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  • 1
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract A method for the analysis of vapour phases using the initial section of the column for sample collection and concentration of the components to be determined has been carefully standardized and compared to the well known gas tight syringe injection technique. The new method makes it possible to demonstrate the interference of different diffusion rates of liquid mixtures in equilibrium with their vapour phases. The standard deviation has been determined by investigating the vapourliquid equilibria of two binary systems.
    Notes: Zusammenfassung Eine Methode zur Dampfraumanalyse, bei der der Anfang der Trennsäule zur Probenentnahme und zur Anreicherung der zu bestimmenden Bestandteile dient, wird nach gründlicher Eichung mit der bekannten Dosierung mittels Spritzen verglichen. Mit Hilfe der neuen Methode wird der störende Einfluß unterschiedlicher Diffusiongeschwindigkeiten in mit Flüssigkeitsgemischen im Gleichgewicht stehenden Dampfphasen aufgezeigt. An zwei binären Systemen, deren Dampf-Flüssigkeits-Gleichgewicht gaschromatographisch untersucht worden ist, wird die relative Standardabweichung ermittelt.
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  • 2
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract The thermolysis of diethyl methanetricarboxylate anilide has been re-examined and found to give mainly 2.4-dioxo-3.3-bis-(carboxanilino)-1.2.3.4-tetrahydro-quinoline (6) and not 6-anilino-3.4-dihydro-3-phenyl-2H-1.3-oxazin-2.4-dion (3) as proposed byIngold andWeaver 1.
    Notes: Zusammenfassung Dem nachIngold undWeaver 1 aus Methantricarbonsäurediäthylesteranilid (1) durch Thermolyse darstellbaren Produkt kommt nicht die Struktur des 6-Anilino-3-phenyl-2,4-dioxo-3,4-dihydro-2H-1,3-oxazins (3), sondern die des 2,4-Dioxo-3,3-bis-(carboxyanilino)-1,2,3,4-tetrahydro-chinolins (6) zu.
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  • 3
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung IR-spektroskopische Untersuchungen an den Malonesterbetainen1–7 geben Hinweise auf die Schwerpunkte der Ladungsverteilung. Während die Lage der CO-Banden der Betaine1 und2 mit rein aliphatischer Esterkomponente auf vollständige Resonanz zwischen den Estercarbonylen hinweist, ist bei jenen mit aromatischen Estergruppen (4, 5 und7) eine CO-Funktion zu beobachten, die schon auf einen gewissen Ylidanteil schließen läßt. Damit im Einklang stehen auch ihre chemischen Eigenschaften. Z. B. zersetzt sich das Bisphenoxycarbonylbetain4 beim Schmelzpunkt vollständig. Die Thermolyse von1 und2 führt dagegen sowohl zu Picolin- als auch zu Kohlensäureestern. Der Reaktionsmechanismus wird diskutiert.
    Notes: Abstract An IR-spectroscopic investigation concerning the malonate betaines1–7 gives an insight in the charge density distribution. The position of the C=O frequencies of the betaines1 and2 with alkyl ester groups shows complete resonance between the ester carbonyls, while with the phenolic esters4,5 and7 and C=O absorption is observed which shows a considerable ylid participation. the chemical properties of the betaines agree with this; e.g. the bis-phenoxycarbonylbetaine4 is decomposed totally at its melting point. However, the thermolysis of1 and2 gives picolinic acid esters and carbonic acid esters. The mechanism of these reactions is discussed.
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  • 4
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract On the basis of a method outlined in a preceding1 paper it is shown how the temperature dependence of the composition of the vapour phase, obtained by gas chromatography, can be used to determine thermodynamic quantities as isothermal partial and total vapour pressures and the excess free enthalpy of mixing. On the one hand this permits to check data obtained by other methods since gas chromatography is less sensitive to impurities, on the other hand it opens a convenient access to insufficiently treated multicomponent systems. For an illustration of the method the positive azeotropic system benzene—ethanol and the negative system dioxane-acetic acid was chosen.
    Notes: Zusammenfassung Nach der soeben1 beschriebenen Methode wird gezeigt, wie aus der Temperaturabhängigkeit der gas-chromatographisch gewonnenen Zusammensetzung der Dampfphase thermodynamische Größen, wie die isothermen Partial- und Totaldampf-druckkurven und die freie Überschußenthalpie, gewonnen werden können. Dies gibt einerseits eine Kontrollmöglichkeit von auf anderem Wege erhaltenen Daten wegen der geringen Empfindlichkeit gegenüber Verunreinigungen, andererseits auch einen bequemen Zugang zu noch nicht genügend untersuchten Mehrstoffsystemen. Zur Kontrolle und Illustration der Methode wählten wir das positive Azeotrop Benzol-Äthanol und das negative Azeotrop Dioxan-Essigsäure.
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  • 5
    ISSN: 1434-4475
    Keywords: Alkaline degradation ; Carbohydrates ; Kinetic studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Der alkalische Abbau von Cellobiose wurde mit 0.01N bis 0.1N NaOH im Temperaturbereich von 60 bis 85°C untersucht. Gleichzeitig wurden die gebildete Glucose und Fructose analysiert. Bei niedrigen Alkalikonzentrationen wird derpH Wert stark herabgesetzt, sodaß es innerhalb kurzer Reaktionszeiten zu einer Beendigung der Reaktion kommt. Bei höheren Alkalikonzentrationen ist diepH-Abnahme wesentlich geringer und der alkalische Abbau von Cellobiose gehorcht einer Reaktion 1. Ordnung. Durch die Anwendung eines vereinfachten Reaktionsschemas konnten auch die Folgereaktionen der Glucose- und Fructosebildung mathematisch erfaßt werden.
    Notes: Abstract The alkaline degradation of cellobiose by 0.01 to 0.1N NaOH at temperatures between 60 and 85°C was studied. At the same time the formation of glucose and fructose was analyzed. At lower alkali concentrations, the production of acidic compounds lowered thepH to such an extent that the hydrolyzing reaction ceased within a relatively short time. At higher alkali concentrations thepH change is much smaller and first order reaction rates of the cellobiose degradation were obtained. Through the application of a simplified reaction mechanism the consecutive reactions of the glucose and fructose formation were evaluated mathematically.
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  • 6
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Hydrazino-(2-oxo-1,2-dihydrophenanthrylidene)-acetodinitrile was formed in the reaction of 9-dicyanomethylene-9,10-dihydro-10-phenanthren-one with asymmetric dimethylhydrazine as well as in the reaction with unsubstituted hydrazine. The mechanism of this reaction involving the removal of two methyl groups is discussed on the basis of secondary reaction products detected byGLC.
    Notes: Zusammenfassung Es wird gezeigt, daß bei der Umsetzung von 9-Dicyanmethylen-9,10-dihydro-10-phenanthrenon mit asymm. Dimethylhydrazin dasselbe Hydrazino-(2-oxo-1,2-dihydro-phenanthryliden)-essigsäuredinitril entsteht, wie bei der Umsetzung von unsubstit. Hydrazin. Ein Mechanismus dieser Reaktion, bei welcher es zu einer Ablösung von zwei Methylgruppen kommt, wird an Hand der gaschromatographisch nachgewiesenen Folgeprodukte diskutiert.
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  • 7
    ISSN: 1432-1424
    Keywords: Electroneutral ; Asymmetric anion exchange ; Butyrate-gradient-stimulated Cl uptake ; Cl-SCFA exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The cellular model of short chain fatty acid stimulation of electroneutral Na-Cl absorption in large intestine proposes that SCFA, following its uptake across the apical membrane, recycles and is coupled to functional Na-H and Cl-short chain fatty acid exchanges. To establish the presence of a Cl-butyrate exchange (used as a model short chain fatty acid), studies of 36Cl and 14C-butyrate uptake across apical membrane vesicles of rat distal colon were performed. An outward butyrate-gradient stimulated transient accumulation of 36Cl uptake that was not inhibited by pH clamping with valinomycin (a K ionophore) and FCCP (a proton ionophore). Outward butyrate-gradient-stimulated 36Cl uptake was inhibited by 4,4′-diisothiocyanatostilbene2,2′-disulfonic acid (DIDS) with a half-maximal inhibitory concentration (IC50) of 68.4 μm, and was saturated by both increasing extravesicular Cl concentration (K m for Cl of 26.8 ±3.4 mm and a V max of 12.4±0.6 nmol/mg protein·9 sec) and increasing intravesicular butyrate concentration (K m for butyrate of 5.9 mm and a V max for Cl of 5.9 nmol/mg protein · 9 sec). 36Cl uptake was also stimulated by outward gradients of other short chain fatty acids (e.g., propionate, acetate and formate). In contrast, an outward Cl gradient failed to enhance 14C-butyrate uptake. Extravesicular Cl more than extravesicular butyrate enhanced 36Cl efflux from apical membrane vesicles. These studies provide compelling evidence for the presence of an electroneutral, pH-activated, Cl-butyrate exchange which in concert with Na-H exchange is the mechanism by which butyrate stimulates electroneutral Na-Cl absorption.
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  • 8
    ISSN: 1573-4994
    Keywords: Lipid membrane ; C12E n ; fluorescence resonance energy transfers ; surface area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fluorescence resonance energy transfer (FRET) from NBD-PE to rhodamine-PE has been used to measure the average area occupied by surfactant molecules in lipid bilayers. The Foerster radius has been determined from the spectral overlap of donor fluorescence and acceptor absorption (R 0=4.6 nm). The results of steady-state as well as of time-resolved investigations have been compared. The analysis of time-resolved fluorescence data by means of nonexponential decay functions yields an average area per lipid of 0.65 nm2 in pure POPC bilayers. The area per surfactant in two-component C12E n /POPC-membranes (n=2, 4, 6) has been determined and compared with the results of X-ray investigations. The surfactant head group seems to adapt a predominantly disordered confirmation within the bilayer.
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  • 9
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The redox behaviour of solid quinones has been examined by potential sweep and cyclic voltammetry. A number of quinones are insoluble in aqueous electrolytes and can be completely discharged and recharged without appreciable polarization, as found, for example, with solid chloranil (tetrachloro-p-benzoquinone) and solid duroquinone (tetramethyl-p-benzoquinone). Hence quinones are reversible redox systems not only in solutions but also in the solid state. During discharge and recharge in dilute sulphuric acid only slight polarization occurs, which is attributed to a pure diffusion overvoltage. Polarization is not much greater in salt solutions. In this case, however, the peaks of the voltammetric curves are broader. In ammonium chloride solutions a double peak corresponding to the two electron transfers is obtained for chloranil both anodically and cathodically; this shows that the semiquinone is stable in ammonium chloride solution. Duroquinone also gives two peaks, but these are observed only in non-stationary measurements so that they do not correspond to the state of equilibrium. The pH dependence of the redox potential is 59 mV per pH unit. Only chloranil in ammonium chloride solution shows two redox potentials, depending on the discharge depth, which are both lower than the potential corresponding to the pH. The possible application of quinones in secondary battery cathodes is discussed.
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  • 10
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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