Zur Darstellung eines sehr wirksamen Platinmohrs

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Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

Untersuchung von Fetten, ?len und fetthaltigen Produkten

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Eine Reaktion zur Erkennung von Kunsthonigen

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Absolute spectroscopic determination of cross-membrane potential

Spectroscopic determination of the cross-membrane electric potential has been used for more than 20 years. This method, which usually employs absorption or fluorescence measurements, allows for a rapid and noninvasive study of the electrical properties of the membranes of cells and liposomes. However, the usual fluorescence techniques preferably allow monitoring changes in the potential on triggerable or excitable membranes, and not the absolute value of the potential. They also do not provide means for measuring the potential on single cells. This paper reviews three methods that solve these issues. Nernstian dyes which partition between intra-and extracompartmental volumes enable a fluorescence microscopic determination of a single cell and even a single organelle. Dual-wavelength ratiometric recording from membrane-staining dyes also provides means for measuring the field on a single cell. Resonance Raman probes provide a spectroscopic method with a natural internal standard for the absolute measurement of membrane potential.     

Molecular orbital calculations of the active site complex of two iron ferredoxins

The results presented here are the first part of a systematic theoretical study of some of the physical and biochemical properties of two iron ferredoxins obtained by the use of an Extended Hückel Self-Consistent Charge iteration method of molecular orbital calculations. In this initial study, attention is focused on the calculation of electronic energies as a function of molecular geometry and the nature of the bonding ligands at the active site in order to determine the most stable form of the active site complex. Included in the active site complex are two iron atoms, two acid labile sulfur atoms of unknown inorganic origin and four sulfur atoms presumably from nearby cysteine residues. Fifteen chemical-conformational variations of this basic active site complex were considered. Among these conformational variations of the sulfur ligands, Fe-Fe distances, bond lengths and angles and chemical variations such as the effect of axial ligands, disulfide bonds and added protons were included. Our results indicate that that with all reasonable variations of the ligands, the preferred molecular geometry about 4-coordinated Fe is tetrahedral rather than planar. The planar conformation is somewhat stabilized by the addition of axial ligands, but is still less favorable than the tetrahedral conformation. In this model, interactions between the two iron atoms occur automatically since they are both part of the same active site complex. Hence the absence of low temperature paramagnetism in the oxidized state is readily explained. Preliminary investigations of the reduced state with one additional electron indicate that the odd electron is delocalized, as observed in both ESR and ENDOR. Its presence apparently substantially destabilizes all of the molecular orbital energies in accord with the observation that only one electron can be added to these proteins without decomposing them.

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Zusammenfassung Die vorliegenden Ergebnisse stellen den ersten Teil einer systematischen theoretischen Untersuchung einiger physikalischer und biochemischer Eigenschaften des Fe₂-Ferredoxins mit Hilfe einer selbstkonsistenten erweiterten Hückelmethode dar. In diesem ersten Teil wird besonders die elektronische Energie in Abhängigkeit von der Molekülgeometrie und der Art der Liganden an der aktiven Stelle untersucht, um die stabilste Form des Komplexes der aktiven Stelle zu finden. Dieser Komplex enthält zwei Eisenatome, zwei saure, nicht fest gebundene Schwefelatome unbekannter anorganischer Herkunft sowie vier Schwefelatome, vermutlich aus nahegelegenen Cysteinresten. Bei den 15 untersuchten Konformationen der Schwefelliganden wurden Änderungen der Fe-Fe-Abstände, Bindungslängen und -winkel sowie chemische Variationen wie die Einwirkung der axialen Liganden, der Disulfidbindungen und zusätzlicher Protonen berücksichtigt. Es ergibt sich, daß das Eisen vierfach tetraedrisch koordiniert ist und nicht planar, selbst bei der Addition axialer Liganden. In diesem Modell ergeben sich Wechselwirkungen zwischen den beiden Eisenatomen zwanglos, da sie zum gleichen aktiven Komplex gehören. Dadurch wird das Fehlen eines Tieftemperatur-Paramagnetismus im oxydierten Zustand hinreichend erklärt. Eine vorläufige Untersuchung des reduzierten Zustandes mit einem zusätzlichen Elektron zeigt, daß dieses delokalisiert ist, genau wie es mit ESR und ENDOR beobachtet wird. seine Gegenwart destabilisiert offenbar alle MO-Energien, was in Übereinstimmung mit der Beobachtung steht, daß nur ein Elektron von diesen Proteinen addiert werden kann, ohne sie zu zerstören.

     

Photodynamic effect of hypericin and a water-soluble derivative on isolated crayfish neuron and surrounding glial cells

Hypericin (Hyp) has been proposed as a fluorochrome for fluorescence diagnostics and as a photosensitizer for photodynamic therapy of cancer. However, its insolubility in water is a serious drawback. A novel water-soluble hypericin derivative (Hyp-S) has been constructed, using polyvinylpyrrolidone as a carrier. We used the crayfish stretch receptor, consisting of receptor neuron and satellite glial cells, for comparison of the photodynamic effects of Hyp and Hyp-S. Hyp-S was more toxic in the dark than Hyp and inactivated the neurons at concentrations exceeding 4 microM while Hyp was toxic to the neurons only at the concentrations larger than 20 microM. Electrophysiological investigations revealed polyphasic neuron responses to photosensitization with Hyp as well as with Hyp-S (1 microM concentration, 30 min incubation; irradiation with filtered light from a lamp with an emission maximum near 600 nm and an intensity of 0.2 W/cm2). In the concentration range 1-4 microM Hyp-S was more phototoxic than Hyp. Fluorescence microscopy showed that both sensitizers were predominately localized in the glial envelope surrounding the neuron. A minor fraction of hypericin was found in the neuron perinuclear area rich in cytoplasm organelles. This suggests the potential application of Hyp and Hyp-S for visualization and selective photodynamic treatment of malignant gliomas.     

Azo-1,3,5-triazines

The synthesis of variously substituted bis-triazinylhydrazines and their subsequent oxidation preferably with chlorine in a two-phase system to azo-1,3,5-triazines starting from cyanuric chloride is reported. Reaction of ethoxycarbonylhydrazine with cyanuric chloride followed by oxidation gave access to mono- and bis-ethoxycarbonyl-1,3,5-triazines, respectively. Azo-1,3,5-triazines proved to be very reactive dienophiles.