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Renewable and environmentally responsive materials are an energy- and resource-efficient approach in terms of civil engineering applications, e.g. as so-called smart building skins. To evaluate the influence of different environmental stimuli, like humidity or solar radiation, on the long-term actuation behavior and mechanical robustness of these materials, it is necessary to precisely characterize the magnitude and range of stimuli that trigger reactions and the resulting kinetics of a material, respectively, with suitable testing equipment and techniques. The overall aim is to correlate actuation potential and mechanical properties with process- or application-oriented parameters in terms of demand-oriented stimuli-responsive element production. In this study, the impact of solar radiation as environmental trigger on the cellulose-based humidity-sensing material Cottonid, which is a promising candidate for adaptive and autonomously moving elements, was investigated. For simulating solar radiation in the lab, specimens were exposed to short-wavelength blue light as well as a standardized artificial solar irradiation (CIE Solar ID65) in long-term aging experiments. Photodegradation behavior was analyzed by Fourier-transform infrared as well as electron paramagnetic resonance spectroscopy measurements to assess changes in Cottonid���s chemical composition. Subsequently, changes in micromechanical properties on the respective specimens���surface were investigated with roughness measurements and ultra-micro-hardness tests to characterize variations in stiffness distribution in comparison to the initial condition. Also, thermal effects during long-term aging were considered and contrasted to pure radiative effects. In addition, to investigate the influence of process-related parameters on Cottonid���s humidity-driven deformation behavior, actuation tests were performed in an alternating climate chamber using a customized specimen holder, instrumented with digital image correlation (DIC). DIC was used for precise actuation strain measurements to comparatively evaluate different influences on the material���s sorption behavior. The infrared absorbance spectra of different aging states of irradiated Cottonid indicate oxidative stress on the surface compared to unaged samples. These findings differ under pure thermal loads. EPR spectra could corroborate these findings as radicals were detected, which were attributed to oxidation processes. Instrumented actuation experiments revealed the influence of processing-related parameters on the sorption behavior of the tested and structurally optimized Cottonid variant. Experimental data supports the definition of an optimal process window for stimuli-responsive element production. Based on these results, tailor-made functional materials shall be generated in the future where stimuli-responsiveness can be adjusted through the manufacturing process., Functional composite materials;Vol. 2. 2021, Art.No. 9

Zugleich: Dissertation, Universität Kassel, 2020

Die Arbeit beleuchtet die Zusammenhänge zwischen strukturellen Merkmalen und verschiedenen chemischen Eigenschaften der untersuchten Verbindungen. Dabei stehen neben der strukturellen Aufklärung der Verbindungen aus den Verbindungsklassen der Wolframate, Oxoborate, Oxonitridoborate, Boratfluoride und Fluorooxoborate auch deren thermische, optische und spektroskopische Eigenschaften im Vordergrund.

Ionische Flüssigkeiten sind in ihrer Struktur variierbare Verbindungen, welche interessante Anordnungen an der fest/flüssig-Grenzfläche zeigen. Damit bietet diese Verbindungsklasse großes Anwendungspotenzial auf den Gebieten der Batterieforschung, der Katalyse, als Kondensatoren oder Schmiermittel. Obwohl schon lange bekannt ist, dass die chemische Struktur des Kations und des Anions signifikanten Einfluss auf die Eigenschaften der ionischen Flüssigkeit hat, fehlt bisher das grundlegende Verständnis zwischen Struktur und Wirkung. In der vorliegenden Arbeit wird gezeigt, dass die bekannte Multilagenbildung an der Grenzfläche keine intrinsische Eigenschaft ist. Im Gegenteil, die Bildung dieser wird durch Randbedingungen wie Oberflächenladung, Oberflächenchemie und Feuchtigkeit verursacht.

Epithelial adhesins from Candida glabrata Epithelial adhesins (Epa) are crucial proteins in the colonization, pathogenesis and virulence of Candida glabrata. These adhesins have a similar modular structure to Saccharomyces cerevisiae flocculins, with an N-terminal adhesive A domain, a central neck-like B domain, and an anchorage C-terminal C domain. A hallmark of many fungal adhesins is the presence of a calcium binding PA14 domain within the A domain. The PA14 domain is responsible for carbohydrate binding in a calcium dependent manner, which allows for the classification of these proteins as C-type lectins[1]. In this study, it was possible to elucidate the crystal structures of Epa1A and three variants at resolutions from 1.4 to 2.0 Å. The latter were meant to emulate the specificities of Epa2, Epa3 and Epa6 adhesive domains. The results yielded a profound knowledge of the binding pocket of Epa1A and the mechanisms through which specificity is controlled in the Epa A domain. Especially surprising was the fact that, even though the proteins were crystallized in the presence of lactose, the protein co-crystals never showed the aforementioned sugar. Instead, a galactoseβ1-3glucose disaccharide unit could be modeled into the electron density. The disaccharide is commonly found on cell surfaces and milk derivates, from which the employed lactose was obtained[2]. Epa1A , Epa1→2A, Epa1→3A and Epa1→6A were also functionally characterized by semi- quantitative, high-throughput methodologies. In collaboration with the consortium for functional glycomics, fluorescently labeled proteins were set in contact with large-scale glycan arrays. The results showed a marked preference for galactoseβ1-3 terminal oligosaccharides in the case of Epa1A. For the other proteins, varying degrees of promiscuity were noted. Epa1→6A presented a very similar binding profile to the one presented by Zupancic et. al. in 2008 for Epa6A, demonstrating the validity of the method. Epa1→2A and Epa1→3A were much less active, and presented a preference for sulfated glycans, along with terminal galactose. Fluorescence titrations showed for Epa1A a ~20 time stronger affinity for the T antigen (galactoseβ1-3N-acetyl- galactosamine) than for the milk-derived lactose, showing how marked the adhesin preference for β1-3 linkages is, as compared to β1-4 glycosidic bonds. Adhesins of Helicobacter pylori The adhesins of H. pylori have been shown to be critical for the colonization and immune recognition of the bacterium during gastric invasion and disease development[3]. BabA and SabA figure prominently, as the former is the primary adhesin during early stage colonization, while the latter binds strongly to inflamed tissue[4]. Both of them are autotransporters, with a C-terminal, membrane bound translocation unit and an N-terminal passenger domain which contains the adhesive portion of the protein[5]. Pure, soluble passenger domains of BabA and SabA were successfully overproduced by recombinant expression in Escherichia coli. BabA could be functionally characterized by the same method as the Epa proteins. The results showed that BabA activity was strongly pH dependent, with a ~100 times stronger activity at pH 5.8 than at pH 2.5. This behavior could be further characterized through circular dichroism spectroscopy and size exclusion chromatography, which showed that BabA is in a reversible molten globule-like, aggregation-prone and relaxed conformation at pH 2.5. At pH 5.8, on the other hand, the protein is in a much more compact, defined conformation with a strong tendency to precipitate. H. pylori has been shown to present many pH dependent virulence factors, like the urea transporter, but up to now no direct biochemical data had been presented supporting pH dependent conformational changes in its adhesins., Epitheladhäsine von C. glabrata Die Epitheladhäsine (Epa) sind zentrale Proteine in der Kolonisierung, Pathogenese und Virulenz von C. glabrata. Diese Adhäsine haben einen ähnlichen modularen Aufbau wie S. cerevisiae Flokuline, mit einer N-terminalen adhäsiven A-Domäne, einer halsartigen B-Domäne und einer C-terminalen C-Domäne, die als Verankerung an der Zellwand dient. Flokulin-artige Adhäsine können in vielen Fällen eine Calcium-bindende PA14 Domäne innerhalb der A-Domäne beinhalten. Diese Proteinen wurden als C-Typ Lektine eingestuft, da die PA14 Domäne für eine Calcium abhängige Glycan-Bindung verantwortlich ist[1]. In der folgenden Arbeit war es möglich, die Kristallstrukturen von Epa1A und drei Varianten mit Auflösungen von 1,4 bis 2,0 Å zu lösen. Die Varianten sollten die Spezifitäten der Epa2-, Epa3- und Epa6- adhäsiven A-Domänen emulieren. Diese Erkenntnisse erlaubten eine detaillierte Beschreibung der Bindungstasche von Epa1A und die Mechanismen, durch die die Spezifität in der Epa A- Domäne bestimmt werden. Besonders überraschend war die Tatsache, dass, obwohl die Proteine in Gegenwart von Laktose kristallisiert wurden, die Co-Kristalle keine Laktose zeigten. Stattdessen konnte nur ein Galaktoseβ1-3glukose Disaccharid in die Elektronendichte modelliert werden. Dieses Disaccharid findet sich für gewöhnlich auf Zelloberflächen und in Milchderivaten[2], aus denen die verwendete Laktose stammte. Die funktionelle Charakterisierung von Epa1A , Epa1→2A, Epa1→3A und Epa1→6A verlief über semiquantitative, Hochurchsatz Analysen in Zusammenarbeit mit dem Consortium for Functional Glycomics (CFG). Mit Fluoroforen markierte Proteine wurden mit Glykan Arrays in Kontakt gesetzt. Die Ergebnisse zeigten eine deutliche Präferenz im Falle von Epa1A für Oligosaccharide mit einer terminalen Galaktoseβ1-3 Verknüpfung. Für die anderen Proteinen konnte gezeigt werden, dass die Spezifität in unterschiedlichen Massen verringert war. Das Epa1→6A Bindungsprofil konnte mit der von Zupancic et. al. 2008 publizierten Daten für Epa6A verglichen werden und zeigte große Ähnlichkeit. Epa1→2A und 3A waren deutlich weniger aktiv, zeigten aber eine Präferenz für sulfatierte Glykane sowie für terminale Galaktosen. Quantitative Fluoreszenztitrationen ergaben ungefähr zwanzigfach höhere Affinitäten für das T-Antigen als für die aus Milch gewonnene Laktose, wodurch die Präferenz für β1-3 über β1-4 Verbindungen weiter bestätigt werden konnte. 1.4 Adhäsine von Helicobacter pylori Die Adhäsine von H. pylori zeigten sich als kritisch bei der Kolonisierung und Immunerkennung des Bakteriums während des Eindringens in den Magen und der Entstehung und Entwicklung der Krankheit[3]. BabA und SabA sind zwei besonders wichtige Adhäsine, da ersteres bei einer frühen Kolonisierung als Primäradhäsin wirkt, während SabA stark an entzündetes Gewebe bindet[4]. Es handelt sich bei beiden um Autotransporter, die mit einer C-terminalen, membrangebundenen Translokationseinheit und einer N-terminalen, adhäsiven transportierte Domäne versetzt sind. Reine, lösliche transportierte Domänen von BabA und SabA wurden in großen Mengen in Escherichia coli rekombinant überproduziert. BabA konnte, wie die Epa Proteine, mit Hilfe von Glykan Arrays funktionell charakterisiert werden. BabA-Aktivität erwies sich als stark pH-abhängig, da sich bei pH 5.8 eine etwa hundertfach stärkere Bindung als bei pH 2.5 zeigte. Dieses Verhalten konnte durch Circular-Dichroismus Spektroskopie und chromatographische Analyse weiter untersucht werden. Es zeigte sich, dass BabA bei pH 2.5 sich in eine relaxierten, molten-globule ähnlichen Konformation befand, die leicht aggregierte. Bei pH 5.8 andererseits befand sich das Protein in einer viel kompakteren, klarer definierten Konformation mit einer starken Tendenz zur Präzipitat-Entstehung. Es konnten schon mehrere H. pylori Virulenzfaktoren gefunden werden, deren Aktivität pH abhängig ist, aber bis jetzt gab es noch keine biochemischen Daten, die pH abhängige Konformationsänderungen bei ihren Adhäsinen belegten.

This work aimed to elucidate basic aspects of the influence of chemical structure and surface topography on the surface properties of a polymer material in order to minimize the work of adhesion. End-functionalised aromatic perfluorinated oligo/polyesters have been chosen to clarify effect of chemical structure. Here, the comprehensive investigation of the influence of molecular architecture on processes of fluorine segregation in the topmost surface layer and surface properties of the end-functionalised aromatic perfluorinated linear and branched oligo-and polyesters were performed. It has been shown, that the character of the surface segregation of fluorinated moieties can be influenced by different factors i.e. conditions of preparation of polymer layers (by means of spin-coated and melt films), chemical structure of fluorinated tail and polymer backbone and slightly by molecular weight. Analysis of obtained results allows distinguishing contribution of each factor. Experimentally obtained results showed a good correlation with Scheutjens-Fleer self-consistent mean-field theory extended by Kumar and Koberstein, which corresponds to the surface segregation of various chemical functional moieties located on functional polymers of different architectures. In correlation with a self-consistent field approach, observed results confirmed that polymers with end fluorinated groups are promising for producing of low-energy surfaces.The effect of surface topography has been studied on the example of regular and irregular structured surfaces fabricated from core-shell particles. A simple and effective approach for designing regularly patterned surfaces with specifically designed surface roughness and chemistry using core-shell colloidal particles was demonstrated. The chemistry was varied by covalent grafting of polymer brushes onto silica particles or by chemisorption of fluorosilane. The modified colloidal spheres were organized into closely packed hemispherical hexagonal arrays either by a vertical deposition technique or by sedimentation on slightly inclined coated silicon wafers. In this way, an increase in the vertical roughness was achieved with increasing particle radius, but without changing the Wenzel roughness factor. Controllable variations in the surface chemistry and morphology were used for a systematic study of the wetting phenomenon on regular structured arrays. The regularity and periodicity of particle structures allowed modelling of wetting. The wetting was modelled according to WENZEL, CASSIE-BAXTER, EXTRAND theories as well as minimal and maximal possible contact angles introduced by SHUTTLEWORTH and BAILEY.It has been found that none of these theories completely describe the experimental results for all particle sizes except for the surfaces made from 0.2 Mikrometer large particles. It was revealed that wetting behaviour on fluorosilane modified particles with the diameter of 0.2 Mikrometer is close to the equilibrium contact angle described by WENZEL and CASSIE-BAXTER theories. It has been shown that the deviations contact angle from equilibrium state increase with increasing particle size, decreasing intrinsic contact angle, and increasing solid free energy of the particle ´shell´. This provides the experimental evidence for the theory proposed by JOHNSON and DETTRE. It was revealed that ultrahydrophobic surfaces couldn´t be observed on layers made from regularly packed core-shell particles. Design of fractal irregular surfaces is an appropriate way for preparation of ultrahydrophobic self-cleaning surfaces. It was demonstrated that fluorination is not an obligatory factor for design of water repellent coatings. The obtained results are of essential interest for industrial application.

The octamethyltrisilazane, Me2Si[N(H)SiMe3]2, can be used to ligade several metallic elements by substitution of the hydrogen atoms at nitrogen. In general it has been found that, in the absence of basic solvents, two octamethyltrisilazyl ligands act as a "chelating entity", coordinating a variety of metal centers. The formal charge in these centers is 4+. Simple displacement reactions allow the synthesis of a great variety of heterometallic silyl amides, a class of compounds until now only poorly described in the literature. The compounds can be classified by three general formulae: [Me2Si(NSiMe3)2]2-MIIIMI [MI=Li, MIII=Al, Fe, In; MI=Na, K, In, Tl, MIII=In), [Me2Si(N-SiMe3)2]2MIIMI2 (MII=Pb, MI=Li) and [Me2Si(NSiMe3)2]2MI2MI'2 (MI=Li, MI'=Tl). So far we have been able to synthesize only one compound with more than two octamethyltrisilazyl (omts) ligands: [Me2Si(NSiMe3)2]3Cd2Li2. The new compounds have been characterized by spectroscopic methods (1H-NMR, MS) and their solid state structures have been elucidated by singel crystal X-ray diffraction analyses. The metallic elements tend to optimize their coordination numbers by Lewis acid-base interactions with ligand nitrogen atoms, resulting in the formation of bicyclic, tricyclic, tetracyclic and cage structures. The greater the number of metallic centers present, the more the nitrogens are involved in coordination.