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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of medicinal chemistry 29 (1986), S. 1418-1423 
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 917-926 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Kinetic isotope effects (KIEs) for the thermal decomposition of N2O catalyzed by chlorine were experimentally determined in the temperature range 773–923 K, and may be expressed as follows: KIEt(15N)=(4100/T−1.90)±0.15, KIEp(15N)=(3940/T−2.35)±0.10 and KIE(18O)=(6990/T−3.60)±0.25. An Arrhenius fit to the measured rate constants resulted in an activation energy of 136±8 kJ mol−1 and a preexponential factor of 7.7×107±0.1 m3 mol−1 s−1. The KIEs were interpreted according to the Bigeleisen formalism. Furthermore, we calculated the activation energy following the Sanderson bond-energy–bond-order relationship, and the preexponential factor from transition state theory and compared them to experimental values. Additionally, ab initio molecular theory was employed to study parts of the potential energy surface of the elementary bimolecular reaction between a N2O molecule with a Cl atom. Equilibrium geometries, energies and harmonic vibrational frequencies were calculated at the HF/6-31G* and MP2/6-31G* level for some distinct stationary points on the potential energy surface, with energy refinements at the MP2/6-311G* level. In our study the transition state was located by the eigenvalue-following method. The ab initio properties of the transition state and reactants were also used for an evaluation of the kinetic isotope effects. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9410-9416 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The lowest doublet (2A′) potential energy surface for the reaction N2O+Br→N2+OBr was investigated using ab initio and nonlocal density functional theory calculations. Geometries, energies and vibrational frequencies for stationary points were evaluated at HF/6-31G(d), MP2/6-31G(d) and B3LYP/6-31G(d) levels of theory. All levels of calculation give a similar geometry for the transition state, but the MP2 barrier is narrower. Intrinsic reaction coordinate (IRC) calculations starting from the transition state and proceeding toward the two local minima confirmed that IRC trajectories reached the reactant and product regions, respectively. Calculations of kinetic isotope effects were also performed. They are influenced by the theoretical level and the B3LYP method gives results in best agreement with experimental data. The HF method predicts the relative values of both the primary and secondary nitrogen kinetic isotope effects less accurately. At the MP2 level of calculations only the oxygen kinetic isotope effect is reproduced satisfactorily. Finally, the best value for the activation energy is again provided by the B3LYP method. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1189-1200 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of hybrid quantum mechanical and molecular mechanical (QM/MM) potentials to the study of chemical reactions in enzymes is outlined. The discussion is general and addresses the difficulties encountered in an enzyme QM/MM study. First, general criteria for determining whether a particular enzyme is an appropriate candidate for a QM/MM approach are outlined. Methods for obtaining starting structures are detailed. The importance of choosing appropriate levels of ab initio or semiempirical theory is emphasized. Approaches for interfacing the QM and MM regions are briefly discussed, with greater detail given to describing our CHARMM-GAMESS interface. Techniques for partitioning the system into QM and MM regions are explored. Link atom placement, as distant from reacting atoms as possible within the confines of computational efficiency, is examined in some detail. Methods for determining reaction paths are also discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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