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  • Wiley-Blackwell  (13)
  • Nature Publishing Group  (3)
  • Washington, DC : United States Gov. Print. Off.
  • American Association of Petroleum Geologists (AAPG)
  • 11
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 5 (1967), S. 61-68 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical possibilities for investigation of nucleic acids with high molecular weight are restricted to the determination of the adsorption behavior. According to our experience the alternating current polarography (Breyer-polarography) is mainly appropriate for the characterization of changes in the secondary structure of DNA. The Breyer-polarogram shows the alternating current of the dropping electrode in dependence on their potential which varied from 0-2 v. negative against the normal calomel electrode (NCE). By addition of native DNA to the supporting electrolyte (buffer solution) the current drops down in the range of adsorption between 0 and 1 v. At 1.16 v. against NCE the desorption takes place together with the formation of a rounded desorption peak. The investigation was carried out in phosphate buffer solution 0.1m with 0.075m NaCl or in a phosphate buffer 0.18m with 0.03m NaCl. In the pH range above pH 8 NaOH was added to realize the higher pH values. A calf thymus DNA sample having a mean molecular weight of about 18 million was used. The concentration of DNA was 5 × 10-3-1 × 10-1 wt.-%. The polarographic measurements were performed with an a.c./d.c.-polarograph “GWP 564” from Akademiewerkstätten für Forschungsbedarf der Deutschen Akademie der Wissenschaften zu Berlin (DAW). The denaturation of the double helix causes a sharp desorption peak at negative potentials of the alternating current polarogram. This new criterion for the helix-coil transition is due to formation of unpaired bases. These nearly free bases undergo a specific adsorption and the desorption takes place within a narrow potential range. Nevertheless, at present time an electron transfer to particular bases cannot be excluded at special conditions. The increase of the sharp peak permits to estimate: (a) the melting curve of the double helix in agreement with spectroscopic measurements; (b) the photolysis of the double helix; (c) the strand separation in acid and alkaline solution. In the alkaline range the sharp peak increases and reaches its maximum at pH 〉 12. In the acid range, however, no sharp peak is observed and the rounded desorption peak decreases. Therefore, the best way of following the conformation changes is to measure the current difference between the curves of the solutions with and without DNA at electrocapillary-zero-potential. On the classical d.c.-polarogram one can measure small current steps only, which may be caused mainly by capacity changes. Moreover, the scission of the molecule by ultrasonic action can be followed. In this case the rounded peak of DNA increases but the sharp peak does not appear. Similar alternating current polarograms are obtained with poly-A in the native state, because helical and unordered regions coexist in the same molecule. The very rapid indication of these structure changes allows one to carry out kinetic measurements at a fixed potential with this method.
    Additional Material: 5 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 319 (1977), S. 848-856 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Physico-chemical Analysis of the Hydrolysis of N-(2-Cyanethylene-)ureaBy means of pulse-polarography, infrared and n.m.r.-spectroscopy and electronattachment-mass-spectroscopy the hydrolysis of N-(2-cyanethylene-)urea (BA 1) under relatively mild conditions has been evidenced (pH 5,6 to 9.0; T = 37° C and 22° C). With rising pH value the rate of hydrolysis increases. At pH 5.6 the hydrolysis is very slow (half life time ca. 6 days), but condensation products are already demonstrable. At pH 9.0 nearly all of BA 1 molecules are hydrolysed within 2 days under splitting of the heterocycle and formation of various hydrolysis products. On the middle pH range from 7.3 to 8.3 the formation of 2-cyanaziridine was followed and after cycle splitting various resultant products were observed. The half life time of BA 1 hydrolysis at pH 7.3 and T = 37° C has been determined to 103 ± 1 hours (0.144 m BA 1, phosphate buffer).
    Notes: Mit Pulspolarographie, Infrarot- und NMR-Spektroskopie sowie Elektronenanlagerungs-Massenspektrographie wurde die Hydrolyse von N-(2-Cyanäthylen-)harnstoff (BA 1) unter noch relativ milden Bedingungen (pH 5,6 bis 9,0; T = 37°C und 22°C) nachgewiesen. Die Hydrolysegeschwindigkeit nimmt mit steigendem pH-Wert zu. Bei pH 5,6 erfolgt die Hydrolyse sehr langsam (Halbwertszeit etwa 6 Tage), wobei auch schon Kondensationsprodukte nachweisbar sind. Bei pH 9,0 ist bereits nach 2 Tagen BA 1 unter Ringspaltung weitgehend hydrolysiert, und eine Reihe Kondensationsprodukte sind entstanden. Im mittleren pH-Bereich von 7,3 bis 8,3 wurde das Auftreten von 2-Cyanaziridin, aber auch schon Ringspaltung und hydrolytische Folgeprodukte beobachtet. Die Halbwertszeit der BA 1-Hydrolyse konnte bei pH 7,3, 37°C für eine 0,144 molare Lösung in Phosphatpuffer zu 103 ± 1 h bestimmt werden.
    Additional Material: 6 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 319 (1977), S. 522-525 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polarographic Differentiation between 6-Azalumazines and 1,2,4-Triazines
    Additional Material: 1 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 320 (1978), S. 270-278 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polarographic Reduction of β-Aminovinylimines of the Indene SeriesThe mechanism of electrolytic reduction of aminovinylimine (AVI) is suggested, based on results of the identification of electrolysis products and on the dependence of polarographic curves. It is shown that this mechanism becomes complicated by the kinetics of hydrolysis of starting substances and intermediates. The determination of complex forming constants for AVI and bovine serum albumine is determined and compared by polarography and spectroscopy.
    Additional Material: 2 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 75 (1963), S. 868-870 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 75 (1963), S. 302-302 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 80 (1968), S. 565-566 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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