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  • 1
    ISSN: 0138-4988
    Keywords: Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: By aid of lipases, e.g. of Mucor michei, in n-hexane wax esters were produced from usual primary fatty alcohols and unusual hydroxy fatty acids (in part of microbial origin). Thus, (S)-17-hydroxyoctadecanoic acid dodecyl ester and (R)-3-hydroxy decanoic acid dodecyl ester were formed. In measurements of the film pressure using a LANGMUIR film balance the monolayers of both compounds indicated good stability compared to the non-hydroxy wax esters. Glycolipids de novo produced by microorganisms did not show suitable wetting properties, but they were able to lower ze surface tension of water to a higher extent than the unusual waxes.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1436-5073
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Über die allgemeine Auslegung und die Betriebsweise einer Tridestilla-tionsapparatur aus Quarzglas für die kontinuierliche Darstellung hochreinen Wassers wurde berichtet. Weiterhin wurden einige Methoden zur Reinheitsbestimmung und Charakterisierung hochreinen Wassers, nämlich spezifische elektrische Leitfähigkeit, UV-Spektrometrie, Fluoreszenzspektrometrie, AAS, pH-Messung und GC diskutiert. Abschließend wurden Vorsichtsmaßnahmen und Empfehlungen gegeben, die bei der Darstellung hochreinen Wassers durch Destillationsverfahren berücksichtigt werden sollten.
    Notes: Summary The general features and the performance of a three-stage distillation unit constructed from quartz for the continuous production of ultrapure water are described. Additionally, some methods for the determination and characterization of water purity, such as specific conductivity measurement, ultraviolet absorption spectrometry, fluorescence spectrometry, AAS, pH determination and GC are outlined. Finally, general precautions and recommendations for the production of ultrapure water by distillation techniques are given.
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  • 3
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Weitere Ergebnisse zur Methode der Reinheitsbestimmung durch simulierte DSC-Kurven werden vorgestellt. Die Geräteparameter eines Wärmeflußkalorimeters werden für zwei Temperaturen berechnet, womit genauere Ergebnisse erzielt werden können. Das Kalorimetermodell wird an ein weiteres Wärmeflußkalorimeter angepaßt. Die Methode bietet aufgrund der Berücksichtigung von Geräte- und Substanzeigenschaften auch die Möglichkeit einer genaueren Schmelztemperaturbestimmung. Weiterhin wird eine Fehlerabschätzung zum van't Hoffschen Gesetz durchgeführt, welches eine vereinfachte Beschreibung der Koexistenzkurven eines eutektischen Phasensystems und damit der Gefrierpunktserniedrigung darstellt. Dabei ergibt sich, daß der relative Gesamtfehler proportional zur Verunreinigungskonzentration ist und in der gleichen Größenordnung wie diese liegt.
    Abstract: Резюме Представлены дальне йшие результаты по определению чистоты с помощью мод ельных кривых ДСК. Инструментальные па раметры для ДСК с тепловым пот оком были определены при двух температурах, вследс твии чего улучшена то чность получаемых результа тов. Дополнительно к этом у, данная модель калориметра приспособлена к друг ому калориметру. Мето д также позволяет более точное определение т емпературы плавлени я. Закон Вант-Гоффа значительно упрощен но описывает сосущес твование кривых на эвтектичес кой фазовой диаграмме. Де тальный анализ ошибок пяти упрощений привел к то му, что закон показал, ч то введенная относител ьная общая ошибка пропорц иональна концентрации примес и и является такой вели чиной, как и сама конце нтрация.
    Notes: Abstract This paper presents further results of the purity determinations by simulated DSC curves. The instrumental parameters of a heat-flux DSC are now determined at two temperatures whereby the accuracy of the results is improved. In addition the calorimeter model is adapted to another calorimeter. The method also allows a more exact determination of fusion temperature. Van't Hoff's law is a considerably simplified description of the coexistence curves in a eutectic phase diagram. A detailed error analysis of the five simplifications leading to this law shows that the relative total error introduced is proportional to the impurity concentration and is of same magnitude as the latter.
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  • 4
    ISSN: 1572-8943
    Keywords: sugar alcohols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The glass transition of isomalt and its components, the enthalpy of solution (crystalline state, glassy state) and the enthalpy of melting are reported. From the measured data (solution enthalpy, enthalpy of fusion and heat capacities) a cycle like the BORN-HABER cycle can be constructed. It is possible to calculate the amounts of amorphous isomalt from measured solution enthalpies; however, the values obtained do not agree with those provided by X-ray powder diffraction studies.
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  • 5
    ISSN: 1572-8943
    Keywords: calibration material ; calibration procedure ; DSC ; heat calibration ; heat flow rate calibration ; standards ; temperature calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Metrologically based measuring procedures and evaluation methods are recommended as guidance for practical temperature, heat and heat flow rate calibration of DSC instruments which are largely independent of instrumental, test and sample parameters. The relevant terms are defined, the measuring procedures and evaluation methods described, calibration materials and their characteristic data stated and guidance for the sample handling provided. Reference is made to three extended papers on calibration. The recommendations were developed by the working group ‘Calibration of Scanning Calorimeters’ of the German Society of Thermal Analysis (GEFTA).
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  • 6
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Silane des Typs R1R2Si(H)CH2OE10xR y 3 mit R=organyl; E1=C (x=y=1), S(x=2, y=1) oder P (x=1,y=2) zeigen eine thermisch induzierte Umlagerung zu Silanen des Typs R1R2Si(CH3)OE10xR y 3 . Energetische (Reaktionsenthalpie) und kinetische Daten (Reaktionsordnung, Aktivierungsenthalpie und -entropie) dieser Umlagerungsreaktion wurden mittels DSC ermittelt. Die mechanistischen Aspekte der Ergebnisse werden diskutiert.
    Abstract: РЕжУМЕ сИлАНы тИпА R1R2Si(H)OE1(O)xR y 3 , гДЕ R=ОРгАНИЧЕскИИ РАДИкАл, E1=C (x=y=1), S (x=2,y=1), P (x=1,y=2), пОДВЕРгАУтсь т ЕРМИЧЕскИ НАВЕДЕННОМУ пРЕВРАЩ ЕНИУ с ОБРАжОВАНИЕМ сИлАНОВ тИпА R1R2Si(CH3)OE1(O)xR y 3 . с п ОМОЩьУ Дск БылИ ОпРЕДЕлЕНы ЁНЕРгЕтИ ЧЕскИЕ (ЁНтАльпИь РЕАкцИИ) И кИНЕтИЧЕск ИЕ пАРАМЕтРы (пОРьДОк РЕАкцИИ, ЁНтАльпИь И ЁНтРОпИь АктИВАцИИ) ЁтОИ РЕАкцИИ. пОлУЧЕН НыЕ РЕжУльтАты ОБсУж ДЕНы НА ОсНОВЕ МЕхАНИстИЧЕс кИх пРЕДстАВлЕНИИ.
    Notes: Abstract Silanes of the type R1R2Si(H)CH2OEl(O)xR y 3 [R=organyl; El=C (x=y=1), S (x=2,y=1), P (x=1y=2)] undergo a thermally induced rearrangement to give silanes of the type R1R2Si (CH3)OEl(O)xR y 3 . The energetic (reaction enthalpy) and kinetic data (reaction order, enthalpy and entropy of activation) of this reaction were determined by means of differential scanning calorimetry. The results obtained are discussed in terms of mechanistic aspects.
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  • 7
    ISSN: 1572-8943
    Keywords: caffeine hydrate ; solid state reaction kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Entwicklung und Aufbau der Zeit- und Temperaturaufgelösten Röntgenpulverdiffractometrie werden beschrieben. Die Methode ermöglicht weit tiefere Einblicke in das Reaktionsgeschehen bei Reaktionen fester Stoffe als die üblichen thermoanalitischen Methoden wie Dynamische Differenz-Kalorimetrie (DDK/DSC) und Thermogravimetrie. Als Beispiel wurde die Dehydration von Coffeinhydrat untersucht. Dabei wurde festgestellt, daß zu Beginn der Reaktion offenbar Keimbildungsvorgänge Geschwindigkeitsbestimmend sind, während bei höheren Umsatzgraden zunehmend Diffusionshemmung eintritt.
    Notes: Abstract Development and experimental setup of the time-, and temperature -resolved X-ray powder diffractometry are described. This method allows far deeper insight into solid state reactions than conventional thermoanalytical methods like differential scanning calorimetry (DSC) or thermogravimetry. As an example, the dehydration of caffeine hydrate was investigated. We found that in earlier stages the reaction is nucleation controlled, whereas for higher extent of reaction diffusion limitation becomes rate-controlling.
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  • 8
    ISSN: 1572-8943
    Keywords: azobenzene ; DSC ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Contrary to the situation in the field of temperature, heat and heat flow rate calibration, so far no generally accepted and easily practicable chemical reaction exists with regard to a kinetic evaluation. A possible reaction would be the well-known first-order cis-trans isomerization of subcooled liquid azobenzene. Surprisingly, the evaluation of measurements performed with a power compensated calorimeter yields activation parameters, which are dependent on the heating rate. The desmearing of the curves does not produce any improvements. However, constant activation parameters are obtained, if a small self-heating of the sample during the exothermic reaction is taken into account.
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  • 9
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé La cafféine présente une forme basse température (β) et haute température (α). Les données suivantes ont été déterminées par ATD quantitative: température de transformation 141±2°, enthalpie de transition 4.03±0.1 kJ·mole−1, enthalpie de fusion 21.6±0.5 kJ ·mole−1, chaleur spécifique molaire $$\begin{array}{*{20}c} {{\vartheta \mathord{\left/ {\vphantom {\vartheta {^\circ C}}} \right. \kern-\nulldelimiterspace} {^\circ C}}} & {100(\beta )} & {100(\alpha )} & {150(\alpha )} & {100(\alpha )} \\ {{{C^\circ _\mathfrak{p} } \mathord{\left/ {\vphantom {{C^\circ _\mathfrak{p} } {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} \right. \kern-\nulldelimiterspace} {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} & {271 \pm 9} & {287 \pm 10} & {309 \pm 11} & {338 \pm 10} \\ \end{array} $$ en bon accord avec les données obtenues par calorimétrie à chute. Les mesures sous pression de vapeur statique effectuées sur la cafféine liquide et solide (α) ainsi que les mesures d'effusion sur la cafféine liquide et solide (α) ainsi que les mesures d'effusion sur la cafféine solide (β) ont donné pour les constantes de l'équation lg(p/Pa)=−A/T+ B: $$\begin{array}{*{20}c} {A = 3918 \pm 37; 5223 \pm 28; 5781 \pm 35K^{ - 1} } \\ {B = 11.143 \pm 0.072; 13.697 \pm 0.057; 15.031 \pm 0.113} \\ \end{array} $$ . Le coefficient d'évaporation de la cafféineβ est 0.17±0.03.
    Abstract: Zusammenfassung Es wurde festgestellt, daß Caffein bei niedrigen Temperaturen eineβ- und bei hohen Temperaturen eineα-Modifikation besitzt. Durch quantitative DTA wurden folgende Angaben bestimmt: Umwandlungstemperatur 141±2 °C, Umwandlungsenthalpie 4.03±0.1 kJ·Mol−1 Schmelzenthalpie 21.6±0.5 kJ·Mol−1, molare Wärmekapazität $$\begin{array}{*{20}c} {{\vartheta \mathord{\left/ {\vphantom {\vartheta {^\circ C}}} \right. \kern-\nulldelimiterspace} {^\circ C}}} & {100(\beta )} & {100(\alpha )} & {150(\alpha )} & {100(\alpha )} \\ {{{C^\circ _\mathfrak{p} } \mathord{\left/ {\vphantom {{C^\circ _\mathfrak{p} } {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} \right. \kern-\nulldelimiterspace} {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} & {271 \pm 9} & {287 \pm 10} & {309 \pm 11} & {338 \pm 10} \\ \end{array} $$ Sie stimmten gut mit den tropfkalorimetrischen Daten überein. Statische Dampfdruckmessungen an flüssigem und festemα- und Effusionsmessungen an festemβ-Caffein ergaben für die Konstanten der Gleichung lg(p/Pa)=−A/T+ B: $$\begin{array}{*{20}c} {A = 3918 \pm 37; 5223 \pm 28; 5781 \pm 35K^{ - 1} } \\ {B = 11.143 \pm 0.072; 13.697 \pm 0.057; 15.031 \pm 0.113} \\ \end{array} $$ . Der Verdampfungskoeffizient vonβ-Caffein beträgt 0.17±0.03.
    Notes: Abstract Caffeine has been found to display a low-temperatureβ- and a high-temperatureα-modification. By quantitative DTA the following data were determined: transformation temperature 141±2°; enthalpy of transition 4.03±0.1 kJ·mole−1; enthalpy of fusion 21.6±0.5 kJ·mole−1; molar heat capacity $$\begin{array}{*{20}c} {{\vartheta \mathord{\left/ {\vphantom {\vartheta {^\circ C}}} \right. \kern-\nulldelimiterspace} {^\circ C}}} & {100(\beta )} & {100(\alpha )} & {150(\alpha )} & {100(\alpha )} \\ {{{C^\circ _\mathfrak{p} } \mathord{\left/ {\vphantom {{C^\circ _\mathfrak{p} } {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} \right. \kern-\nulldelimiterspace} {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} & {271 \pm 9} & {287 \pm 10} & {309 \pm 11} & {338 \pm 10} \\ \end{array} $$ in good accord with drop-calorimetric data. For the constants of the equation log (p/Pa)=−A/T+B, static vapour pressure measurements on liquid and solidα-caffeine, and effusion measurements on solidβ-caffeine yielded: $$\begin{array}{*{20}c} {A = 3918 \pm 37; 5223 \pm 28; 5781 \pm 35K^{ - 1} } \\ {B = 11.143 \pm 0.072; 13.697 \pm 0.057; 15.031 \pm 0.113} \\ \end{array} $$ . The evaporation coefficient ofβ-caffeine is 0.17±0.03.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 43 (1987), S. 591-592 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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