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  • 1990-1994
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  • Chemistry  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 9 (1970), S. 445-457 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The change in apparent molal volume φ of DNA on thermal denaturation in carbonate buffer at pH 11.0 has been determined by the dilatometric method. It was found that φ increases sigmoidally during the helix-coil transition. Several methods, including a colorimetric technique that closely simulates the conditions used in the dilatometric experiments, were employed to estimate the protons lost by the DNA during the transition. These measurements indicated that the extent of the proton loss depends on the counterion present, increasing in the order Li+ 〈 Na+ 〈 K+ 〈 Cs+. The major part of the volume changes observed during the denaturation is due to the volume changes expected to accompany the transfer of protons from the bases guanine and thym ne to carbonate ions. As has been previously reported for the denaturation of DNA at neutral pH, the volume change directly due to the change in shape of the polymer molecules is so small as to be experimentally undetectable.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 0721-3115
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The appearance of a significant deuterium isotope effect during the combustion of the solid HMX compound verifies that the chemical reaction kinetics is a major contributor in determining the experimentally observed or global burn rate. Burn rate comparison of HMX and its deuterium labeled HMX-d8 analogue reveals a primary kinetic deuterium isotope effect (1° KDIE) at 500 psig (3.55 MPa) and l000 psig (6.99 MPa) pressures and selectively identifies covalent carbon-hydrogen bond rupture as the mechanistic step which ultimately controls the HMX bum rate under the static combustion conditions of this experiment. The 1° KDIE value further suggests the rate-limiting C—H bond rupture occurs during the solid state HMX decomposition/deflagration portion of the overall combustion event and is supported by other independently published studies. A possible anomalous KDIE result at 1500 psig (10.4 MPa) is addressed. This condensed phase KDIE approach illustrates a direct link between lower temperature/pressure thermal decomposition and deflagration processes and their potential applicability to the combustion regime. Most importantly, a new general method is demonstrated for mechanistic combustion investigations which selectively permits an in-situ identification of the compound's burn rate-controlling step.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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