Publikationen

This paper provides a selective description of the development of nanostructured materials and the fabrication of the devices for optical applications. Examples are interference coatings, refractive and diffractive lenses, and macro- and micro-GRIN (graded refractive index) optical elements. Hybrid materials containing nanoparticles are of particular interest for the production of optical elements because, by exploiting the intrinsic solid state properties of the nanoparticles, nanocomposites can be tailored to exhibit the desired properties. A particular advantage of wet chemical processing lies in its great flexibility for depositing functional coatings.

Die Arbeit beschreibt die Entwicklung eines neuen Materials, das auf eine mechanische Belastung zehnmal empfindlicher reagiert als die heute genutzten metallischen DMS-Materialen. In diesem Kompositmaterial liegen mit Kohlenstoff umhüllte Nickelcluster mit einem Durchmesser zwischen 10 nm und 20 nm vor. Die Umhüllungen bestehen aus einigen gebogen Graphenlagen, die die Nickelcluster wie Zwiebelschalen umgeben. Elektronenmikroskopische Aufnahmen zeigten, dass die Metallcluster isoliert voneinander vorliegen, sich also nicht berühren, so dass der Stromtransport durch die Hüllen aus Kohlenstoff beeinträchtigt ist. Wird nun eine Dehnung oder Verzerrung dieses komplexen Materials zB durch einen äußeren Druck hervorgerufen, so beeinflusst dies den Stromtransport durch das Material, also seinen elektrischen Widerstand, sehr stark. Dies ermöglicht eine sehr empfindliche elektrische Messung des Drucks oder der Kraft. Neben einer um den Faktor elf erhöhten Dehnungsempfindlichkeit (k-Faktor bis zu 22) im Gegensatz zu herkömmlichen DMS-Materialen weisen diese Dünnschichten einen auf null einstellbaren Temperaturkoeffizienten des elektrischen Widerstands auf (TKR kleiner als ±25 ppm/K). Erste Prototypen in Form von Stahlmembran-Drucksensoren zeigen eindrucksvoll das Potenzial dieser Dünnschichten für Sensoranwendungen auf. Die hohe Dehnungsempfindlichkeit konnte bestätigt werden, auch viele weitere Sensorparameter wie z. B. das Kriechen, die Linearität der Kennlinie und das Signalrauschen konnten untersucht werden und liegen in für diese Sensoren typischen Bereichen.

The aim of our present study was the development of a drug multilayer-based carrier system for delivery of water-insoluble drugs. As drug, we applied the anticancer drug 5,10,1 5,20-tetrakis(3-hydroxyphenyl)porphyrin, mTHPP. which is a model photosensitizer or photodynamic therapy. Gold nanoparticles (AuNP) with a diameter of 14.5 +/- 0.9 am were prepared and used as template for the layer-by-layer approach. The drug and the negatively charged polyelectrolyte (PC) poly(styrene sulfonate) sodium salt (PSS) were complexed with a new developed method using freeze-drying. The complexation efficiency was determined to be similar to 11-12 monomers PSS per mTHPP molecule by CHNS analysis and UV/vis measurement. Molecular (locking simulations revealed pi-pi interactions and H-bonding to be the responsible mechanisms. A drug multilayer system based on the layer-by-layer (LbL) technique utilized the water-soluble complex is anionic layer material and poly(allylamine hydrochloride) (PAH) as cationic layer. The modified AuNP were characterized by different physicochemical techniques such as UV/vis. zeta-potential, ICP-OES, and TEM. To the best of our knowledge. We could demonstrate for the first time the adsorption of three drug layers to a nanoparticulate system. Furthermore, the adaptation of the LbL-technique resulted in drastically increased drug deposition efficiency (factor of 100). Furthermore, we developed a new and comfortable way to solubilize water-insoluble drugs in water.

A theoretical framework for dislocation dynamics in quasicrystals is provided according to the continuum theory of dislocations. Firstly, we present the fundamental theory for moving dislocations in quasicrystals giving the dislocation density tensors and introducing the dislocation current tensors for the phonon and phason fields, including the Bianchi identities. Next, we give the equations of motion for the incompatible elastodynamics as well as for the incompatible elasto-hydrodynamics of quasicrystals. We continue with the derivation of the balance law of pseudomomentum thereby obtaining the generalized forms of the Eshelby stress tensor, the pseudomomentum vector, the dynamical Peach-Koehler force density and the Cherepanov force density for quasicrystals. The form of the dynamical Peach-Koehler force for a straight dislocation is obtained as well. Moreover, we deduce the balance law of energy that gives rise to the generalized forms of the field intensity vector and the elastic power density of quasicrystals. The above balance laws are produced for both models. The differences between the two models and their consequences are revealed. The influences of the phason fields as well as of the dynamical terms are also discussed.

Plant shoots have thick, polylamellate outer epidermal walls based on crossed layers of cellulose microfibrils, but the involvement of microtubules in such wall lamellation is unclear. Recently, using a long-term movie system in which Arabidopsis seedlings were grown in a biochamber, the tracks along which cortical microtubules move were shown to undergo slow rotary movements over the outer surface of hypocotyl epidermal cells. Because microtubules are known to guide cellulose synthases over the short term, we hypothesised that this previously unsuspected microtubule rotation could, over the longer term, help explain the cross-ply structure of the outer epidermal wall. Here, we test that hypothesis using Arabidopsis plants expressing the cellulose synthase GFP-CESA3 and show that cellulose synthase trajectories do rotate over several hours. Neither microtubule-stabilising taxol nor microtubule-depolymerising oryzalin affected the linear rate of GFP-CESA3 movement, but both stopped the rotation of cellulose synthase tracks. Transmission electron microscopy revealed that drug-induced suppression of rotation alters the lamellation pattern, resulting in a thick monotonous wall layer. We conclude that microtubule rotation, rather than any hypothetical mechanism for wall self-assembly, has an essential role in developing cross-ply wall texture.

The unicellular, simply shaped desmid Netrium digitus inhabiting acid bog ponds grows in two phases. Prior to division, the cell elongates at its central zone, whereas in a second phase, polar tip growth occurs. Electron microscopy demonstrates that Netrium is surrounded by a morphologically homogeneous cell wall, which lacks pores. Immunocytochemical and biochemical analyses give insight into physical wall properties and, thus, into adaptation to the extreme environment. The monoclonal antibodies JIM5 and JIM7 directed against pectic epitopes with different degrees of esterification label preferentially growing wall zones in Netrium. In contrast, 2F4 marks the cell wall only after experimental de-esterification. Electron energy loss spectroscopy reveals Ca-binding capacities of pectins and gives indirect evidence for the degree of their esterification. An antibody raised against Netrium mucilage is not only specific to mucilage but also recognizes wall components in transmission electron microscopy and dot blots. These results indicate a smooth transition between mucilage and the cell wall in Netrium.

The formation of defined shapes by cells is one of the challenging questions in biology. Due to the anisotropy of cell walls and of certain biominerals, the LC-PolScope represents a promising tool for tracking dynamic structural changes in vivo non-invasively and, to some extent, quantitatively. A complex three-dimensional biogenic system, the in vitro precipitation of calcium oxalate induced by cellulose stalks produced by Dictyostelium discoideum, was analyzed. Although the retardance values and orientation of the crystals with respect to the stalk were quickly and easily detected, this study raised a number of issues that were addressed in this work. The effect of the refractive index of the embedding medium was examined by taking advantage of the homogeneous size and shape distribution of kiwifruit raphides, a biologically controlled calcium oxalate biomineral and of cotton (Gossypium) seed fibers. The retardance remained consistent when embedding these samples in media with increasing refractive indices from 1.33 to 1.42 or 1.47 for sucrose or glycerol gradients, respectively. The general applicability of LC-PolScope image processing for biominerals and cell wall formation during development in vivo was demonstrated in a particular group of green algae, the Desmidiaceae. Various organization levels of the cell wall were identified, thus confirming earlier findings based on electron microscopy and immunostaining investigations. It can be concluded that LC-PolScope microscopy is an attractive tool for studying dynamic ordering of biomolecules, such as plant cell walls, when additional parameters regarding the structure, composition, and refractive indices of the specimen are available.

We use the existing data of force-extension experiments on F-actin molecules tied into knots to compute a value of 0.15 for the static friction coefficient for contact between different parts of the same molecule with itself. This estimate for protein-protein friction is relevant for the stabilization of the 273 known proteins with knots, one percent of the structures deposited in the Protein Data Bank.

The keratin structure in the cortex of peacocks' feathers is studied by X-ray diffraction along the feather, from the calamus to the tip. It changes considerably over the first 5 cm close to the calamus and remains constant for about 1 m along the length of the feather. Close to the tip, the structure loses its high degree of order. We attribute the X-ray patterns to a shrinkage of a cylindrical arrangement of beta-sheets, which is not fully formed initially. In the final structure, the crystalline beta-cores are fixed by the rest of the keratin molecule. The hydrophobic residues of the beta-core are locked into a zip-like arrangement. Structurally there is no difference between the blue and the white bird.

The aragonite-specific proteins, Pif97 and Pif80, provide new views on remote control of nacre formation. A chitinous membrane is pinned to matured nacre in certain spots until the onset of nucleation of the next layer. In this model, diffusible low-molecular-weight acidic proteins would fulfill an important role as Ca2+/H+ shuttles to avoid local acidification and balance mineralization gradients.