University of Kaiserslautern
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How social are self-effects? -The impact of feedback on the internalization of expressed opinions in online communication
Get PDFOnline communication channels provide rich opportunities for public opinion expression, and the act of posting may lead to an internalization of the expressed views. This research investigated whether such self-effects are affected by feedback comments and whether this influence is stronger in social network sites than in anonymous online forums. In an experiment manipulating valence of feedback and the media context, 161 participants were asked to express their opinion on a current topic. Results showed limited effects of feedback: Negative comments tended to reduce internalization among participants with non-extreme prior attitudes, but this was independent from the media context
Exciton and Multiple Exciton Dynamics in Colloidal Semiconductor Nanocrystals
Get PDFCdSe quantum dots (QDs), owing to their size tunable optoelectronic properties, narrow photoluminescence linewidth, high photoluminescence quantum yields etc., have been a prime interest of intensive research for numerous applications, including light-emitting diodes, solar concentrators, photocatalysis, photovoltaics, and nanocrystal lasers. Upon photoexcitation, QDs generate a pair of an electron and a hole, referred as exciton, and under high excitation density photoexcitation, multiexcitons (multiple pairs of interacting excitons) are formed. The dynamics of excitons and multiexcitons govern the photophysics behind QD-based applications. For example, effective separation of electron and hole enhances photocatalytic efficiency, while multiexcitons with long lifetimes enhance the optical gain, thereby increasing laser performance. In recent years, it has been demonstrated that the properties of excitons and multiexcitons can be modified by altering the size and the surface properties of QDs. To develop a suitable material for optoelectronic applications, it is essential to gain a comprehensive understanding of the mechanisms underlying the size and surface modification induced changes in exciton and multiexciton properties. With this motivation, the thesis ‘Exciton and Multiple Exciton Dynamics in Colloidal Semiconductor Nanocrystals’, investigates the influence of QD size, surface modification, and inter-QD coupling on exciton and multiexciton properties in solution and thin film.
To achieve this, colloidal tri-octylphosphine oxide (TOPO)-capped CdSe QDs were synthesized via the hot injection method, which provided the advantages of size tunability with high precision, surface modification, and solution processing. Surface modification of the TOPO capped QDs were performed via ligand exchange method optimized in this work to prepare mercaptoacids and sulfide (S2−) capped QDs. Strong photoluminescence quenching and enhanced trap-state emission were observed with these surface ligands, having the most pronounced effect with S2−, attributed to hole trapping at surface sites introduced by the ligands, which is evaluated by the extent of luminescence quenching. Additionally, the acoustic phonon modes of the CdSe QDs with these surface ligands were monitored using Raman spectroscopy, as the acoustic phonon vibrations influence both trapping processes and photoluminescence linewidth. A mass loading effect was observed in the acoustic phonon mode frequencies, with lower phonon frequencies noted in heavier surface ligands due to the mechanical strain caused by the surface ligands.
The S2− capped QDs, exhibiting the strongest effect on photoluminescence and phonon properties, were subjected to further investigation of exciton and multiexciton dynamics in comparison to the TOPO capped QDs. Intensity-dependent transient absorption (TA) spectroscopy was performed to evaluate the spectral and dynamical features of excitons and multiexcitons using a global fitting method based on Markov Chain Monte Carlo (MCMC) sampling. Through this approach, multiexcitons up to tetraexcitons were examined by fitting the Auger recombination model. The multiexciton lifetimes in both TOPO and S2− capped QDs exhibit a cubic relationship with QD radius, consistent with previous literature. However, longer multiexciton lifetimes were observed in S2− capped QDs compared to TOPO capped QDs, attributed to suppression of Auger recombination due to reduced carrier wavefunction overlap, originating from strong surface hole trapping in the S2− capped QDs. Due to this, the multiexciton binding energies also were reduced in the S2− capped QDs resulting in significant spectral difference compared to the respective TOPO capped QDs.
Moreover, the exciton and multiexciton properties of TOPO and S2− capped QD thin films were also investigated through intensity-dependent TA spectroscopy. Thin films were fabricated by drop casting the colloidal QDs. In S2− capped QD thin films, a strong electronic coupling between the close packed QDs were observed resulting in a significant red shift in the photoluminescence peak position, while this effect is minimal in the TOPO capped QDs as prevented by the steric hindrance caused by the long-chained TOPO ligands keeping the QDs apart. The intensity-dependent TA spectra and dynamics of the TOPO capped QD thin films follow a similar multiexciton recombination model as compared to the respective QDs in solution. However, in the S2− capped QD thin films, the typical spectral signatures of multiexciton recombination were not observed in contrast to the corresponding solutions. Rather, the unique spectral shapes and kinetic traces in the S2− capped QD thin films suggest that the multiexcitons undergo exciton delocalization in the ultrafast time regime dominating over the Auger recombination process.
Furthermore, the fabrication of QD thin films embedded in a porous silica matrix is demonstrated as a novel approach for the development of thin film materials containing immobilized QDs for optoelectronic applications. Two methods were employed for this purpose: in-situ growth of CdSe NCs in a porous silica matrix and infiltration of pre-synthesized CdSe QDs into the porous matrix. The Successive Ionic Layer Adsorption and Reaction (SILAR) method was employed for the in-situ growth of CdSe NCs within the porous silica matrix. However, the uncontrolled growth observed in the SILAR method results in a broad distribution of NC sizes, which in turn gives rise to broad absorption features and the absence of photoluminescence. This is attributed to the high density of defect states present in the material. To address this challenge, QDs were synthesized via the hot-injection method and infiltrated into the porous matrix through the pores of the silica matrix. The infiltration was achieved in two ways: by drop casting a QD solution on the porous layers or by soaking the porous layers in a QD solution. The QDs infiltrated via these two methods retain their luminescent properties, resulting in thin films of high quality and well-defined immobilized QDs suitable for integration into optoelectronic devices.
The findings of this thesis contribute to the advancement of QD-based optoelectronic applications by providing insights and avenues for the development of novel materials
Morphologische Charakterisierung feiner Gesteinskörnung mittels Computertomographie zur Optimierung von Mörtelzusammensetzungen
Get PDFRessourcenschonung und die Kreislaufführung von Rohstoffen stellen zwei zentrale Herausforderungen für die Beton- und Mörtelherstellung dar. Vor diesem Hintergrund bietet sich der vermehrte Einsatz von Brechsanden an, insbesondere von rezyklierten Brechsanden. Charakteristisch für diese Materialien ist ihre im Vergleich zu natürlichem Sand abweichende Kornform und Eckigkeit. Diese zwei morphologischen Eigenschaf-ten haben wiederum Einfluss auf die Eigenschaften von Mörtel und Beton. Ziele dieser Arbeit sind die morphologische Charakterisierung von Gesteinskörnungen mittels Com-putertomographie sowie die Steuerung von Mörteleigenschaften anhand dieser morpho-logischen Kenngrößen.
Im Rahmen dieser Arbeit wird in einem ersten Schritt unter Berücksichtigung einer tolerablen Messungenauigkeit ein Verfahrensablauf zum Tomographieren von feinen Gesteinskörnungsproben mit Korngrößen kleiner 2 mm als lose Schüttung entwickelt. Als Verfahren zur Trennung von sich berührenden Körnern im Zuge der Bildbearbeitung kommt die adaptive H-Extrematransformation in Kombination mit Wasserscheiden-transformation zum Einsatz. Es zeigt sich, dass die automatisierte Vorgabe der vom Nutzer vorzugebenden Eingangsgrößen für dieses Verfahren anhand der Schüttdichte möglich ist. Basierend auf diesem automatisierten Verfahrensablauf kann ein Set aus vier Kenngrößen in einem weiteren Schritt zur morphologischen Charakterisierung von Schüttungen identifiziert werden, die sowohl die Ausprägung als auch Verteilung von Kornform und Eckigkeit innerhalb der Schüttung beschreiben. Die morphologische Charakterisierung von zehn Schüttungen natürlichen und rezyklierten Ursprungs und unterschiedlicher Korngrößenzusammensetzung findet in einem folgenden Schritt Ein-gang in eine multiple lineare Regressionsanalyse zur Untersuchung des Einflusses dieser Kenngrößen auf Frisch- und Festmörteleigenschaften. Gegenstand der Untersu-chung sind die dynamische Viskosität, Fließgrenze, Setz- und Setzfließmaß sowie Aus-breitmaß als Frischmörteleigenschaften sowie der dynamische Elastizitätsmodul, die Biegezug- und Druckfestigkeit als Festmörteleigenschaften.
Im Hinblick auf die Mörteleigenschaften zeigt sich ein komplexer Einfluss sowohl der Kornform als auch Eckigkeit, der mit anderen Parametern der Mörtelzusammensetzung wie dem Verhältnis von Wasser zu Zement, dem Massenverhältnis von Bindemittelleim zu Gesteinskörnung sowie der Korngrößenzusammensetzung interagiert. Eine erhöhte Länglichkeit von Körnern kann sowohl zu einer Verbesserung der Verarbeitbarkeit füh-ren, als auch zur Steigerung des Entmischungsrisikos. Im Hinblick auf den Einsatz von Brechsand kann eine Verringerung der Eckigkeit bedingt durch den Aufbereitungspro-zess eine Verbesserung der Verarbeitbarkeit ermöglichen, während eine erhöhte Eckig-keit zu einer Steigerung von Biegezug- und Druckfestigkeit führen. Die Ergebnisse der Regressionsanalyse dienen als Grundlage für die Optimierung von Mörtelzusammen-setzungen mit erhöhtem Brechsandanteil. Auch wenn die Vorgaben hinsichtlich der angestrebten Druckfestigkeit nicht vollumfänglich eingehalten werden können, zeigt sich, dass die Berücksichtigung der Auswirkungen morphologischer Eigenschaften der Gesteinskörnung zu einer Erhöhung des Brechsandanteils beitragen kann.Conservation of natural resources as well as cycle management of raw materials are two major challenges of concrete and mortar production. The increasing use of crushed sands, especially recycled crushed sands, could be an approach for solving these prob-lems. A characteristic property for these materials is their deviating shape and angulari-ty in comparison to natural sand. These morphological properties have in turn an influ-ence on the properties of mortar and concrete. Aims of this study are therefore the morphological characterization of aggregates using micro-computed tomography and the control of mortar properties using these morphological characteristics.
In a first step an imaging procedure for packed beds of fine aggregates with particle size below 2 mm is developed considering an appropriate measurement accuracy. For separating touching particles during image processing adaptive h-extrema transform in combination with watershed transform is used. Results indicate that an automatic speci-fication of user-defined input parameters for h-extrema transform is possible based on packing density. Based on this automated process flow, a set of four parameters is identified for morphological characterization of bulk materials taking into account the strength as well as the distribution of shape and angularity features within the sample. The morphological characterization of ten natural or recycled aggregate samples with varying particle size distribution are the input for a multiple linear regression analysis to examine the influence of these characteristics on fresh and hardened mortar properties. Fresh mortar properties are characterized by dynamic viscosity, yield stress, slump, slump flow, and flow table test while hardened mortar properties are characterized by dynamic modulus of elasticity, bending strength, and compressive strength.
With respect to mortar properties results show a complex influence of shape and angu-larity that interacts with other properties of the mortar composition like the mass ratio of water to cement, the mass ratio of binder to aggregates, and the particle sieve size distribution. While an increasing elongation of particles favours a better workability sim-ultaneously the risk of segregation increases. With respect to the use of increasing amounts of crushed sands a reduction of angularity while processing the material could result in a better workability. At the same time an increased angularity of particles re-sults in increased bending and compressive strength. The results of regression analysis are used for optimizing mortar compositions with increased amounts of crushed sands. Although specifications with respect to compressive strength are not fully met the ex-perimental results show that the consideration of morphological properties of aggregates can contribute to an increase in recycled fines content
Novel Pharmacological Approaches to Target Mitochondrial Metabolism and DNA Damage Response in Colorectal Cancer and their Synergism with Established Chemotherapeutics
Get PDFColorectal cancer (CRC) is one of the most frequently diagnosed malignant diseases worldwide and occurs at an alarmingly increasing rate especially in young adults. Ongoing progress in the field of cancer pharmacology has provided new treatment options in recent years, particularly in the form of immunotherapy. Yet, standard chemotherapy has been based on cytostatic agent 5-fluorouracil (5-FU) for over five decades with the more recent addition of leucovorin (LV), oxaliplatin (OXA) and irinotecan (IT). Established chemotherapeutic approaches mainly rely on the induction of DNA damage, which particularly affects rapidly growing cancer cells. The altered tumor metabolism and the DNA repair machinery have more recently been identified as potential drug targets in CRC.
The assessment of novel anticancer drugs for CRC with a focus on induction of DNA damage, inhibition of DNA repair and disruption of mitochondrial metabolism as potential mechanisms constituted the objective of this work. For this purpose, this PhD thesis aimed to evaluate the applicability of antitumor agents which are already clinically used in the treatment of other cancer entities, including the metabolic inhibitor devimistat and the poly (ADP-ribose)-polymerase inhibitors (PARPi) olaparib and veliparib. In addition, the biological activity of novel chemical compounds for CRC treatment was analyzed. The investigated substances were either derived from natural sources (merosesquiterpenes isolated from marine sponges) or chemically synthesized as potential PARPi. CRC cell lines with varying mutational status were applied as surrogates representing the diversity of this disease and experiments with transient genetic knockdown or isogenic knockout cell lines were performed to further detail the pharmacological mode of action of the tested compounds. In addition, murine intestinal tumor organoids and primary organoids as well as patient-derived short-term cultures were used to elucidate the tumor cell specificity of the observed effects. An array of methods was utilized to investigate the underlying cell death mechanisms, including flow cytometry, confocal microscopy, western blot and gene expression analysis. The cytotoxicity of the mitochondrial disruptor devimistat and of PARPi in combination with established CRC chemotherapeutic 5-FU, OXA and IT was analyzed in CRC cell lines to identify a potential synergy. Finally, devimistat was applied either as monotreatment or in combination with IT in a murine xenograft model to evaluate the therapeutic efficacy in vivo.
At first, the tumor cell specific cytotoxicity of the metabolic inhibition by devimistat was revealed, independent of genetic and epigenetic alterations in CRC cell lines and murine tumor organoids. A reduced oxygen consumption rate (OCR), attenuated mitochondrial activity and induction of reactive oxygen species (ROS) were identified as underlying mechanisms, resulting in p53-independent induction of CRC cell death. Synergistic anticancer activity was achieved by combination treatment with the chemotherapeutic agents IT and 5-FU, as demonstrated by a Combenefit-model and Chou-Talalay analyses. Mechanistically, synergism was based on downregulation of antiapoptotic Bcl-2 proteins and posttranslational accumulation of the proapoptotic protein Bim, as demonstrated by transient genetic knockout experiments. Antitumor efficacy and synergistic activity with IT were confirmed by applying human CRC cells in a xenograft mouse model.
In the second study, a compound library comprised of 11 merosesquiterpenes isolated from marine sponges was analyzed and ilimaquinone (IQ), dactylospontriol (DS) and smenospongine (SP) were identified as the most cytotoxic compounds in a panel of three human CRC cell lines. On the mechanistic level, all three compounds induced DNA strand breaks and upregulated the DNA damage response (DDR) irrespective of the mutational status of p53, resulting in cell cycle arrest and activation of the mitochondrial apoptosis pathway. Furthermore, merosesquiterpenes induced pronounced cytotoxicity in murine intestinal tumor organoids, underlining their potential in CRC treatment.
In the third study, the applicability of established and novel PARPi in the treatment of DNA repair deficient and proficient CRC was investigated. Therefore, the two novel compounds X17613 and X17618, which inhibit PARP-1 activity in sub-micromolar concentrations, were identified based on an in silico and in vitro screening of a library of novel 3,4-bifunctionalized and -bridged indole compounds. In contrast to clinically applied PARPi olaparib and veliparib, both compounds showed no cytotoxicity in PARP-1-deficient and -proficient CRC cell line pairs. In accordance, absence of γH2AX formation and low PARP-1 trapping activity compared to olaparib were identified after treatment with X17613 and X17618. In the last step, sensitization of BRCA2 (breast cancer type 2 susceptibility protein)-deficient CRC cells to IT was demonstrated for X17613.
In conclusion, our research assessed the potential of novel therapeutic approaches for CRC treatment, including mitochondrial disruption by the clinically applied metabolic inhibitor devimistat, inhibition of DNA repair by novel PARP-1 inhibitors and DNA damage induction by marine sponge toxins. Our results provide insight into the underlying molecular mechanisms, the potential synergistic activity with clinically applied drugs and the impact of common CRC mutations on sensitivity to guide further development of new therapeutic approaches
Influence of cryogenic turning strategies on the surface morphology and resulting wear behavior of metastable AISI 347 austenitic stainless steel
Get PDFCryogenic turning of metastable austenitic stainless steels can improve wear resistance of the resulting surface due to the phase transformation of γ-austenite into α’- and/or ϵ-martensite in the near surface layer. By using a cryogenic two-step turning process, the amount of deformation-induced α’-martensite in the subsurface regime can be further increased. To determine the influence of the implemented and optimized two-step turning strategy on the tribological properties of countersurfaces for radial shaft seals, an evaluation of wear behavior of the shaft seal countersurface as well as microstructural analyses in subsurface regime is presented and compared to the cryogenic single step turning process. The results show that not only the integral phase transformation in the overall subsurface region, but also the local phase distribution plays an important role when it comes to the surface performance in tribological applications
Auditory Interference in Human Cognition
Get PDFThe Irrelevant Sound Effect (ISE) describes the phenomenon that serial recall of visually presented verbal items, such as digits, letters, or nouns, is impaired by the presence of specific task-irrelevant background sounds. This effect highlights the auditory system’s inherent tendency to automatically process environmental stimuli, regardless of their relevance to the current task. Understanding the ISE is crucial for both theoretical and practical reasons, as most adults and children work or study in noisy environments.
Theoretical explanations of the ISE vary. Some theories suggest that background sounds divert attention away from the to-be-remembered items, while others propose that the effect arises from competing seriation processes between the background sounds and the serial order of the memory material. Additionally, the ISE might impact the short-term memory system by disrupting the phonological representations of verbal items in the phonological store.
Research on the ISE has revealed inconsistent findings between children and adults, indicating that the effect may differ across age groups. It is often argued that children might be more vulnerable to task-irrelevant background sounds due to their less developed attention mechanisms. Moreover, while behavioral studies consistently demonstrate the detrimental impact of the ISE on performance, the neurophysiological mechanisms underlying this effect remain less well understood. Investigating event-related potential (ERP) components
such as the N1, P3a, and MMN can provide valuable insights into various stages of auditory cognitive processing, from early processing demands, to the brain’s pre-attentive auditory discimination mechanisms and automatic orienting responses. Exploring both age-related variations and the neurophysiological mechanisms of the ISE could offer deeper insights into how auditory stimuli influence attention and cognitive performance. The overall purpose of this thesis is to disentangle the roles of seriation, phonological processing and attention capture in the ISE, based on how this effect is evoked. It outlines
various theoretical explanations for the ISE, highlights inconsistencies in its impact across different age groups, and underscores the importance of investigating both behavioral and neurophysiological aspects to gain deeper insights into how auditory distractions affect serial order retention.
In the present thesis, behavioral experiments (Studies 1–4) combined with EEG methodology (Studies 5–6) were performed to investigate the roles of seriation, phonological processing and attention in the ISE
Towards Mental Imagery-Aware Systems using Physiological Sensors and Machine Learning
Get PDFContext-aware systems use their functional environment to provide relevant information or functions to their users.
Currently available context-aware systems, for example, advanced driving assistant systems or mobile learning applications, primarily rely on physical activity or direct user input. This thesis makes the next step and introduces the concept of mental-imagery-aware systems that could enable a more sophisticated perception of users. Mental imagery includes multiple dimensions, whereas this thesis focuses on the two most common forms occurring in daily life: mind-wandering and spatial imagery.
Mind-wandering-aware systems are especially relevant in learning settings, where mind-wandering itself is primarily associated with low learning performance. This work proposes a novel approach for detecting episodes of mind wandering using physiological sensors and machine learning methods. For the first time, it is demonstrated that the electrodermal activity is sufficient for classifying the episodes of mind wandering with outstanding classification accuracy. The fusion of eye-tracker and electrodermal activity data additionally improves the classification performance of the machine learning algorithms.
Next, this thesis introduces a prospect towards spatial imagery and engagement-aware systems. With the rapid increase of automation levels in serial vehicles, there is a need for a better understanding of its impact on spatial imagery required for successful navigation. For this purpose, a highly immersive driving simulation system with an integrated eye-tracking system is deployed. With a real-time application in mind, the proxy of spatial imagery ``engagement with a driving task'' is used to infer the driver's presence in the driving loop. The work demonstrates the feasibility of the eye-tracking features combined with the Gradient boosting algorithm to recognize the disengagement of the driver from the driving loop outperforming the state-of-the-art. Finally, this work pave the wave for the driver's engagement recognition using a UWB-radar and deep learning algorithms. Six driving activities are recorded with a UWB radar and classified using state-of-the-art deep learning models showing promising outcomes
Zur Dynamik von Humor in Organisationen
Get PDFDie vorliegende Literaturarbeit untersucht Humor im Hinblick auf seinen Einsatz in Organisationen. Dabei betrachtet sie aus einer Metaebene heraus, welche Potenziale sich aufgrund seiner wissenschaftlich bestätigten positiven Wirkungen für Organisationen ergeben können. In diesem Zusammenhang werden die Faktoren identifiziert, die sich im Umgang mit Humor in Organisationen als kritisch zeigen und die Potenzialentfaltung behindern können. Anhand dieser
Ergebnisse soll gezeigt werden, wie Humor erfolgreich in Organisationen implementiert werden kann. Ziel dieser Arbeit ist es, Humor als Förderfaktor in Organisationen sichtbar zu machen und Organisationen dahingehend zu sensibilisieren, was im Umgang mit Humor benötigt wird, um ihn
erfolgreich zu implementieren. Dabei werden auch seine Grenzen diskutiert
Entwicklung einer Prüfmethodik für die Bestimmung kurzzeit-dynamischer Materialkennwerte von endlosfaserverstärkten Thermoplasten
Get PDFIn dieser Arbeit wurde eine Prüfmethodik zur einheitlichen Durchführung kurzeit-dynamischer Zugversuche an endlosfaserverstärkten Thermoplasten entwickelt. Sie ermöglicht die Ermittlung von vergleichbaren und reproduzierbaren Materialkennwerten. Im Kern wurde eine taillierte Probekörpergeometrie optimiert und experimentell validiert, die ohne Lasteinleitungselemente robust gegenüber ungültigem Versagen ist und Prüfungen bis zu einer Dehnrate von 100 s-1 ermöglicht. Für die experimentelle Materialprüfung wurden die Wichtigkeit und Grenzen der Messsignalsynchronisation aufgezeigt sowie eine Filtermethodik und Einspannbedingungen definiert. Als Erweiterung zu Validierungskriterien der Materialprüfung wurde ein Kohärenzkriterium zur Bewertung von Signalverläufen unterschiedlicher Messmittel entwickelt. Des Weiteren ermöglicht die Analyse einer Lasteinleitungsfrequenz die Vorhersage von Kontaktverlusten im Lastpfad der Prüfmaschine. Abschließend wurde ein analytisches Metamodell des dehnratenabhängigen Materialverhaltens aufgebaut. Hierdurch können erfolgreich Materialdaten bei konstanten Dehnraten abgeleitet werden.In this work, a test methodology for the uniform performance of short-time dynamic tensile tests on continuous fiber-reinforced thermoplastics has been developed. It enables the determination of comparable and reproducible material properties. In its center, a tapered specimen geometry was optimized and experimentally validated that is robust to invalid failure without load introduction elements and allows testing up to a strain rate of 100 s-1. For experimental material testing, the importance and limitations of measurement signal synchronization were demonstrated, and a filter methodology as well as clamping conditions were defined. As an extension to validation criteria for material testing, a coherence criterion was developed for the evaluation of signal characteristics of different measuring devices. Furthermore, the analysis of a load introduction frequency allows the prediction of contact losses in the load path of the testing machine. Finally, an analytical metamodel of the strain rate dependent material behavior was developed. This allows material data to be successfully derived at constant strain rates
Kritische Analyse der Eignung von Dimedon zur Sulfensäuredetektion und der Relevanz von Wasserstoffperoxid für die Wirkung von Antimalariamitteln
Get PDFZur nukleophilen Detektion von Sulfensäuren werden üblicherweise Dimedon oder Dimedon Derivate eingesetzt. Allerdings haben qualitative Untersuchungen gezeigt, dass Dimedon ebenso mit cyclischen Sulfenamiden reagiert. Unter physiologischen Bedingungen muss Dimedon zudem mit millimolaren Glutathionkonzentrationen konkurrieren, welches ebenfalls ein starkes Nukleophil ist. Um diese kompetitiven Reaktionen quantitativ zu analysieren, wurden die Reaktionskinetiken eines cyclischen Sulfenamid-Modellpeptids (SA) und der Sulfensäure von Glutathion mit Dimedon und Glutathion bestimmt. Da das cyclische Sulfenamid bei niedrigen pH-Werten stabilisiert war und keine Ringöffnung zur Sulfensäure stattgefunden hat, konnte eine direkte Reaktion mit Dimedon eindeutig nachgewiesen werden. Die kinetischen Analysen ergaben vergleichbare Geschwindigkeitskonstanten für die Reaktionen von Dimedon mit SA bzw. Dimedon und der aus SA gebildeten Sulfensäure. Die Geschwindigkeiten der Reaktionen des Konkurrenz-Nukleophils Glutathion mit SA oder der Sulfensäure übertrafen die Reaktionsgeschwindigkeiten mit Dimedon jedoch um mehrere Größenordnungen. Der bisher scheinbar erfolgreiche Einsatz von Dimedon als Detektionsprobe für Sulfensäuren in vivo muss daher auf alternative Reaktionswege oder auf die Detektion kinetisch konkurrierender Redoxspezies zurückzuführen sein. (Anmerkung: übersetzt aus Bischoff E, Lang L, Zimmermann J, Luczak M, Kiefer AM, Niedner-Schatteburg G, Manolikakes G, Morgan B, Deponte M. Glutathione kinetically outcompetes reactions between dimedone and a cyclic sulfenamide or physiological sulfenic acids. Free Radic Biol Med. 2023 Nov 1; 208:165-177. DOI:10.1016/j.freeradbiomed.2023.08.005. Epub 2023 Aug 3. PMID: 37541455.)
Der zweite Teil dieser Arbeit beschäftigt sich mit der oxidativen Stress-Hypothese im Malaria-Parasiten Plasmodium falciparum. Die Gesamtheit aus Hämoglobinabbau, Wachstum und DNA-Synthese verursachen eine metabolisch generierte oxidative Belastung. Durch effiziente Reduktionsmittel wie z. B. Thioredoxine oder Glutathion kann der Parasit das Redox-Gleichgewicht aufrechterhalten, er hat eine physiologische STRESSistance. Es wird außerdem vermutet, dass Superoxidanionen und Wasserstoffperoxid eine bedeutende Rolle im Wirkmechanismus von Antimalariamitteln spielen. In dieser Arbeit sollten kompartimentspezifische Anpassungseffekte oder cytotoxische Effekte, verursacht durch Wasserstoffperoxid untersucht werden. Hierfür wurden transgene Parasiten verwendet, die das heterologe Redoxenzym RgDAAO im Cytosol, der Verdauungsvakuole oder der mitochondrialen Matrix bzw. dem mitochondrialen Intermembranraum enthalten. Durch exogene Zugabe von D-Aminosäuren konnten die Wasserstoffperoxidkonzentrationen kompartimentspezifisch erhöht werden. Zudem war die gebildete Enzymmenge an RgDAAO in Abhängigkeit der Konzentration des Selektionsantibiotikums Blasticidin regulierbar. Zu jedem Konstrukt wurde als Negativkontrolle ein identisches Plasmid mit der Punktmutation R285A generiert und transfiziert, was zur Bildung einer inaktiven Form der RgDAAO im Parasiten führte. Im ersten Schritt konnte die erfolgreiche Bildung der RgDAAO für die verschiedenen 3xHA-getaggten Konstrukte mittels Westernblotanalyse gezeigt werden. Auch die Titrierbarkeit des Systems durch Blasticidin konnte mittels Westernblotanalyse nachgewiesen werden, für den die Parasiten mit unterschiedlichen Blasticidin-Konzentrationen zwischen 4 und 50 µg/ml behandelt wurden. Ab 50 µg/ml Blasticidin kam es zu cytotoxischen Effekten. Die Lokalisation des heterologen Redoxenzyms RgDAAO in den vorgesehenen Kompartimenten wurde mittels Immunofluoreszenzmikroskopie überprüft. Die korrekte Lokalisation wurde für die Kompartimente Cytosol und die mitochondriale Matrix beobachtet, wohingegen trotz erhöhtem Selektionsdruck von 15 µg/ml Blasticidin, keine RgDAAO in der Verdauungsvakuole und dem mitochondrialen Intermembranraum nachgewiesen werden konnte. Schließlich wurden erste IC50-Messungen mit Paraquat als Positivkontrolle und verschiedenen D-Aminosäuren zur kompartimentspezifischen Erhöhung der Wasserstoffperoxidkonzentrationen durch das Redoxenzym RgDAAO durchgeführt. Es konnten kompartimentspezifische Anpassungseffekte und potenzielle cytotoxische Effekte beobachtet werden