Noble metal clusters and C60-buckminsterfullerenes on carbon surfaces : a photoelectron spectroscopy study

Photoelectron spectroscopy (MXPS) studies on chemically synthesized thiol-passivated gold nanoparticles revealed a thiol-chain length dependence on the thermal desorption behavior of the passivating shell, on particle self-assembly properties and on X-ray induced thiol-gold bond breaking. Observed changes in the Au 4f core-level binding energies motivated to study thiolgold interaction in more detail. Adsorption of thiol molecules on gold clusters should yield insight to the nature of the still not fully understood Au-S bond. To avoid exposure to ambient atmosphere cluster deposition and thiol adsorption had to be performed in vacuo. Therefore, the growth of clusters on defect-rich carbon surfaces by means of metal evaporation was studied at first. Investigation of the early stages of cluster nucleation and growth showed a considerable interaction of deposited gold clusters with carbon defects, heavily shifted (≈eV) second feature in the Au 4f core-level spectra. This was attributed to the existence of a bimodal cluster size distribution. It was found that deposition of heated substrates (400-600 ◦ C) represent a possibility to preferentially grow nanoparticles on defect-sites. Having studied nanoparticle growth gold cluster samples were prepared to be exposed to a thiol atmosphere. MXPS spectra were taken before and after exposure to monitor changes in the clusters’ electronic configuration. It could be shown that thiol adsorption induces positive binding energy shift in gold core-level and valence band spectra. This was interpreted as due to electron charge localization by Au-S bonds. Changes in the shape of MXPS valence band spectra where attributed to re-hybridization of Au 5d electrons (creation of Au-S bonds) and a close examination of the Fermi edge region hinted to a thiol-induced metal-to-insulator transition. These results are of high interest concerning the electrical properties of metal-organic contacts. Motivated by the results obtained from cluster deposition on defect-rich carbon surfaces the work was extended to buckminsterfullerene molecules. The interaction of C60 with defects and the thermal stability was investigated by means of UV Photoemission Spectroscopy (UPS). It was demonstrated that fullerenes chemisorb at defects indicated by a higher desorption temperature as on pristine HOPG. This was reflected by significantly shifted and broadened VB features. The higher desorption temperature for C60 attached to defects than for species adsorbed on undamaged HOPG might allow in combination with Focused Ion Beam techniques to prepare fullerene-decorated nanostructures. In conclusion, the different experiments and results presented here have shown that artificially created defects on carbon (esp. HOPG) substrates might be promising way of surface nanostructuring. The choice of carbon is interesting with regard to applications where biocompatibility1 of the substrates is demanded

Taxation and capital structure choice: evidence from a panel of German multinationals

This paper analyzes the impact of taxes and lending conditions on the financial structure of multinationals? foreign affiliates. The empirical analysis employs a large panel of affiliates of German multinationals in 26 countries in the period from 1996 until 2003. In accordance with the theoretical predictions, the effect of local taxes on leverage is positive for both types of debt. Moreover, while adverse local credit market conditions are found to reduce external borrowing, internal debt is increasing, supporting the view that the two channels of debt finance are substitutes. --Corporate Income Tax,Multinationals,Capital Structure,Firm-Level Data

The Impact of Thin-Capitalization Rules on Multinationals’ Financing and Investment Decisions

This paper analyzes the role of Thin-Capitalization rules for capital structure choice and investment decisions of multinationals. A theoretical analysis shows that the imposition of such rules tends to affect not only the leverage and the level of investment but also their tax-sensitivity. An empirical investigation of leverage and investment reported for affiliates of German multinationals in 24 countries in the period between 1996 and 2004 offers some support for the theoretical predictions. While Thin-Capitalization rules are found to be effective in restricting debt finance, investment is found to be more sensitive to taxes if debt finance is restricted.corporate income tax, multinationals, leverage, Thin-Capitalization rules, firm-level data

The impact of thin-capitalization rules on multinationals' financing and investment decisions

This paper analyzes the effectiveness of thin-capitalization rules in preventing debt finance by intercompany loans and explores their consequences for corporate decisions. A theoretical discussion emphasizes that limitations of the deduction of interest owed to foreign affiliates would not only affect multinationals' capital structure choice but also investment. An empirical investigation exploits a large firm-level panel dataset of multinationals in order to analyze the impact of thin-capitalization rules on capital structure choice and investment in the OECD and some further European countries in the time period between 1996 and 2004. The results indicate that thin-capitalization rules are effective in curbing tax planning via intercompany loans. However, investment is found to be adversely affected. --Corporate Income Tax,Multinationals,Leverage,Thin-Capitalization Rules,Firm-Level Data

Monosaccharide transporters in plants: structure, function and physiology

AbstractMonosaccharide transport across the plant plasma membrane plays an important role both in lower and higher plants. Algae can switch between phototrophic and heterotrophic growth and utilize organic compounds, such as monosaccharides as additional or sole carbon sources. Higher plants represent complex mosaics of phototrophic and heterotrophic cells and tissues and depend on the activity of numerous transporters for the correct partitioning of assimilated carbon between their different organs. The cloning of monosaccharide transporter genes and cDNAs identified closely related integral membrane proteins with 12 transmembrane helices exhibiting significant homology to monosaccharide transporters from yeast, bacteria and mammals. Structural analyses performed with several members of this transporter superfamily identified protein domains or even specific amino acid residues putatively involved in substrate binding and specificity. Expression of plant monosaccharide transporter cDNAs in yeast cells and frog oocytes allowed the characterization of substrate specificities and kinetic parameters. Immunohistochemical studies, in situ hybridization analyses and studies performed with transgenic plants expressing reporter genes under the control of promoters from specific monosaccharide transporter genes allowed the localization of the transport proteins or revealed the sites of gene expression. Higher plants possess large families of monosaccharide transporter genes and each of the encoded proteins seems to have a specific function often confined to a limited number of cells and regulated both developmentally and by environmental stimuli

Modulation of the bacterial cell wall by N‐acetylmuramoyl‐L‐alanine amidases

The bacterial cell wall is a highly dynamic structure that undergoes constant change in order to fulfill its various tasks, which range from physical protection against exterior stress and maintaining homoeostasis to immune evasion. A major component of the bacterial cell wall is the peptidoglycan network (PGN). Built up by a carbohydrate backbone of repeating units of N‐acetylglucosamine and N‐acetylmuramic acid linked to a peptide stem containing nonproteinogenic amino acids, PGN is a net‐like structure that harbors various proteins and anchors further components of the cell wall. Depending on the composition of the peptide stems and the type of cross‐linkage between the peptide stems, PGN can be a very dense network or a rather loose mesh. N‐acetylmuramoyl‐L‐alanine amidases cleave the amide bond between the carbohydrate backbone and the peptide stem and represent a class of PGN‐modulating enzymes that ensure its plasticity. My work focused on this class of enzymes in order to better understand the mechanisms that underlie PGN cleavage, and thus its plasticity, by using biochemical and cell biological tools in combination with X‐ray crystallography. The bifunctional major autolysin AtlA of Staphylococcus aureus contains a glucosaminidase and an amidase, which are post‐translationally processed and separated. Deletion of AtlA leads to cell clusters with irregular division patterns, indication a crucial role in cell division. I solved the atomic structure of the catalytic domain of the amidase, AmiA‐cat, in complex with its substrate component muramoyltetrapeptide. Close investigation of the molecular interactions between enzyme and substrate, along with the analyses of the apo‐structure and enzymatic activity assays, elucidated the likely reaction mechanism as well as substrate specificity. Since the intact substrate, including the scissile bond, is present in the complex structure, it moreover serves as a starting point for therapeutics against methicillin‐resistant Staphylococcus aureus. Further studies with AmiA‐cat in this regard involve a fragment‐based screening approach using X‐ray crystallography and the production and evaluation of therapeutic antibodies against AmiA‐cat as possible active agents. AmiC2 of the filamentous cyanobacterium Nostoc punctiforme fulfills a unique task in order to enable communication of neighboring cells within a filament. In contrast to cell‐splitting amidases, AmiC2 drills holes into the septal disk that separates neighboring cells, thus generating a nanopore array used for nutrient exchange and communication. My cooperation partner located AmiC2 in the maturating septum and I solved the structure of the catalytic domain of this enzyme, AmiC2‐cat. In comparison with the homologous enzyme AmiC E. coli, a regulatory α‐helix is missing, and AmiC2‐cat exhibits high activity, which can be abolished by mutation of a catalytic glutamate. Ongoing research is focused on the mechanism that governs activity and specificity of this unusual amidase. In particular, I study the separate and / or cooperative influence of the additional domains, AMIN‐A, AMIN‐B, and the proline‐rich linker of the AmiC2 holo‐enzyme on catalysis and specificity. Furthermore, in cooperation, I am working on elucidating the exact chemical composition of Nostoc PGN, perhaps even differences between nascent, septal, and mature PGN. The results will be essential to generate complex structures, and elucidating potential PGN differences will provide insights into specificity.Die Bakterienzellwand ist eine hochdynamische Struktur, die einem ständigen Wandel unterliegt, um ihre verschiedenen Aufgaben zu erfüllen. Diese reichen von physischem Schutz gegen äußere Belastungen über die Aufrechterhaltung der Zellhomöostase bis zur Immunevasion. Ein Hauptbestandteil der bakteriellen Zellwand ist das Peptidoglycan (PGN). Es ist aus einem Kohlenhydratgerüst mit abwechselnden Einheiten von N‐Acetylglucosamin und N‐Acetylmuraminsäure sowie einem Peptidstamm, der auch nicht‐proteinogene Aminosäuren beinhaltet, aufgebaut. PGN ist eine netzartige Struktur, die außerdem verschiedene Proteine und weitere Komponenten der Zellwand verankert. Je nach Zusammensetzung des Peptidstammes selbst und der Art der Vernetzung zwischen den Peptidstämmen kann das PGN ein sehr dichtes Netz oder ein eher lockeres Geflecht sein. N‐Acetylmuramoyl‐L‐Alanin‐Amidasen spalten die Amidbindung zwischen dem Kohlenhydratgerüst und dem Peptidstamm und stellen eine Klasse von PGN‐modulierenden Enzymen dar, die seine Plastizität sicherstellen. Die vorliegende Arbeit konzentriert sich auf diese Enzymklasse und soll zum Verständnis der zugrunde liegenden Mechanismen jener enzymatischen Spaltung beitragen, die für die Plastizität von PGN verantwortlich ist. Dieser Fragestellung wurde mit Hilfe biochemischer und zellbiologischer Methoden sowie der Röntgenstrukturanalyse nachgegangen. Das bi‐funktionelle Major Autolysin AtlA von Staphylococcus aureus besteht aus einer Glucosaminidase und einer Amidase, welche posttranslational voneinander getrennt werden. Das gezielte Abschalten (Knockout, Nullmutante) von AtlA führt zu Zellclustern mit unregelmäßigem Teilungsmuster, was eine entscheidende Rolle bei der Zellteilung nahelegt. Ich habe die atomare Struktur der katalytischen Domäne der Amidase, AmiA‐cat, im Komplex mit ihrem Substratbestandteil Muramoyltetrapeptid gelöst. Sowohl die genaue Untersuchung der molekularen Wechselwirkungen zwischen Enzym und Substrat sowie die Analyse der apo‐ Struktur als auch enzymatische Aktivitätstests haben Anhaltspunkte für den wahrscheinlichen Reaktionsmechanismus sowie die Substratspezifität des Enzyms geliefert. Da das intakte Substrat einschließlich der zu spaltenden Bindung in der Komplexstruktur vorhanden ist, dient sie ferner als ein guter Startpunkt für Therapeutika gegen den Methicillin‐resistenten Staphylococcus aureus. Weitere Studien mit AmiA‐cat in diese Richtung beinhalten neben einem fragmentbasierten Screeningansatz unter Zuhilfenahme von Röntgenkristallographie auch die Produktion und Tests von therapeutischen Antikörpern gegen AmiA‐cat als mögliche Wirkstoffe. AmiC2 des filamentösen Cyanobakteriums Nostoc punctiforme führt eine einzigartige Reaktion aus, um die Kommunikation von benachbarten Zellen innerhalb eines Filaments zu ermöglichen. Im Gegensatz zu zellspaltenden Amidasen bohrt AmiC2 Löcher in das Septum, welches Nachbarzellen voneinander trennt. Dadurch entsteht ein Nanopore Array, das für Nährstoffaustausch und Kommunikation verwendet wird. Meine Kooperationspartner haben AmiC2 im ausreifenden Septum lokalisiert, und ich habe die Struktur der katalytischen Domäne dieses Enzyms gelöst (AmiC2‐cat). Interessanterweise fehlt eine regulatorische α‐Helix, wie man sie in dem homologen Enzym AmiC E. coli findet. AmiC2‐cat ist katalytisch sehr aktiv, was durch die Mutation eines katalytischen Glutamats aber aufgehoben werden kann. Weitergehende Forschung zielt auf die Aufklärung des Mechanismus ab, der die Aktivität und Spezifität dieser ungewöhnlichen Amidase regelt. Insbesondere wird momentan der getrennte und / oder kooperative Einfluss der zusätzlichen Domänen des AmiC2‐Holoenzyms ‐ AMIN‐A, AMIN‐B sowie Prolin‐reicher Linker ‐ auf die Katalyse und Spezifität von AmiC2‐cat erforscht. Außerdem wird die genaue chemische Zusammensetzung des PGN von Nostoc untersucht, um den physiologischen Liganden von AmiC2 für eine Komplexstruktur zu identifizieren. Weiterhin könnten eventuelle Unterschiede zwischen jungem, septalem und reifem PGN eine Rolle bei der enzymatischen Spezifität spielen

Excuse Me, Something Is Unfair! - Implications of Perceived Fairness of Service Robots

Fairness is an important aspect for individuals and teams. This also applies for human-robot interaction (HRI). Especially if intelligent robots provide services to multiple humans, humans may feel treated unfairly by robots. Most work in this area deals with the aspects of fair algorithms, task allocation and decision support. This work focuses on a different, yet little explored perspective, which looks at fairness in HRI from a human-centered perspective in human-robot teams. We present an experiment in which a service robot was responsible for distributing resources among competing team members. We investigated how different strategies of distribution influence the perceived fairness and the perception of the robot. Our study shows that humans might perceive technically efficient algorithms as unfair, especially if humans personally experience negative consequences. This also had negative impact on human perception of the robot, which should be considered in the design of future robots

An Information-Theoretic Approach for Evaluating Probabilistic Tuning Functions of Single Neurons

Neuronal tuning functions can be expressed by the conditional probability of observing a spike given any combination of explanatory variables. However, accurately determining such probabilistic tuning functions from experimental data poses several challenges such as finding the right combination of explanatory variables and determining their proper neuronal latencies. Here we present a novel approach of estimating and evaluating such probabilistic tuning functions, which offers a solution for these problems. By maximizing the mutual information between the probability distributions of spike occurrence and the variables, their neuronal latency can be estimated, and the dependence of neuronal activity on different combinations of variables can be measured. This method was used to analyze neuronal activity in cortical area MSTd in terms of dependence on signals related to eye and retinal image movement. Comparison with conventional feature detection and regression analysis techniques shows that our method offers distinct advantages, if the dependence does not match the regression model

Probing the active site of homoserine trans-succinylase

AbstractHomoserine trans-succinylase is the first enzyme in methionine biosynthesis of Escherichia coli and catalyzes the activation of homoserine via a succinylation reaction. The in vivo activity of this enzyme is subject to tight regulation by several mechanisms, including repression and activation of gene expression, feedback inhibition, temperature regulation and proteolysis. This complex regulation reflects the key role of this enzyme in bacterial metabolism. Here, we demonstrate – using proteomics and high-resolution mass spectrometry – that succinyl is covalently bound to one of the two adjacent lysine residues at positions 45 and 46. Replacing these lysine residues by alanine abolished the enzymatic activity. These findings position the lysine residues, one of which is conserved, at the active site