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Characterization and Structural Elucidation of the Complex Mixture Thearubigins in Black Tea using Advanced Analytical Mass Spectrometry
No full textThearubigins are the most abundant pigments found in black tea, contributing to a wide range of heterogeneous fractions of polyphenolic oxidation products. The term thearubigins has been introduced fifty years ago but up till now their chemical nature remained unresolved and a challenge for the scientists despite many attempts and efforts made to understand their composition. Detailed structural knowledge of thearubigins is of high interest to understand their sensory properties in order to assist the manufacturing and quality of black tea as an economically important beverage. By employing a strategy in combining a series of advanced powerful mass spectrometry techniques, the chemical composition and structural elucidation of these compounds were achieved. A series of analytical mass spectrometry experiments including ESI-LC tandem mass and ESI-LC-TOF mass spectrometry, MALDI-TOF-TOF mass spectrometry, ESI-UPLC ion mobility mass spectrometry, MALDI imaging mass spectrometry were employed in combination with experimental potentiostatic studies and theoretical computational analysis. In this work, two classes of compounds were identified and a new structural hypothesis in thearubigin formation was further substantiated. The data revealed the presence of polyhydroxylated dimers of the theanaphthaquinone and theasinensin C structures, which were consistent with the polyhydroxylation hypothesis previously formulated. Furthermore, new class of peroxo-/ epoxi- compounds in the series of theasinensin A were identified, thus indicating the presence of H2O2 and its important contribution in the tea fermentation process. A series of novel trimeric and tetrameric catechins were identified. The results showed that the structures of these compounds provide for the first time experimental evidence on oxidative oligomerisation of flavan-3-ols through an oxidative coupling pathway, most notably between theaflavin/ theasinensin and oxidized flavan-3-ols. Furthermore, the regiochemistry of the new trimeric structures were suggested based on computational studies. Isomeric structures were also resolved based on the energy dimension in direct infusion MSn experiments.
An electrochemical model oxidation system was established. Theasinensins, theaflavins and their gallate esters were identified and shown as the main reaction products obtained from the electrochemical oxidation process performed, thus acting as the main precursors for further oxidation processes in thearubigin formation. Since thearubigins are one of the most complex mixtures present in nature, being composed of sets of multiple isomers, the differentiation between isomeric structure of theasinensins, proanthocyanidins B-type, and rutin (Quercetin-3-O-rutinoside) were studied according to their mobility drift times acquired and the assignment of the individual isomeric structures were based on comparison between their experimental drift times and theoretical collisional cross sections. Furthermore, polyphenolic components present in the tea leaves and their spatial distribution were located allowing a molecular mapping of the green tea constituents to be achieved. A new free matrix MS imaging method was developed for the first time, where the biochemical process occurring in a young green tea leaf has been determined. Finally, the importance of thearubigins on the health benefits by studying its inhibitory activity on nutrient cultures containing both gram positive and gram negative bacteria was highlighted.
This study characterizes the thearubigin as a complex mixture, reveals the important reaction mechanism occurring and identifies novel components, shows the main polyphenolic occurring components as main precursors in the oxidation process, demonstrates the isomerism present in thearubigin fractions, reveals the initial biochemical processing in the leaf matrix, and shows its important biological activity. In a word, this study serves a step forward for unraveling the mystery of black tea
Applications engineering of LED technology and products in the context of environmental management system implementation : Challenges and Opportunities
No full textOne of the main global challenges is how we deal with current environmental issues which are amplified by the industrialization of large emerging economies like China and India, as well as the progressing depletion of natural resources. It is only natural that universities and other public institutions with an outreach to many members of society and in the position to transfer the forefront of new technologies to real application to mitigate environmental burdens.
The goal of this PhD project has been to develop an engineering-based strategy to address the energy by focusing on one of the emerging technologies, in order to reduce the energy consumption significantly by quantum leap improvements of the energy efficiency. The technology chosen for this purpose is the LED (light emitting diode) technology, which enables improvement of the energy efficiency for lighting by a factor of 2 – 10, depending on the exact circumstances.
The objective of this study and the research topics are focused on all aspects of applications engineering and other issues regarding the introduction of the new technology. These range from pure technical issues to economic and user perception issues. As a first step, a suite of test procedures has been developed which characterize user relevant characteristics.
As the next step a rating scale has been developed for each of the technical tests, to enable a benchmarking of tested LED devices with respect to a particular application. This rating scale and an algorithm to convert the results from hundreds of different tested LED into an aggregated “figure of merit” for a particular application for each particular application has been tested and found highly acceptable and useful in the context of applications engineering projects, which have been part of this PhD project as a validation of the methods developed.
The scope of this project to investigate how to facilitate new technologies with the aim of reducing the environmental burden has be
Quality management for semi-manually curated ribosomal RNA gene sequence databases
No full textRibosomal RNA gene sequences have emerged as the gold standard for microbial diversity studies over the past decades. Improvements in sequencing technology have led to an ever faster accumulation of sequence data. They amass too fast for a manual quality check, demanding for precise automatic quality screening. Ribosomal RNA gene sequence databases - namely RDP, Greengeens, and SILVA - were created to address this demand and provide high-quality, refined subsets of the publicly available data.
One of the biggest threats for the quality of rRNA gene sequence databases is the inclusion of undetected artificial chimeras, artefacts that are formed in a preparation step required by most sequencing methods. In this thesis, published chimera detection algorithms were examined for the application of quality control of these databases. The evaluation revealed doubts about the reliability of the algorithms for this use case and the occurrence of natural chimeras casts additional doubt on every positive detection result. In the end, the current knowledge about chimeras was found to be insufficient to implement a reliable chimera detection for rRNA gene sequence databases.
The removal or marking of anomalous sequences would, nevertheless, increase the quality of the databases, as would an automatic taxonomic classification of all sequences which are not classified manually. This classification can, in turn, be used for quality control by testing how well a sequence matches its taxonomic group. For this reason, STACL was developed: a hierarchical taxonomic classification algorithm including outlier and anomaly detection. The algorithm was applied to the SILVA database and it detected major classification errors in the dataset which were neither detected by manual nor by automatic quality control previously. Thus, the overarching aim of this thesis was reached: to improve the quality management of semi-manually curated rRNA gene sequence databases
Determinants of leaders' success: Toward an integrated model of personality, beliefs, behavior, and diversity
No full textLeaders are important organizational members. The impact of leaders' actions in companies is probably greater than actions from any other member in organizations, since they are able to affect attitudes, cognitions, and behaviors of individuals, and processes and performance of teams and organizations. Due to the high impact of leaders, many researchers tried to investigate the following question: What determines a leader's success? The answers are diverse and include leaders' personality (e.g., Guion & Gottier, 1965), behavior (e.g., Fleischman, 1953), and beliefs (e.g., Ajzen & Fishbein, 1980) as well as contingency factors such as diversity (e.g., Fiedler, 1967; Kaiser, Hogan, & Craig, 2008).
Interestingly, although it is highly likely that these factors (leaders' personality, behavior, and beliefs as well as diversity) indeed all affect a leader's success, they have rarely been studied in combination (e.g., Avolio, 2007). In the pursuit to better understand leaders' success and its influencing factors, this dissertation used an integrated approach to investigate the role of leaders' personality, leaders' beliefs, leaders' behaviors, and diversity, and their links to each other in predicting leaders' success (see the Figure on the next page). Thereby, I proposed that personality and behavior should be investigated in combination, that certain behaviors are more or less effective in different situations, and that leaders' beliefs might affect their behavior. These predictions were examined in three papers in which different parts of the model have been tested.
First, I present a meta-analysis, in which I studied the role of the Big 5 personality traits and the sub-dimensions of the transformational leadership theory on leaders' success. Predicting that the Big Five traits would be related to transformational leadership behavior and leader success, the findings supported the mediating role of transformational leadership and its sub-dimensions in the personality-leader performance relationship. However, the overall transformational leadership measure and the sub-dimensions of transformational leadership were influenced by different combinations of the Big 5 personality traits. For instance, whereas inspirational motivation was positively related to extraversion, openness to experience, agreeableness, and conscientiousness and negatively related to neuroticism, individualized consideration was positively correlated with openness to experience and agreeableness. These findings imply that a simple combination of the transformational leadership sub-dimensions into one overall construct seems to be inappropriate and reveal that organizations can use personnel selection and leadership training to produce effective leaders.
Moreover, this thesis focused on leader-member exchange – a theory that focusses on the one-to-one relationships between leaders and followers (Cogliser & Schriesheim, 2000; Schyns, Maslyn, & Weibler, 2010) – as one process via which transformational leaders influence critical organizational outcomes. Findings of a meta-analysis supported the prediction that leader-member exchange mediates the relationships between transformational leadership and job satisfaction, organizational commitment, and leader performance. Furthermore, the meta-analysis showed that transformational leadership and leader-member exchange contribute to different extents to the outcomes, depending on the type of the outcome. These findings emphasize that it is highly important to distinguish between outcome variables when studying the leadership processes.
Finally, I investigated the role of transformational leadership and leaders' diversity beliefs in predicting anticipated affective, relational, and task-related outcomes in nationality diverse teams. I proposed that transformational leaders in diverse teams influence not only task-related outcomes by promoting information sharing processes (e.g., Kearney & Gebert, 2009), but also affective and relational outcomes by creating a social identity within the team (e.g., Kunze & Bruch, 2010; Van Vugt & De Cremer, 1999). A vignette and an experimental study supported this prediction. Additionally, I predicted that the content of the vision of the leader, in this study the leader's diversity beliefs, determines whether a (transformational) leader has a positive or negative effect in diverse teams. In this respect, the data supported a three-way interaction between nationality diversity, transformational leadership, and diversity beliefs on sub-group perceptions. Participants in homogenous teams perceived less subgroups than did those in diverse teams. Furthermore, participants in diverse teams led by a highly transformational leader with positive diversity beliefs perceived less subgroups than did those in diverse teams with a high transformational leadership - negative diversity beliefs leader, as well as with in a low transformational leadership - positive diversity leader. Interestingly, we found that members of a diverse team led by a high transformational leader with positive diversity beliefs had similar subgroups perceptions as members of a diverse team led by a low transformational leader with negative diversity beliefs. However, no other three-way interactions were found, which is on contrast with my own and others' predictions (Beyer, 1999; De Hoogh & Den Hartog, 2009; House & Howell, 1992).
Concluding, this dissertation provides an integrative picture pertaining to the different factors that might influence leaders' success. It illustrates that leaders' personality, leadership behavior, diversity, and partially leaders' beliefs influence the success of leaders together rather than in isolation. This research suggests that personality affects leadership success directly and indirectly via transformational leadership behavior; that transformational leadership behavior influences leadership success directly and indirectly via leader-member exchange; that transformational leadership has a positive influence on the link between nationality diversity and leadership success; and that the promising role of leader's beliefs about diversity in the relationship between nationality diversity, transformational leadership, and leadership success needs further research. These findings have important implications for research and organizations in the area of leadership and diversity management
Study of the channel proteins in the cell wall of the Actinomycetales
No full textThis thesis is composed of three major studies about channel proteins of the order Actino-mycetales.
The cell wall of Streptomyces coelicolor A(3)2 was found to contain a channel-forming protein in reconstitution experiments using artificial lipid bilayer. Membrane experiments indicated that the channel protein has a single-channel conductance of 1.75 nS in 1 M KCl. The channel presumably represents a general diffusion pore for transport of antibiotics as it binds several antibiotics. To identify the gene coding for this channel within the known genome of S. coelicolor A(3)2, the pore-forming protein was sequenced, the candidate genes were inactivated and each mutant was inspected for channel forming activity. Unfortunately, none of the mutants lacked the described pore-forming activity and the identity of the gene could not be attributed to any of the candidate genes.
The cell wall of Dietzia maris contained a pore-forming protein as observed from reconstitution experiments with artificial lipid membranes. The porin had a molecular mass of about 120 kDa and formed ion-permeable channels in lipid bilayer membranes with a single-channel conductance of about 5.8 nS in 1 M KCl. Further biophysical analysis indicated that the porin exhibit selectivity for cations because of negative charges localized at the channel mouth. The 120 kDa porin is voltage dependent and has a diameter of 2.1 nm. The porin was subjected to protein analysis by mass spectrometry but its sequence had no significant homology to any known porin sequences which could be indicative of a novel kind of porin.
The existence of a cell wall channel of Rhodococcus erythropolis composed of 8.4 kDa monomers has already been described. Based on partial sequencing of the pure protein, we were able to identify the corresponding gene within the genome of R. erythropolis. In order to confirm whether this gene is responsible for the channel activity of R. erythropolis, it was cloned in different expression vectors including the shuttle vector pXMJ19, pXHis and pGEX-2T. The new constructs were transformed into Corynebacterium glutamicum ΔporHΔporA and Escherichia coli BL21 (DE3) Omp8 host cells. However, the expression was problematic as we used other host rather than Rhodococcus and it is conceivable that the protein degraded due to incorrect folding during or after expression
Cysteine cathepsin localization and function in intestine epithelial and carcinoma cells
No full textCysteine cathepsins are proteases involved in distinct processes essential for cellular homeostasis in a variety of tissues including the gastrointestinal tract. Since cathepsins are part of a complex proteolytic network, any imbalance in their localization and activity can influence the structural and functional integrity of the intestine. In the present study, we demonstrate that absence of cathepsin B in mice results in elevated levels of cathepsin X in a segment-specific manner. Furthermore, we provide evidence for the notion that each part of the gastrointestinal tract is characterized by its distinct proteolytic profile which requires tightly balanced protein transport logistics in intestine epithelial cells.
Moreover, several reports have shown that the so called “endo-lysosomal” enzymes of the gastrointestinal tract often localize to unusual sites such as in the cytosol or in mitochondria, and in the nuclei of both, epithelial and carcinoma cells. Therefore, in our subsequent in vitro study, we investigated the localization and expression of cathepsins B and L in the normal enterocyte cell line IEC6 in comparison with the colon carcinoma cell lines Caco2, HCT116, and SW620 throughout different phases of the cell cycle. Our results revealed the presence of cathepsins B and L in the nucleus of colon carcinoma cells, and demonstrated the abundance of cytosolic cathepsins which were found to be co localized with β tubulin during M phase in the carcinoma cells, while cathepsin L was the only enzyme detectable in the nuclei of normal epithelial cells. Additionally, immunoblotting of subcellular fractions demonstrated a distinct molecular form of cathepsin B in the nuclei of carcinoma cells. Furthermore, the cell cycle analysis demonstrated the necessity of cathepsin L activity for cell cycle progression of HCT116 cells. Next, we compared the trafficking of enhanced green fluorescent protein tagged full length and N terminally truncated cathepsins B and L in colon carcinoma cells, which exhibited a juxtanuclear localization in aggresomes of HCT116 cells, whereas full-length cathepsin B followed the expected transport pathway to endo lysosomes.
Overall, our studies showed the segment-specific profile of cysteine cathepsins in the gastrointestinal tract of mice, and suggested a significant role of cysteine cathepsins during cell cycle progression. The results of this study are important to understand the normal gastrointestinal tract homeostasis, and contribute to shedding light on the onset and progression of colon cancer
Logistic Target Achievement In Scope Of The Lead Time Syndrome Of Manufacturing Control : Validation Of The Syndrome And Development Of A Methodology To Avoid It In Practice
No full textThe aim of PPC is to ensure the achievement of the logistic targets while maintaining productivity and quality targets. If order due dates are missed, a common intuitive reaction of production planners is to adjust planned lead times. How often and to what extent updates are reasonable has previously been unclear because, while trying to improve the logistic target achievement, planned lead time adjustments may actually cause an opposite effect, which is known as the Lead Time Syndrome of Manufacturing Control (LTS). Although the LTS was described as early as 1977, the cause-and-effect relationships in the LTS still have not been sufficiently investigated. Thus, this thesis has the overall target of investigating the influence of the LTS of manufacturing control on logistic target achievement by firstly validating the LTS line of argumentation by Mather & Plossl (1977) and secondly developing a roadmap to mitigate the LTS in practice. For the validation initially a mathematical model of LTS interactions by means of the Funnel Model and statistics is presented, which also enables determining the main triggers of the LTS. The insights are then validated and extended in a control theoretic model of the LTS and transferred into strategies to avoid or dampen the LTS. Finally, the derived propositions are evaluated and confirmed in a case study of a job-oriented manufacturing process. To develop a roadmap in the second step, the questions of when, how often, and on which value should planned lead times be adjusted are addressed. The results are finally transferred into a methodology to avoid the LTS in practice. In summary, this thesis validates the LTS line of argumentation and shows the relevance of the problem in today’s manufacturing systems. The roadmap finally transfers the results from theory into practice to support planners in the process of decision-making and prevent accidentally wrong adjustments that might lead to a decrease in performance
Controlling Recurrent Neural Networks by Conceptors
No full textThe human brain is a dynamical system whose extremely complex sensordriven neural processes give rise to conceptual, logical cognition. Understanding the interplay between nonlinear neural dynamics and concept-level cognition remains a major scientific challenge. Here I propose a mechanism of neurodynamical organization, called conceptors, which unites nonlinear dynamics with basic principles of conceptual abstraction and logic. It becomes possible to learn, store, abstract, focus, morph, generalize, de-noise and recognize a large number of dynamical patterns within a single neural system; novel patterns can be added without interfering with previously acquired ones; neural noise is automatically filtered. Conceptors help explaining how conceptual-level information processing emerges naturally and robustly in neural systems, and remove a number of roadblocks in the theory and applications of recurrent neural networks
Macroecological properties of phytoplankton communities in a changing ocean
No full textMicroscopic photoautotrophs play crucial roles in global marine ecosystems by influencing food-webs, nutrient cycles and Earth's climate. Therefore, investigating the mechanisms that drive phytoplankton communities in the ocean is a task of fundamental importance. Scientists use broad temporal and spatial observations together with numerical models to study the response of these marine microbial communities to different environmental conditions. However, many studies have been describing much of the ecological and environmental variation with methods deeply rooted in the observed natural complexity. This approach prevents us from obtaining valuable insights on the underlying mechanisms that determine the diversity and composition of phytoplankton communities. In the present thesis this issue was tackled by applying a simple framework based on three prominent perspectives in ecology, namely: macroecology, trait-based community ecology and complex adaptive systems. Specifically, here it is shown how the application of a coerced structure, based on the mentioned concepts, helps to identify large-scale biogeographic patterns of phytoplankton community size structure in the global ocean, and to mathematically describes with a size-based model the phytoplankton communities under modern and future environmental regimes. The first prominent result showed that the size structure of a phytoplankton community can be adequately described by a parsimonious probabilistic model of temperature and nutrients. Second, simulations based on present and future environmental conditions obtained with the size-based model suggested that the major mechanisms shaping the functional diversity and structure of marine microbial communities are nutrient availability and grazing pressure. The model was contrasted with observations of nutrient concentrations, phytoplankton biomass and community size distribution. In addition, the relevance of the top-down and bottom-up controls in reorganizing the phytoplankton communities where thoroughly tested with a number of sensitivity analyses. Overall this study contributed to the knowledge of marine phytoplankton ecology by proposing a new probabilistic approach to assess the biogeographic patterns of size structured microbial communities and their relationships with prevailing environmental conditions. In addition, this work provides a simple and consistent mechanistic description of marine phytoplankton communities, which links its total biomass, its community size structure and its functional diversity with changes in the environment. This contribution presents an advancement from classical approaches by describing the dynamics of a whole phytoplankton community by its aggregate properties
Visual Communication on Social Network Sites: The Dynamics of Visual Production, Self-Presentation, and Computer-Mediated Communication
No full textThe availability of Web 2.0 for public use has brought new forms of interpersonal and public interaction opportunities, which affect people’s daily lives by stimulating the complex process of socialization. Online acquaintances are becoming common leading to offline communication or strengthening the existing online connections. Social networking users use massive visual and textual data for self-presentation. Profile images play a significant role in this regard. It investigates profile image typologies: production technique, visual motif, and photographic perspective. To answer the research questions, 1,028 randomly selected profile images, 90 online survey questionnaires and 7 in-depth interviews were randomly and purposefully collected from students at Duke University (USA) and Jacobs University Bremen (Germany). Content analysis and visual context analysis were used to analyze the collected data. The results show that profile images carry intended connotations meaningfully selected by profile owners. Images connote users’ feelings, emotions, and desires; they are used to tell personal stories, remember significant others, endorse people, promote products and institutions, and announce events. The vast majority of Facebook users prefer to use candid, person profile images, for modifying entails misleading relatives and friends. Moreover, the majority of the profile images are close-up, frontal, eye-level photographs which convey posed but authentic self-presentation. The process of visual self-presentation is analyzed from the perspective of hyperpersonal communication; it is asynchronous in that profile owners spend time with a purpose to choose relatively stable profile images suitable for most audiences. Online self-presentation in images is not about the individual profile owner; it is essentially about the complex interplay among the event, the subject, the photographer, and the technology. This research, therefore, provides both empirical and theoretical foundations of not only the power and significance of images in computer‐mediated communication but also the complex relationship among visual production, self-presentation, and computer-mediated communication