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Vacancy formation energy as a descriptor of the exfoliability of MAX phases to MXenes
No full textA thermodynamic descriptor for chemical exfoliation of MXenes remains elusive, primarily because the process is dynamic and MXenes are inherently metastable. Here we show that vacancy formation energies provide such a descriptor. Synthesized MXenes exhibit positive vacancy formation energies for M and X elements, while non-synthesized MXenes show negative energies for M or X elements, or both. Similarly, exfoliable precursor MAX phases are characterized by negative vacancy formation energies for A elements. Using this correlation, we identify seven hitherto unreported MXenes as potentially synthesizable in HF at pH = 2. At higher pH, additional unknown MXenes are identified as locally stable together with their exfoliable MAX phases but remain inaccessible in HF, highlighting the need for alternative alkaline etchants. The exfoliable precursor MAX phases are predominantly Al-based. The proposed descriptor is transferable to other 2D materials such as MBenes and may be adapted to other acidic or alkaline etchants
40 Jahre Wirtschaftsinformatik an der TU Darmstadt
Get PDFIm Zuge der Etablierung eines Informatikstudiums in Deutschland entstand Anfang der 1970er Jahre innerhalb der Wirtschaftswissenschaften der Wunsch nach einem eigenen EDV-basierten Studiengang. An der TH Darmstadt wurde 1972 die Einrichtung eines Studiengangs Wirtschaftsinformatik beschlossen. Initiator war der damalige BWL-Professor Hartmut Wedekind (gleichzeitig Zweitmitglied im Fachbereich Informatik). 1974 wurde eine Kommission gebildet, mit dem Auftrag, eine Studienordnung für einen künftigen Studiengang Wirtschaftsinformatik auszuarbeiten. Die Federführung lag dabei beim Fachbereich Rechts- und Wirtschaftswissenschaften in Kooperation mit dem Fachbereich Informatik
El Lissitzky: Architekt - Künstler - Visionär
Get PDFWenn man den Namen El Lissitzky hört, kommt einem dieser merkwürdig vertraut vor. Und nicht nur Darmstädter Architekturstudierende sollten nun hellhörig werden. El Lissitzky (vollständiger Name Eliezer (Lazar) Markovič Lisickij, geboren am 22. November
1890 in Potschinok, gestorben am 30. Dezember 1941 in Moskau) war ein russischer Student jüdischen Glaubens, der mit Unterbrechungen von 1910/11 bis 1914 an der damaligen TH Darmstadt Architektur studierte
Geheimrat Thiel und die »Landwirtschaftliche Schule« am Polytechnikum Darmstadt
Get PDFIn der Zeit der industriellen Hochkonjunktur durchlebte auch die Vorgängereinrichtung der Technischen Hochschule Darmstadt, die »Technische Schule«, einen Wandel. Aufgrund drastisch sinkender Studentenzahlen konnte ihr Erhalt nur durch die Reorganisation bestehender Strukturen gewährleistet werden. Die Technische Schule
wurde im Herbst 1869 zur Großherzoglich Hessischen Polytechnischen Schule erhoben. Das Polytechnikum war einer Universität gleichgestellt, bildete in technischen Fächern aus und bereitete auf das Lehramt für Mathematik und Naturwissenschaften vor. Die Anstalt war in sechs Schulen, darunter auch die Landwirtschaftliche Schule, organisiert
Zur Bedeutung des kritischen Anthropomorphismus in der holistischen Umweltethik nach Martin Gorke. Der Weg zu reflektierter Handlungsorientierung statt Begründungsdilemmata
Get PDFDie Masterarbeit untersucht die Rolle des „kritischen Anthropomorphismus“ im Rahmen der holistischen Umweltethik Martin Gorkes. Im Zentrum steht die Frage, wie sich ein Perspektivwechsel vollziehen lässt, der über anthropozentrische und pathozentrische Ansätze hinausgeht und der gesamten Natur – inklusive unbelebter Entitäten – moralische Berücksichtigungswürdigkeit zuspricht. Alexander Geis entwickelt in Auseinandersetzung mit Gorkes Konzept des Eigenwerts der Natur eine theoretische Fundierung und praxisnahe Ausgestaltung dieses Perspektivwechsels. Der kritische Anthropomorphismus wird dabei als methodisches Mittel vorgestellt, um über Analogiebildung und Selbstreflexion zu einer reflektierten, empathischen Handlungsorientierung gegenüber der Mitwelt zu gelangen. Die Arbeit beleuchtet sowohl die erkenntnistheoretischen Voraussetzungen als auch praktische Herausforderungen eines solchen Ansatzes und diskutiert die Relevanz für die Erweiterung der Moralgemeinschaft – bis hin zur Berücksichtigung künstlicher Entitäten
Multiple phenotypic traits as triggers of host attacks towards ant symbionts: body size, morphological gestalt, and chemical mimicry accuracy
Get PDFBackground: Ant colonies are plagued by a diversity of arthropod guests, which adopt various strategies to avoid or to withstand host attacks. Chemical mimicry of host recognition cues is, for example, a common integration strategy of ant guests. The morphological gestalt and body size of ant guests have long been argued to also affect host hostility, but quantitative studies testing these predictions are largely missing. We here evaluated three guest traits as triggers of host aggression—body size, morphological gestalt, and accuracy in chemical mimicry—in a community of six Eciton army ant species and 29 guest species. We quantified ant aggression towards 314 guests in behavioral assays and, for the same individuals, determined their body size and their accuracy in mimicking ant cuticular hydrocarbon (CHC) profiles. We classified guests into the following gestalts: protective, myrmecoid, staphylinid-like, phorid-like, and larval-shaped. We expected that (1) guests with lower CHC mimicry accuracy are more frequently attacked; (2) larger guests are more frequently attacked; (3) guests of different morphological gestalt receive differing host aggression levels.
Results: Army ant species had distinct CHC profiles and accuracy of mimicking these profiles was variable among guests, with many species showing high mimicry accuracy. Unexpectedly, we did not find a clear relationship between chemical host similarity and host aggression, suggesting that other symbiont traits need to be considered. We detected a relationship between the guests’ body size and the received host aggression, in that diminutive forms were rarely attacked. Our data also indicated that morphological gestalt might be a valuable predictor of host aggression. While most ant-guest encounters remained peaceful, host behavior still differed towards guests in that ant aggression was primarily directed towards those guests possessing a protective or a staphylinid-like gestalt.
Conclusion: We demonstrate that CHC mimicry accuracy does not necessarily predict host aggression towards ant symbionts. Exploitation mechanisms are diverse, and we conclude that, besides chemical mimicry, other factors such as the guests’ morphological gestalt and especially their body size might be important, yet underrated traits shaping the level of host hostility against social insect symbionts
Sequence-specific response of collagen-mimetic peptides to osmotic pressure
Get PDFNative collagen molecules usually contract upon dehydration, but the details of their interaction with water are poorly understood. Previous molecular modeling studies indicated a spatially inhomogeneous response, with a combination of local axial expansion and contraction. Such sequence-dependent effects are difficult to study with native collagen. In this article, we use collagen-mimetic peptides (CMPs) to investigate the effect of osmotic pressure on several collagen-mimetic sequences. Synchrotron x-ray diffraction combined with molecular dynamics simulations shows that CMPs pack differently depending on osmotic pressure and exhibit changes in the helical rise per residue of individual molecules. Infrared spectroscopy reveals that osmotic pressure affects the stability of the triple helix through changes in triple helix-stabilizing hydrogen bonds. Surprisingly, CMPs with the canonical collagen sequence glycine–proline–hydroxyproline are found to elongate upon dehydration, while sequence modifications are able to reverse this tendency. This strongly suggests that the overall contraction of native collagen molecules is not programmed into the canonical sequence but is specific to local amino acids that substitute for proline or hydroxyproline along the protein chain. Collagen is an essential protein in mammalian extracellular tissues and a better understanding of its mechanical function is important both from a materials science and from a biomedical viewpoint. Recently, collagen has been shown to contract along the fibre direction when subjected to osmotic stress, a process that could play important roles in strengthening bone and in developing tissue tension during extracellular matrix development. The present work uses collagen-like short peptides to show that the canonical collagen sequence is not responsible for this contraction. The conclusion is that the collagen amino acid sequence must have evolved to include guest sequences within the canonical glycine-proline-hydroxyproline repeat that provide the observed contractility.
Impact statement: Collagen is an essential protein in mammalian extracellular tissues and a better understanding of its mechanical function is important both from a materials science and from a biomedical viewpoint. Recently, collagen has been shown to contract along the fibre direction when subjected to osmotic stress, a process that could play important roles in strengthening bone and in developing tissue tension during extracellular matrix development. The present work uses collagen-like short peptides to show that the canonical collagen sequence is not responsible for this contraction. The conclusion is that the collagen amino acid sequence must have evolved to include guest sequences within the canonical glycine-proline-hydroxyproline that provide the observed contractility
The home bias and the local bias: A survey
Get PDFThe home bias like the disposition effect is a well-researched economic phenomenon in investor behaviour which has been examined in finance journal articles for decades. While there is little doubt about the existence of the bias, its magnitude varies across countries and investor groups. The home bias has to be regarded as a multifactorial phenomenon, a combination of numerous causes which all synergistically contribute. In contrast to other biases the home bias can at least partially be explained by reasons beyond irrational investor behaviour. While institutional restrictions play a minor role, informational asymmetries and superior information of domestic investors are important factors. Thus, the performance of investments may well benefit from a home bias, and the bias then no longer would be a puzzle but rather rational behaviour as a lower diversification level may lead to higher returns. The contemporary understanding of the home bias gains in relevance as the ongoing political debate in Germany has to clarify an institutional framework for long-run retirement savings plans of private households based on equity investments
Characterization of the FK506 binding protein 51-Glucocorticoid Receptor-p23 complex in living cells
Get PDFFKBP51 is a co-chaperone known for its inhibitory role in GR signaling. Besides FKBP51, there are multiple other co-chaperones known to interact with the GR, such as the small protein p23 which ensures the correct folding and activity of the GR. Understanding the complex formation and protein-protein interactions in these complexes are crucial for comprehending the regulation and activity of proteins.
In this work I analyzed the interaction of FKBP51 and p23 as well as the interaction of the GR and p23.
I utilized photoinducible crosslinking which relies on the incorporation of an unnatural amino acid at the surface of a protein. This unnatural amino acid can form a covalent bond with another protein in the vicinity upon UV irradiation. The covalent bond formation can then be analyzed by e.g. Western Blotting and deliver information about interaction sites between two proteins.
I used this method in this work to show that (i) FKBP51 and p23 interact in dependence of Hsp90; (ii) the FKBP51-p23-Hsp90 complex can exist independently of the GR; (iii) the interaction of FKBP51 and p23 can be partially abolished by addition of the GR; (iv) FKBP51, GR and p23 can participate in a Hsp90 associated complex; and (v) FKBP51 enhances the GR p23 interaction while FKBP52 does not.
Taken together, I showed the existence of a FKBP51-GR-p23-complex for the first time in cellulo.
In addition to the data about FKBP51-p23 interactions, I also provided novel insights into the GR p23 interaction: I showed that (i) the GR carries two distinct interaction sites with p23; (ii) each interaction hotspot binds to a different region of the C-terminal domain of p23; and (iii) the C-terminal tail of p23 is necessary to enhance the GR activity, even though it is not as relevant for the interaction of the probed GR residues with p23.
Overall, the data about the FKBP51-p23 and FKBP51-GR-p23 interaction I gathered provide additional information about the structures of the mentioned complexes in cellulo. This will prove useful in the future for further understanding of the GR regulation and ultimately may result in novel ways to manipulate the GR.
In addition to the FKBP51-GR interaction, I also investigated the role of FKBP51 in NF κB signaling. I investigated multiple cell lines, different readouts and stimuli and was not able to determine an effect of FKBP51 degradation or inhibition on the NF κB activity in the chosen context
Impact of S-sulfocysteine on Chinese hamster ovary cells
Get PDFIn the biopharmaceutical industry, Chinese hamster ovary (CHO) cells are the primary workhorse for therapeutic protein production (monoclonal antibodies, fusion proteins) in large-scale processes — constantly undergoing optimization to increase the product yield. In this context, optimized cell culture media and feeds are critical and often rely on cysteine (Cys) analogues to overcome the Cys-related stability and solubility issues at neutral pH. Previously, the Cys analogue, S-sulfocysteine (SSC), was successfully applied in cell culture, implying the SSC uptake, metabolization and biological activity, though the latter have not yet been characterized thoroughly. Furthermore, SSC also demonstrated a concentration-dependent toxicity in cells. Therefore, the present study sought to investigate the SSC metabolism and activity in more detail to provide an enhanced understanding and knowledge surrounding its beneficial, non-toxic and toxic characteristics.
In the first part of the study, the CHO-K1 model clone was investigated in the presence of SSC at a non-toxic concentration to understand its metabolism/activity, and underlying mechanism(s) of action. Therefore, a CHO-K1-based fed-batch process (+ pH control), multi-omics and mechanistic approaches were performed, pointing out the following hallmarks: (1) SSC/glutathione (GSH) mixed disulfide formation, (2) glutaredoxin 1- and glutathione reductase (GR)-conveyed reduction and (3) sulfur species liberation, followed by their diversion towards catabolic pathways. The SSC-derived molecules, GSH, taurine and sulfite, were identified as those that are most likely conferring the favorable activity via their antioxidant and protective roles.
In the second part of the study, the CHO-K1 clone was examined using SSC at toxic concentrations to understand the mechanism(s) of toxicity. The CHO-K1 fed-batch process (± pH control) pointed to the SSC toxicity in the pH- surrounding that correlated with an extracellular pH decrease — likely reflecting an intracellular pH drop. The sulfo-glutathione (GS-SO3) mixed disulfide reduction, particularly the GR-conveyed GSH recycling, was strongly hampered at lower pH levels in vitro. Complementary to these findings, CHO-K1 cells experienced an aggravated SSC toxicity upon a GSH decrease triggered by buthionine sulfoximine, while control cells (without SSC treatment) remained vital. These results underline the importance of GSH, though its deficit appeared not to be solely driving the toxicity. Intensified SSC toxicity further correlated with a hindered GS-SO3 reduction and export. Mitigation strategies to prevent the SSC toxicity through the addition of sodium carbonate, sodium glutamate and copper (II) sulfate to the feed were successful.
In the third part of the study, the CHO-K1, CHOZN and CHO-DG44 clones, exhibiting phenotypic heterogeneity, were explored using SSC at wide-ranging doses to provide complementary data. The CHO-DG44 clone showed the lowest SSC sensitivity that was linked to a putative lower SSC uptake capacity, as well as a higher reactive sulfur and oxygen species scavenging capacity. This SSC-related knowledge regarding its dual nature paves the way for further research, and may be transferred to other clones that may respond differently to this modified amino acid