Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
Search Results
Item Open Access Oleathydratase katalysierte stereoselektive Hydratisierungsreaktionen kurzkettiger Alkene(2025) Härterich, Natalie; Hauer, Bernhard (Prof. Dr.)Item Open Access Growth of oxide materials with Ruddlesden-Popper- and garnet-type structures via the optical float zone method: investigations of scintillation, optical, and magnetic properties, and post-growth modifications of single crystals via topochemical routes(2025) Yilmaz, Hasan; Clemens, Oliver (Prof. Dr.)With the continuous progress in materials science, the global market demand for high-performance functional materials, especially those with customized optical and magnetic properties, has increased significantly due to their critical role in next-generation technologies such as photonic devices, data storage systems, quantum computing, and biomedical applications. With this motivation, this dissertation is focused on the growth of high-quality oxide single crystals with Ruddlesden-Popper (RP) and garnet-type structures using the optical floating zone (OFZ) method and the detailed investigation of their scintillation, optical and magnetic properties. Furthermore, the use of chemical doping and post-growth topochemical modifications as strategies to modify material properties and stabilise metastable structures is also covered. With these approaches, we can classify this study into two parts: optical and magnetic properties. In the first part of this work, RP-type n = 1 LaSrGaO4 (LSGO) and Garnet-type Gd3In2Ga3O12 (GIGG) single crystals doped with different Rare Earths (RE) including Eu, Sm, Ho, Nd have been grown via OFZ method to investigate their luminescence, decay time kinetics and scintillation properties. To compare the scintillation behaviour, a well-known commercial scintillator, Gd2.98Ce0.02Al2Ga3O12 (0.02Ce:GAGG) single crystal, was synthesised and characterised using the same methods. This limits deviations in scintillation properties caused by different synthesis methods. Powder X-ray diffraction (XRD) and Single Crystal X-ray diffraction (SC-XRD) measurements together with Rietveld analysis confirmed phase purity and crystallinity, while Scanning Electron Microscopy (SEM-EDX) and backscatter electron imaging (BSE) confirmed the homogeneous distribution of the dopants. In addition to these analytical methods, Photoluminescence Spectroscopy (PL) and luminescence decay measurements have demonstrated that these RE-doped single crystals have strong emission, which is related to the low phonon energy of their host lattices. However, scintillation measurements under 137Cs gamma-ray point source excitation resulted in a limited gamma ray response. This response was significantly weaker than observed for the well-known commercial scintillator 0.02Ce:GAGG. Inefficient absorption of high-energy excitation or inadequate energy transfer to the activator ions in these materials are responsible for this relatively low scintillation performance. The second part of the thesis is focused on bilayer Ruddlesden-Popper nickelates. Single crystals of Sr3Ni2-xAlxO7-δ (SNAO) and its Y-substituted modification YᵧSr3-yNi2-xAlxO7-δ (YSNAO) have been grown by using strategically chemical substitutions and high oxygen pressure conditions to stabilize the RP phase. XRD and SC-XRD analysis confirmed the existence of the n = 2 RP-type structure by doping with Al, while thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) indicated successful oxygen incorporation and corresponding changes in the Ni oxidation state. Magnetic susceptibility measurements (SQUID magnetometry) have demonstrated the antiferromagnetic ordering transitions in these doped nickelate single crystals, and transport measurements have shown enhanced electrical conductivity compared to the undoped parent compound. In addition, a topochemical fluorination process has been investigated as a post-growth modification for n = 1 RP-type La2NiO4+δ single crystals. Fluorine has been introduced into the crystal lattice at moderate temperatures using polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and CuF2 as fluorination reagent. PTFE has been found to be the most effective fluorinating agent, resulting in partially fluorinated La2NiO4+δ with a diffusion-limited penetration pattern. EDX and EDX-mapping analyses have demonstrated an inhomogeneous F distribution, indicating that fluorine incorporation is limited by diffusion kinetics. This inhomogeneity should be carefully considered in future structural and functional analyses as it may affect the accurate characterisation of intrinsic properties in fluorinated crystals. In summary, the results of this thesis demonstrate the flexibility of the optical floating zone technique for the growth of high-quality functional oxides and show how structural stability, and functional properties can be modified using specific chemical doping approaches. To optimise scintillation performance in novel garnet-type hosts and to improve the magnetic and electronic behaviour of RP-type nickelates, the combined approach of crystal growth and post-growth modification could provide an additional parameter for material modification.Item Open Access Nano-analysis of surface reaction kinetics of automotive exhaust gas catalyst(2025) Lee, Yoonhee; Schmitz, Guido (Prof. Dr. Dr. h.c.)This study aims to advance our comprehension of the reaction kinetics occurring in nano-sized noble metal catalysts. Advanced microscopy techniques were employed to investigate the precise details of oxidation and diffusion behavior at different temperatures. In particular, atom probe tomography (APT), a highly sophisticated characterization technique, was utilized to obtain accurate and detailed information regarding these processes. By employing this microscopy technique, a comprehensive analysis of the reaction kinetics of nano-sized noble metal catalysts could be achieved, contributing to the development of more efficient catalysts for automotive applications. Noble metal nanoparticles such as Pt, Pd, and PtPd exhibit distinct oxidation behaviors during NO conversion. Understanding the alterations in the catalyst surface is crucial, as it has a direct effect on the performance of the catalytic converter. For this study, wires were utilized made of pure Pt, pure Pd, and PtPd alloy to create sharp tip samples through electrochemical polishing or FIB annular milling. The hemispherical shape of the tip apex serves as a model for the nanosized catalyst surface. The tips were oxidized in the reaction chamber and investigated by APT. The effective oxide thicknesses were determined and compared to the NO conversion rates measured using a Flat Bed Reactor (FBR). Additionally, experimental results of studying the interdiffusion behavior of the Pt-Pd binary system at various temperatures are presented and discussed. To achieve this purpose, the samples were prepared and examined with two different methods, depending on the heating temperatures. For the temperature range between 673 and 973 K, the samples made of nano-sized multiple layers were investigated using APT. For the temperature range between 1073 and 1243 K micro-sized Pt/Pd diffusion couples were annealed and analyzed using energy dispersive X-ray spectroscopy (EDX). The interdiffusion coefficients for both methods were determined by representing them as Fourier series and the Boltzmann-Matano method, respectively. The latter study was conducted in collaboration with the department of Materials design. Consequently, the interdiffusion coefficients were compared with the results of density functional theory (DFT) simulations.Item Open Access Synthesis and characterization of ternary and quaternary nitrides of the main group elements(2025) Link, Lukas; Niewa, Rainer (Prof. Dr.)Im Rahmen dieser kumulativen Dissertation werden insbesondere die Nitride in Systemen der Art Erdalkalimetall - Tetrel - Stickstoff beleuchtet, sowie das kristallographische Computerprogramm Polynator vorgestellt. Der Fokus liegt auf ternären Nitridogermanaten, Nitridosilicaten, sowie inversen Perowskiten. Letztere auch als Antiperowskite bekannt und treten hier mit Erdalkalimetallkationen, kleinen Nitridanionen und größeren Tetrelidanionen auf. Für diese Verbindungen werden Elpasolithartige Überstrukturen sowie drei vormals ganz unbekannte Vertreter beschrieben. In Form von Silicid-Silicaten bzw. Germanid-Germanaten werden die ersten Verbindungen von Silicium und Germanium vorgestellt, die das jeweilige Element sowohl in seiner höchsten Oxidationsstufe +IV, als auch in seiner niedrigsten Oxidationsstufe -IV enthalten. Zudem werden unter anderem die ersten Nitridogermanate(III) vorgestellt, wobei ein neuartiges, ethananaloges Molekülanion gefunden wurde. Das Programm Polynator dient zur Identifikation von Polyedern und anderen Baueinheiten in Kristallstrukturen, sowie zur quantitativen Analyse ihrer Geometrie, Symmetrie und Verknüpfungsmuster. Dabei macht es innovativen Gebrauch von dynamischen Modellen, die nicht nur eine bestimmte Form repräsentieren, sondern ein Kontinuum von verwandten Formen (zum Beispiel alle trigonalen Prismen). Es verfügt über eine graphische Benutzeroberfläche und ist in der Lage, CIF- XYZ- und MOL-Dateien einlesen.Item Open Access From muscle spindle to spinal cord : a modelling approach of the hierarchical organization in sensorimotor control(Stuttgart : Institut für Modellierung und Simulation Biomechanischer Systeme, Computational Biophysics and Biorobotics, 2025) Santana Chacon, Pablo Filipe; Schmitt, Syn (Prof. Dr. rer. nat.)The muscle spindle is an essential proprioceptor, significantly involved in sensing limb position and movement. Although biological spindle models exist for years, the gold-standard for motor control in biomechanics are still sensors built of homogenized spindle output models due to their simpler combination with neuro-musculoskeletal models. The performance of new studies that consider different structures of the hierarchical sensorimotor control system, implementing physiologically-motivated neuromechanical models aligned to proprioception, is essential to enable a more holistic understanding about movement. The incorporation of more biological proprioceptive and neuronal circuit models to muscles can make neuro-musculoskeletal systems more appropriate to investigate and elucidate motor control. Therefore, initially, this doctoral dissertation presents a more physiological model of the muscle spindle that considers the individual characteristics of involved tissue compartments, aligned to the advantage of easy integration into large-scale musculoskeletal models. Different stretches in the intrafusal fibers were simulated in the model's variations following the spindle afferent recorded in previous experiments in feline soleus muscle. Additionally, the proposed enhanced Hill-type spindle models had their parameters extensively optimized to match the experimental conditions, and the resulting model was validated against data from rats’ triceps surae muscle. As result, the model exhibits a stable and valid prediction of experimentally observed muscle spindle responses. At the same time, it presents a well-tuned Hill-type model as muscle spindle fibers – accounting for real sarcomere force-length and force-velocity aspects - and its activation dynamics is similar to the one applied to Hill-type model for extrafusal fibers, making it more easily integrated in multi-body simulations. Furthermore, this dissertation aims to demonstrate that the afferent firings from the muscle spindle model can be processed by neuronal networks and are important for motor control. Hence, the spindle model was integrated to a previous implemented extrafusal fiber model, inside of the demoa multi-body simulation framework. This structure composed by extrafusal (muscle) and intrafusal (spindle) fibers replaced the muscle-tendon units (MTUs) of a prior developed arm model composed by two degrees of freedom and six MTUs, into the same simulation framework. Additionally, a spinal cord model, based on literature, was implemented in the Nest spiking neural network simulator. The spinal network has 6 neurons per muscle - alpha, dynamic gamma and static gamma motoneurons, together with Ia, propriospinal and Renshaw interneurons – and their respective physiological connections. The coupling between demoa and Nest simulators was implemented using a Cython interface. The spinal cord network - in its two variations of complete and simpler circuitry (including only Renshaw pathway, without spindle proprioception) - had its synaptic weights optimized to perform a center-out reaching task using the musculoskeletal model, without and with perturbation (increment of lower arm segment in 1 kg). As result, the complete spinal cord circuitry learned how to successfully reach all the evaluated targets without and with perturbation, demonstrating the sensorimotor control learning in the environment formed from muscle spindle to spinal circuitry, encompassing the two simulators. On the other hand, the simpler spinal cord circuitry did not succeed in the task of reach all the targets, also demonstrating reduced performance with perturbation. Moreover, the spindle afferent synapses in the complete circuitry were intensified for the higher targets (considered more difficult under gravity) when comparing the scenarios without and with perturbation. Therefore, the muscle spindle connections were strengthened for difficult targets under perturbation, highlighting the importance of spindle proprioception in these more difficult scenarios, as well as indicated by the circuitry that does not consider proprioception and did not show a similar successful performance. Finally, this dissertation offers a novel possibility of neuro-musculoskeletal modelling environment formed with demoa and Nest simulators. Future outlook includes the integration of the musculoskeletal and spinal cord models with higher-level models of Central Nervous System, aligned to further sophisticated details of the current modelling, to allow a more comprehensive understanding of sensorimotor behavior.Item Open Access Development pathway from chitin-based organisms to chitosan-based photoresponsive thin-films with modulation in physiochemical properties during irradiation(2025) Seggern, Nils von; Stegbauer, Linus (Prof. Dr.)Item Open Access Probabilistic modelling of population variability(2025) Wagner, Vincent; Radde, Nicole (Prof. Dr. rer. nat.)Vincent Wagner's dissertation summarises progress in the probabilistic modelling of population variability. It comprises two chapters with complementary approaches to this challenging and broad topic. The first chapter deals with the Method of Moments for the Chemical Master Equation, while the second chapter uses random variable transformations to estimate distributed simulation model parameters.Item Open Access Enzymkatalysierte regioselektive cofaktorfreie Hydratisierung von Terpenen und Terpenoiden(2025) Horz, Philip; Hauer, Bernhard (Prof. Dr.)Die konzeptionell einfache, regioselektive Addition von Wasser an nicht aktivierte C-C-Doppelbindungen von einfachen Olefinen wie Terpenen gilt als große Herausforderung der synthetischen Chemie. Terminal hydratisierte Terpene und Terpenoide haben große Bedeutung als Duft- und Geschmackstoffe sowie als pharmazeutische Wirkstoffe und Insektenschutzmittel. Aufgrund von mehreren Doppelbindungen in den zu hydratisierenden Vorläufermolekülen ist dieser Ansatz sehr komplex und erfordert aufwendige, mehrstufige Schutzgruppensynthesen, um die terminale Prenyleinheit regioselektiv zu hydratisieren. Die Natur hat für diese Art der Reaktion hochspezifische Katalysatoren evolviert, die sich für diese Herausforderung zu Nutze gemacht werden können - die Hydratasen. Diese Enzyme katalysieren die Addition von Wasser mit einer herausragenden Regioselektivität unter milden Bedingungen. Aus der Literatur ist bekannt, dass die Carotinoid 1,2-Hydratase aus Rubrivivax gelatinosus strain S1 (RgCrtC_S1) in der Lage ist, sowohl das natürliche Substrat Lycopin (C40) als auch das unphysiologische Substrat Geranylgeraniol (C20) terminal zu hydratisieren. Des Weiteren wurde beschrieben, dass diese Hydratase ein eingeschränktes Substratspektrum aufweist und Substrate ≤ C20 nicht akzeptiert. Das Ziel dieser Arbeit war es, die Carotinoid 1,2-Hydratase aus Rubrivivax gelatinosus strain IL144 (RgCrtC_IL144), welche eine natürlich vorkommende Enzymvariante der RgCrtC_S1 ist, zu untersuchen und deren Synthesepotential gegenüber Terpenen und Terpenoiden im Ganzzellsystem zu erweitern. Im ersten Teil dieser Arbeit wurde das Ziel verfolgt, eine geeignete Modellreaktion zu etablieren, die im Ganzzellsystem durchführbar ist, um nachfolgende Untersuchungen in einem experimentell gut zugänglichen und reproduzierbaren System zu ermöglichen. Aufgrund der begrenzten Membrangängigkeit von Lycopin erwies sich das natürliche Substrat jedoch als ungeeignet für das Ganzzellsystem und konnte in diesem nicht hydratisiert werden. Aus diesem Grund wurde das Terpenoid Farnesylaceton (C18) untersucht, welches eine bessere Membrangängigkeit aufwies. In einem ersten Versuch konnte dieses Substrat mit 35 % zum terminalen Hydratisierungsprodukt umgesetzt werden. Um die Aktivität der in der Literatur beschriebenen Variante RgCrtC_S1 zu untersuchen, wurden das in der Literatur genutzte und das in dieser Arbeit verwendete Expressionssystem miteinander verglichen. Das literaturbekannte System basiert auf einem high-copy Plasmid mit einer schwach regulierten, lactoseinduzierten Expression. Im Gegensatz dazu verwendet das in dieser Arbeit eingesetzte System ein low-copy Plasmid mit einer rhamnoseinduzierten Expression, die eine stärkere Regulation der Genexpression ermöglicht. Der Vergleich ergab, dass die Produktbildung von RgCrtC_S1 mit dem in dieser Arbeit genutzten Expressionssystem um das 150-Fache höher war als im Literatursystem. Darüber hinaus konnte mit der in dieser Arbeit verwendeten Kombination aus RgCrtC_IL144 und Expressionssystem eine 175-fache Erhöhung der Produktbildung, im Vergleich zur literaturbekannten Kombination aus RgCrtC_S1 und dem Literatursystem, erzielt werden. Nach erfolgreicher Expression der aktiven Hydratase wurden die optimalen Reaktionsbedingungen mit 50 mM KPi pH 7,0 + 1 mM. 2-Hydroxypropyl-beta-cyclodextrin + 1 mM Substrat bei 30 °C für das Ganzzellsystem bestimmt. Unter Verwendung des optimierten Reaktionsansatzes sollte das Substratsektrum der RgCrtC_IL144 untersucht werden. Dabei wurden 36 Terpene und Terpenoide mit unterschiedlichen C-Kettenlängen (C10-C20) und funktionalisierten Kopfgruppen getestet. Aus diesem Spektrum wurden 20 Substrate mit Kettenlängen von C12-C20 und Alkohol-, Vinylalkohol-, Keton-, Carbonsäure-, Ether-, Ester-, Thioester- und nicht funktionalisierten-Kopfgruppen akzeptiert und mit Umsätzen von bis zu 78 % terminal hydratisiert. Aufgrund des hohen Umsatzes im analytischen Maßstab wurden semi-präparative Ansätze mit sechs verschiedenen Substraten und einer Substratkonzentration von bis zu 50 mM durchgeführt. Dabei konnten Produkte mit bis zu 1,1g (70 % isolierte Ausbeute) isoliert und chemisch charakterisiert werden. Zudem konnte der einfache Einsatz der lyophilisierten Zellen anhandeiner im basischen durchgeführten One-Pot Aldolkondensation mit direkter Hydratisierung, bei der OH-Pseudoionon aus Aceton und Citral hergestellt wurde, gezeigt werden. Im letzten Teil der Arbeit wurden die aktive Tasche und der Substrattunnel von RgCrtC_IL144 mithilfe des erstellten AlphaFold-Modells und Docking-Studien analysiert. Auf Grundlage dieser Analysen konnten die für die Hydratisierung relevanten katalytischen Aminosäuren D268, W110, W283, W285 und Y112 durch gezielte Substitution charakterisiert werden. Darüber hinaus zeigten die Docking-Studien, dass die Ausrichtung der funktionellen Gruppe der Substrate im aktiven Zentrum sowie die Ausbildung von Wasserstoffbrückenbindungen mit spezifischen Ankerpositionen einen entscheidenden Einfluss auf deren Umsatz hatten. Mit drei unterschiedlichen Mutageneseansätzen (FuncLib, Sättigungsmutagenese und Consensusmutagenese) sollten sowohl das Substratspektrum gegenüber kleinen Terpenen und Terpenoide (≤ C12) erweitert, als auch die Aktivität der Hydratase gesteigert werden. Mithilfe des Consensus Ansatzes konnte die Aktivität der Hydratase gegenüber Pseudoionon um das 2,5-fache gesteigert werden. Diese Ergebnisse bilden eine Grundlage für zukünftige Engineering-Ansätze zur Optimierung dieser Hydratasen.Item Open Access Locomotion of small-scale magnetic robots in biological environments(2025) Jeong, Moon Kwang; Schmitt, Syn (Prof. Dr.)Recent advances in small-scale robots for biomedical applications have demonstrated significant potential by using optimized wireless actuation schemes. One of the most promising modalities is magnetics due to advantages in controllability, large force transmission, and negligible effects on biological tissues. However, many approaches may not be suitable for the challenges imposed by biological environments such as viscous media, constrained spaces, and low-friction surfaces. The overall goal of this thesis is to develop millimeter-scale robots capable of actively operating in complex biological environments to perform biomedical tasks. Two major research questions are investigated to address the challenges: the development of suitable magnetic actuation schemes as locomotion modalities to perform biomedical tasks at a human-relevant scale and the design of structural features to enable locomotion in narrow lumens. To address the first research questions to overcome the challenges imposed by biological environments, two permanent-based magnetic actuation set-ups are designed and built for controlling the robots. The set-up for TwistBot consists of four specially arranged identical permanent magnets, which rotate about the same axis at a given frequency to generate a homogeneous rotating magnetic field of approximately 54 mT in the working volume of 15 mm x 15 mm x 15 mm. Finite element simulations are used to model the superimposed magnetic field, which is then verified by experimental results. Another magnetic actuation set-up possesses a larger accessible volume. It consists of a pair of static magnets and one rotating magnet, which is customizable for adjusting the magnetic field strength and offers two degrees of freedom. It generates a magnetic field of approximately 6 mT within a working volume of ∅50 cm x 28 cm. The resulting magnetic field is modeled analytically to estimate the robot's motion, which is further verified through finite element simulations. The analytical solution can be utilized to optimize and adapt the robot’s motion on different surfaces by calculating the magnetic field distribution with less computational resources. To tackle the second research questions, two distinct locomotion strategies are explored: swimming-based propulsion, demonstrated by TwistBot for efficient movement in viscous fluids, and crawling-based locomotion, employed by GearBot, TrainBot, and BipedBot, which rely on surface interaction to navigate biological environments. While magnetic helical small-scale robots are well known for their efficiency in viscous fluids, fabricating such helical structures without complex machinery remains challenging. The unique shape-transforming capability of TwistBot not only facilitates propulsion through narrow lumens but also enables it to carry and deliver solid cargo to target locations. However, in biological environments, the presence of slippery mucus layers can cause robots to slip uncontrollably during propulsion. To overcome this limitation, BipedBot utilizes sharp spikes to anchor onto biological tissues, allowing it to carry loads up to four times its weight while deploying liquid cargo to target locations. Similarly, GearBot, with its gear-shaped 3D-printed structure, is designed to traverse complex trajectories and narrow lumens on biological tissue phantoms. Despite these capabilities, a single robot may lack sufficient propulsion force on slippery biological tissues to transport heavy medical instruments, such as catheters or electrosurgical electrodes. To overcome this limitation, TrainBot demonstrates a cooperative crawling strategy, where multiple small-scale robots work together to navigate narrow lumens, providing enhanced friction and controllability. For the first time, it is shown that a convoy of robots is capable of successfully performing electrocauterization in an obstructed bile duct to create a tunnel for fluid drainage and drug delivery.Item Open Access Neuromusculoskeletal modeling of human bipedal gaits : exploring the role of reflexes in locomotion(Stuttgart : Institut für Modellierung und Simulation Biomechanischer Systeme, Computational Biophysics and Biorobotics, 2025) Bunz, Elsa K.; Schmitt, Syn (Prof. Dr. rer. nat.)