7Li residual quadrupolar couplings as a powerful tool to identify the degree of organolithium aggregation

Lithium in the gel: The NMR spectroscopic properties of common organolithium and lithium amide reagents are investigated in the anisotropic environment of a stretched polystyrene (PS) gel. PS is stable towards reactive organometallic compounds and can be used at low temperatures. The residual quadrupolar couplings (RQCs) from a single (7)Li?NMR spectrum can distinguish between high (hexamer, tetramer) and low (dimer, monomer) aggregation states (see scheme).     

Model‐independent structure factors from powder X‐ray diffraction: a novel approach

Under the experimental condition that all Bragg peaks in a powder X‐ray diffraction (PXRD) pattern have the same shape, one can readily obtain the Bragg intensities without fitting any parameters. This condition is fulfilled at the P02.1 beamline at PETRA III using the seventh harmonic from a 23 mm‐period undulator (60 keV) at a distance of 65 m. For grain sizes of the order of 1 µm, the Bragg peak shape in the PXRD is entirely determined by the diameter of the capillary containing the powder sample and the pixel size of the image plate detector, and consequently it is independent of the scattering angle. As an example, a diamond powder has been chosen and structure factors derived which are in accordance with those calculated from density functional theory methods of the WIEN2k package to within an accuracy that allows a detailed electron density analysis.     

Ageing of polymer bonds: a coupled chemomechanical modelling approach

With the increasing number of requirements on joinings, it gets more and more important to understand and predict an assemblies properties. Nowadays, in industrial applications, combinations of different materials get more common. In most of those cases, it is, besides other advantages, useful to connect such parts with adhesives to avoid local cells. Thus, the knowledge about the mechanical behaviour of adhesives over the whole time of utilisation is an essential element of engineering. As it is well known, ageing due to environmental influences such as oxygen, radiation, ozone and others plays a major role in polymers properties. So, for the prediction of applicability over the whole lifetime of a technical component, the change in mechanical properties due to ageing is necessary. In this contribution, we introduce a material model which takes into account the internal structure of an adhesive. Therefore, an interphase zone is introduced. In the interphase, which is developed due to the contact of an adhesive with an adherent, the materials properties change continuously from the surface to the centre of the joint, where the polymer is in a bulky state. Built up on this geometry dependency, the materials ageing as a function of the position is described. To model the change of the polymers state, we use a parameter representing chain scission processes and another one for the reformation of a new network. In a last step, the model is transferred into a finite element code for exemplary calculations.     

Size-dependent melting of self-assembled indium nanostructures

We have measured the melting temperature of nanoscale indium islands on a WSe(2) substrate using perturbed angular correlations combined with scanning tunneling microscopy. The indium islands are self-assembled nanostructures whose diameter can vary between about 5 and 100 nm, depending on deposition conditions. The melting point decreases due to surface energies as the islands get smaller. This decrease depends on the faceting of the crystalline nanostructures and interactions between the islands and the substrate.     

Quality control of food with near-infrared-excited Raman spectroscopy

Summary The former considerable handicap of Raman spectroscopy in the visible range, the disturbing fluorescence of impurities, has now been eliminated: Raman spectra are excited by light quanta of the near-infrared range; their energy, however, is too small to excite fluorescence spectra. Now Raman spectroscopy can be applied to many real world samples, to quality control of raw material, to production and product control. This paper gives examples of the application to food analysis. Many problems can be solved without a special sample preparation, even by using fibre bundles on-line at the sample site, in containers and in real time for production control. The configuration and amount of C=C bonds in lipids can be determined directly, also the nature and amount of proteins and carbohydrates, and the composition of food products. Natural and synthetic colours, flavours and vitamins can be detected on TLC plates, especially if Raman scattering is enhanced by resonance. Traces of distinct compounds can be detected by the SERS technique (the surface-enhanced Raman spectroscopy). The powerful new tool of analytical chemistry promises many useful applications and the replacement of time-consuming traditional methods.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Photosensitizing and radiosensitizing effects of hypericin on human renal carcinoma cells in vitro

The renal cell carcinoma (RCC) is extremely resistant to chemotherapy and radiotherapy. The prognosis of patients with metastatic RCC still remains poor, the median survival is less than 12 months. Therefore, new therapeutic options are desirable. The aim of this study was to investigate the photosensitizing and radiosensitizing effects of hypericin on human RCC cells in vitro. First the RCC-derived cell lines A498 and ACHN were incubated with different concentrations of hypericin. In vitro uptake and intracellular distribution of hypericin were confirmed by fluorescence microscopy. Subsequently cells were illuminated and irradiated with a dose of 2-8 Gy, respectively. Finally, metabolic activity, apoptosis and clonogenic survival were investigated. Uptake of hypericin was observed for almost all cells. Hypericin treatment combined with illumination led to a 94-97% decrease in metabolic activity and caused apoptosis in nearly 100% of RCC cells. Hypericin enhanced the radiosensitivity of A498 cells in vitro. The clonogenic survival after irradiation was significantly reduced by hypericin treatment. Taken together, the photosensitizing and radiosensitizing effects of hypericin on human RCC cells we found in this investigation could be of clinical relevance, e.g. for radiotherapy and intraoperative photodynamic therapy, respectively.     

Dissipative heating of elastomers: a new modelling approach based on finite and coupled thermomechanics

Especially in the automotive industries, elastomers take an important role. They are used in different types of bearings, where they inhibit vibration propagation and thereby significantly enhance driving performance and comfort. That is why several models have already been developed to simulate the material’s mechanical response to stresses and strains. In many cases, these models are developed under isothermal conditions. Others include the temperature-dependent mechanical behaviour to represent lower stiffness’s for higher temperatures. In this contribution it is shown by some exemplary experiments that viscoelastic material heats up under dynamic deformations. Hence, the material’s properties change due to the influence of the temperature without changing the surrounding conditions. With some of these experiments, it is shown that a fully coupled material model is necessary to predict the behaviour of bearings under dynamic loads. The focus of this contribution lies on the modelling of the thermoviscoelastic behaviour of elastomers. In a first step, a twofold multiplicative split of the deformation gradient is performed to be able to describe both mechanical and thermal deformations. This concept introduces different configurations. The stress tensors existing on these configurations are used to formulate the stress power in the first law of thermodynamics which allows to simulate the material’s self-heating. To formulate the temperature dependency of the mechanical behaviour, the non-equilibrium part of the Helmholtz free energy function is formulated as a function of the temperature and the deformation history. With the introduced model, some FE calculations are carried out to show the model’s capability to represent the thermoviscoelastic behaviour including the coupling in both directions.