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  • 1
    ISSN: 1573-515X
    Keywords: Catchment ; isotope fractionation ; sulfur cycling ; stable isotopes ; δ34S ; δ18Osulfate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The isotopic composition of SO 4 2- in bulk precipitation, canopy throughfall, seepage water at three different soil depths, stream water, and groundwater was monitored in two forested catchments in the Black Forest (Germany) between November 1989 and February 1992. Isotope measurements on aqueous sulfate were complemented by δ34S-analyses on SO2 in the air, total sulfur and inorganic sulfate in the soil, and bedrock sulfur, in order to identify sources and biogeochemical processes affecting S cycling in catchments with base poor, siliceous bedrock. Stable S isotope data indicated that atmospheric deposition and not mineral weathering is the major source of S in both catchments since δ34S-values for sulfate in the soil, in seepage water, and in stream water were generally found to be similar to the mean δ34S-values of precipitation SO 4 2- (+2.1. However, δ18O-values of seepage water SO 4 2- at 30 cm and especially at 80 cm depth were depleted by several per mil with respect to those of the atmospheric deposition (+7.5 to +13.5. This indicates that in both catchments a considerable proportion of the seepage water SO 4 2- is derived from mineralization of carbon-bonded soil S and must therefore have cycled through the organic soil S pool. δ34S-values for different S compounds in the solid soil were found to differ markedly depending on S fraction and soil depth. Since atmospheric S deposition with rather constant δ34S-values was identified as the dominant S source in both catchments, this is interpreted as a result ofin situ isotope fractionation rather than admixture of isotopically different S. The differences between the δ34S-values of seepage water and soil sulfate and those of organic soil S compounds are consistent with a model in which SO 4 2- uptake by vegetation and soil microorganisms favours34SO 4 2- slightly, whereas during mineralization of organic soil S to aqueous SOSO 4 2- ,32S reacts preferentially. However, the data provide evidence for negligible isotope fractionation during physico-chemical S transformations such as adsorption/desorption in aerated forest soils.
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  • 2
    ISSN: 1573-5036
    Keywords: atmospheric deposition ; δ15N ; δ34S ; forest decline ; nitrogen ; Picea abies ; stable isotopes ; sulfur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Concentrations and natural isotope abundance of total sulfur and nitrogen as well as sulfate and nitrate concentrations were measured in needles of different age classes and in soil samples of different horizons from a healthy and a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to study the fate of atmospheric depositions of sulfur and nitrogen compounds. The mean δ15N of the needles ranged between −3.7 and −2.1 ‰ and for δ34S a range between −0.4 and +0.9 ‰ was observed. δ34S and sulfur concentrations in the needles of both stands increased continuously with needle age and thus, were closely correlated. The δ15N values of the needles showed an initial decrease followed by an increase with needle age. The healthy stand showed more negative δ15N values in old needles than the declining stand. Nitrogen concentrations decreased with needle age. For soil samples at both sites the mean δ15N and δ34S values increased from −3 ‰ (δ15N) or +0.9 ‰ (δ34S) in the uppermost organic layer to about +4 ‰ (δ15N) or +4.5 ‰ (δ34S) in the mineral soil. This depth-dependent increase in abundance of 15N and 34S was accompanied by a decrease in total nitrogen and sulfur concentrations in the soil. δ15N values and nitrogen concentrations were closely correlated (slope −0.0061 ‰ δ15N per μmol eq N gdw −1), and δ34S values were linearly correlated with sulfur concentrations (slope −0.0576 ‰ δ34S per μmol eq S gdw −1). It follows that in the same soil samples sulfur concentrations were linearly correlated with the nitrogen concentrations (slope 0.0527), and δ34S values were linearly correlated with δ15N values (slope 0.459). A correlation of the sulfur and nitrogen isotope abundances on a Δ basis (which considers the different relative frequencies of 15N and 34S), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292). These correlations indicate a long term synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied by element-specific isotope fractionations. Based on different sulfur isotope abundance of the soil (δ34S=0.9 ‰ for total sulfur of the organic layer was assumed to be equivalent to about −1.0 ‰ for soil sulfate) and of the atmospheric SO2 deposition (δ34S=2.0 ‰ at the healthy site and 2.3 ‰ at the declining site) the contribution of atmospheric SO2 to total sulfur of the needles was estimated. This contribution increased from about 20 % in current-year needles to more than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age dependent sulfate accumulation in the needles. In contrast to the accumulation of atmospheric sulfur compounds nitrogen compounds from atmospheric deposition were metabolized and were used for growth. The implications of both responses to atmospheric deposition are discussed.
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  • 3
    ISSN: 1573-5036
    Keywords: managed forest stands ; stable isotopes ; sulphur cycling ; S-turnover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Sulphur cycling was evaluated in a 20 to 60 year old Norway spruce (Picea abies L. Karst) ecosystem in the Black Forest near Schluchsee, SW Germany, by means of stable sulphur isotope analysis. Soil and plant material were analysed for S-content and S-isotopic composition to gather information on the S-distribution in the ecosystem. Two out of three adjacent watershed areas, highly comparable to each other were fertilized with MgSO4 and (NH4)2SO4 respectively, where sulphate was enriched in the 34S-isotope compared to the sulphur present in the ecosystem. As the fertilizer S served as a tracer, comparison of the S-isotopic composition of total and inorganic S in the soil and S in spruce needles from both the treated and the control sites led to new information of S-turnover processes. The S-isotopic composition of spruce needles changed markedly after the fertilizer application. Within half a year a shift towards the S-isotopic composition of the fertilizers sulphate indicated uptake of the sulphate by the trees, although this uptake did not become visible with the S content of the needles. Regarding the soil, a shift in the S-isotopic composition of the total sulphur was not that striking as with the needles, although the phosphate extractable sulphate showed a clear shift towards the S-isotopic composition of the fertilizer sulphate.
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the ethylene polymerization catalyzed by Ti(CH2C6H5)4/TiBr4 in toluene at 0°C was studied. The effects of the mole ratio of the catalyst components and of the quantity of catalyst on the polymerization were investigated. Using the number of active centres, the rate constant of the propagation reaction was evaluated. The number of active centres was determined by quenching the polymerization with 1-butanol tritiated at the hydroxyl group. Compared with the kinetic data of the catalyst system Ti(CH2C6H5)4/AlBr3, the present results indicate that the nature of the cocatalyst mainly affects the conditions for the formation of active centres, but has no essential influence on their reactivity. These results support the concept of monometallic structure of the active centres in Ziegler-Natta catalysts.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: D,L-Phenylalanin reagiert mit einem Überschuß von N,N′-Carbonyl-di-imidazol in abs. Tetrahydrofuran unter Auflösen der Aminosäure. Nach Abtrennung des bei der Reaktion freigewordenen Imidazols konnte jedoch kein D,L-Phenylalanin-N-carbonsäureanhydrid gefunden werden. Aus dem Rohprodukt wurde das N,N′-Carbonyl-bis-D,L-phenylalanin isoliert und durch Überführung in den Dimethylester und die 5-Benzylhydantoin-3β-phenylpropionsäure, sowie durch Hydrolyse zum D,L-Phenylalanin identifiziert. Es wird angenommen, daß die Reaktion nicht über das N-Carbonsäureanhydrid verläuft, da dieses bei Gegenwart von Imidazol sofort zu Poly-D,L-phenylalanin kondensiert.
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  • 6
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eine wäßrige Lösung von ε-aminocapronsaurem Natrium reagiert mit Phosgen unter Bildung der Carbamido-ε-dicapronsäure, die beim Erhitzen unter Abspaltung von einem Mol CO2 und einem Mol H2O zu einem linearen Polyamid kondensiert (DBP 888847). Versuche, Carbamido-α-dicarbonsäuren durch Umsetzungen der Natriumsalze verschiedener α-Aminosäuren mit Phosgen herzustellen, verliefen negativ. Beim Erhitzen der auf anderen Wegen erhaltenen Carbamido-dicarbonsäuren des D, L-Alanins, D,L-Phenylalanins und D,L-Norleucins wurde ebenfalls CO2 und H2O abgespalten, jedoch nicht in einem Verhältnis, das auf die Bildung von linearen oder cyclischen Polyaminosäuren schließen läßt.  -  Die Kondensation der Carbamido-ε-dicarbonsäure zum linearen Polyamid verläuft sehr wahrscheinlich über das ε-Caprolactam. Eine geringe Menge dieser Verbindung konnte isoliert werden. Carbamido-δ-divaleriansäure, die nach dem Patentverfahren in glatter Reaktion entsteht, geht beim Erhitzen größtenteils in δ-Valerolactam über.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Es wurden die als Phthalochromogene bezeichneten Komplexverbindungen des Eisen-II-phthalocyanins mit Imidazol und einigen Imidazolderivaten dargestellt. Die Imidazol-Phthalochromogene wurden auf ihre Beständigkeit untersucht.
    Additional Material: 1 Ill.
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  • 8
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1983 (1983), S. 1551-1560 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthese eines desoxanalogen von (3S)-Citryl-CoA: (3RS)-3,4-Dicarboxy-3-hydroxybutyl-CoADer Citrylthioester 1 wurde im mmol-Maßstab mit Natriumtetrahydroborat in 70proz. Ausbeute zu 2-Hydroxy-2-(2-hydroxyethyl)butandisäure (2) reduziert. Die Säure wurde in den Dimethylester 3 und weiter in das 2-(2-Bromethyl)-Derivat 4 umgewandelt. Dessen Reaktion mit Coenzym A lieferte die Titelverbindung 7, entweder im Eintopfverfahren oder durch Hydrolyse des isolierten Dimethylesters 6. Die mit 7 und dem Enzym Citratsynthase des Tricarbonsäurezyklus erzielten kinetischen und röntgenstrukturanalytischen Ergebnisse werden diskutiert.
    Notes: The citryl thioester 1 was reduced in mmol scale with sodium tetrahydroborate to yield 2-hydroxy-2-(2-hydroxyethyl)butanedioic acid (2) in 70% yield. The acid was converted into the dimethyl ester 3 and further to the 2-(2-bromoethyl) derivative 4. This bromide was used to prepare the title compound 7 by reaction with coenzyme A, either directly, or by hydrolysis of the isolated dimethyl ester 6. The kinetic and X-ray crystallographic results obtained with 7 and the enzyme citrate synthase of the tricarboxylic acid cycle are discussed.
    Additional Material: 1 Tab.
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