Sedan början av 2000-talet har ett stort antal transformatorer havererat av en initialt, okänd anledning. Problemet visade sig vara att en antioxidationstillsats i oljan, dibensyl disulfid (DBDS), reagerat med kopparen i lindningarna och vilket gett upphov till avlagringar på isolationspapperet i form av kopparsulfid. Kopparsulfiden i sin tur försvagade papperets isolationsförmåga och allvarliga driftstörningar eller driftstopp på grund av kortslutningar kan ske. Ett stort antal studier har genomförts för att ge klarhet i vad som händer, varför det händer och vad man kan göra åt problemet. Bakgrunden till detta examensarbete är att en 230MVA transformator har, trots att ägaren vidtagit rekommenderade försiktighetsåtgärder, havererat. Denna studie visar att ett flertal faktorer, såsom värme, svavelhalt och dåliga skarvar i lindningarna, påskyndar korrosionen av koppar och bildandet av kopparsulfid. Riskerna för haveri kan minskas genom att tillsätta Irgamet 39 i ett tidigt skede eller genom att byta/avsvavla oljan om transformatorn är äldre. Den redan bildade kopparsulfiden går däremot inte att avlägsna, så ett viktigt första steg är att stärka det elektriska skyddet genom att se över avledarna på transformatorn / Since the early 2000 a great number of transformers have broken down, without any apparent reason at first. The problem was identified to be an anti-oxidization-additive in the oil, dibenzyl disufide (DBDS), that had reacted with the copper in the windings. This gave rise to copper sulfide deposits on the isolating paper, which in turn reduced the isolating properties of the paper. A large number of studies have been completed to clarify what’s happening, why it’s happening and what can be done about it. The background for this thesis is that a 230MVA transformer broke down, despite the fact that the owner had taken the recommended precautions. This study will show that a number of factors, such as heat, Sulphur content and bad joints in the windings can accelerated the corrosion of copper and the formation of copper sulfide. The risks of a break-down can be reduced by adding Irgamet 39 at an early stage or by an oil change/desulphurization if the transformer is older. The already formed copper sulfide, on the other hand, cannot be removed and so an important first step is to fortify the electrical protection of the transformer by looking over the surge-arresters.

Upon synthesis, nascent polypeptide chains are subject to major rearrangements of their side chains to obtain an energetically more favorable conformation in a process called folding. About one third of all cellular proteins pass through the secretory pathway and undergo oxidative folding in the endoplasmic reticulum (ER). During oxidative folding, the conformational rearrangements are accompanied by the formation of disulfide bonds – covalent bonds between cysteine side chains that form upon oxidation. Protein disulfide isomerase (PDI) assists in the folding of substrates by catalyzing the oxidation of pairs of cysteine residues and the isomerization of disulfide bonds as well as by acting as chaperones. In addition to PDI itself, a family of related ER-resident proteins has formed. All PDI family members share the thioredoxin fold in at least one of their domains and exhibit a subset of the PDI activities. Despite many studies, the role of most PDI family members remains unclear. The project presented in this thesis was aimed to establish tools for the biochemical characterization of single members of the PDI family and their role in the folding process. A combination of fluorescence based assays was developed to selectively study single functions of PDI family members and relate their properties of either catalysis of oxidation or catalysis of isomerization or chaperone activity to the rest of the protein family. A binding assay using isothermal titration calorimetry (ITC) was established to complement the activity assays. Using ITC we could show for the first time that members of the PDI family can distinguish between folded and unfolded proteins selectively binding the latter. The unique information provided by this method also revealed a two-site binding of unfolded proteins by PDI itself. In addition to the functional characterization, experiments were conducted to further investigate the oligomeric state of PDI. We could show that the equilibrium between structurally different states of PDI is heavily influenced by the redox state of the protein and its environment. This new data could help to further our understanding of the interplay between oxidases like PDI and their regenerative enzymes like Ero1, which may be governed by structural changes in response to the change in redox status. Another structural approach was the screening of all investigated PDI family members for suitable crystallization conditions. As a result of this screening we could obtain protein crystals of human ERp27 and were able to solve the structure of this protein with X-ray crystallography. The structure gives insight into the mechanisms of substrate binding domains within the PDI family and helps to understand the interaction of ERp27 with the redox active ERp57. In collaboration with the group of Heike Hermanns we could further show the physiological importance of this interaction under oxidative stress. In conclusion, the project presented in this thesis provides novel tools for an extensive analysis of the activities of single PDI family members as well as a useful set of methods to characterize novel oxidoreductases and chaperones. The initial results obtained with the our novel methods are very promising. At the same time, the structural approach of this project could successfully solve the structure of a PDI family member and give information about the interplay within the PDI family. / Umlagerungsprozess nennt man Proteinfaltung. Schätzungsweise ein Drittel aller zellulären Proteine werden über den sekretorischen Transportweg geschleust und durchlaufen die oxidative Proteinfaltung im endoplasmatischen Retikulum (ER). Während der oxidativen Faltung werden zusätzlich zur Umlagerung von Seitenketten auch Disulfidbrücken gebildet. Dies sind kovalente Bindungen zwischen Zystein-Seitenketten durch Oxidation entstehen. Protein Disulfid Isomerase (PDI) unterstützt die Faltung von Proteinen im ER indem es die Oxidation zweier Zystein- Seitenketten katalysiert. Neben der Oxidation katalysiert PDI ebenfalls die Isomerisierung von fehlverknüpften Disulfidbrücken und wirkt als Chaperon der Aggregation entgegen. Im Laufe der Evolution hat sich zusätzlich zu PDI eine Gruppe verwandter ER-lokalisierter Proteine gebildet. Diese Mitglieder der PDI-Familie weisen alle das Thioredoxin-Faltungsmotiv in mindestens einer ihrer Domänen auf und besitzen mindestens eine der drei PDI-Aktivitäten. Trotz eingehender Untersuchung ist die Rolle der meisten dieser PDI Familienmitglieder weiterhin unklar. Im Rahmen des Projekts, welches dieser Dissertation zugrunde liegt, wurden Methoden zur biochemischen Charakterisierung einzelner Mitglieder der PDI-Familie, und deren Rolle im Faltungsprozess, entwickelt. Eine Kombination von Fluoreszenzexperimenten wurde etabliert mit der selektiv einzelne Aktivitäten von Faltungshelfern analysiert und qualitativ in die PDI- Familie eingeordnet werde können. Diese fluoreszenzbasierten Methoden wurden durch isothermale Titrationkalorimetrie (ITC) ergänzt. Mit ITC konnten wir als Erste zeigen, dass PDI- Familienmitglieder gefaltete von ungefalteten Proteinen unterscheiden können und letztere selektiv binden. Die zusätzlichen Informationen, die in einem ITC-Experiment gewonnen wurden, zeigten, dass PDI mit Substraten mit Hilfe von zwei unterschiedlichen Bindungsstellen interagiert. Neben der funktionellen Analyse der PDI-Familie wurde Experimente durchgeführt um den oligomeren Zustand von PDI näher zu untersuchen. Wir konnten zeigen, dass das Gleichgewicht zwischen strukturell verschiedenen Zuständen entscheidend vom Redox-Status von PDI abhängt. Diese neuen Daten werfen ein neues Licht auf die Interaktion zwischen Oxidasen wie PDI und ihren regenerativen Enzymen wie Ero1. Diese Interaktion könnte sehr wohl durch strukturelle Veränderungen, ausgelöst durch Redox-Reaktionen, reguliert werden. Als weiteren strukturellen Ansatz zur Erforschung der PDI-Familie wurden alle verwendeten Familienmitglieder auf aussichtsreiche Kristallisationsbedingungen hin untersucht. Durch dieses Screening konnte ERp27 kristallisiert und seine Struktur durch Röntgenkristallografie aufgeklärt werden. Die so gewonnene Struktur gibt Aufschluss über die Mechanismen der Substratbindung in der PDI- Familie und hilft ebenfalls dabei, die Interaktion zwischen ERp27 und dem redoxaktiven ERp57 besser zu verstehen. Auf Grund dieser Daten konnten wir gemeinsam mit der Gruppe von Heike Hermanns die physiologische Bedeutung dieser Interaktion bei oxidativem Stress aufzeigen. Zusammenfassend konnten im Rahmen dieses Projektes neue Werkzeuge zur eingehenden Analyse der PDI-Familie etabliert werden, welche auch zur Charakterisierung neuer Oxidoreduktasen und Chaperone verwendet werden können. Die ersten Ergebnisse die mit Hilfe dieser neuen Methoden gewonnen werden konnten sind vielversprechen. Gleichzeitig konnten wir mit ERp27 die Struktur eines weiteren PDI-Familienmitgliedes lösen und so weitere Einblicke in das komplexe Netzwerk der PDI-Familie gewinnen.

Techn. University, Diss., 2006--München.

[pt] O dissulfeto de molibdênio bidimensional (MoS2 2D) tem atraído significativa atenção devido às suas propriedades eletrônicas e ópticas únicas, tornando-se um material promissor para diversas aplicações, como dispositivos optoeletrônicos e sistemas de armazenamento de energia. Esta tese investiga métodos para aprimorar a emissão de fotoluminescência (PL) de MoS2 monocamada por meio de diferentes tratamentos. Os experimentos realizados visaram criar defeitos na estrutura cristalina de forma controlada, atacando o MoS2 2D com íons. As amostras foram obtidas via Deposição Química a Vapor (CVD). As alterações morfológicas e características eletro-ópticas foram avaliadas por Microscopia de Força Atômica (AFM), Espectroscopia Raman Ressonante e Espectroscopia de Fotoluminescência (PL). A primeira rodada de experimentos utilizou um tratamento de Plasma de Nitrogênio. Evidências de AFM da integridade da morfologia são apresentadas, embora o sinal de PL tenha sido significativamente atenuado para os parâmetros utilizados. A Espectroscopia Raman mostra uma evolução de características-chave à medida que defeitos são progressivamente criados, a saber, a Largura a Meia Altura (FWHM) dos modos vibracionais de segunda ordem 2LA(K) e 2LA(M). Posteriormente, um tratamento com feixes de íons de Hélio foi aplicado, levando a resultados positivos ao controlar o tempo e a energia do tratamento. Os espectros de emissão de fotoluminescência revelam que a intensidade do sinal foi aumentada em até duas vezes. Medidas de Raman Ressonante indicaram que a criação de defeitos foi controlada (com características de segunda ordem praticamente inalteradas). A análise de AFM demonstrou que não houve mudança da escala micrométrica devido aos tratamentos. Este tratamento constitui um método fácil para aprimorar a emissão de fotoluminescência de amostras de MoS2 monocamada crescidas via CVD para futuras aplicações em dispositivos. / [en] Two-dimensional molybdenum disulfide (2D MoS2) has gained significant attention due to its unique electronic and optical properties, making it a promising material for various applications, such as optoelectronic devices and energy storage systems. This thesis investigates methods to enhance the photoluminescence (PL) emission of monolayer MoS2 through different treatments. The experiments performed aimed to achieve this by creating defects on the crystal structure in a controlled manner, attacking the 2D MoS2 with ions. The samples were obtained via Chemical Vapor Deposition (CVD). The changes in morphology and electro-optical features were assessed via Atomic Force Microscopy (AFM), Resonant Raman Spectroscopy, and Photoluminescence (PL) Spectroscopy. The first round of experiments employed a Nitrogen Plasma treatment. AFM evidence of the integrity of the morphology is presented, although the PL signal was significantly quenched for the parameters used. Raman Spectroscopy shows an evolution of key features as defects are progressively created, namely the second-order 2LA(K) and 2LA(M) vibrational modes Full Width at Half Maximum (FWHM). Afterwards, a Helium ion beam treatment was applied, yielding positive results when controlling treatment time and energy. Photoluminescence emission spectra revealed the signal intensity was enhanced by up to a factor of 2. Resonant Raman measurements indicated a controlled defect creation was achieved (with practically unchanged second-order features). AFM analysis demonstrated no change in the micrometer scale dut to the treatments. This treatment constitutes a facile method for enhancing CVD grown monolayer MoS2 samples PL emission for future device applications.