Neural network activity in the neonatal acute slice, slice culture and cell culture

Information processing and storage in the brain may be presented by the oscillations and cell assemblies. Here we address the question of how individual neurons associate together to assemble neural networks and present spontaneous electrical activity. Therefore, we dissected the neonatal brain at three different levels: acute 1-mm thick brain slice, cultured organotypic 350-µm thick brain slice and dissociated neuronal cultures. The spatio-temporal properties of neural activity were investigated by using a 60-channel Micro-electrode arrays (MEA), and the cell assemblies were studied by using a template-matching method. We find local on-propagating as well as large- scale propagating spontaneous oscillatory activity in acute slices, spontaneous network activity characterized by synchronized burst discharges in organotypic cultured slices, and autonomous bursting behaviour in dissociated neuronal cultures. Furthermore, repetitive spike patterns emerge after one week of dissociated neuronal culture and dramatically increase their numbers as well as their complexity and occurrence in the second week. Our data indicate that neurons can self-organize themselves, assembly to a neural network, present spontaneous oscillations, and emerge spatio-temporal activation patterns. The spontaneous oscillations and repetitive spike patterns may serve fundamental functions for information processing and storage in the brain.

In-vitro synthesis and reconstitution of cytochrome bo 3 ubiquinol oxidase in artificial membranes

Forschung über Membranenproteine stellt strenge Hindernisse, seit ruhigem gerade wenige Beispiele der Membranenproteinsorten sind gekennzeichnet worden in den verwendbaren experimentellen Plattformen gegenüber. Die Hauptherausforderung ist, ihre ausgezeichnete entworfene strukturelle Vollständigkeit zu konservieren, während die Ausdruck-, Lokalisierungs- und Wiederherstellungprozesse auftreten. In-vitro übersetzungssysteme können Vorteile über auf Zellenbasisgenausdruck zum Beispiel haben, wenn das über-ausgedrückte Produkt zur Wirtszelle giftig ist oder wenn fehlende Pfosten-Übersetzungsänderung in den bakteriellen Ausdrucksystemen die Funktionalität der Säugetier- Proteine oder Mangel an vorhandenem Membranenraum verdirbt, Funktionsausdruck verbieten.rn Der Nachahmer von biologische Membranen wie feste gestützte Lipidmembranen sind als Plattform am meisten benutzt, Proteinmembraneninteraktionen nachzuforschen. Wir sind in der Lage, Membranenproteinsorte, da wir eine Plattform für Membranenproteinsynthese vorstellen, nämlich die in-vitrosynthese der Membranenproteine in ein Peptid gestütztes Membranensystem zu adressieren. Die Wiederherstellung der Membranenproteine in den Lipid bilayers resultiert im Allgemeinen mit verschiedenen Proteinanpassungen. Als Alternative erforschen wir dieses System zum ersten Mal, um genaueres Modell zu den zellularen Membranen zu verursachen und ihre Funktion, wie Proteineinfügung, Proteinfunktion und Ligandinteraktionen nachzuahmen.rn In dieser Arbeit ist unser Ziel, komplizierte Transmembraneproteine, wie des Cytochrome bo3-ubiquinol Oxydase (Cyt-bo3) direkt innerhalb der biomimetic vorbildlichen Membrane zu synthetisieren. In unserem System wird festes gestütztes tBLM wie, P19/DMPE/PC als Plattform benutzt. Dieses künstliche Membranensystem mimiks die amphiphile Architektur eines Zelle-abgeleiteten Membranensystems.rn

Electrostatically self-assembled nanoparticles based on biomolecules

In this work, two different systems were investigated to develop fundamental understanding of the self-assembly behavior of polyelectrolytes and small organic counterions with a certain geometry. Complexes formed were characterized by light scattering in solution, as well as UV-Vis spectroscopy, analytical ultracentrifugation, gel electrophoresis, zeta potential and IR spectroscopy. The morphologies of the aggregates were observed by AFM in dried state on surface. The charge ratio, the valence and the structure of the counterion were shown to represent key parameters in the complexation. The influence of polyelectrolyte type and molecular weights was also determined for the structure formed.rnrnOne system was mainly focused on the association of double-strand DNA with non-intercalating divalent and tetravalent organic counterions. The other model system involved linear NaPSS and oligolysines. In addition, various influences on the morphology of the charged self-assembly complexes in AFM studies were discussed. It was shown that electrostatic self-assembly of DNA and non-intercalating counterions as well as of a linear synthetic polyelectrolyte with oligolysine counterions that can build mutual hydrogen bonds can yield supramolecular aggregates of a defined size. Various morphologies (flower-like, rod-like, toroidal and spherical) of the assemblies were obtained for different combinations of polyelectrolyte and counterions. Results presented in this work are of importance for the fundamental understanding of the association behavior of various polyelectrolytes and organic counterions. The selection of biopolymers for the study may give an opportunity to transfer the basic research results into biological applications, such as gene therapy or drug delivery.rn

Biomimetic bilayer membranes made from polymers and lipids

Amphiphile Blockcopolymere sind in der Lage in Wasser Morphologien auszubilden, die analog sind zur hydrophil-hydrophob-hydrophil-Struktur von natürlichen Lipiddoppelschichten. In dieser Arbeit wird zum ersten Mal die Präparation und Charakterisierung von oberflächengestützten Polymerdoppelschichten aus Polybutadien-b-Polyethylenoxid (PB-PEO) beschrieben. Für die Herstellung dieser Strukturen wurden zwei unterschiedliche Präparationsstrategien verfolgt. Der erste Weg besteht aus einer zweistufigen Methode, bei der im ersten Schritt organisierte Monoschichten mittels Langmuir-Blodgett-Transfer auf Gold übertragen und kovalent angebunden werden. Im zweiten Schritt werden hydrophobe Wechselwirkungen ausgenutzt, um über Langmuir-Schaefer-Transfer eine weitere Schicht aufzubringen. Somit wurden homogene Architekturen erzeugt, die oberflächengestützten Lipiddoppelschichten gleichen. Als alternativer, einstufiger Ansatz zur Herstellung von Polymerdoppelschichten wurde das Spreiten von Polymervesikeln auf Gold verfolgt. Auch hierdurch ließen sich Doppelschichtstrukturen mit einer vollständigen Oberflächenbedeckung erzeugen. Die hergestellten Polymerdoppelschichten besitzen eine Dicke von 11-14 nm, die von der Präparationsmethode abhängt. Die Polymerstrukturen weisen bei Trocknung für 1.5 h eine Stabilität gegenüber Luft auf. Bei längeren Trocknungszeiten von ca. 12 h kommt es zu einer Reorganisation der Oberfläche. Dies deutet darauf hin, dass Wasser dazu notwendig ist die Strukturen auf lange Sicht zu stabilisieren. Um die Biokompatibilität der Polymerschichten nachzuweisen, wurden die Wechselwirkungen mit dem membranaktiven Peptid Polymyxin B und dem Transmembranprotein α-Haemolysin gezeigt. Mobilität ist ein wichtiger Faktor für die korrekte Funktion vieler Transmembranproteine. Um die laterale Diffusionsdynamik innerhalb der künstlichen Strukturen zu untersuchen, wurde die Mobilität eines integralen Modellpeptids und von fluoreszierenden Membransonden gemessen. Es konnte mit einzelmolekülempfindlichen Techniken gezeigt werden, dass das α-helikale Peptid und die kleinen Fluoreszenzfarbstoffe frei im hydrophoben Kern der Polymerdoppelschicht diffundieren können. Die Diffusion von beiden Spezies scheint stark von der Fluidität der Polymermatrix beeinflusst zu sein. Ein weiterer Teil dieser Arbeit widmet sich der Entwicklung eines angemessenen, lipidbasierten Referenzsystems für zukünftige Proteinuntersuchungen. Hierzu wurde eine neue Methode zu Herstellung von peptidgestützten Lipiddoppelschichtmembranen entwickelt. Dies wurde durch kovalente Befestigung eines Thiopeptids an einen Goldfilm und darauffolgende Anbindung eines Lipids erreicht. Zur Ausbildung der Lipiddoppelschicht auf dem Lipopeptidunterbau wurder der Rapid Solvent Exchange verwendet. Die Ausbildung der Lipiddoppelschicht wurde sowohl auf microskopischer als auch auf makroskopischer Ebene nachgewiesen. Im letzten Schritt wurde die Anwendbarkeit des Modelsystems für elektrochemische Messungen durch den funktionalen Einbau des Ionentransporters Valinomycin unter Beweis gestellt.

Assessing the functional structure of molecular transporters by EPR spectroscopy

In this thesis, the self-assembled functional structure of a broad range of amphiphilic molecular transporters is studied. By employing paramagnetic probe molecules and ions, continuous-wave and pulse electron paramagnetic resonance spectroscopy reveal information about the local structure of these materials from the perspective of incorporated guest molecules. First, the transport function of human serum albumin for fatty acids is in the focus. As suggested by the crystal structure, the anchor points for the fatty acids are distributed asymmetrically in the protein. In contrast to the crystallographic findings, a remarkably symmetric entry point distribution of the fatty acid binding channels is found, which may facilitate the uptake and release of the guest molecules. Further, the metal binding of 1,2,3-triazole modified star-shaped cholic acid oligomers is studied. These biomimetic molecules are able to include and transport molecules in solvents of different polarity. A pre-arrangement of the triazole groups induces a strong chelate-like binding and close contact between guest molecule and metal ion. In absence of a preordering, each triazole moiety acts as a single entity and the binding affinity for metal ions is strongly decreased. Hydrogels based on N-isopropylacrylamide phase separate from water above a certain temperature. The macroscopic thermal collapse of these hydrogels is utilized as a tool for dynamic nuclear polarization. It is shown that a radical-free hyperpolarized solution can be achieved with a spin-labeled gel as separable matrix. On the nanoscale, these hydrogels form static heterogeneities in both structure and function. Collapsed regions protect the spin probes from a chemical decay while open, water-swollen regions act as catalytic centers. Similarly, thermoresponsive dendronized polymers form structural heterogeneities, which are, however, highly dynamic. At the critical temperature, they trigger the aggregation of the polymer into mesoglobules. The dehydration of these aggregates is a molecularly controlled non-equilibrium process that is facilitated by a hydrophobic dendritic core. Further, a slow heating rate results in a kinetically entrapped non-equilibrium state due to the formation of an impermeable dense polymeric layer at the periphery of the mesoglobule.

A threshold hypothesis of institutional change: collective action in the Italian Alps during the 13th - 19th centuries.

This dissertation is about collective action issues in common property resources. Its focus is the “threshold hypothesis,” which posits the existence of a threshold in group size that drives the process of institutional change. This hypothesis is tested using a six-century dataset concerning the management of the commons by hundreds of communities in the Italian Alps. The analysis seeks to determine the group size threshold and the institutional changes that occur when groups cross this threshold. There are five main findings. First, the number of individuals in villages remained stable for six centuries, despite the population in the region tripling in the same period. Second, the longitudinal analysis of face-to-face assemblies and community size led to the empirical identification of a threshold size that triggered the transition from informal to more formal regimes to manage common property resources. Third, when groups increased in size, gradual organizational changes took place: large groups split into independent subgroups or structured interactions into multiple layers while maintaining a single formal organization. Fourth, resource heterogeneity seemed to have had no significant impact on various institutional characteristics. Fifth, social heterogeneity showed statistically significant impacts, especially on institutional complexity, consensus, and the relative importance of governance rules versus resource management rules. Overall, the empirical evidence from this research supports the “threshold hypothesis.” These findings shed light on the rationale of institutional change in common property regimes, and clarify the mechanisms of collective action in traditional societies. Further research may generalize these conclusions to other domains of collective action and to present-day applications.

Synthese organisch-anorganischer Hybridmaterialien in Mehrkomponenten-Lösungsmittelsystemen

Die Funktionalisierung anorganischer Nanopartikel stellt einen Schlüsselschritt in der Herstellung von Nanokompositen dar. Nanokomposite erzielen ein wachsendes Interesse im Bereich der Polymer- und der Materialwissenschaften, da die Kombination mehrerer Materialien mit unterschiedlichen Eigenschaften, wie etwa die Kombination anorganischer Nanopartikel mit Polymeren, große Synergieeffekte erhoffen lässt.rnrnDer Einbau anorganischer Nanopartikel in polymere Matrixmaterialien zur Verbesserung oder Einführung mechanischer, optischer oder magnetischer Eigenschaften von Polymeren bedarf allerdings der Modifizierung der Oberfläche des anorganischen Materials, um die für die positiven Synergieeffekte essentielle Kompatibilität zwischen Füllstoff und Matrix zu erreichen.rnrnEine Vielzahl anorganischer Partikel ist bereits als wässrige Dispersion erhältlich (SiO2, Al2O3, CeO2, ZrO2, ...). Mehrkomponenten- Lösungsmittelsysteme ermöglichen den Transfer dieser Partikel in eine unpolare Umgebung und gleichzeitig deren Funktionalisierung mit amphiphilen Copolymeren. Aufgrund der reversiblen Schaltbarkeit dieser Lösungsmittelsysteme zwischen einem einphasigen und zweiphasigen Zustand werden die zu Beginn in zwei nichtmischbaren Phasen vorliegenden Reaktionspartner durch Übergang in einen einphasigen Zustand unter homogenen Bedingungen in Kontakt gebracht und durch eine erneute Phasentrennung isoliert.rnEin weiterer Vorteil dieser Lösungsmittelsysteme ist deren Tolerierung funktioneller Gruppen in den verwendeten amphiphilen Copolymeren, welche nicht in Wechselwirkung mit der Partikeloberfläche stehen. Beispielsweise können Amine in den amphiphilen Copolymeren für die Wechselwirkung der funktionalisierten Partikel mit einer Polyurethanmatrix dienen, Alkine können mittels einer 1,3-dipolaren Cycloaddition umgesetzt werden oder aber perfluorierten Seitenketten in den Seitenketten der amphiphilen Copolymere die Kompatibilisierung der funktionalisierten Partikel mit einem perfluorierten Polymer gewährleisten.

Structured antibody surfaces for bio-recognition and a label-free detection of bacteria

Antibody microarrays are of great research interest because of their potential application as biosensors for high-throughput protein and pathogen screening technologies. In this active area, there is still a need for novel structures and assemblies providing insight in binding interactions such as spherical and annulus-shaped protein structures, e.g. for the utilization of curved surfaces for the enhanced protein-protein interactions and detection of antigens. Therefore, the goal of the presented work was to establish a new technique for the label-free detection of bio-molecules and bacteria on topographically structured surfaces, suitable for antibody binding.rnIn the first part of the presented thesis, the fabrication of monolayers of inverse opals with 10 μm diameter and the immobilization of antibodies on their interior surface is described. For this purpose, several established methods for the linking of antibodies to glass, including Schiff bases, EDC/S-NHS chemistry and the biotin-streptavidin affinity system, were tested. The employed methods included immunofluorescence and image analysis by phase contrast microscopy. It could be shown that these methods were not successful in terms of antibody immobilization and adjacent bacteria binding. Hence, a method based on the application of an active-ester-silane was introduced. It showed promising results but also the need for further analysis. Especially the search for alternative antibodies addressing other antigens on the exterior of bacteria will be sought-after in the future.rnAs a consequence of the ability to control antibody-functionalized surfaces, a new technique employing colloidal templating to yield large scale (~cm2) 2D arrays of antibodies against E. coli K12, eGFP and human integrin αvβ3 on a versatile useful glass surface is presented. The antibodies were swept to reside around the templating microspheres during solution drying, and physisorbed on the glass. After removing the microspheres, the formation of annuli-shaped antibody structures was observed. The preserved antibody structure and functionality is shown by binding the specific antigens and secondary antibodies. The improved detection of specific bacteria from a crude solution compared to conventional “flat” antibody surfaces and the setting up of an integrin-binding platform for targeted recognition and surface interactions of eukaryotic cells is demonstrated. The structures were investigated by atomic force, confocal and fluorescence microscopy. Operational parameters like drying time, temperature, humidity and surfactants were optimized to obtain a stable antibody structure.

Structure and properties of nanostructures from polyelectrolytes and porphyrins: Self-Assembly in aqueous solution

In this work self-assembling model systems in aqueous solution were studied. The systems contained charged polymers, polyelectrolytes, that were combined with oppositely charged counterions to build up supramolecular structures. With imaging, scattering and spectroscopic techniques it was investigated how the structure of building units influences the structure of their assemblies. Polyelectrolytes with different chemical structure, molecular weight and morphology were investigated. In addition to linear polyelectrolytes, semi-flexible cylindrical bottle-brush polymers that possess a defined cross-section and a relatively high persistence along the backbone were studied. The polyelectrolytes were combined with structural organic counterions having charge numbers one to four. Especially the self-assembly of polyelectrolytes with different tetravalent water-soluble porphyrins was studied. Porphyrins have a rigid aromatic structure that has a structural effect on their self-assembly behavior and through which porphyrins are capable of self-aggregation via π-π interaction. The main focus of the thesis is the self-assembly of cylindrical bottle-brush polyelectrolytes with tetravalent porphyrins. It was shown that the addition of porphyrins to oppositely charged brush molecules induces a hierarchical formation of stable nanoscale brush-porphyrin networks. The networks can be disconnected by addition of salt and single porphyrin-decoratedrncylindrical brush polymers are obtained. These two new morphologies, brush-porphyrin networks and porphyrin-decorated brush polymers, may have potential as functional materials with interesting mechanical and optical properties.

Hyperbranched polyether polyols as building blocks for complex macromolecular architectures

The present thesis deals with the development of new branched polymer architectures containing hyperbranched polyglycerol. Materials investigated include hyperbranched oligomers, hyperbranched polyglycerols containing functional initiator-cores at the focal point, well-defined linear-hyperbranched block copolymers and also negatively charged hyperbranched polyelectrolytes.rnHyperbranched oligoglycerols (DPn = 7 and 14) have been synthesized for the first time. The materials show narrow polydispersity (Mw/Mn ca. 1.45) and a very low content in cyclic homopolymers. 13C NMR evidences the dendritic structure of the oligomers and the DB could be calculated (44% and 52%). These new oligoglycerols were compared with the industrial products obtained by polycondensation which exhibit narrow polydispersity (Mw/Mn<1.3) butrnmultimodal distribution in SEC. Detailed 13C NMR and Maldi-ToF studies reveal the presence of branched units and cyclic compounds. In comparison, the hyperbranched oligoglycerols comprise a very low proportion of cyclic homopolymer which render them very interesting materials for biomedical applications for example.rnThe site isolation of the core moiety in dendritic structure offers intriguing potential with respect to peculiar electro-optical properties. Various initiator-cores (n-alkyl amines, UVabsorbing amines and benzophenone) for the ROMBP of glycidol have been tested. The bisglycidolized amine initiator-cores show the best control over the molecular weight and the molecular weight distribution. The photochemical analyses of the naphthalene containingrnhyperbranched polyglycerols show a slight red shift, a pronounced hypochromic effect (decrease of the intensity of the band) compared with the parent model compound and the formation of a relative compact structure. The benzophenone containing polymers adopt an open structure in polar solvents. The fluorescence measurements show a clear “dendritic effect” on the fluorescence intensities and the quantum yield of the encapsulated benzophenone.rnA convenient 3-step strategy has been developed for the preparation of well-defined amphiphilic, linear-hyperbranched block copolymers via hypergrafting. The procedure represents a combination of carbanionic polymerization with the alkoxide-based, controlled ring-opening multibranching polymerization of glycidol. Materials consisting of a polystyrene linear block and a hyperbranched polyglycerol block exhibit narrow polydispersity (1.01-1.02rnfor 5.4% to 27% wt. PG and 1.74 for 52% wt. PG) with a high grafting efficiency. The strategy was also extended to materials with a linear polyisoprene block.rnDetailed investigations of the solution properties of the block copolymers with linear polystyrene blocks show that block copolymer micelles are stabilized by the highly branched block. The morphology of the aggregates is depending on the solvent: in chloroform monodisperse spherical shape aggregates and in toluene ellipsoidal aggregates are formed. On graphite these aggregates show interesting features, giving promising potential applications with respect to the presence of a very dense, functional and stable hyperbranched block.rnThe bulk morphology of the linear-hyperbranched block copolymers has been investigated. The materials with a linear polyisoprene block only behave like complex liquids due to the low Tg and the disordered nature of both components. For the materials with polystyrene, only the sample with 27% wt. hyperbranched polyglycerol forms some domains showing lamellae.rnThe preparation of hyperbranched polyelectrolytes was achieved by post-modification of the hydroxyl groups via Michael addition of acrylonitrile, followed by hydrolysis. In aqueous solution materials form large aggregates with size depending on the pH value. After deposition on mica the structures observed by AFM show the coexistence of aggregates andrnunimers. For the low molecular weight sample (PG 520 g·mol-1) extended and highly ordered terrace structures were observed. Materials were also successfully employed for the fabrication of composite organic-inorganic multilayer thin films, using electrostatic layer-bylayer self-assembly coupled with chemical vapor deposition.

Detektion und Synthese eines liganden-gesteuerten Ionenkanals im mikrofluidischen Analysesystem

Membranproteine spielen eine wichtige Rolle bei physiologischen Prozessen wie Signalweiterleitung oder Immunreaktion. Deshalb stehen sie im Fokus der pharmakologischen Wirkstoffentwicklung und es besteht großes Interesse, Membranproteinbasierte Biosensoren zu entwickeln, die sich z.B. als Screening-Plattformen eignen. Allerdings stellt die Handhabung von Membranproteinen wegen ihrer amphiphilen Struktur eine große Herausforderung dar. Membranproteine werden meist in Zellkultur oder in bakteriellen Expressionssystemen synthetisiert. Diese Verfahren liefern aber oft nur eine geringe Ausbeute und erlauben wenig Kontrolle über die Expressionsbedingungen. Als alternativer Ansatz bietet sich stattdessen die in vitro Synthese von Proteinen an, die in einer zellfreien Umgebung stattfindet. Ziel der vorliegenden Arbeit war die Etablierung eines miniaturisierten Analysesystems, das Aktivitätsmessungen an in vitro synthetisierten Ionenkanälen erlaubt. Dafür wurde ein Labon- Chip entwickelt, der elektrochemische und optische Nachweismethoden in parallelen Anätzen ermöglicht. Als amphiphile Umgebung für die Inkorporation von Membranproteinen wurden vier verschieden biomimetische Membranaufbauten hinsichtlich ihrer Dichtigkeit und ihrer Reproduzierbarkeit untersucht. Als Methode fanden insbesondere die Impedanzspektroskpie und die Oberflächenplasmonen-Resonanzspektroskopie Anwendung. Die peptide cushioned Bilyer Lipid Membranes (pcBLM) eignete sich dabei am besten für Untersuchungen an Membranproteinen. Zur Detektion der Ionenkanalaktivität wurde eine neue Messmethode etabliert, die auf der Messung der Impedanz bei fester Frequenz basiert und u.a. eine Aussage über die Änderung des Membranwiderstandes bei Aktivierung erlaubt. Am Beispiel des nicotinischen Acetylcholinrezeptors (nAchR) konnte gezeigt werden, dass sich die Aktivität von Ionenkanälen mit dem entwickelten Chip-System nachweisen ließ. Die Spezifität der Methode konnte durch verschiedene Kontrollen wie die Zugabe eines nicht-aktivierenden Liganden oder Inhibition des Rezeptors nachgewiesen werden. Weiterhin konnte die in vitro Synthese des Ionenkanals a7 nAchR durch Radioaktivmarkierung nachgewiesen werden. Die Inkorporation des Rezeptors in die biomimetischen Membranen wurde mit Immunodetektion und elektrochemischen Methoden untersucht. Es zeigte sich, dass die funktionelle Inkorporation des a7 nAchR davon abhing, welcher biomimetische Membranaufbau verwendet wurde.

Surface patterning with colloidal monolayers

This thesis focuses on the controlled assembly of monodisperse polymer colloids into ordered two-dimensional arrangements. These assemblies, commonly referred to as colloidal monolayers, are subsequently used as masks for the generation of arrays of complex metal nanostructures on solid substrates.rnThe motivation of the research presented here is twofold. First, monolayer crystallization methods were developed to simplify the assembly of colloids and to produce more complex arrangements of colloids in a precise way. Second, various approaches to colloidal lithography are designed with the aim to include novel features or functions to arrays of metal nanostructures.rnThe air/water interface was exploited for the crystallization of colloidal monolayer architectures as it combines a two-dimensional confinement with a high lateral mobility of the colloids that is beneficial for the creation of high long range order. A direct assembly of colloids is presented that provides a cheap, fast and conceptually simple methodology for the preparation of ordered colloidal monolayers. The produced two-dimensional crystals can be transformed into non-close-packed architectures by a plasma-induced size reduction step, thus providing valuable masks for more sophisticated lithographic processes. Finally, the controlled co-assembly of binary colloidal crystals with defined stoichiometries on a Langmuir trough is introduced and characterized with respect to accessible configurations and size ratios. rnSeveral approaches to lithography are presented that aim at introducing different features to colloidal lithography. First, using metal-complex containing latex particles, the synthesis of which is described as well, symmetric arrays of metal nanoparticles can be created by controlled combustion of the organic material of the colloids. The process does not feature an inherent limit in nanoparticle size and is able to produce complex materials as will be demonstrated for FePt alloy particles. Precise control over both size and spacing of the particle array is presented. rnSecond, two lithographic processes are introduced to create sophisticated nanoparticle dimer units consisting of two crescent shaped nanostructures in close proximity; essentially by using a single colloid as mask to generate two structures simultaneously. Strong coupling processes of the parental plasmon resonances of the two objects are observed that are accompanied by high near-field enhancements. A plasmon hybridization model is elaborated to explain all polarization dependent shifts of the resonance positions. Last, a technique to produce laterally patterned, ultra-flat substrates without surface topographies by embedding gold nanoparticles in a silicon dioxide matrix is applied to construct robust and re-usable sensing architectures and to introduce an approach for the nanoscale patterning of solid supported lipid bilayer membranes. rn

The calcite(10-14) surface: a versatile substrate for molecular self-assembly

This thesis presents a detailed and successful study of molecular self-assembly on the calcite CaCO3(10-14) surface. One reason for the superior applicability of this particular surface is given by reflecting the well-known growth modes. Layer-by-layer growth, which is a necessity for the formation of templated two-dimensional (2D) molecular structures, is particularly favoured on substrates with a high surface energy. The CaCO3(10-14) surface is among those substrates and, thus, most promising. rnrnAll experiments in this thesis were performed using the non-contact atomic force microscope (NC-AFM) under ultra-high vacuum conditions. The acquisition of drift-free data became in this thesis possible owing to the herein newly developed atom-tracking system. This system features a lateral tip-positioning precision of at least 50pm. Furthermore, a newly developed scan protocol was implemented in this system, which allows for the acquisition of dense three-dimensional (3D) data under room-temperature conditions. An entire 3D data set from a CaCO3(10-14) surface consisting of 85x85x500 pixel is discussed. rnrnThe row-pairing and (2x1) reconstructions of the CaCO3(10-14) surface constitute most interesting research subjects. For both reconstructions, the NC-AFM imaging was classified to a total of 12 contrast modes. Eight of these modes were observed within this thesis, some of them for the first time. Together with literature findings, a total of 10 modes has been observed experimentally to this day. Some contrast modes presented themselves as highly distance-dependent and at least for one contrast mode, a severe tip-termination influence was found. rnrnMost interestingly, the row-pairing reconstruction was found to break a symmetry element of the CaCO3(10-14) surface. With the presence of this reconstruction, the calcite (10-14) surface becomes chiral. From high-resolution NC-AFM data, the identification of the enantiomers is here possible and is presented for one enantiomer in this thesis. rnrnFive studies of self-assembled molecular structures on calcite (10-14) surfaces are presented. Only for one system, namely HBC/CaCO3(10-14), the formation of a molecular bulk structure was observed. This well-known occurence of weak molecule-insulator interaction hinders the investigation of two-dimensional molecular self-assembly. It was, however, possible to force the formation of an island phase for this system upon following a variable-temperature preparation. rnFor the C60/CaCO3(10-14) system it is most notably that no branched island morphologies were found. Instead, the first C60 layer appeared to wet the calcite surface. rnrnIn all studies, the molecules arranged themselves in ordered superstructures. A templating effect due to the underlying calcite substrate was evident for all systems. This templating strikingly led either to the formation of large commensurate superstructures, such as (2x15) with a 14 molecule basis for the C60/CaCO3(10-14) system, or prevented the vast growth of incommensurate molecular motifs, such as the chicken-wire structure in the trimesic acid (TMA)/CaCO3(10-14) system. rnrnThe molecule-molecule and the molecule-substrate interaction was increased upon choosing molecules with carboxylic acid moieties in the third, fourth and fifth study, using terephthalic acid, TMA and helicene molecules. In all these experiments, hydrogen-bonded assemblies were created. rnrnDirected hydrogen bond formation combined with intermolecular pi-pi interaction is employed in the fifth study, where the formation of uni-directional molecular "wires" from single helicene molecules succeeded. Each "wire" is composed of heterochiral helicene pairs, well-aligned along the [01-10] substrate direction and stabilised by pi-pi interaction.

Mitochondrial respiratory supercomplex association limits production of reactive oxygen species from Complex I

Evidence accumulated in the last ten years has demonstrated that a large proportion of the mitochondrial respiratory chain complexes in a variety of organisms is arranged in supramolecular assemblies called supercomplexes or respirasomes. Besides conferring a kinetic advantage (substrate channeling) and being required for the assembly and stability of Complex I, indirect considerations support the view that supercomplexes may also prevent excessive formation of reactive oxygen species (ROS) from the respiratory chain. Following this line of thought we have decided to directly investigate ROS production by Complex I under conditions in which the complex is arranged as a component of the supercomplex I1III2 or it is dissociated as an individual enzyme. The study has been addressed both in bovine heart mitochondrial membranes and in reconstituted proteoliposomes composed of complexes I and III in which the supramolecular organization of the respiratory assemblies is impaired by: (i) treatment either of bovine heart mitochondria or liposome-reconstituted supercomplex I-III with dodecyl maltoside; (ii) reconstitution of Complexes I and III at high phospholipids to protein ratio. The results of this investigation provide experimental evidence that the production of ROS is strongly increased in either model; supporting the view that disruption or prevention of the association between Complex I and Complex III by different means enhances the generation of superoxide from Complex I . This is the first demonstration that dissociation of the supercomplex I1III2 in the mitochondrial membrane is a cause of oxidative stress from Complex I. Previous work in our laboratory demonstrated that lipid peroxidation can dissociate the supramolecular assemblies; thus, here we confirm that preliminary conclusion that primary causes of oxidative stress may perpetuate reactive oxygen species (ROS) generation by a vicious circle involving supercomplex dissociation as a major determinant.

Fluorenbasierende amphiphile Kammpolymere zur Ausbildung definierter Strukturen an Oberflächen und in Lösungen

Die Dissertation beschreibt die Darstellung und Charakterisierung von neuartigen, amphiphilen Carbazol- und Fluoren-(co)-polymeren, die infolge ihres strukturellen Aufbaus sowohl selbstorganisierende als auch optoelektronische Eigenschaften kombinierten. Zum einen wurden Kammpolymere mit konjugierten, steifen Rückgraten und flexiblen sowie konformativ schaltbaren Polyelektrolytseitenketten dargestellt und auf eine pH-abhängige Selbstorganisation in Lösung und an Oberflächen untersucht. Des Weiteren wurden neutrale, methanollösliche Polyfluorene synthetisiert, die in Kombination mit einem unpolaren Polyindenofluorenderivat zum Aufbau mehrschichtiger PLEDs mittels nasschemischer Verfahren eingesetzt wurden. Zum anderen fand die Synthese von amphiphilen Polyfluorenen statt, die als Emulgatoren zur Stabilisierung von inversen Emulsionen eingesetzt wurden. Dabei konnten mit Hilfe eines bereits für die Darstellung von anorganisch-organischen Kern-Schale-Partikeln etablierten in situ-Verfahrens formanisotrope, kristalline Zinkoxidkerne mit konjugierter Polymerhülle erhalten werden.