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  • Wiley-Blackwell  (4)
  • American Geophysical Union (AGU)
  • American Association of Petroleum Geologists (AAPG)
  • 1975-1979  (4)
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu2+ ions with native DNA at low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation at low relative ligand concentrations and at low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu2+ ions with atoms N(7) of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N(7) and O of C(6) of the guanine bases, as well as the formation of specific intestrand crosslink complexes at adjacent G°C pairs of the sequence dGpC. CD spectra of the resulting nondenatured complex (DNA-Cu2+)nat may be interpreted in terms of a conformational change of DNA from the B-form to a C-like form on ligand binding. A slow cooperative denaturing complex formation occurs at increased copper concentrations and/or at increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA-Cu2+)denat, indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA.From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu2+ ions to atoms N(3) of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G·C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu2+ ions between atoms N(7) and O of C(6) of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G·C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence-specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu2+, Cd2+, and Zn2+ ions with DNA.In temperature-jump experiments with the nondenatured complex (DNA-Cu2+)nat, a specific kinetic effect is observed, namely, the appearance of a lag in the response to the perturbation. The resulting sigmoidal shape of the kinetic curves is considered to be a consequence of the necessity of disrupting a certain number of the crosslinks existing in the nondenatured complex before the local unwinding of the binding regions (a main step of denaturing complex formation) may proceed.
    Additional Material: 19 Ill.
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