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  • Atomic, Molecular and Optical Physics  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Normal-mode vibrational frequencies and thermodynamic properties of uracil and 4-hydroxyuracil (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 323-329 
    Details
    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: Normal-mode vibrational frequencies were obtained for uracil and 4-hydroxyuracil with the MINDO/3 SCF method. MINDO/3 vibrational frequencies and the moments of inertia for STO-3G optimized geometries yielded a ΔST0 for U ⇄ U* of 1.06 e.u./mol by standard statistical thermodynamic equations. ΔGT0 is then 6.29 kcal/mol in the gas phase for U ⇄ U*. The reaction field continuum model of solvent effect lowers ΔGT0 to 5.3 kcal/mol in aqueous solution. The tautomeric equilibrium constant in solution is then 1.3 × 10-4, in good agreement with experimental values.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180146
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  • 2
    Electronic Resource
    Electronic Resource
    STO-3G study of uracil, thymine, 5-fluorouracil, 5-methoxyuracil, and their 4-hydroxytautomeric forms (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 22 (1982), S. 639-647 
    Details
    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: Ab initio molecular orbital calculations with an STO-3G basis have been performed to investigate the energetics and electronic properties of some 5-substituted uracils and their 4-OH tautomer forms with R including F, CH3, and OMe. In all cases, the diketo form is more stable. An excellent linear correlation between the calculated and experimental ionization potentials was found.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560220313
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Uracil and the tautomer 4-hydroxyuracil: An ab initio study with geometry optimization (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 171-177 
    Details
    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: Ab initio STO-3G geometries and relative energies for uracil (U) and the tautomer 4-hydroxyuracil (U*) were obtained with the HONDO program utilizing the rapidly convergent method of Murtaugh and Sargent for geometry optimization. ΔE for U⇄U* is 6.61 kcal/mole. The reaction field continuum model for solvent effect indicates a preferential stabilization of U* by 1.0 kcal/mole. The calculated gas phase Kt and solution Kt for U⇄U* are 1.44×10-5 and 1.3×10-4, respectively.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190115
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Optimum geometries and relative energies for cytosine, thymine, uracil, the imino tautomer of cytosine, the enol tautomer of thymine, and the enol tautomer of uracil by the MINDO/2 SCF MO method (1978)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 14 (1978), S. 851-860 
    Details
    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: A MINDO/2 SCF MO geometry optimization of cytosine (C), thymine (T), uracil (U), the imino tautomer of cytosine (C*), the enol tautomer of thymine (T*), and the enol tautomer of uracil (U*)was made. The optimized geometries for cytosine, thymine, and uracil agree well with crystallographic data. The optimized geometries for the tautomers show the correct trends in bond lengthening and bond angle except for the C4 - O4 length and C4 - O4 - H angle of T* and U*. The energies of tautomerization were found to be 10.3, -9.0, and -14.2 kcal/mol for C⇌C*, T⇌T*, and U⇌U*, respectively, when optimized geometries are used. The overestimation of the C4 - O4 - H angle is speculated to arise because of an inadequacy in the parametrization of the one-center integrals in MINDO/2.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560140615
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    Paper (German National Licenses)
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