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Hybrid organic-inorganic polyoxometalates functionalized by diorganotin groups
No full textPolyoxometalates (POMs) represent an important class of inorganic cluster compounds which exhibit a unique compositional and structural versatility resulting in applications in many different areas including catalysis, medicine, materials science and nano/biotechnology. Discrete molecular hybrid organic-inorganic POMs are of special interest because they combine the unique properties of the metal-oxo fragment with those of the attached organic groups. The prime objective of this project was to synthesize and structurally characterize discrete POMs functionalized by diorganotin groups. Reaction of diorganotin electrophiles with a variety of lacunary POM precursors in aqueous media over a wide range of pH, temperature, concentration etc. resulted in the first examples of diorganotin-POMs. Monomeric, dimeric, trimeric, tetrameric and dodecameric derivatives were prepared and structurally characterized by FTIR, single crystal X-ray diffraction, multinuclear NMR, electrochemistry (Prof. L. Nadjo and Dr. B. Keita, Université Paris-Sud, France), scanning tunneling microscopy/spectroscopy (Prof. P. Müller, Universität Erlangen-Nürnberg), and dynamic light scattering (Prof. M. Winterhalter, IUB). All of the above is described in Part I of this thesis. In Part rt II the synthesis and structural characterization of a monophenyltin-containing POM is reported. This species was fully characterized in solution and in the solid state. In Part III the synthesis and structural characterization of three novel dimeric, trimeric and tetrameric titanium-containing POMs is described. The oxidation catalysis properties of these species are currently under investigation. In Parts IV and V the synthesis and structural characterization of tetra-cadmium as well as tri- and tetra-indium substituted POMs is reported. The tri-indium Keggin and Wells-Dawson derivatives represent the first examples of a Weakley-type polyanion dimer with a vacancy in one of the central positions
Hubbard trees and kneading sequences for unicritical and cubic polynomials
No full textWe investigate two combinatorial models for polynomial dynamics: Hubbard trees and kneading sequences. We consider abstract versions of unicritical and cubic Hubbard trees and kneading sequences and study their interdependence. This gives structure to the set of Hubbard trees, from which we derive results on the structure of the unicritical and cubic connectedness loci. In the first part, we consider unicritical Hubbard trees and kneading sequences and show that they are equivalent concepts. We determine which kneading sequences come from unicritical polynomials. On the parameter level we introduce a partial order < on the set of kneading sequences which is based on comparing periodic orbits in Hubbard trees. Transitivity of < follows from a forcing relation on periodic orbits between comparable Hubbard trees. Our main result in parameter space shows that the space of kneading sequences is structured like a tree. The motor of this study are results on the structure of periodic and precritical points in Hubbard trees. We conclude the unicritical part by discussing alternative approaches to define a partial order for the set of Hubbard trees. In the e second part, we investigate the interaction of abstract cubic Hubbard trees and kneading sequences. As a consequence of the existence of two critical points, it is not immediate how these concepts relate. Still, we show that there is an injection, but not a bijection, from the set of Hubbard trees into the set of kneading sequences. As in the unicritical case, we first explore the dynamical properties of Hubbard trees. On the parameter level, we define a partial order < on two special subsets of Hubbard trees, namely trees with only one free critical point and trees of disjoint type. Again we need a forcing relation on periodic orbits to establish transitivity of <. We give sufficient conditions that guarantee orbit forcing and provide examples that without them, orbit forcing might or might not be possible
Contribution of the lysosomal cysteine protease cathepsin B to extracellular matrix remodeling during keratinocyte migration and wound healing
No full textIn this work, the involvement of the lysosomal cysteine peptidase cathepsin B in regeneration after scratch-wounding and in spontaneous keratinocyte migration was investigated. As cellular model systems, the human keratinocyte cell line HaCaT and normal human epidermal keratinocytes were used. In a standardized scratch-wounding assay, it was shown that inhibition of extra- and intracellular cathepsin B using specific inhibitors led to an impairment of keratinocyte migration. This was true for the cell line HaCaT and also for NHEK, demonstrating that HaCaT cells represent a suitable model to study keratinocyte migration. Furthermore, we wanted to identify the binding-partner for cathepsin B at the plasma membrane of migrating keratinocytes. The possibility of annexin-II being the plasma membrane receptor for secreted cathepsin B was ruled out. As alternative candidate, we investigated the LRP1 as a possible binding partner. Using immunofluorescence, it was shown that cathepsin B and LRP1 co-localize at the plasma membrane. By incubating HaCaT keratinocytes with an endogenous inhibitor for LRP1, it was detected that blocking of the ligand binding domains of LRP1 after scratch-wounding resulted in increased amounts of soluble cathepsin B in the culture media. Likewise, the levels of plasma membrane-associated cathepsin B were decreased, suggesting that LRP1 is in fact the binding partner for cathepsin B. To enable the direct observation of cathepsin B sorting and trafficking in living keratinocytes, we designed a plasmid encoding for a chimeric protein of HaCaT cells derived cathepsin B and eGFP. Our results showed that the secreted lysosomal cysteine peptidase cathepsin B is important for the process of keratinocyte migration after scratch-wounding, and we additionally showed that LRP1 is most likely the binding-partner at the plasma membrane of migrating keratinocytes to localize cathepsin B
Localization, trafficking and functional role of cysteine cathepsins in thyroid epithelial cells
No full textCathepsin B-eGFP chimeras were used to test whether intrinsic sequences of a protease influence its trafficking. The expression of rat cathepsin B-eGFP versus human tumor cell-derived cathepsin B-eGFP showed that the latter chimeras were abundantly present within the ER, probably due to a 5-amino-acid insertion at the C-terminal portion of the enzyme, which might have caused this trafficking defects. The analysis of the distribution patterns of rat cathepsin B-eGFP as compared to the active-site mutant cathepsin B-C29A-eGFP showed, that both chimeras were transported to ER, Golgi and endo-lysosomal vesicles. By use of activity based probes, designed to distinguish between active and inactive cysteine proteases, it was observed that both, active and inactive proteases, were present within the same compartments, ruling out that sorting signals were altered by mutagenesis of the active-site residues. The study was extended to a set of other cysteine proteases, namely cathepsins K, L, and S, which were in addition to cathepsin B analyzed with reference to their localization within human- or mouse thyroid tissue. Co-localization studies showed a major endo-lysosomal localization for cathepsins B, K and L. Double-labeling revealed cathepsin L-positive vesicles lacking cathepsin S, proving that endo-lysosomal vesicles contain distinct sets of proteases. Consequently, cells may comprise different vesicle loading mechanisms. All four cathepsins tested were detected within the extracellular follicle lumen and partly re-associated with the apical cell surface where Tg-processing is believed to begin. To test for the capability of the cysteine proteases to cleave Tg under extracellular, non-favorable conditions, an in vitro-degradation approach was chosen, proving that all cathepsins tested were able to partially degrade their substrate Tg. The experiments showed that subcellular location and timing of proteolysis are crucial steps in the regulation of proteolytic events
Interaktion zwischen älteren Menschen und Jugendlichen : ein psychologisch förderlicher sozialer Kontext für beide Seiten? : eine experimentelle Laborstudie im theoretischen Rahmen der Entwicklungspsychologie der Lebensspanne
No full textIn this dissertation, it is proposed that intergenerational relations outside the family can contribute to positive development both in old age and adolescence. Based on Erikson´s theory (Erikson, 1963), it is argued that this type of social interaction has got a powerful motivational basis, because developmental tasks of old age (generativity) and of adolescence (identity) complement one another. In a laboratory experiment, the assumption was tested that this motivational match compensates for typical age-related deficits in cognitive and personality functioning (old age) and social orientation (adolescence). Using a between- subjects design, 90 older women (70-74 years) and 90 adolescent girls (14-15 years) were randomly assigned to three experimental conditions. In each of the conditions, participants collaborated dyadically with an unfamiliar partner. The conditions varied according to the age of the interaction partner (adolescent vs. old) and to which degree they were judged to be supportive of the generativity-identity constellation (high vs. low support). Individual performance measures were assessed immediately after the interaction. As expected, performance settings judged to be highly supportive of the generativity-identity constellation increased fluid intelligence and cognitive-affective complexity in older women. Furthermore, the same conditions increased adolescents´ prosocial behavior with a new person.In dieser Dissertation wird argumentiert, dass intergenerationelle Beziehungen außerhalb der Familie zur positiven Entwicklung im hohen Alter und in der Adoleszenz beitragen können. Ausgehend von Eriksons Entwicklungstheorie (Erikson, 1963) wird die Annahme hergeleitet, dass die Beziehung zwischen älteren Menschen und Jugendlichen eine günstige motivationale Basis hat, weil sich die Entwicklungsaufgaben des Alters (Generativität) und der Adoleszenz (Identität) gegenseitig ergänzen. Angenommen wird, dass die Realisation dieser motivationalen Passung in einer konkreten Interaktionssituation typische Defizite des Alters (fluide Intelligenz und kognitiv-affektive Komplexität) und der Adoleszenz (soziale Orientierung) kompensiert. Diese Annahme wurde in einem experimentellen Laborsetting an einer Stichprobe von 90 jugendlichen (14-15 Jahre) und 90 älteren Frauen (70-74 Jahre) untersucht. In allen drei Bedingungen bearbeiteten ad hoc Dyaden unterschiedlicher Alterszusammensetzung zunächst bestimmte vorgegebene Aufgaben, die sich systematisch danach unterschieden, inwieweit sie die motivationale Passung förderten. Die Interaktionspartner wurden unmittelbar nach dieser Interaktion getrennt voneinander in den abhängigen Variablen untersucht. Hypothesenkonform zeigten die älteren Teilnehmerinnen in der die motivationale Passung fördernden Experimentalbedingung ein höheres Ausmaß an kognitiver Leistungsfähigkeit und kognitiv-affektiver Komplexität als die älteren Teilnehmerinnen in den beiden Kontrollgruppen, welche die motivationale Passung nicht unterstützten bzw. ihr zuwider liefen. Außerdem zeigten die jugendlichen Teilnehmerinnen unter der Experimentalbedingung häufiger prosoziales Verhalten als jugendliche Teilnehmerinnen unter den beiden Kontrollbedingungen. Die Ergebnisse deuten insgesamt auf das psychologische Potential der Beziehung zwischen älteren Menschen und Jugendlichen hin
Newton's method as a dynamical system
No full textWe study transcendental and rational mappings that arise as Newton maps of entire functions. Our first result is that "in between" any two accesses to infinity of an immediate basin, a Newton map exhibits either another immediate basin, a virtual immediate basin or infinitely many preimages of some point. This result is joint work with Dierk Schleicher and allows to locate virtual immediate basins. An important corollary is a proof of the folklore result that for Newton maps of polynomials, every complementary component of an immediate basin contains another immediate basin. Our second main result, which is joint work with Xavier Buff, shows an interesting connection between virtual immediate basins of the Newton map N_f and asymptotic values of f, answering a 2003 question of Douady: in many cases, 0 is an asymptotic value of f if N_f has a virtual immediate basin. Conversely, if f has an asymptotic value of logarithmic type at 0, then N_f has a virtual immediate basin. We show by way of counterexamples that this is not true for other types of asymptotic values. Our third main result gives a combinatorial classification of a class of Newton maps of polynomials. Let N be the Newton map of a polynomial such that all critical points of N land on a fixed point after finitely many iterations. In this case, we construct a graph that characterizes N uniquely up to Möbius conjugation. Conversely, we show that every graph with an associated map that satisfies several natural conditions is realized by a unique Newton map. In an appendix, we introduce a class of bounded type transcendental entire functions with the property that its set of escaping points is organized in the form of unbounded rays. This fourth main result is joint work with Günter Rottenfußer, Lasse Rempe and Dierk Schleicher, and is part of an answer to a long-standing conjecture of Fatou and Eremenko
Preparation and characterization of Pt and Pd nanoclusters modified with chiral ligands : examination of catalytic activity in hydrogenation of ethyl pyruvate
No full textStudies of the interactions of organic substrates with nanoscale metals and metal oxides are of fundamental importance for both fundamental scientific understanding and the development of commercial applications. Additionally, the development of heterogeneous (solid/liquid or solid/gas) enantioselective catalysts is of great interest for the pharmaceutical industry. Here, the adsorption of chiral ligands on metal surfaces to develop heterogeneous asymmetric catalysts is presented. Functionalizing metal nanoparticles with chiral ligands facilitates increased surface coverage and the observed activity of these catalysts is significantly higher than their conventional phase counterparts. The first two chapters are an introduction to the enantioselective catalysis and nanosized materials. As described in the chapter 3, the primary objectives of this work are 1. to synthesize Pt and Pd nanoclusters modified by specific chiral ligands by 'bottom up' chemical synthesis, 2. to determine the geometric orientation of adsorbed modifier with respect to the metal surface via DRIFTS (Diffuse Reflectance Infra-red Fourier Transform Spectroscopy) and molecular modeling, 3. test enantioselective activity of the obtained samples in the hydrogenation of ethyl pyruvate. The special effort has been given for investigation of cinchonidine as modifier (chapter 4, 5, 6). Among the following chiral ligands: quiphos (chapter 7), "quiphos-spider" (chapter 8), binap and synphos (chapter 10), only diop (chapter 9) was found to be able to induce low enantioselectivity, that was qualitatively explained through comparison with cinchonidine/Pt system
Cathepsins during intestinal trauma
No full textExtracellular cathepsins are involved in physiological and in pathological conditions, in which they may cause disturbances of normal balances of enzymatic activity. To determine whether cathepsins contribute to the onset of inflammatory responses leading to post-operative ileus (POI), we used a rat model of standardized small intestine trauma. In non-damaged tissue, cathepsins were located in endocytic vesicles of enterocytes. After trauma, a localized release of cathepsin B was observed along with degradation of components of the ECM. Hence, extracellular cathepsin activity might lead to an impairment of mucosal barrier function, making cathepsin B a potential candidate for promotion of inflammatory responses after trauma. To better characterize molecular mechanisms underlying POI, an in-vitro model system for mechanical manipulation of enterocytes was developed. The established compressive loading system allows to reproducibly induce damage, which is characterized by necrotic cell death leading to release of cathepsins. Released cathepsins B and D were proteolytically active as soluble enzymes in conditioned media of damaged cells, whereas cathepsin L re-associated with the cell surfaces. Hence, released cathepsins may serve proteolytic functions as soluble or cell surface-immobilized enzymes. To elucidate the underlying secretion mechanisms in damaged tissues, we took advantage of an intestine specific gene-expression driven by the A33-antigen-promotor which contains regulatory elements including CDX binding sites. The activity of the intestine-specific transcription factor Cdx1 is pivotal for an intestinal expression pattern of the A33 antigen gene. We cloned the A33 antigen-promoter into a cathepsin B-EGFP vector. Co-transfection with Cdx1 enabled A33-antigen promoter-controlled expression of cathepsin B-EGFP in CHO cells. The long-term objective of these in vitro experiments is to apply the results in order to establish a transgenic mouse model
Generating exponentially many periodic attractors with linearly growing Echo State Networks
No full textWhen a human listens to a novel piece of music, wherein a reasonably short motif (likewise novel to the listener) is repeated twice, the human is able to (1) detect this fact, (2) continue to reproduce the motif periodically. A similar phenomenon is iterated phone number rehearsal to keep a phone number in short-term memory. Mathematically, these are cases where a dynamical system (the brain) hosts a huge number of periodic attractors, into which it can be driven by feeding the corresponding periodic time series as a cue input. Here we demonstrate how this phenomenon can be modelled using Echo State Networks featuring a spatial encoding of musical pitch. The network is trained as a pure delay-line memory. The number of periodic attractors that a given, trained ESN can produce without further parameter adjustment scales exponentially with the network size. A stability analysis of the attractors is provided
Time Warping Invariant Echo State Networks
No full textEcho State Networks (ESNs) is a recent simple and powerful approach to training recurrent neural networks (RNNs). In this report we present a modification of ESNs - time warping invariant echo state networks (TWIESNs) that can effectively deal with time warping in dynamic pattern recognition. The standard approach to classify time warped input signals is to align them to candidate pro- totype patterns by a dynamic programming method and use the alignment cost as a classification criterion. In contrast, we feed the original input signal into specifically designed ESNs which intrinsically are invariant to time warping in the input. For this purpose, ESNs with leaky integrator neurons are required, which are here presented for the first time, too. We then explain the TWIESN architecture and demonstrate their functioning on very strongly warped, synthetic data sets