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    Wyświetlanie 1-5 z 5
    Tytuł:
    Role of Thermochemical Decomposition in Energetic Material Initiation Sensitivity and Explosive Performance
    Autorzy:
    Shackelford, S. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/358845.pdf
    Data publikacji:
    2008
    Wydawca:
    Sieć Badawcza Łukasiewicz - Instytut Przemysłu Organicznego
    Tematy:
    energetic material
    thermochemical decomposition
    kinetic deuterium isotope effect
    KDIE
    initiation sensitivity
    performance
    Opis:
    Catastrophic initiation of an energetic material consists of a complex, interactive, sequential train of mechanistic mechanical, physical, and chemical processes which occur over a finite time period and proceed from macroscopic into sub-microscopic composition levels (bulk > crystalline > molecular > atomic). Initiation results when these processes proceed at a rate which generates sufficient energy (heat) to reach a threshold stage within this finite time period. Thus, the rate at which these mechanistic processes occur defines initiation sensitivity and affects performance. Thermochemical decomposition processes regulate the rate at which heat energy is released at the molecular level, and therefore to some extent, control energetic material initiation sensitivity and performance characteristics. Kinetic deuterium isotope effect (KDIE) data, obtained during the ambient pressure thermochemical decomposition process, identifies the mechanistic rate-controlling bond rupture which ultimately regulates the energy release rate of a given energetic material. This same rate-controlling bond rupture also appears as a significant rate-limiting feature in higher order deflagration, combustion, and explosion phenomena. The effect the KDIE-determined rate-controlling bond rupture exerts on initiation sensitivity, and its potential influence in combustion and explosion performance is delineated.
    Źródło:
    Central European Journal of Energetic Materials; 2008, 5, 1; 75-101
    1733-7178
    Pojawia się w:
    Central European Journal of Energetic Materials
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    DFT/PM3 study of the enoyl-CoA hydratase catalyzed reaction
    Autorzy:
    Pawlak, J.
    Bahnson, B.
    Anderson, V.
    Powiązania:
    https://bibliotekanauki.pl/articles/146962.pdf
    Data publikacji:
    2002
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    coenzyme-A
    density functional theory
    enoyl-CoA hydratase
    kinetic isotope effect
    ONIOM model
    stepwise mechanism
    thiolester enolate
    Opis:
    The enoyl-CoA hydratase catalyzed hydration of alfa,beta-unsaturated thiolesters has been modeled by using the crystal structure of 4-(N,N-dimethylamino)cinnamoyl-CoA bound at the active site. The quantum chemical calculation used the ONIOM mixed level procedure to permit the substrate thiolester and water molecule to be modeled using B3LYP/6-31G(d) level of theory and the active site residues modeled at a semiempirical level using the PM3 Hamiltonian. The results permitted the identification of a stable thiolester enolate intermediate, supporting a stepwise reaction mechanism. The calculation also suggests that the same proton removed from the nucleophilic water molecule is transferred to C alfa in the subsequent protonation of the enolate intermediate. This observation reconciles the stepwise mechanism with the previously reported double isotope effect study [3].
    Źródło:
    Nukleonika; 2002, 47,suppl.1; 33-36
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Elucidation of reaction mechanisms using kinetic isotope effects of short-lived radionuclides
    Autorzy:
    Matsson, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/146955.pdf
    Data publikacji:
    2002
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    carbon-11
    fluorine-18
    kinetic isotope effect
    reaction mechanism
    short-lived radionuclide
    Opis:
    The use of the short-lived radionuclides 11C and 18F for the elucidation of organic reaction mechanisms is described. Examples of the different mechanistic problems that are discussed include concerted vs. stepwise base catalysed elimination (E2 or E1cB) and finding the rate limiting step for nucleophilic aromatic substitution (SNAr). The use of radionuclides to learn details about transition state structure for concerted nucleophilic aliphatic substitution (SN2) is also described.
    Źródło:
    Nukleonika; 2002, 47,suppl.1; 43-45
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Carbon-14 kinetic isotope effects in the debromination of p-nitrodibromocinnamic acid
    Autorzy:
    Bukowski, J.
    Kanski, R.
    Kanska, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/147051.pdf
    Data publikacji:
    2002
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    bromine
    carbon-14
    elimination
    kinetic isotope effect
    mechanism
    p-nitrodibromocinnamic acid
    Opis:
    The kinetic isotope effect (KIE) method was applied to study the mechanism of elimination of bromine from p-nitro-erythro-alfa,beta-dibromocinnamic acid labeled at the alfa-carbon. This compound was obtained starting from [2-14C]malonic acid via [2-14C]cinnamic acid and subsequent addition of bromide. The value of 14C KIE determined for alfa-position of side chain of p-nitro-erythro-alfa,beta-dibromocinamic acid proves that elimination of bromine leading to formation of (E)-p-nitrocinnamic acid proceeds via E2 mechanism.
    Źródło:
    Nukleonika; 2002, 47, 4; 133-136
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Carbon isotope distribution along pine needles [Pinus nigra Arnold]
    Autorzy:
    Barszczowska, L
    Jedrysek, M.O.
    Powiązania:
    https://bibliotekanauki.pl/articles/57836.pdf
    Data publikacji:
    2005
    Wydawca:
    Polskie Towarzystwo Botaniczne
    Tematy:
    Croatia
    pine
    inhomogeneity
    needle
    growth
    distribution
    kinetic isotope effect
    black pine
    Spain
    Pinus nigra
    carbon isotope
    Opis:
    In this paper we show spatial carbon isotope variations in black pine (Pinus nigra Arnold) needles, collected in spring 2001 and autumn 2003, from trees at the coast of south-western Croatia island (Žirje) and southern Spain (Benalmadena near Malaga), respectively. Needles were segmented perpendicularly to the longer axis (base, middle and top) and each segment was analysed separately. d13C values in needles from Croatia varied between -26.65‰ to -24.43‰ (2 months old needles) and from -28.25‰ to -25.21‰ (1 year old needles), while d13C values in needles from Spain varied from -27.58‰ to -25.27‰. The difference between d13Cb (base) and d13Ct (top) in the same needle (D13Cb-t) varied from 1.85 to 2.05‰ (in young needles from Croatia), from 0,02 to 1,80‰ (young needles from Spain), and 1.16 to 2.32‰, (in old needles from Croatia). The average D13Cb-t values were 0.78‰ and 1.73‰ in Spain and Croatia, respectively. In each needle the base of the needle was always 13C-enriched as compared to the top of the same needle. This evidences that carbon isotopes are not retranslocated after its fixation into the leaf structure (after the growth process is over). Temperature variation was most probably negligible for the discovered intraneedle carbon isotope distribution. Although, the intraneedle carbon isotope inhomogeneity can be partly the result of seasonal variation in d13C of atmospheric CO2, most probably the remarkably high D13Cb-t values, and regular pattern, are predominantly resulting from isotopic and chemical composition of primary and secondary products contained in the growin part of needle and kinetic isotope fractionation during decomposition of storage materials at the base.
    Źródło:
    Acta Societatis Botanicorum Poloniae; 2005, 74, 2
    0001-6977
    2083-9480
    Pojawia się w:
    Acta Societatis Botanicorum Poloniae
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-5 z 5

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