ALBERT

Notizen: Me3SiCl bildet mit N-Methylimidazol (NMI) eine bei Raumtemperatur beständige, kristalline 1:1 Verbindung. Nach der Röntgenstrukturanalyse entsteht unter Spaltung der Si—Cl-Bindung und Anlagerung eines NMI-Rings eine Verbindung ionischer Struktur [Me3Si(NMI)]+Cl- 1. Die Reaktion von Me2HSiCl mit NMI (Molverhältnis 1:2) führt unter Spaltung der Si—Cl-Bindung und Koordination von zwei NMI-Ringen zur Verbindung [Me2HSi(NMI)2]+Cl- 2. Bei der analogen Umsetzung von Me2SiCl2 mit NMI (Molverhältnis 2:1) entsteht eine Verbindung, die Me2SiCl2 und NMI im Molverhältnis 1:2 enthält. Bei der Sublimation werden Einkristalle der Verbindung [Me2Si(NMI)3]2+ 2 Cl-· NMI 3 erhalten.

Notizen: One of the basic prerequisites for rational and high quality production of plastic parts is a tool layout tailored to the production process. To date, both design and construction have generally been based on values acquired by experience. This first, necessitates highly qualified personnel and second, involves what is frequently time consuming and costly finishing work. Experience acquired so far with computer-aided layout of injection molds shows that even a designer with little experience reaches the target more quickly and more reliably. At the same time he is able to draw on the results of intricate calculation and simulation methods which he was unable to apply in the past for reasons of time alone. This paper thus sets out the possibilities currently open and the experience available for computer-aided mold layout. The chief point of focus here is a system for the layout of injection molds. Working on from this system, however, the potentials for computer application are presented for blow mold- and foaming mold-design. After finding the mold principle, mold layout essentially divides up into two major areas, namely dimensioning calculations (CAE) and compilation of production documents (CAD). In dimensioning, the different functional elements of the mold are calculated. The aids that have been developed and the potentials of computer-aided dimensioning are presented with examples from the fields of rheological, thermal, and mechanical mold layout. Computer-aided rheological layout divides up into two steps. The first gives information on qualitative filling behavior (filling picture, flow paths) and the second provides quantitative results (pressures, shear stresses, temperatures). Computer-aided thermal layout similarly divides up into part steps. These are a rough overall energy balance, a rough layout of the tempering system, a segmented layout, and a homogeneity check, which involves simulating the temperature conditions in the mold by means of difference methods. When it comes to mechanical layout of the mold, programs are available for deformation calculations on basic cases and these will frequently be sufficient. For more complex cases of loading and deformation, a finite element program is used. Graphic data processing units can be used to supply extra facilities - first, to provide an aid for the simulation programs in dimensioning and second, to rationalize the compilation of the production documents. An illustration of a CAD workplace is given, incorporating the necessary computer configuration and peripherals. Compiling production documents is essentially a problem of variant design. The variants in this case are the individual components of the mold and a number of standardized accessories that can be called up as “standardized components.” The mold cavity, however, always has to be a free design. All programs are dialogue driven and are in a standardized manner so that even designers with no data processing experience can use the computer as an aid. The CAD/CAE system presented duly fulfils all these requirements. It allows the designer, at a single computer work station, to carry out both simulation and dimensioning calculations, to obtain information on material data, and to compile production documents on the basis of variant and free design. This provides the designer with a readily manageable aid and makes a considerable contribution towards improving the design result. Finally, the capacity of different computer concepts and the CAE/CAD/CAM systems on the market are discussed. For the future it will be possible to establish a computer-aided link between the different areas of design, from development of the molded part, via mold design and production, through setting the processing parameters of the injection molding machine.

Notizen: Thermo-oxidative ageing processes were investigated in films (100 μm thick) made from isotactic polypropylene with different antioxidant concentrations between 0% and 0.1% using isothermal long-term differential thermal analysis (ILDTA). The end of the oven life of polypropylene coincided with the loss of mechanical properties which was confirmed by tensile tests at temperatures far below the crystallite melting range. Already prior to the beginning of autocatalytic decomposition, ILDTA experiments permits conclusions to be drawn on the thermal history of the specimens and statements made regarding the end of thermo-oxidative stability of the polymer, which is accompanied by a deterioration in the mechanical properties.In consequence of the correlation between oxidation time and antioxidant concentration the local antioxidant concentration in sheets or films can be measured by ILDTA. Thus, investigating the diffusion of an antioxidant in polypropylene using ILDTA is possible.

Notizen: Recently, it was suggested that parallel β-sheets have a significant dipole moment, in contrast to antiparallel sheets. Ab initio molecular-orbital (MO) calculations on parallel and antiparallel β-strands of tetra(Gly) show that they have very similar charge distributions. Interaction energies between two and three strands of tetra(Gly), obtained using the direct reaction field Hamiltonian, show that a particular choice of point charges is probably not crucial for calculating interactions within β-sheets, but that it might be for calculating interactions between these sheets and other parts of a protein, in particular, α-helices. The point-charge representation of our MO-SCF results will probably reduce the hazard of introducing artefacts in electrostatic calculations of protein conformational energies, provided the short-range interactions are treated in a more realistic way, i.e., such that intra- and interchain induction effects are included.

Notizen: Double-stranded DNA can be readily adsorbed on mica or directly on carbon coated grids from the surface of solutions containing ethidium bromide, actinomine, or propidium diiodide. The DNA molecules are unfolded, well separated, and show a length distribution similar to molecules prepared by protein monolayer techniques.Since the intercalating dyes tested do not lead to an increased apparent diameter of the nucleic acid the method is useful for the study of nucleic acid-protein complexes. As a model, the binding of E. coli RNA polymerase to phage T7 and T3 DNA was examined under different conditions. The enzyme can easily be identified and its position along the DNA molecule can be mapped.

Notizen: Die tetrasubstituierten [2.2]Paracyclophane 4a - e werden durch Cycloaddition der symmetrischen Acetylenderivate 2a - e an 1,2,4,5-Hexatetraen (1) dargestellt und ihre Konstitution und Konfiguration durch spektroskopische Methoden. Abbau- und Pyrolyseversuche bewiesen. Der Tetramethylester 4a wird zum Tetraalkohol 4g reduziert und die Tetracarbonsäure 4c in das Bisanhydrid 4f bzw. [2.2] Paracyclophan (4h) übergeführt. Bei der Anlagerung von Propiolsäure-methylester (5a) an 1 werden alle isomeren disubstituierten [2.2]paracyclophanes 6 erhalten. Weitere symmetrische und unsymmetrische Acetylenderivate reagieren nicht mit 1.

Notizen: Eugenon, ein Inhaltsstoff aus wild wachsenden Gewürznelken, besitzt die Bruttoformel C13H16O5. Seine Konstitution des 2,4, 6- Trimethoxy-benzoylacetons folgt aus Abbaureaktionen und dem Vergleich mit einem synthetischen Produkt. Das Eugenon stellt den ersten in der Natur aufgefundenen Vertreter des Benzoylacetons dar.