Elektronischer Handel im Lichte der Bestreitbarkeit von Märkten

Information and communication technologies are transforming economies and societies around the world. In this respect, E-Commerce has the capability to build a new global economy. That is why government, industries, non-profit organisations, trade unions and consumers would like to come together to set up a regulatory framework. As set out in our paper competition effects have to be considered when doing so. We identify and discuss various regulatory and private entry barriers to electronic markets and answer the question wether or not there is any need for international policy cordination in E-Commerce.E-Commerce; competition; regulation

Molekulare Analyse von CHO-Zellen der Komplementationsgruppe Lec8 : Ableitung von Struktur-Funktions-Beziehungen für den UDP-Galactose Transporter

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Unimolecular Micelles and their Application Possibilities via the Passerini Three-Component Reaction

Unimolekulare Mizellen zeigen aufgrund ihrer vielseitigen Materialeigenschaften interessante Anwendungsmöglichkeiten, welche auf ihre kovalent verknüpften Kern-Schale-Architekturen zurückzuführen sind. Sie können unter anderem als Drug-Delivery-Systeme verwendet werden. Diese kovalent verknüpften Strukturen begünstigen eine erhöhte Stabilität in Lösung im Vergleich zu klassischen Mizellen, welche durch Selbstassemblierung von niedermolekularen amphiphilen Molekülen gebildet werden. Aufgrund des kovalenten Charakters der unimolekularen Mizellen liegt kein dynamisches Gleichgewicht zwischen Mizelle und den amphiphilen Molekülen vor. Die chemischen Strukturen solcher Kern-Schale-Architekturen basieren insbesondere auf Dendrimeren, hyperverzweigten Polymeren oder amphiphilen, sternförmigen Blockcopolymeren. In der vorliegenden Arbeit wurde eine neue Stufenwachstumspolymerisation auf Basis einer Passerini-Dreikomponentenreaktion (Passerini-3KR) entwickelt, um gezielt solche sternförmigen Blockcopolymere herzustellen. Die Passerini-3KR ist aufgrund der hohen Ausbeuten und Atomökonomie, der einfach umsetzbaren Reaktionsführung, der hundertprozentigen Endgruppentreue und vor allem der großen strukturellen Vielfalt der Produkte ein beliebtes Synthesetool in der organischen und Polymerchemie. Von großer Wichtigkeit für diese Arbeit war auch, dass bei dieser Reaktion die Wahl der Seitengruppen nahezu frei ist, was wiederum die Einstellung der Eigenschaften, wie Polarität und Funktionalität im Kern der amphiphilen, unimolekularen Mizellen ermöglichte. Zusammen mit der in dieser Arbeit beschriebenen Molekulargewichtskontrolle bietet die Passerini-3KR ein einfaches und vielfältiges makromolekulares Design. Die Molekulargewichtskontrolle konnte durch die Einführung eines monofunktionellen irreversiblen Kettentransferreagenzes (ICTA) in den Polymerisationsprozess realisiert werden. Durch das Verhältnis von ICTA zu Monomer konnte das Molekulargewicht gezielt eingestellt werden (analog zu dem Initiator zu Monomer Verhältnis bei lebenden/kontrollierten Polymerisationen, aber mechanistisch vollkommen unterschiedlich). Durch die Verwendung eines tri- und tetrafunktionalen ICTA konnten mittels der Passerini 3KR auch drei- und vierarmige Sternpolymere hergestellt werden. Die daraus erhaltenen Sternpolymere wurden anschließend mit einer wasserlöslichen Polyethylenglycol (PEG)-basierten Schale funktionalisiert, um amphiphile Sternblockcopolymere mit unimolekularem, mizellarem Verhalten zu generieren. Hierfür wurden die vorhandenen Carbonsäure-Endgruppen der Sternpolymere mit einem PEG-Aldehyd und einem Isocyanid bzw. PEG-Isocyanid in einer weiteren Passerini-3KR umgesetzt, um so eine wasserlösliche Schale mit und ohne Verzweigung am Verknüpfungspunkt der Polymerblöcke zu erhalten. Des Weiteren wurde der Einfluss des Molekulargewichtes der PEG-Reste auf das Aggregationsverhalten der Sternblockcopolymere in wässriger Lösung untersucht. Durch die Anzahl an Wiederholeinheiten im Kern und durch die Wahl unterschiedlicher Isocyanide als Seitenketten, sowie durch die Oxidation der Thioether-Funktionen zu Sulfonen im Polymerrückgrad, konnte die Polarität und die Mikroumgebung im Kern gezielt eingestellt und an die Einkapselung von gewünschten Gastmolekülen angepasst werden. Das Aggregationsverhalten in wässriger Lösung, sowie das Einschlussverhalten und der Transport verschiedener Farbstoffe wurde sowohl visuell oder mittels Dynamischer Lichtstreuung (DLS), als auch mit UV/VIS Spektroskopie und Hochleistungsflüssigkeitschromatographie (HPLC) untersucht. In letztgenannten Untersuchungen konnte zudem gezeigt werden, dass diese Polymere biokompatibel sind und sich für Anwendungen als Drug-Delivery-Systeme eignen, was Zelluntersuchungen, sowie die Einkapselung als auch die Freilassung eines Wirkstoffes (Azithromycin) bestätigten

Equilibrium isotope fractionation factors of H exchange between steam and soil clay fractions

Rationale Steam equilibration overcomes the problem of the traditional measurements of H isotope compositions, which leave an arbitrary amount of adsorbed water in the sample, by controlling for the entire exchangeable H pool, including adsorbed water and hydroxyl-H. However, the use of steam equilibration to determine nonexchangeable stable H isotope compositions in environmental media (expressed as δ2Hn values) by mathematically eliminating the influence of exchangeable H after sample equilibration with waters of known H-isotopic composition requires the knowledge of the equilibrium isotope fractionation factor between steam-H and exchangeable H of the sample (αex-w), which is frequently unknown. Methods We developed a new method to determine the αex-w values for clay minerals, topsoil clay fractions, and mica by manipulating the contributions of exchangeable H to the total H pool via different degrees of post-equilibration sample drying. We measured the δ2H values of steam-equilibrated mineral and soil samples using elemental analyzer-pyrolysis-isotope ratio mass spectrometry. Results The αex-w values of seven clay minerals ranged from 1.071 to 1.140, and those of 19 topsoil clay fractions ranged from 0.885 to 1.216. The αex-w value of USGS57 biotite, USGS58 muscovite, and of cellulose was 0.965, 0.871, and 1.175, respectively. The method did not work for kaolinite, because its small exchangeable H pool did not respond to the selected drying conditions. Structurally different mineral groups such as two- and three-layer clay minerals or mica showed systematically different αex-w values. The αex-w value of the topsoil clay fractions correlated with the soil clay content (r = 0.63, P = 0.004), the local mean annual temperature (r = 0.68, P = 0.001), and the δ2H values of local precipitation (r = 0.72, P < 0.001), likely to reflect the different clay mineralogy under different weathering regimes. Conclusions Our new αex-w determination method yielded realistic results in line with the few previously published values for cellulose. The determined αex-w values were similar to the widely assumed values of 1.00–1.08 in the literature, suggesting that the adoption of one of these values in steam equilibration approaches is appropriate

Non‐exchangeable stable hydrogen isotope ratios in clay minerals and soil clay fractions: A method test

Stable hydrogen isotope ratios (δ$^{2}$H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non-exchangeable H preserves the environmental forensic and paleoclimate information (δ$^{2}$H$_{n}$ value). To measure δ$^{2}$H$_{n}$ values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ$^{2}$H$_{n}$ values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ$^{2}$H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ$^{2}$H$_{n}$ values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon-richest sample. Our results demonstrate that δ$^{2}$H$_{n}$ values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction

Plant diversity influenced gross nitrogen mineralization, microbial ammonium consumption and gross inorganic N immobilization in a grassland experiment

Gross rates of nitrogen (N) turnover inform about the total N release and consumption. We investigated how plant diversity affects gross N mineralization, microbial ammonium (NH4+) consumption and gross inorganic N immobilization in grasslands via isotopic pool dilution. The field experiment included 74 plots with 1–16 plant species and 1–4 plant functional groups (legumes, grasses, tall herbs, small herbs). We determined soil pH, shoot height, root, shoot and microbial biomass, and C and N concentrations in soil, microbial biomass, roots and shoots. Structural equation modeling (SEM) showed that increasing plant species richness significantly decreased gross N mineralization and microbial NH4+ consumption rates via increased root C:N ratios. Root C:N ratios increased because of the replacement of legumes (low C:N ratios) by small herbs (high C:N ratios) and an increasing shoot height, which was positively related with root C:N ratios, with increasing species richness. However, in our SEM remained an unexplained direct negative path from species richness to both N turnover rates. The presence of legumes increased gross N mineralization, microbial NH4+ consumption and gross inorganic N immobilization rates likely because of improved N supply by N2 fixation. The positive effect of small herbs on microbial NH4+ consumption and gross inorganic N immobilization could be attributed to their increased rhizodeposition, stimulating microbial growth. Our results demonstrate that increasing root C:N ratios with increasing species richness slow down the N cycle but also that there must be additional, still unidentified processes behind the species richness effect potentially including changed microbial community composition

The biodiversity - N cycle relationship: a 15^{15}N tracer experiment with soil from plant mixtures of varying diversity to model N pool sizes and transformation rates

We conducted a $^{15}$N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity xperiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH$_{4}$$^{+}$ and NO3$^{-}$ in soil solution, and exchangeable NH$_{4}$$^{+}$) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH$_{4}$$^{+}$ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO$_{3}$$^{-}$ immobilization, adsorption of NH$_{4}$$^{+}$) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH$_{4}$$^{+}$ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH$_{4}$$^{+}$ pool, gross N mineralization, and NH$_{4}$$^{+}$immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples

Biocompatible unimolecular micelles obtained via the Passerini reaction as versatile nanocarriers for potential medical applications

A Passerini three-component polymerization was performed for the synthesis of amphiphilic star-shaped block copolymers with hydrophobic cores and hydrophilic coronae. The degree of polymerization of the hydrophobic core was varied from 5 to 10 repeating units, and the side chain ends were conjugated by performing a Passerini-3CR with PEG-isocyanide and PEG-aldehyde (950 g/mol). The resulting amphiphilic star-shaped block copolymers contained thioether groups, which could be oxidized to sulfones in order to further tune the polarity of the polymer chains. The ability of the amphiphilic copolymers to act as unimolecular micellar encapsulants was tested with the water-insoluble dye Orange II, the water-soluble dye Para Red and the macrolide antibiotic azithromycin. The results showed that the new copolymers were able to retain drug cargo at pH levels corresponding to circulating blood and selectively release therapeutically effective doses of antibiotic as measured by bacterial cell kill. The polymers were also well-tolerated by differentiated THP-1 macrophages in the absence of encapsulated drugs

Synthesis of Passerini-3CR Polymers and Assembly into Cytocompatible Polymersomes

© 2020 The Authors. Published by Wiley-VCH GmbH The versatility of the Passerini three component reaction (Passerini-3CR) is herein exploited for the synthesis of an amphiphilic diblock copolymer, which self-assembles into polymersomes. Carboxy-functionalized poly(ethylene glycol) methyl ether is reacted with AB-type bifunctional monomers and tert-butyl isocyanide in a single process via Passerini-3CR. The resultant diblock copolymer (P1) is obtained in good yield and molar mass dispersity and is well tolerated in model cell lines. The Passerini-3CR versatility and reproducibility are shown by the synthesis of P2, P3, and P4 copolymers. The ability of the Passerini P1 polymersomes to incorporate hydrophilic molecules is verified by loading doxorubicin hydrochloride in P1DOX polymersomes. The flexibility of the synthesis is further demonstrated by simple post-functionalization with a dye, Cyanine-5 (Cy5). The obtained P1-Cy5 polymersomes rapidly internalize in 2D cell monolayers and penetrate deep into 3D spheroids of MDA-MB-231 triple-negative breast cancer cells. P1-Cy5 polymersomes injected systemically in healthy mice are well tolerated and no visible adverse effects are seen under the conditions tested. These data demonstrate that new, biodegradable, biocompatible polymersomes having properties suitable for future use in drug delivery can be easily synthesized by the Passerini-3CR