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  • 1
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 119Sn- and 13C-NMR Spectroscopic Investigations of Tri-n-butyltin Derivatives of Amino Acids
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0365-9496
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 10 (1970), S. 169-187 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The possibilities for a systematic selection of the conditions for fractional precipitation in polymer/solvent/nonsolvent-systems based on data of the turbidimetric titrations have been tested experimentally. As criticism for the fractionation efficiency the molecular weight distribution of the fractions (determined by ultra-centrifuge) and the uniformity M̄w/M̄n (calculated therefrom) was taken. The successiv- and subfractionation, the dependence of the initial concentration and particularly the influence of the solvent/nonsolvent-system on the fractionation efficiency were investigated. Therefore a simple new method was developed, which allows to arrange systematically different solvent/nonsolvent-systems with few turbidimetric titrations as to be suitable for fractionation. For three selected solvent/non-solvent-systems the correctness of the selection method could be proved experimentally.
    Notes: Die Möglichkeiten zur gezielten Auswahl der Fraktionierbedingungen einer Fällfraktionierung in Systemen Polymeres/Lösungsmittel/Fällungsmittel auf der Grundlage von Fällungstitrationsdaten wurden einer experimentellen Prüfung unterzogen. Als Kriterium für die Güte der Trennwirkung diente die in der Ultrazentrifuge bestimmte Molekulargewichtsverteilung der gewonnenen Fraktionen und die daraus berechnete Einheitlichkeit (M̄w/M̄n/). Neben der Sukzessiv- und Unterfraktionierung wurde der Einfluß der Ausgangskonzentration und insbesondere des Lösungs-/Fällungsmittelsystems auf die Fraktionierwirkung untersucht. Dazu wurde eine einfache Methode entwickelt, welche verschiedene Lösungs-/Fällungsmittel-Systeme auf Grund weniger Trübungstitrationen bezüglich ihrer Eignung als Fraktioniersystem systematisch zu ordnen gestattet. Am Beispiel der Fraktionierung mit drei ausgewählten Lösungs-/Fällungsmittel-Systemen konnte die Richtigkeit der Auswahlmethode experimentell gesichert werden.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: To prepare very narrow distributed polystyrene samples, a two step procedure of polymerization is proposed, which includes a change of solvent. The first solvent, used for the initiation step, has to be characterized by a high value of vst/vp, while the second one, used for the propagation step, should guarantee a good control of temperature during the polymerization reaction. In our case, tetrahydrofuran and benzene were chosen and n-Li-butyl has been used for the initiation.The polymerization products have been characterized by MW-averages and MW-distribution. Finally a preparative fractionation has been carried out to separate the low and high MW tail of the distribution thus leading to samples whose values for M̄w/M̄n can be shown to be about 1,01.
    Notes: Zur Herstellung hocheinheitlicher Polystyrole wird ein Verfahren angegeben, das auf einer zweistufigen Lösungspolymerisation mit Austausch des Lösungsmittel beruht. Die Lösungsmittel müssen so gewählt werden, daß bei der Vorpolymerisation die Startgeschwindigkeit wesentlich größer ist als die Wachstumsgeschwindigkeit, für die weitere Polymerisation jedoch die Reaktion thermisch gut kontrolliert werden kann; in dem beschriebenen Verfahren wurden Tetrahydrofuran und Benzol verwenigte Polymere entstehen sollten.Die Polymerisationsprodukte wurden durch ihr mittleres Molekulargewicht und ihre Molekulargewichts-Verteilungskurve charakterisiert. Nach einer Spitzenfraktionierung zur Abtrennung der hoch- und niedermolekularen Ausläufer liegt die erreichte Einheitlichkeit bei einem Wert M̄w/M̄n ≈ 1,01.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 69 (1978), S. 189-210 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The solution instability (also called ageing or degradation) of high purity polyacrylamides(PAAm) was examined for a number of different molecular weights. This instability set in by a decrease of the solution viscosity and of [η] depending on time with simultaneous loss of flocculation activity.The instability appears only at molecular weights M̄ 〉 1,5 mill. in aqueous solutions; in formamide and ethyleneglycole PAAm-solutions however are stable. The viscosity loss was observed at a concentration range c = 0,001 to 5%. The standardization of several pH-values at a range from 1 to 12 by means of buffer substances as well as the addition of hydrochinone, chinone, NaNO2 and Na2SO3 do not lead to a stable solution. Only at pH = 5 a stable solution was obtained but by changing the buffer substance at the same pH the solution became instable again. Addition of isopropanol leads to stable aqueous PAAm-solutions from technical products as well as high purity polyacrylamides.The mechanism of the solution instability is not a decrease of the molecular weight due to chain scission but a change of conformation of the solution structure from single molecules based on hydrogen bonds.
    Notes: Die Lösungsinstabilität(auch Alterung oder Viskositätsabbau genannt) von hochreinen Polyacrylamiden (PAAm) verschiedener Molekulargewichte wurde untersucht. Diese Instabilität äßert sich durch eine Abnahme der Lösungsviskosität und des [η] in Abhängigkeit von der Zeit bei gleichzeitigem Flockungsverlust.Die Lösungsinstabilität tritt nur bei Molekulargewichten M̄ 〉 1,5 Mill. in wäßriger Lösung auf. PAAm.-Lösungen in Formamid und äthylenglykol sind stabil. Die Viskositätsabnahme erfolgt in einem Konzentrationsbereich von c = 0,001 bis 5%. Die Einstellung verschiedener pH-Werte im Bereich von pH = 1 bis 12 mittels Puffersubstanzen sowie die Zusätze von Hydrochinon, Chinon, NaNO2 und Na2SO3 führen nicht zu einer Lösungsstabilität. Nur pH = 5 zeigte sich eine Stabilisierung der Lösung, die jedoch beim Wechsel der Puffersubstanz bei gleichem pH wiederum in eine Instabilität überging. Zusätze von Isopropanol führen sowohl bei technischen Handelsprodukten als auch bei hochreinen Laborprodukten zu einer Stabilisierung wäßriger PAAm-Lösungen.Der Mechanismus der Lösungsinstabilität besteht nicht in einem Molekulargewichtsabbau durch Kettenbruch, sondern offenbar in einer änderung der Lösungsstruktur der Einzelmoleküle unter Beteiligung von Wasserstoff-Brücken.
    Additional Material: 14 Ill.
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  • 6
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Microbial desulfurization of coal by pyrite oxidizing bacterial enrichment cultures has been studied in air-agitated slurry reactors of 4- and 20-L volumes. Batch experiments showed that inoculation with an active bacterial culture is essential to minimize the lag phase, although a considerable number of pyrite oxidizing bacteria was found on the coal prior to desulfurization. For detailed investigations of kinetics, energy requirements, and technical applicability, a bioreactor equipment consisting of a cascade of eight stages was developed and operated continuously. Microbial desulfurization of coal - monitored by measuring the axial profile of dissolved iron concentration, real and maximum oxygen consumption rates, and cell concentration - at pulp densities to 30% was performed over a period of 200 days without any disturbances concerning the aeration system, fluidization, transport of solids and microbial growth. At a pulp density of 20%, a pyrite conversion of 68% was achieved after the third reactor stage at a total residence time of five days in the first three stages. The kinetics of pyrite degradation were found to be well described by a rate equation of first order in pyrite surface area concentration if the pyrite is directly accessible for microbial attack. Rate constants were determined to 0.48 mg pyrite/(cm2 day) in the first and to 0.24 mg pyrite/(cm2 day) in the following reactor stages. Kinetic models taking into account adsorption/desorption as well as growth kinetics failed to describe the observed reaction rates. However, a model treating pyrite degradation and microbial growth kinetics formalistically seems to be applicable when backmixing between the reactor stages can be avoided. The advantage of a multistage reactor in comparison to single-stage equipment was shown by calculation. To obtain a pyrite conversion of 68%, a three-stage reactor would require only 58% of the volume of single-stage equipment.Measurement of oxygen consumption rates proved to provide quickly and easily measurable parameters to observe microbial coal desulfurization in technical scale: the real oxygen consumption rate is correlated to the pyrite oxidation rate and the maximum oxygen consumption rate is correlated to the concentration of viable cells. The Yo/s coefficient for the amount of oxygen consumed per mass unit of pyrite oxygen was determined to approximately 0.33 in comparison to 1.0 which can be calculated from stoichiornetry. This could yet not be explained. Chemical leaching experiments as well as sulfur analyses of desulfurized coal samples showed that the microorganisms play the main role in degradation of pyrite from coal and that pyrite oxidation by ferric iron can be neglected.
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 1 (1955), S. 105-111 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The reactions involved in the removal of nitrogen oxides from gases by reaction with water are reversible and proceed at a finite rate. It is possible therefore that the over-all process is controlled by the rate of the chemical reactions. On this basis an analysis of the process has been developed by the application of chemical kinetics, with consideration of reactions involving both nitrogen dioxide and dinitrogen tetroxide. The resulting differential equation has been simplified and integrated to give a final equation which can be tested experimentally.Theoretical methods are presented for predicting the extent of absorption of nitrogen oxides at various gas rates and concentrations and are compared with the experimental results.The paper presents some new concepts of the factors which control the rate of absorption of nitrogen dioxide and dinitrogen tetroxide in water. An understanding of the controlling factors in the process should indicate methods for improving the design of absorption towers in nitric acid plants and aid in the design of scrubbers for removing nitrogen oxides from waste gases.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 23 (1981), S. 1057-1065 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Whole cells of the methanogen Methanosarcina barkeri were immobilized in an alginate network which was crosslinked with Ca2+ ions. The rates of methanol conversion to methane of entrapped cells were found to be in the same range as the corresponding rates of free cells. Furthermore, immobilized cells were active for a longer period than free cells. The particle size of the spherical alginate beads (1.2 mm-3.7 mm φ) and thus diffusion had no obvious influence on the turnover of methanol. The half-value period for methanol conversion activity determined in a buffer medium was approximately 4 days at 37°C for entrapped cells. The apparent Km value Km′ for such cells was nearly 140mM and the Vmax value was about 1.2 μmol methanol/min/mg entrapped protein. Therefore the high rates of methanol degradation measured, e.g., 0.5 μmol methanol/min/mg entrapped protein, indicated that the immobilization technique preserved the cellular functions of this methanogenic bacterium.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 14 (1970), S. 1927-1938 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: All current fractionation techniques - based on sol-gel equilibria - are characterized by a variation of the solvent power after each fractionation step in a discontinuous as well as in a continuous way. Overlapping of consecutive fractions is the consequence of this procedure. It can be shown that this overlapping can be diminished essentially by a multistage technique based on complete extraction at a given solvent power which then will be changed in discontinuous steps. As a further consequence, it is possible to obtain very homogeneous fractions of M̄w/M̄n 〈 1.03. A theoretical analysis of this technique on the basis of phase equilibrium data will be given, the results of which can be confirmed experimentally.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 287 (1895), S. 161-183 
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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