could be shown that the catalytic iron in the HypCD-complex, the central element of the maturation process, contains all three diatomic ligands. Furthermore, this study describes, for the first time in [NiFe]-hydrogenases, a specific biosynthetic route of the rare and toxic diatomic CO-ligand. Starting from the alpha-carbon of glycine the tetrahydrofolate (THF)-dependent one-carbon metabolism is replenished with one-carbon units. Subsequently the formyl group from N10-formyl-THF is hydrolyzed by the enzymatic activity from HypX and further converted to carbon monoxide as determined by isotopic labeling and infrared spectroscopy.

Die SPOT-Synthese an Zellulosemembranen wurde 1992 als eine hocheffiziente Methode zur parallelen Synthese von Peptiden beschrieben. Die wichtigste Anwendung der so synthetisierten Verbindungen ist das direkte Festphasen-Screening. Im Rahmen dieser Arbeit ist es gelungen, das Anwendungsgebiet der SPOT-Methode von Peptiden auf verschiedene Peptidmimetika auszudehnen und durch Screening entsprechender Bibliotheken bioaktive Substanzen zu identifizieren. (1) Peptoid-Synthese an Zellulosemembranen Die Ähnlichkeit von Oligo-N-alkylglycinen (Peptoiden) zu Peptiden sowie die Vereinbarkeit ihrer Synthese mit den Bedingungen der SPOT-Technik ließen sie als besonders geeignete Kandidaten für eine Erweiterung der SPOT-Synthese von Peptiden auf Peptidmimetika erscheinen. Die Peptoide wurden nach der 1992 für die Synthese am Harz beschriebenen Sub-Monomer-Methode synthetisiert, bei der die N-Alkylglycin-Monomere zweistufig durch Bromacetylierung und nachfolgende Bromsubstitution durch ein primäres Amin aufgebaut werden. Die Kernaufgabe bei der Anpassung der Synthesebedingungen an Zellulosemembranen war dabei die Entwicklung einer N/O-selektiven Bromacetylierungsmethode, da die Anwesenheit freier Membran-Hydroxyfunktionalitäten ein Reagenz erfordert, welches eine N-Acylierung in Anwesenheit von O-Nukleophilen zuläßt. Durch Untersuchung mehrerer Aktivester der Bromessigsäure konnte gezeigt werden, daß der kristalline Bromessigsäure-2,4-dinitrophenylester im Hinblick auf Ausbeute und N/O-Selektivität optimale Eigenschaften besitzt. Im Anschluß an die Bromacetylierungsmittel wurden 46 primäre Amine auf ihre Anwendbarkeit bei der Synthese von Modell-Tripeptoiden untersucht. Aus den Ergebnissen konnten Gesetzmäßigkeiten abgeleitet werden, die eine Abschätzung der Verwendbarkeit von Aminen für die Peptoidsynthese im Hinblick auf Flüchtigkeit, sterischen Anspruch, Nukleophilie des Stickstoffatoms sowie vorhandene funktionelle Gruppen in Seitenketten ermöglichen. (2) Synthese und Screening von Peptoid-Bibliotheken Unter den optimierten Synthesebedingungen wurden zwei Bibliotheken mit jeweils 8000 Tri- bzw. Hexapeptoiden synthetisiert. Die Trimeren-Bibliothek beinhaltete dabei den gesamten Sequenzraum basierend auf 20 Bausteinen, während die Verbindungen der Hexameren-Bibliothek aus einem wesentlich größeren, auf 40 Bausteinen basierenden Sequenzraum statistisch ausgewählt wurden. Um zu überprüfen, ob sich die Bibliotheken zur "de novo" Auffindung von Protein-Liganden eignen, wurden sie auf Bindung zum monoklonalen Antikörper Tab-2 untersucht. Es konnten in beiden Fällen bioaktive Oligomere identifiziert werden (Trimere: KD >= 87 µM, Hexamere: KD >= 2.7 µM), die sich vom Peptid-Epitop des Antikörpers [VVSHFND] deutlich unterschieden. (3) Rückgratmodifizierte Peptoide Mit dem Ziel, Rückgratmodifikationen in Peptoide einzufügen, wurden neun Biselektrophile im Rahmen eines "chemischen Screenings" zur Synthese eines Modell-Trimers verwendet. Vier der Bausteine waren geeignet und ermöglichten damit die Einführung von beta-Peptoid-, m- und p-Aminomethylbenzoesäure- sowie Carbamat-Einheiten in Peptoide. Beim Versuch, in analoger Weise auch Harnstoffe zugänglich zu machen, wurde unter den Linker-Spaltungsbedingungen eine Cyclisierung zu Hydantoinen beobachtet. Diese interessante Reaktion wurde näher untersucht, um die SPOT-Methode auf die Synthese von Hydantoinen als heterocyclische Struktur zu erweitern. (4) Synthese von Hydantoinen an Zellulosemembranen Die Bildung von Hydantoinen in einer Cyclisierungsreaktion, bei der Ammoniak aus einem Amid freigesetzt wird, wurde an fester Phase noch nicht genutzt, während dieser Reaktionstyp in Lösung bereits intensiv untersucht wurde. Durch eine Optimierung der Cyclisierungsbedingungen ließ sich die zunächst unvollständige Reaktion zur Vollständigkeit bringen. Auch C-substituierte Hydantoine konnten durch Verwendung von alpha-Aminosäureamiden bzw. -tert.-butylestern enantiomerenrein zugänglich gemacht werden. / SPOT-synthesis on cellulose membranes was introduced as a highly efficient method for the parallel synthesis of peptides in 1992. The most important applications of libraries synthesized by SPOT-synthesis are solid phase binding assays. Within this work the extension of the SPOT-method to the synthesis of various peptidomimetics and the identification of bioactive substances by screening of corresponding libraries is described. (1) peptoid synthesis on cellulose membranes The similarity of oligo-N-alkylglycines (peptoids) and peptides as well as the compatibility of their synthesis with the conditions of the SPOT-technique made them ideally suited for the extension of the SPOT-synthesis from peptides to peptidomimetics. The peptoids were synthesized by the sub-monomer approach originally developed for the synthesis on standard resins in 1992. N-alkylglycine monomers are hereby synthesized in a stepwise manner by bromoacetylation and subsequent substitution of the bromine atom by a primary amine. The most critical point in the adaptation of the synthesis conditions was the development of an N/O-selective reagent for bromoacetylation due to the presence of free hydroxyl functionalities of the membrane support requiring a reagent suitable for N-acylation in the presence of O-nucleophiles. Several active esters of bromoacetic acid were synthesized and tested whereby crystalline 2,4-dinitrophenylbromoacetate gave the best results with respect to yield and N/O-selectivity. After optimization of bromoacetylation 46 primary amines were applied to the synthesis of model tripeptoids. Rules for the applicability of amines in peptoid synthesis with respect to volatility, sterical demand, nucleophilicity of the nitrogen atom and compatibility with sidechain functional groups were derived from the results. (2) synthesis and screening of peptoid libraries Two libraries consisting of 8000 tri- and hexapeptoids respectively were synthesized under optimized conditions. The library of trimers displayed the entire sequence space based on 20 building blocks, whereas the sequences of the hexamers were selected statistically from the sequence space based on 40 building blocks. In order to examine the suitability of the libraries for the "de novo" identification of protein ligands they were screened for binding to the monoclonal antibody Tab-2. Bioactive peptoids could be identified in both cases (trimers: KD >= 87 µM, hexamers: KD >= 2.7 µM) both differing significantly from the peptide epitope [VVSHFND]. (3) backbone modified peptoids In order to introduce backbone modifications into peptoids nine biselectrophiles were applied in the synthesis of model trimers in a chemical screening. Four of the building blocks were well suited allowing the incorporation of beta-peptoid, m- and p-aminomethylbenzoic acid and carbamate units into peptoids. When the introduction of urea-units in a similar approach was attempted hydantoins were formed during cleavage from the solid support. This interesting reaction was examined in detail in order to extend SPOT-synthesis to the synthesis of heterocycles. (4) synthesis of hydantoins on cellulose membranes The formation of hydantoins from terminal amides was not yet described in a solid phase synthesis, whereas it was examined intensively in solution. By optimizing the conditions of cyclization the reaction could be driven to completion. C-substituted hydantoins were obtained as single enantiomers, when alpha-amino acid-amides or -tert. butylesters were used in the synthesis.