Copper and zinc stable isotope ratios as tracers of biogeochemical processes, sources and transport of Cu and Zn in soils

Copper and Zn are essential micronutrients for plants, animals, and humans; however, they may also be pollutants if they occur at high concentrations in soil. Therefore, knowledge of Cu and Zn cycling in soils is required both for guaranteeing proper nutrition and to control possible risks arising from pollution.rnThe overall objective of my study was to test if Cu and Zn stable isotope ratios can be used to investigate into the biogeochemistry, source and transport of these metals in soils. The use of stable isotope ratios might be especially suitable to trace long-term processes occurring during soil genesis and transport of pollutants through the soil. In detail, I aimed to answer the questions, whether (1) Cu stable isotopes are fractionated during complexation with humic acid, (2) ���65Cu values can be a tracer for soil genetic processes in redoximorphic soils (3) ���65Cu values can help to understand soil genetic processes under oxic weathering conditions, and (4) ���65Cu and ���66Zn values can act as tracers of sources and transport of Cu and Zn in polluted soils.rnTo answer these questions, I ran adsorption experiments at different pH values in the laboratory and modelled Cu adsorption to humic acid. Furthermore, eight soils were sampled representing different redox and weathering regimes of which two were influenced by stagnic water, two by groundwater, two by oxic weathering (Cambisols), and two by podzolation. In all horizons of these soils, I determined selected basic soil properties, partitioned Cu into seven operationally defined fractions and determined Cu concentrations and Cu isotope ratios (���65Cu values). Finally, three additional soils were sampled along a deposition gradient at different distances to a Cu smelter in Slovakia and analyzed together with bedrock and waste material from the smelter for selected basic soil properties, Cu and Zn concentrations and ���65Cu and ���66Zn values.rnMy results demonstrated that (1) Copper was fractionated during adsorption on humic acid resulting in an isotope fractionation between the immobilized humic acid and the solution (���65CuIHA-solution) of 0.26 �� 0.11��� (2SD) and that the extent of fractionation was independent of pH and involved functional groups of the humic acid. (2) Soil genesis and plant cycling causes measurable Cu isotope fractionation in hydromorphic soils. The results suggested that an increasing number of redox cycles depleted 63Cu with increasing depth resulting in heavier ���65Cu values. (3) Organic horizons usually had isotopically lighter Cu than mineral soils presumably because of the preferred uptake and recycling of 63Cu by plants. (4) In a strongly developed Podzol, eluviation zones had lighter and illuviation zones heavier ���65Cu values because of the higher stability of organo-65Cu complexes compared to organo-63Cu complexes. In the Cambisols and a little developed Podzol, oxic weathering caused increasingly lighter ���65Cu values with increasing depth, resulting in the opposite depth trend as in redoximorphic soils, because of the preferential vertical transport of 63Cu. (5) The ���66Zn values were fractionated during the smelting process and isotopically light Zn was emitted allowing source identification of Zn pollution while ���65Cu values were unaffected by the smelting and Cu emissions isotopically indistinguishable from soil. The ���65Cu values in polluted soils became lighter down to a depth of 0.4 m indicating isotope fractionation during transport and a transport depth of 0.4 m in 60 years. ���66Zn values had an opposite depth trend becoming heavier with depth because of fractionation by plant cycling, speciation changes, and mixing of native and smelter-derived Zn. rnCopper showed measurable isotope fractionation of approximately 1��� in unpolluted soils, allowing to draw conclusions on plant cycling, transport, and redox processes occurring during soil genesis and ���65Cu and ���66Zn values in contaminated soils allow for conclusions on sources (in my study only possible for Zn), biogeochemical behavior, and depth of dislocation of Cu and Zn pollution in soil. I conclude that stable Cu and Zn isotope ratios are a suitable novel tool to trace long-term processes in soils which are difficult to assess otherwise.rn

The grain-scale distribution and behaviour of melt and fluid in crystalline analogue systems

The production, segregation and migration of melt and aqueous fluids (henceforth called liquid) plays an important role for the transport of mass and energy within the mantle and the crust of the Earth. Many properties of large-scale liquid migration processes such as the permeability of a rock matrix or the initial segregation of newly formed liquid from the host-rock depends on the grain-scale distribution and behaviour of liquid. Although the general mechanisms of liquid distribution at the grain-scale are well understood, the influence of possibly important modifying processes such as static recrystallization, deformation, and chemical disequilibrium on the liquid distribution is not well constrained. For this thesis analogue experiments were used that allowed to investigate the interplay of these different mechanisms in-situ. In high-temperature environments where melts are produced, the grain-scale distribution in ���equilibrium��� is fully determined by the liquid fraction and the ratio between the solid-solid and the solid-liquid surface energy. The latter is commonly expressed as the dihedral or wetting angle between two grains and the liquid phase (Chapter 2). The interplay of this ���equilibrium��� liquid distribution with ongoing surface energy driven recrystallization is investigated in Chapter 4 and 5 with experiments using norcamphor plus ethanol liquid. Ethanol in contact with norcamphor forms a wetting angle of about 25��, which is similar to reported angles of rock-forming minerals in contact with silicate melt. The experiments in Chapter 4 show that previously reported disequilibrium features such as trapped liquid lenses, fully-wetted grain boundaries, and large liquid pockets can be explained by the interplay of the liquid with ongoing recrystallization. Closer inspection of dihedral angles in Chapter 5 reveals that the wetting angles are themselves modified by grain coarsening. Ongoing recrystallization constantly moves liquid-filled triple junctions, thereby altering the wetting angles dynamically as a function of the triple junction velocity. A polycrystalline aggregate will therefore always display a range of equilibrium and dynamic wetting angles at raised temperature, rather than a single wetting angle as previously thought. For the deformation experiments partially molten KNO3���LiNO3 experiments were used in addition to norcamphor���ethanol experiments (Chapter 6). Three deformation regimes were observed. At a high bulk liquid fraction >10 vol.% the aggregate deformed by compaction and granular flow. At a ���moderate��� liquid fraction, the aggregate deformed mainly by grain boundary sliding (GBS) that was localized into conjugate shear zones. At a low liquid fraction, the grains of the aggregate formed a supporting framework that deformed internally by crystal plastic deformation or diffusion creep. Liquid segregation was most efficient during framework deformation, while GBS lead to slow liquid segregation or even liquid dispersion in the deforming areas.

Influence of pollination and seed dispersal on the genetic population structure of two Commiphora species in Madagascar and South Africa

Pollination and seed dispersal are important ecological processes for the regeneration of plant populations and both vectors for gene exchange between plant populations. For my thesis, I studied the pollination ecology of the South African tree Commiphora harveyi (Burseraceae) and compared it with C. guillauminii from Madagascar. Both species have low visitation rates and a low number of pollinating insect species, resulting in a low fruit set. While their pollination ecology is very similar, they differ in their seed dispersal with a low seed dispersal rate in the Malagasy and a high seed dispersal rate in the South African species. This should be reflected in a stronger genetic differentiation among populations in the Malagasy than in the South African species. My results, based on AFLP markers, contradict these expectations, the overall differentiation was lower in the Malagasy (FST = 0.05) than in the South African species (FST = 0.16). However, at a smaller spatial scale (below 3 km), the Malagasy species was genetically more strongly differentiated than the South African species, which was reflected by the high inter-population variance within the sample site (C. guillauminii: 72.2 - 85.5 %; C. harveyi: 8.4 - 14.5 %). This strong differentiation could arise from limited gene flow, which was confirmed by spatial autocorrelation analyses. The shape of the autocorrelogram suggested that gene exchange between individuals occurred only up to 3 km in the Malagasy species, whereas up to 30 km in the South African species. These results on the genetic structure correspond to the expectations based on seed dispersal data. Thus, seed dispersal seems to be a key factor for the genetic structure in plant populations on a local scale.

Nanostructuring by templated synthesis of nanowires and controlled crystallization of calcium phosphate on self-assembled monolayers

The idea was to obtain nanowires in a chemical laboratory under convenient and simple conditions by employing templates. Thus it was possible to produce nanochains by interlinking of gold colloids synthesized by the two-phase-method of M. Brust with by making use of vanadiumoxide nanotubes as template. The length of the resulting nanowires is varying between 1100 nm and 200 nm with a diameter of about 16 nm. Due to a flexible linker the obtained nanowires are not completely rigid. These unique structural features could make them interesting objects for structuring and assembling in the nanoscale range. Another way to produce gold nanowires was realized by a two-step surface metallization procedure, using type I collagen fibres as a template. Gold colloids were used to label the collagen fibres by direct electrostatic interaction, followed by growth steps to enhance the size of the adsorbed colloidal gold crystals, resulting in a complete metallization of the template surface. The length of the resulting gold nanowires reaches several micrometers, with a diameter ~ 100 to 120 nm. To gain a deeper insight into the process of biomineralization the cooperative effect of self-assembled monolayers as substrate and a soluble counterpart on the nucleation and crystal growth of calcium phosphate was studied by diffusion techniques with a pH switch as initiator. As soluble component Perlucin and Nacrein were used. Both are proteins originally extracted from marine organisms, the first one from the Abalone shell and the second one from oyster pearls. Both are supposed to facilitate the calcium carbonate formation in vivo. Studies with Perlucin revealed that this protein shows a clear cooperative effect at a very low concentration with a hydrophobic surface promoting the calcium phosphate precipitation resulting in a sponge like structure of hydroxyapatite. The Perlucin molecule is very flexible and is unfolded by adsorbing to the hydrophobic surface and uncovers its active side. Hydrophilic surfaces did not have a deeper impact. Studies with Nacrein as additive have shown that the protein stabilizes octacalcium phosphate at room temperature on carboxylic self-assembled monolayer and at 34 ��C on all other employed surfaces by interaction with the mineral. On the hydroxyl-, alkyl-, and amin-terminated self-assembled monolayers at room temperature the octacalcium phosphate get transformed to hydroxyapatite. Main analytical techniques which are used in this work are transmission electron microscopy, high resolution scanning electron microscopy, surface plasmon resonance spectroscopy, atomic force microscopy, Raman micro-spectroscopy and quartz crystal microbalance.

Influence of habitat and climate change on European bird communities

Die Fragmentierung von Waldgebieten, der Verlust geeigneter Habitate, die Invasion exotischer Arten und globale Klimaver��nderung haben auf Artengemeinschaften erhebliche Auswirkungen. V��gel dienen in vielen F��llen als Indikatorarten f��r Umweltver��nderungen und, besonders, f��r Ver��nderungen im Zusammenhang mit globaler Erw��rmung. In meiner Arbeit habe ich zuerst einen Literatur��berblick ��ber die Auswirkungen globaler Klimaver��nderung auf die Verbreitungsgebiete, den Artenreichtum und die Zusammensetzung von Vogelgemeinschaften dargestellt. Zahlreiche Untersuchungen zeigen, da�� die Grenzen der Verbreitungsgebiete der meisten Vogelarten mit klimatischen Faktoren korrelieren. Verschiebungen der Verbreitungsgebiete in n��rdliche Richtung oder in h��here Regionen im Gebirge konnten bereits f��r viele temperate Vogelarten beobachtet werden. Weiterhin wurde ein zunehmender Artenreichtum besonders in n��rdlichen Breiten und in h��heren Lagen f��r viele temperate Vogelgemeinschaften vorhergesagt. In trockenen Gebieten ist dagegen mit einer Abnahme des Artenreichtums zu rechnen. Im zweiten Teil meiner Arbeit habe ich untersucht, ob beobachtete Ver��nderungen in der Zusammensetzung europ��ischer Vogelgemeinschaften tats��chlich durch aktuelle Klimaver��nderungen beeinflu��t werden. Das Zugverhalten der Arten war dabei ein Schwerpunkt der Untersuchung, weil zu erwarten war, da�� Vogelarten mit verschiedenem Zugverhalten unterschiedlich auf Klimaver��nderungen reagieren. Ich habe ein Regressionsmodell genutzt, welches die r��umliche Beziehung zwischen dem Anteil von Langstreckenziehern, Kurzstreckenziehern und Standv��geln in europ��ischen Vogelgemeinschaften und verschiedenen Klimavariablen beschreibt. F��r 21 Gebiete in Europa habe ich Daten ��ber beobachtete Ver��nderungen in der Struktur der Vogelgemeinschaften und isochrone Klimaver��nderungen zusammengetragen. Mit Hilfe dieser Klimaver��nderungen und dem r��umlichen Regressionsmodell konnte ich berechnen, welche Ver��nderungen in den Vogelgemeinschaften aufgrund der ver��nderten Klimabedingungen zu erwarten w��ren und sie mit beobachteten Ver��nderungen vergleichen. Beobachtete und berechnete Ver��nderungen korrelierten signifikant miteinander. Die beobachteten Ver��nderungen konnten nicht durch r��umliche Autokorrelationseffekte oder durch alternative Faktoren, wie z.B. Ver��nderungen in der Landnutzung, erkl��rt werden. Im dritten Teil der Arbeit untersuchte ich f��r eine mitteleurop��ische Vogelgemeinschaft welchen Einflu�� Habitatver��nderungen, die Invasion exotischer Arten und die Klimaver��nderung auf Ver��nderungen der H��ufigkeit und Verbreitungsgr����e der 159 Vogelarten am Bodensee zwischen 1980-1981 und 2000-2002 hatten. Dabei konnte gezeigt werden, da�� Ver��nderungen in der regionalen Abundanz sowohl durch Habitatver��nderungen als auch durch Klimav��nderungen hervorgerufen wurden. Exotische Arten schienen in dieser Zeit keinen bedeutenden Einflu�� zu haben. Besonders bei Agrarlandarten, Arten mit n��rdlicheren Verbreitungsgebieten und bei Langstreckenziehern konnten signifikante Abnahmen in der Abundanz beobachtet werden. Vor allem die anhaltenden negativen Bestandsver��nderungen bei Langstreckenziehern und die in den letzten zehn Jahren aufgetretenen Abnahmen n��rdlicher verbreiteter Vogelarten deuten darauf hin, da�� die Klimaver��nderung aktuell als der gr����te Einflu�� f��r V��gel in Europa angesehen werden mu��. Insgesamt zeigen die Ergebnisse dieser Arbeit, da�� sich der anhaltende Druck auf die Umwelt in erster Linie durch Habitat- und Klimaver��nderungen manifestiert.

A study of nitronyl and imino nitroxide radicals attached to heterocyclic cores

Stabile organische Radikale mit zus��tzlichen Funktionalit��ten wie Donor/Akzepotor Eigenschaften und Ligandeneignung f��r ��bergangsmetallkomplexierung repr��sentieren eine synthetische Herausforderung beim Streben nach der Konstruktion hochdimensionaler heterospin Strukturen. In diesem Hinblick wurden acht neue Hochspinbiradikal-Molek��le zusammen mit ihren Monoradikal- Pendants in dieser Arbeit hergestellt. Die Wahl der Liganden als organische Distanzhalter der Radikaleinheiten wurde auf stickstoffhaltige Heterozyklen (Pyridin und Pyrazol) gelenkt. Diese wurden weiterhin mit den stabilen Spintr��gern Nitronylnitroxid- (NN) und Iminonitroxidfragmenten (IN) dekoriert. Ihre Synthese beinhaltete mehrstufige Umsetzungen (Brominierung, Iodierung, N- und Carbaldehyd Schutzgruppen, Stille-Kupplung, Grignard Reaktion, etc.) um die Mono- und Dicarbaldehyd-heterocyclenderivate als Schl��sselvorl��ufer der Radikaleinheiten zu gewinnen. Die Carbaldehyd-Zwischenstufen wurden Kondensationsreaktionen mit 2,3-Dimethyl-2,3-bis(hydroxylamino)-butan unterworfen (��blicherweise in Dioxan unter Argon f��r ~ 7 Tage), gefolgt von der Oxidation der Bis-hydroxylimidazolidin-Vorl��ufer unter Phasentransferkatalyse (NaIO4/H2O). Die Radikalmolek��le wurden mit verschiedenen spektroskopischen Methoden untersucht (FT/IR, UV/Vis/ EPR etc.) und ihre Einkristalle mit R��ntgenstrahlbeugung gemessen. Die UV/VIS- L��sungsspektren zeigten in einem breiten Bereich verschiedener L��sungsmittelpolarit��ten keine spezifische Wechselwirkung zwischen L��sungsmittel und Radikaleinheit, w��hrend ihre Stabilit��ten in protischen L��sunsgmitteln wie MeOH stark abnahmen. Als Pulver konnten sie jedoch im K��hlschrank an der Luft f��r eine Jahr gelagert werden, ohne sich zu zersetzen. Die spektroskopischen Fingerabdr��cke der Radikale wurden eindeutig identifiziert and erschienen stark abh��ngig vom Typ des pi-Ringsystems an das die Spintr��ger gekoppelt wurden. Basierend auf diesen Informationen wurde ein schnelles Protokoll etabliert, das eine direkte Zuordnung der Art der Radikale und ihrer Anzahl erm��glicht, sowie ihre Reinheit und Verunreinigungen zu definieren. In L��sung best��tigte die Analyse der EPR Spektren der Biradikale die starke Austauschwechselwirkung J zwischen den Radikalfragmenten ��ber die Kopplungseinheiten (J >> an, an ist die Stickstoffhyperfeinkopplungskonstante). Dies wurde weiter unterst��tzt durch die Beobachtungen in gefrorener L��sung ��ber die Nullfeldaufspaltungen und verbotenen Halbfeld��berg��nge (��ms = 2). Die Temperaturabh��ngigkeiten der ��ms = 2 - EPR Signale wurden bis herunter auf 4 K gemessen und das exakte Vorzeichen und die Gr����e von J ermittelt. Diese Arbeit unterstreicht die M��glichkeit ��ber synthetische Chemie eine Feineinstellung der ���through bond��� Austauschwechselwirkung zwischen verwandten pi���- und sigma- konjugierten Heterozyklen zu erreichen, in denen der S = 1 Grundzustand angenommen wird. Zus��tzlich zeigten diese Resultate, dass die ��bertragung der Spinpolarisation durch verschiedene Koppler sehr effektiv war.

Size-selective investigations of spectral and emission properties of small particles and nanotubes

In dieser Arbeit wurde die Elektronenemission von Nanopartikeln auf Oberfl��chen mittels spektroskopischen Photoelektronenmikroskopie untersucht. Speziell wurden metallische Nanocluster untersucht, als selbstorganisierte Ensembles auf Silizium oder Glassubstraten, sowie ferner ein Metall-Chalcogenid (MoS2) Nanor��hren-Prototyp auf Silizium. Der Hauptteil der Untersuchungen war auf die Wechselwirkung von fs-Laserstrahlung mit den Nanopartikeln konzentriert. Die Energie der Lichtquanten war kleiner als die Austrittsarbeit der untersuchten Proben, so dass Ein-Photonen-Photoemission ausgeschlossen werden konnte. Unsere Untersuchungen zeigten, dass ausgehend von einem kontinuierlichen Metallfilm bis hin zu Clusterfilmen ein anderer Emissionsmechanismus konkurrierend zur Multiphotonen-Photoemission auftritt und f��r kleine Cluster zu dominieren beginnt. Die Natur dieses neuen Mechanismus` wurde durch verschiedenartige Experimente untersucht. Der ��bergang von einem kontinuierlichen zu einem Nanopartikelfilm ist begleitet von einer Zunahme des Emissionsstroms von mehr als eine Gr����enordnung. Die Photoemissions-Intensit��t w��chst mit abnehmender zeitlicher Breite des Laserpulses, aber diese Abh��ngigkeit wird weniger steil mit sinkender Partikelgr����e. Die experimentellen Resultate wurden durch verschiedene Elektronenemissions-Mechanismen erkl��rt, z.B. Multiphotonen-Photoemission (nPPE), thermionische Emission und thermisch unterst��tzte nPPE sowie optische Feldemission. Der erste Mechanismus ��berwiegt f��r kontinuierliche Filme und Partikel mit Gr����en oberhalb von mehreren zehn Nanometern, der zweite und dritte f��r Filme von Nanopartikeln von einer Gr����e von wenigen Nanometern. Die mikrospektroskopischen Messungen best��tigten den 2PPE-Emissionsmechanismus von d��nnen Silberfilmen bei ���blauer��� Laseranregung (h��=375-425nm). Das Einsetzen des Ferminiveaus ist relativ scharf und verschiebt sich um 2h��, wenn die Quantenenergie erh��ht wird, wogegen es bei ���roter��� Laseranregung (h��=750-850nm) deutlich verbreitert ist. Es zeigte sich, dass mit zunehmender Laserleistung die Ausbeute von niederenergetischen Elektronen schw��cher zunimmt als die Ausbeute von h��herenergetischen Elektronen nahe der Fermikante in einem Spektrum. Das ist ein klarer Hinweis auf eine Koexistenz verschiedener Emissionsmechanismen in einem Spektrum. Um die Gr����enabh��ngigkeit des Emissionsverhaltens theoretisch zu verstehen, wurde ein statistischer Zugang zur Lichtabsorption kleiner Metallpartikel abgeleitet und diskutiert. Die Elektronenemissionseigenschaften bei Laseranregung wurden in zus��tzlichen Untersuchungen mit einer anderen Anregungsart verglichen, der Passage eines Tunnelstroms durch einen Metall-Clusterfilm nahe der Perkolationsschwelle. Die elektrischen und Emissionseigenschaften von stromtragenden Silberclusterfilmen, welche in einer schmalen L��cke (5-25 ��m Breite) zwischen Silberkontakten auf einem Isolator hergestellt wurden, wurden zum ersten Mal mit einem Emissions-Elektronenmikroskop (EEM) untersucht. Die Elektronenemission beginnt im nicht-Ohmschen Bereich der Leitungsstrom-Spannungskurve des Clusterfilms. Wir untersuchten das Verhalten eines einzigen Emissionszentrums im EEM. Es zeigte sich, dass die Emissionszentren in einem stromleitenden Silberclusterfilm Punktquellen f��r Elektronen sind, welche hohe Emissions-Stromdichten (mehr als 100 A/cm2) tragen k��nnen. Die Breite der Energieverteilung der Elektronen von einem einzelnen Emissionszentrum wurde auf etwa 0.5-0.6 eV abgesch��tzt. Als Emissionsmechanismus wird die thermionische Emission von dem ���steady-state��� hei��en Elektronengas in stromdurchflossenen metallischen Partikeln vorgeschlagen. Gr����enselektierte, einzelne auf Si-Substraten deponierte MoS2-Nanor��hren wurden mit einer Flugzeit-basierten Zweiphotonen-Photoemissions-Spektromikroskopie untersucht. Die Nanor��hren-Spektren wiesen bei fs-Laser Anregung eine erstaunlich hohe Emissionsintensit��t auf, deutlich h��her als die SiOx Substratoberfl��che. Dagegen waren die R��hren unsichtbar bei VUV-Anregung bei h��=21.2 eV. Eine ab-initio-Rechnung f��r einen MoS2-Slab erkl��rt die hohe Intensit��t durch eine hohe Dichte freier intermedi��rer Zust��nde beim Zweiphotonen-��bergang bei h��=3.1 eV.

���This is TZ power! Kenkey can���t do this!��� : Die performative Aushandlung nationaler Kultur ; das National Festival of Arts and Culture in Ghana /// Arbeitspapiere / Institut f��r Ethnologie und Afrikastudien ; 92

Der vorliegende Artikel besch��ftigt sich mit der performativen Aushandlung nationaler Kultur auf dem National Festival of Arts and Culture, das 2006 in Wa, Nordwestghana, stattfand. Die Autorin nahm an der Vorbereitung und Planung des Festivals in lokalen staatlichen Kulturinstitutionen teil, und beobachtete die Diskussionen um die Repr��sentation einer (imaginierten) spezifischen Kultur des Nordens in scharfer Abgrenzung zu der des als dominant und diskriminierend empfundenen S��dens. In diesem Zusammenhang werden Fragen der Authentizit��t und Authentifizierung, wie sie in der Planung und Rezeption diskutiert wurden, aufgegriffen und mit der Konzeption des Festivals als gleichzeitig einheitsstiftendes Vehikel f��r nationale Identit��t und als Austragungsort eines Wettbewerbs der Regionen um Anerkennung und Ressourcen in Verbindung gesetzt. Das Festival, so die Argumentation, ist eine cultural performance, die das Wesen einer ���Kultur��� nicht nur abbildet, sondern auch die M��glichkeit des Wandels und der Subversion birgt. Performance meint hier also gleichzeitig die Auff��hrung und das Skript der Diskurse, die der Auff��hrung Bedeutung zuschreiben. Diesen doppelten Ansatz verfolgt der Artikel durch die Verkn��pfung von Festivalbeobachtungen und Komiteesitzungsmitschriften im Rahmen der Vorbereitung.

DNA hybrid materials consisting of oligonucleotides and organic molecules: synthesis, characterization and applications

The goal of this thesis was to increase the functionality of pristine DNA scaffolds by functionalizing them with fluorescent dyes and hydrophobic moieties. Two important steps were necessary to realize this aim successfully. First, nucleic acids needed to be synthesized making use of multidisciplinary toolbox for the generation and manipulation of polynucleic acids. The most important techniques were the solid phase synthesis involving the incorporation of standard and modified phosphoramidite building blocks as well as molecular biology procedures like the polymerase chain reaction, the bacterial amplification of plasmids and the enzymatic digestion of circular vectors. Second, and evenly important, was the characterization of the novel bioorganic hybrid structures by a multitude of techniques, especially optical measurements. For studying DNA-dye conjugates methods like UV/Vis and photoluminescence spectroscopy as well as time resolved luminescence spectroscopy were utilized. While these measurements characterized the bulk behavior of an ensemble of DNA-dye hybrids it was necessary for a complete understanding of the systems to look at single structures. This was done by single-molecule fluorescence spectroscopy and fluorescence correlation spectroscopy. For complete analysis the optical experiments were complemented by direct visualization techniques, i.e. high resolution transmission electron microscopy and scanning force microscopy.

Characterization of structure and dynamics of submicrometric systems via fluorescence correlation spectroscopy

The presented thesis revolves around the study of thermally-responsive PNIPAAm-based hydrogels in water/based environments, as studied by Fluorescence Correlation Spectroscopy (FCS).rnThe goal of the project was the engineering of PNIPAAm gels into biosensors. Specifically, a gamma of such gels were both investigated concerning their dynamics and structure at the nanometer scale, and their performance in retaining bound bodies upon thermal collapse (which PNIPAAm undergoes upon heating above 32 ��C).rnFCS���s requirements, as a technique, match the limitations imposed by the system. Namely, the need to intimately probe a system in a solvent, which was also fragile and easy to alter. FCS, on the other hand, both requires a fluid environment to work, and is based on the observation of diffusion of fluorescents at nanomolar concentrations. FCS was applied to probe the hydrogels on the nanometer size with minimal invasivity.rnVariables in the gels were addressed in the project including crosslinking degree; structural changes during thermal collapse; behavior in different buffers; the possibility of decreasing the degree of inhomogeneity; behavior of differently sized probes; and the effectiveness of antibody functionalization upon thermal collapse.rnThe evidenced results included the heightening of structural inhomogeneities during thermal collapse and under different buffer conditions; the use of annealing to decrease the inhomogeneity degree; the use of differently sized probes to address different length scale of the gel; and the successful functionalization before and after collapse.rnThe thesis also addresses two side projects, also carried forward via FCS. One, diffusion in inverse opals, produced a predictive simulation model for diffusion of bodies in confined systems as dependent on the bodies��� size versus the characteristic sizes of the system. The other was the observation of interaction of bodies of opposite charge in a water solution, resulting in a phenomenological theory and an evaluation method for both the average residence time of the different bodies together, and their attachment likelihood.

Synthesis and characterization of temperature- and light-responsive polymers and block copolymers

In summary, thermoresponsive polyacrylamides with various amounts of different photoswitchable side groups, i. e. azobenzene, salicylideneaniline and fulgimide were successfully prepared. As such, in a first step three different chromophores with an amine functionality were synthesized. The synthesis of the stimuli-responsive materials was based on the RAFT polymerization of activated ester acrylates followed by a polymer analogous reaction with different amines. The procedure has been designed to allow the synthesis of well-defined materials with functional groups. All copolymers prepared in this way showed a LCST in aqueous solution. The LCST was in general decreased by increasing the amount of hydrophobic dye incorporated into the thermoresponsive polymer. However, in the case of the fulgimide, the LCST was hardly affected by the chromophore. For azobenzene containing PNIPAM polymers and analogues, higher LCST values were measured after irradiation of the polymer sample solutions with UV-light (Delta LCSTmax = 7.3��C). A reversible light-induced solubility change within a certain temperature range was possible. In contrast to this, irradiated samples of salicylideneaniline containing thermoresponsive copolymers showed an irreversible increase in the LCST (Delta LCSTmax = 13.0��C). Fulgimide chromophores did not influence the LCST of PNIPAM based copolymers after UV-light exposure.rnSimilar to the thermoresponsive polyacrylamides with azobenzene side groups, poly(oligo(ethylene glycol) methyl ether methacrylate) [P(OEGMA)] polymers with azobenzene end groups showed a LCST shift upon UV-irradiation. These polymers were synthesized by RAFT polymerization using a functional chain transfer agent (CTA). For this, PFP-CTA was used as a RAFT-agent for end group functionalization of (thermoresponsive) polymers. In contrast to the statistically arranged copolymers with azobenzene side groups, P(OEGMA) polymers with terminal azobenzene showed a linear increase of the LCST shifts with increasing amount of chromophore (Delta LCSTmax = 4.3��C). Noteworthy, the chemical nature of the end group exhibited a strong influence on the LCST in the case of short thermoresponsive P(OEGMA) polymers.rnThe investigation on temperature- and lightresponsive polymers was transferred onto block copolymers capable to self-assemble into polymeric micelles. Therefore, PEO-b-PNIPAM block copolymers with azobenzene moieties were synthesized successfully. These polymers showed a ���smart��� behavior in aqueous solution, as the reversible formation and disruption of the micelles could either be controlled by temperature or using light as a stimulus. The usefulness of these materials was demonstrated by encapsulation of a hydrophobic dye in the core of the micelle. Such materials might have a great potential as a model system for several technical or biological applications.rnFinally, double thermoresponsive block copolymers forming micellar structures in a certain temperature range with functional end groups could successfully be synthesized. These ���smart materials��� based on POEGMA-b-PNIPMAM have been demonstrated to be very promising for a temperature selective immobilization on a protein surface. This might be a suitable concept for further biological applications.rnConcluding, different thermoresponsive copolymers and block copolymers with lightresponsive moieties arranged along the backbone or located at the chain ends were successfully prepared and investigated. By controlling the nature of functional groups and their respective incorporation ratios, the LCST could be dialed in precisely. Further, the LCST of the polymers could be triggered by light. A light-controlled disruption of micellar structures could be shown for functional block copolymers. The importance of end groups of thermoresponsive polymers was demonstrated by a temperature-controlled protein-polymer binding of a terminal biotin-functionalized double thermoresponsive polymer. The synthetic approaches and the material properties presented here should be promising for further research and applications beyond this dissertation.rn

Structure and properties of quaternary and tetragonal Heusler compounds for spintronics and spin transfer torque applications

Diese Dissertation ist in zwei Teile aufgeteilt: Teil 1 befasst sich mit der Vorhersage von Halb-Metallizit��t in quartern��ren Heuslerverbindungen und deren Potential f��r Spintronik-Anwendungen. Teil 2 befasst sich mit den strukturellen Eigenschaften der Mn2-basierenden Heuslerverbindungen und dem Tuning von ihrer magnetischen Eigenschaften bzgl. Koerzitivfeldst��rke und Remanenz. Diese Verbindungen sind geeignet f��r Spin-Transfer Torque-Anwendungen.rnrnIn Teil 1 wurden die folgenden drei Probenserien quartern��rer Heuslerverbindungen untersucht: XX��MnGa (X = Cu, Ni und X�� = Fe, Co), CoFeMnZ (Z = Al, Ga, Si, Ge) und Co2���xRhxMnZ (Z = Ga, Sn, Sb). Abgesehen von CuCoMnGa wurden alle diese Verbindungen mittels ab-initio Bandstrukturrechnungen als halbmetallische Ferromagnete prognostiziert. In der XX��MnGa-Verbindungsklasse besitzt NiFeMnGa zwar eine zu niedrige Curie-Temperatur f��r technologische Anwendungen, jedoch NiCoMnGa mit seiner hohen Spinpolarisation, einem hohen magnetischen Moment und einer hohen Curie-Temperatur stellt ein neues Material f��r Spintronik-Anwendungen dar. Alle CoFeMnZ-Verbindungen kristallisieren in der kubischen Heuslerstruktur und ihre magnetischen Momente folgen der Slater-Pauling-Regel, was Halbmetalizit��t und eine hohe Spinpolarisation impliziert. Die ebenfalls hohen Curie-Temperaturen erm��glichen einen Einsatz weit ��ber Raumtemperatur hinaus. In der strukturellen Charakterisierung wurde festgestellt, dass s��mtliche Co2���xRhxMnZ abgesehen von CoRhMnSn verschiedene Typen von Unordnung aufweisen; daher war die ermittelte Abweichung von der Slater-Pauling-Regel sowie von der 100%-igen Spinpolarisation dieser Verbindungen zu erwarten. Die Halbmetallizit��t der geordneten CoRhMnSn-Verbindung sollte nach den durchgef��hrten magnetischen Messungen vorhanden sein.rnrnIm zweiten Teil wurden Mn3���xCoxGa und Mn2���xRh1+xSn synthetisiert und charakterisiert. Es wurde gezeigt, dass Mn3���xCoxGa im Bereich x = 0.1 ��� 0.4 in einer tetragonal verzerrten inversen Heuslerstruktur kristallisiert und im Bereich x = 0.6���1 in einer kubisch inversen Heuslerstruktur. W��hrend die tetragonalen Materialien hartmagnetisch sind und Charakeristika aufweisen, die typischerweise f��r Spin-Transfer Torque-Anwengungen attraktiv sind, repr��sentieren die weichmagnetischen kubischen Vertreter die 100% spinpolarisierten Materialien, die der Slater-Pauling-Regel folgen. Mn2RhSn kristallisiert in der inversen tetragonal verzerrten Heuslerstruktur, weist einernhartmagnetische Hystereseschleife auf und folgt nicht der Slater-Pauling-Regel. Bei hohen Rh-Gehalt wird die kubische inverse Heuslerstruktur gebildet. Alle kubischen Proben sind weichmagnetisch und folgen der Slater-Pauling-Regel.

Hard x-ray photoelectron spectroscopy of bulk and thin films of Heusler compounds

X-ray photoemission spectroscopy (XPS) is one of the most universal and powerful tools for investigation of chemical states and electronic structures of materials. The application of hard x-rays increases the inelastic mean free path of the emitted electrons within the solid and thus makes hard x-ray photoelectron spectroscopy (HAXPES) a bulk sensitive probe for solid state research and especially a very effective nondestructive technique to study buried layers.rnThis thesis focuses on the investigation of multilayer structures, used in magnetic tunnel junctions (MTJs), by a number of techniques applying HAXPES. MTJs are the most important components of novel nanoscale devices employed in spintronics. rnThe investigation and deep understanding of the mechanisms responsible for the high performance of such devices and properties of employed magnetic materials that are, in turn, defined by their electronic structure becomes feasible applying HAXPES. Thus the process of B diffusion in CoFeB-based MTJs was investigated with respect to the annealing temperature and its influence on the changes in the electronic structure of CoFeB electrodes that clarify the behaviour and huge TMR ratio values obtained in such devices. These results are presented in chapter 6. The results of investigation of the changes in the valence states of buried off-stoichiometric Co2MnSi electrodes were investigated with respect to the Mn content �� and its influence on the observed TMR ratio are described in chapter 7.rnrnMagnetoelectronic properties such as exchange splitting in ferromagnetic materials as well as the macroscopic magnetic ordering can be studied by magnetic circular dichroism in photoemission (MCDAD). It is characterized by the appearance of an asymmetry in the photoemission spectra taken either from the magnetized sample with the reversal of the photon helicity or by reversal of magnetization direction of the sample when the photon helicity direction is fixed. Though recently it has been widely applied for the characterization of surfaces using low energy photons, the bulk properties have stayed inaccessible. Therefore in this work this method was integrated to HAXPES to provide an access to exploration of magnetic phenomena in the buried layers of the complex multilayer structures. Chapter 8 contains the results of the MCDAD measurements employing hard x-rays for exploration of magnetic properties of the common CoFe-based band-ferromagnets as well as half-metallic ferromagnet Co2FeAl-based MTJs.rnrnInasmuch as the magnetoresistive characteristics in spintronic devices are fully defined by the electron spins of ferromagnetic materials their direct measurements always attracted much attention but up to date have been limited by the surface sensitivity of the developed techniques. Chapter 9 presents the results on the successfully performed spin-resolved HAXPES experiment using a spin polarimeter of the SPLEED-type on a buried Co2FeAl0.5Si0.5 magnetic layer. The measurements prove that a spin polarization of about 50 % is retained during the transmission of the photoelectrons emitted from the Fe 2p3/2 state through a 3-nm-thick oxide capping layer.rn

Hundertneunundzwanzig Xe NMR for investigations of complex and dynamic systems

In this work, the remarkable versatility and usefulness of applications of Xe-129 NMR experiments is further extended. The application of Xe-129 NMR spectroscopy to very different system is studied, including dynamic and static, solid and liquid, porous and non-porous systems. Using the large non-equilibrium polarization created by hyperpolarization of Xe-129, time-resolved NMR measurements can be used for the online-monitoring of dynamic systems. In the first part of this work, several improvements for medical applications of hyperpolarized Xe-129 are achieved and their feasibility shown experimentally. A large gain in speed and reproducibility of the accumulation process of Xe-129 as ice and an enhancement of the usable polarization in any experiment requiring prior accumulation are achieved. An enhancement of the longitudinal relaxation time of Xe-129 is realized by admixture of a buffer gas during the storage of hyperpolarized Xe-129. Pursuing the efforts of simplifying the accumulation process and enhancing the storage time of hyperpolarized Xe-129 will allow for a wider use of the hyperpolarized gas in (medical) MRI experiments. Concerning the use of hyperpolarized Xe-129 in MRI, the influence of the diffusion coefficient of the gas on parameters of the image contrast is experimentally demonstrated here by admixture of a buffer gas and thus changing the diffusion coefficient. In the second part of this work, a polymer system with unique features is probed by Xe-129 NMR spectroscopy, proving the method to be a valuable tool for the characterization of the anisotropic properties of semicrystalline, syndiotactic polystyrene films. The polymer films contain hollow cavities or channels with sizes in the sub-nanometer range, allowing for adsorption of Xe-129 and subsequent NMR measurements. Despite the use of a ���real-world��� system, the transfer of the anisotropic properties from the material to adsorbed Xe-129 atoms is shown, which was previously only known for fully crystalline materials. The anisotropic behavior towards atomar guests inside the polymer films is proven here for the first time for one of the phases. For the polymer phase containing nanochannels, the dominance of interactions between Xe-129 atoms in the channels compared to interactions between Xe atoms and the channel walls are proven by measurements of a powder sample of the polymer material and experiments including the rotation of the films in the external magnetic field as well as temperature-dependent measurements. The characterization of ���real-world��� systems showing very high degrees of anisotropy by Xe-129 are deemed to be very valuable in future applications. In the last part of this work, a new method for the online monitoring of chemical reactions has been proposed and its feasibility and validity are experimentally proven. The chemical shift dependence of dissolved Xe-129 on the composition of a reaction mixture is used for the online monitoring of free-radical miniemulsion polymerization reactions. Xe-129 NMR spectroscopy provides an excellent method for the online monitoring of polymerization reactions, due to the simplicity of the Xe-129 NMR spectra and the simple relationship between the Xe-129 chemical shift and the reaction conversion. The results of the time-resolved Xe-129 NMR measurements are compared to those from calorimetric measurements, showing a good qualitative agreement. The applicability of the new method to reactions other than polymerization reactions is investigated by the online monitoring of an enzymatic reaction in a miniemulsion. The successful combination of the large sensitivity of Xe-129, the NMR signal enhancements due to hyperpolarization, and the solubility of Xe-129 gives access to the large new field of investigations of chemical reaction kinetics in dynamic and complex systems like miniemulsions.

Efficient certification of feasibility and objective value of linear programs and its applications

The use of linear programming in various areas has increased with the significant improvement of specialized solvers. Linear programs are used as such to model practical problems, or as subroutines in algorithms such as formal proofs or branch-and-cut frameworks. In many situations a certified answer is needed, for example the guarantee that the linear program is feasible or infeasible, or a provably safe bound on its objective value. Most of the available solvers work with floating-point arithmetic and are thus subject to its shortcomings such as rounding errors or underflow, therefore they can deliver incorrect answers. While adequate for some applications, this is unacceptable for critical applications like flight controlling or nuclear plant management due to the potential catastrophic consequences. We propose a method that gives a certified answer whether a linear program is feasible or infeasible, or returns unknown'. The advantage of our method is that it is reasonably fast and rarely answers unknown'. It works by computing a safe solution that is in some way the best possible in the relative interior of the feasible set. To certify the relative interior, we employ exact arithmetic, whose use is nevertheless limited in general to critical places, allowing us to rnremain computationally efficient. Moreover, when certain conditions are fulfilled, our method is able to deliver a provable bound on the objective value of the linear program. We test our algorithm on typical benchmark sets and obtain higher rates of success compared to previous approaches for this problem, while keeping the running times acceptably small. The computed objective value bounds are in most of the cases very close to the known exact objective values. We prove the usability of the method we developed by additionally employing a variant of it in a different scenario, namely to improve the results of a Satisfiability Modulo Theories solver. Our method is used as a black box in the nodes of a branch-and-bound tree to implement conflict learning based on the certificate of infeasibility for linear programs consisting of subsets of linear constraints. The generated conflict clauses are in general small and give good rnprospects for reducing the search space. Compared to other methods we obtain significant improvements in the running time, especially on the large instances.