Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

Ver?nderungen der Molmassen von Weizenkleberproteinen nach schwacher Proteolyse

Zusammenfassung Weizenkleber und -mehl werden einer schwachen Proteolyse, entsprechend den Bedingungen des Enzymeinsatzes in der Backwarenindustrie, unterworfen. Die Substrate werden in einem Lösungs-smittelgemisch aus Essigsäure, Harnstoff und Cetyltrimethylammoniumbromid gelöst und an Sepharose 4 B fraktioniert. Durch die Protease werden etwa 8% der hochmolekularen Glutenine (Molmasse > 5. 10⁵ g/mol) abgebaut, die Proteine mit einer Molmasse < 5 · 10⁵ g/mol nehmen um diesen Betrag zu. Rasterelektronenmikroskopische Aufnahmen zeigen nur einen geringen Unterschied zwischen Kontrolle und enzymbehandelter Probe. Die schwache Proteolyse bewirkt jedoch einen deutlichen rheologischen Effekt.

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Changes in the molecular weights of the proteins of wheat gluten weak proteolysis

Summary Gluten and wheat flour are submitted to a weak proteolysis corresponding to the conditions for the application of enzymes in the baking industry. The substrates are dissolved in a mixture of acetic acid, urea and cetylmethylammoniumbromide and fractionated on Sepharose 4 B. About 8% of the high molecular glutenins (molecular weight > 5 · 105 g/mol) are degraded, increasing the amount of proteins with molecular weights < 5 · 10⁵ g/mol by the same percentage. Scanning electron microscopy reveals only small differences between the samples treated with proteinases and the control. The weak proteolysis however leads to a distinct rheological effect.

     

Reduction of 2,4,6-trinitrotoluene by iron metal: kinetic controls on product distributions in batch experiments

The reaction kinetics and product distributions for the reduction of 2,4,6-trinitrotoluene (TNT) by granular iron metal (Fe0) were studied in batch experiments under a variety of initial concentrations of TNT and Fe0. Although the kinetics of TNT disappearance were found to behave in accord with the standard theory for surface-mediated reactions, a complex relationship was found between the initial concentrations of TNT and Fe0 and the appearance of the expected nitro reduction product, 2,4,6-triaminotoluene (TAT). TNT was completely converted to TAT only when the initial concentration of TNT was low and/or the initial concentration of Fe0 was high. Mathematical analysis of a range of generic reaction schemes that produce stable end products in addition to TAT showed that (i) surface complexation of TAT is insufficient to describe all of our data and (ii) polymerization reactions involving TAT and/or various reaction intermediates are the likely source of the incomplete conversion of TNT to TAT at high initial TNT concentration and low Fe0 concentration. The relationship between TAT production and reaction conditions is shown to imply that passivation due to reaction products is more likely when the ratio of initial TNT concentration to Fe0 concentration is high and, therefore, that passivation rates observed at the laboratory scale are likely to be faster than those which would be observed at the field scale.     

Nachweis der Raffination/Bleichung von Fetten und ?len

Summary The isolation of the germination specificamylase by extraction from germinated rye (Secale cereale), adsorption on rye or wheat starch, sedimentation by ethanol and Chromatographic fractionation on a carboxymethylcellulose column is described. This resulted in an approximate 84-fold increase in purification with a recovery of about 15%. In order to characterize the purified enzyme the influence of pH (optimum at pH 5.5; nearly no loss of activity at pH 6–10 after storage at 4° C and different pH values) and temperature (optimum over a 3min incubation period at 65° C; activity loss of 40% after incubation without substrate for 4 h at 55° C) were investigated.

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Untersuchungen zur keimungsspezifischen -Amylase und deren Inhibitor im Roggen (Secale cereale)I. Isolierung und Charakterisierung des Enzyms

Zusammenfassung Es wird die Isolierung der keimungsspezifischen-Amylase durch Extraktion aus gekeimtem Roggen (Secale cereale), Anlagerung an Roggen- oder Weizenstärke, Ethanolfällung und säulenchromatographische Fraktionierung an Carboxymethylcellulose beschrieben. Dabei wird ein Reinigungsfaktor von etwa 84 erreicht, die Ausbeute beträgt etwa 15%. Zur Charakterisierung des gereinigten Enzyms werden das pH-Verhalten (Optimum bei pH 5,5; nahezu kein Aktivitätsverlust bei pH 6–10 nach 24 h Lagerung bei 4 °C und unterschiedlichen pH-Werten) und das Temperaturverhalten untersucht (Optimum bei 3 min Bebrütung 65 °C; 40% Aktivitätsverlust nach 4 h substratfreier Bebrütung bei 55 °C).

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We thank Jürg Hempel for his interest and help in translating.     

Bestimmung und Vorkommen von Zearalenon in Getreide und Mischfuttermitteln

Zusammenfassung Ein HPLC-Verfahren mit Fluorescenzdetektion zur Bestimmung von Zearalenon in Getreide und Mischfuttermitteln wird beschrieben. Die Extraktion erfolgt mit Chloroform bei einem niedrigen pH-Wert. Anschließend werden die Proben mittels Säure-Base-Behandlung oder Gelpermeationschromatographie gereinigt. Mischfuttermittel müssen aufgrund der komplexen Zusammensetzung zusätzlich über Extraktionssäulen gereinigt werden. Mit dem beschriebenen Extraktionsverfahren und der gelpermeationschromatographischen Reinigung wird auch Ochratoxin A erfaßt. Die Bestimmbarkeitsgrenze für Zearalenon liegt bei 2,5 g/kg. Die durchschnittliche Wiederfmdungsrate bei Zulagen im Bereich von 3,5 bis 85 g/kg lag bei rund 97%. Mit dieser Methode wurden 91 Getreide- und Mischfutterproben des Erntejahres 1989 untersucht. Die Kontaminationsrate lag bei 42%. Die gefundenen Gehalte werden diskutiert.

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Determination and occurrence of zearalenone in cereals and mixed feeds

Summary An HPLC method with fluorescence detection is described for the determination of zearalenone in cereals and mixed feeds. Samples are extracted with chloroform at low pH and cleaned up using an acid-base treatment or gel-permeation chromatography (GPC). Mixed feeds must additionally be cleaned up with extraction columns, because of their different compositions. With the extraction procedure described and GPC clean-up, ochratoxin A can be determined simultaneously. The limit of determination for zearalenone is 2.5 g/kg. The average recovery rate, tested in the range 3.5 to 85 g/kg was found to be 97%. Using this method, 91 samples of cereals and mixed feeds, harvested in 1989, were examined. The contamination rate was 42%. The results are discussed.