Ein Beitrag zum mechanischen Relaxationsverhalten von Polyäthylen,Polypropylen, Gemischen aus diesen und Mischpolymerisaten aus Propylen und äthylen

Zusammenfassung Mit der Torsionsschwingungsmethode nachSchmieder undWolf wurde das Relaxationsverhalten von Polyäthylen, Polypropylen verschiedener Taktizität, Gemischen aus diesen beiden Polymerisaten, sowie Mischpolymerisaten aus Propylen und äthylen in einem Temperaturbereich von –180 C bis 160 C untersucht.Während sich bei Polymerisatgemischen einfache Mischungsregeln für den Gleitmodul und die Dämpfung ergeben, zeigen Mischpolymerisate gleicher chemischer Zusammensetzung ein komplizierteres Verhalten, welches an Hand der gemessenen Kurven diskutiert wird. Außerdem wird das Relaxationsverhalten einer langsam abgekühlten Niederdruckpolyäthylen-Probe mit demjenigen einer abgeschreckten Probe verglichen. Bei Polypropylen konnte eine zeitabhängige Nachkristallisation nachgewiesen werden.Herrn Dr.Knappe vom Deutschen Kunststoffinstitut, Darmstadt, sei für Diskussionen und wertvolle Ratschläge, den Firmen Stickstoffwerk Hibernia A. G., Wanne-Eickel, und C. Freudenberg, Weinheim/Bergstraße, für die Erlaubnis zur Veröffentlichung dieser Arbeit und meinen Mitarbeitern H. Becker,W. Hering undU. Wenster für die Durchführung der Messungen gedankt.     

Phospholipid mesophases at solid interfaces: in-situ X-ray diffraction and spin-label studies

In this work, we report on recent investigations, both on the global and on the local molecular architecture of supported phospholipid model membranes. A brief theoretical introduction explains how global structural information on supramolecular lipid ensembles can be retrieved from surface X-ray diffraction measurements as well as how spin-label electron paramagnetic resonance spectroscopy (EPR) provides complementary information on the local environment of probe molecules. The combination of especially designed X-ray cells with the technique of small- and wide-angle X-ray surface scattering makes it possible to explore various fields of lipid research and its applications. Examples for different physico-chemical conditions are presented: (i) in situ chemistry under excess of water conditions demonstrating how solid-supported lipid films sense salinity, (ii) the 3D electron density reconstruction of a vesicle-fusion intermediate under controlled humidity, and (iii) complementary temperature and pressure effects on oriented phospholipid samples. Further, special attention has been given to the influence of different film preparation techniques with respect to quality and the defect structure manifestation. To resolve the proportions and local properties of defects in a hydrated lipid-deposited surface, spin-label EPR was applied. The results from 9.6 GHz EPR as well as from 1.2 GHz EPR suggest the alignment to be in the range between 30% and 80%. In addition, slow time-dependent EPR measurements point to nano-structural rearrangements due to water flow and reduction of alignment quality.     

A quantum-chemical study of dinitrogen reduction at mononuclear iron-sulfur complexes with hints to the mechanism of nitrogenase

The mechanism of biological dinitrogen reduction is still unsolved, and the structure of the biological reaction center, the FeMo cofactor with its seven iron atoms bridged by sulfur atoms, is too complicated for direct attack by current sophisticated quantum chemical methods. Therefore, iron-sulfur complexes with biologically compatible ligands are utilized as models for studying particular features of the reduction process: coordination energetics, thermodynamic stability of intermediates, relative stability of isomers of N2H2, end-on versus side-on binding of N2, and the role of states of different multiplicity at a single iron center. From the thermodynamical point of view, the crucial steps are dinitrogen binding and reduction to diazene, while especially the reduction of hydrazine to ammonia is not affected by the transition metal complex, because the complex-free reduction reaction is equally favored. Moreover, the abstraction of coordinated ammonia can be easily achieved and the complex is recovered for the next reduction cycle. Our results are discussed in the light of studies on various model systems in order to identify common features and to arrive at conclusions which are of importance for the biological mechanism.     

Kiesels?urebestimmung mittels einfacher Titration

Zusammenfassung Es wurde eine Arbeitsvorschrift für eine einfache Titrationsmethode ausgearbeitet, mit deren Hilfe Kieselsäurebestimmungen in Kieselsol und in Alkalisilicatlösungen rasch und genau durchgeführt werden können.

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Summary A simple titration method has been worked out for the rapid and accurate determination of silicic acid in silica sols and alkali silicate solutions.

     

Motor-protein "roundabouts": microtubules moving on kinesin-coated tracks through engineered networks

Nanotechnology promises to enhance the functionality and sensitivity of miniaturized analytical systems. For example, nanoscale transport systems, which are driven by molecular motors, permit the controlled movement of select cargo along predetermined paths. Such shuttle systems may enhance the detection efficiency of an analytical system or facilitate the controlled assembly of sophisticated nanostructures if transport can be coordinated through complex track networks. This study determines the feasibility of complex track networks using kinesin motor proteins to actively transport microtubule shuttles along micropatterned surfaces. In particular, we describe the performance of three basic structural motifs: (1) crossing junctions, (2) directional sorters, and (3) concentrators. We also designed track networks that successfully sort and collect microtubule shuttles, pointing the way towards lab-on-a-chip devices powered by active transport instead of pressure-driven or electroosmotic flow.     

Pr?parative Gaschromatographie

Zusammenfassung Es werden zwei neue, sehr selektive Trennflüssigkeiten, Äthylenglykol-bis(propionitril)-äther und Glycerin-tri(propionitril)-äther, angegeben. Die Trennflüssigkeiten sind so selektiv wie ,-Bis(propionitril)-äther, erlauben aber höhere Arbeitstemperaturen von 140° bzw. 170°C. An Säulen kleinen Querschnittes wird die präparative Trennung größerer Mengen unter Ausnutzung der Selektivität dieser Trennflüssigkeiten aufgezeigt.Die Trennwirksamkeit und die Belastbarkeit von Säulen verschiedenen Durchmessers zwischen 1–10 cm wird angegeben. Die Trennwirksamkeit liegt in der gleichen Größenordnung wie die der analytischen Säulen. Die Belastbarkeit steigt proportional dem Querschnitt an.I. Mitteilung: E. Bayer u. H. G. Witsch, diese Z. 170, 278 (1959).     

Strukturuntersuchungen an Derivaten des Nickelkomplexes Ni(ONO) (ONO2− = Dianion einer dreizähnigen Schiffschen Base)

Structure Studies on Derivatives of the Nickel Complex Ni(ONO) (ONO^2? = Dianion of a Tridentate Schiff Base) The thermodynamically stable form of the solvent free, formally tri-coordinate complex Ni(ONO) (ONO^2? = dianion of N-(2-hydroxyphenyl)-2-ethoxycarbonyl-3-ox(o-butene(1) amine(1)) as well as the mono adducts Ni(ONO)X with X = ammonia and X = diphenyl thiourea (DPT) have been characterized by X-ray structure analysis. In all cases the central atom is coordinated in a square-planar fashion, only for the adduct Ni(ONO)(DPT) a pyramidal distortion is observed which is due to the formation of hydrogen bonds. The solvent free form is a dimer [Ni(ONO)]₂, and represents one of the few examples of dinuclear nickel complexes with a planar [NO₃] coordination. The phenolic O-atoms act as bridging ligands. Due to their reduced π-donor strength the bond lengths Ni? O trans to the bridges are significantly shortened. In contrast to the analogous complex with an aliphatic bridge, “NiEIA”, both halves of the dimeric molecules are coplanar with a Ni? Ni distance of 3.29 Å.     

An Efficient Synthesis of <Emphasis Type="Italic">O</Emphasis>-Methyl Protected Emodin Aldehyde and Emodin Nitrile

Summary. An efficient synthesis of tri-O-methylemodin aldehyde was achieved via bromination of tri-O-methylemodin utilizing N-bromosuccinimide yielding the monobromo and dibromo derivatives. Sommelet reaction of the monobromomethyl derivative as well as hydrolysis of the dibromomethyl analog with aqueous silver nitrate afforded the protected aldehyde in good yield. Accordingly, both bromo derivatives can be used even when they are obtained as a mixture of the bromination reaction, which could not be controlled easily to yield the bromo products selectively. From the aldehyde the tri-O-methylemodin nitrile was prepared in a one-pot reaction using hydroxylamine-O-sulfonic acid.Received February 18, 2003; accepted March 3, 2003 Published online June 2, 2003