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  • 1
    ISSN: 1432-2234
    Keywords: Protonated cytosine ; Protonated thymine ; Tautomeric forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Proton affinities of several of the tautomeric forms of cytosine and thymine have been calculated using theab initio Hartree-Fock-Roothaan SCF method. Several of the most stable protonated forms may be obtained by direct protonation from one of the two most stable neutral forms. The calculated total energies do not exclude the possibility of the coexistence of several protonated forms in acidic solutions.
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  • 2
    ISSN: 1432-2234
    Keywords: Mutually consistent field calculations ; solvation energies ; glycine-water-system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have performed calculations of the glycine zwitterion surrounded by water molecules with the help of the mutually consistent field (MCF) method and perturbation theoretical expressions. Two different models for the hydration shell have been chosen, the glycine·6H2O and glycine·12H2O complexes, representing the most probable first and second solvation shell, respectively. To calculate the exchange and charge transfer energy contributions we have applied approximative expressions derived from perturbation theory for weakly overlapping subunits. For the sake of comparison we also calculated the interaction energy in the supermolecule approach for the smaller of the two solvation complexes. Furthermore, we have investigated the part of the potential energy surface which is determined by varying the lengths of the hydrogen bonds between glycine and water in the complex glycine·12H2O using the electrostatic approach. The exchange energy contribution to the interaction energy for different points on the surface was approximated with the help of an analytical expression fitted to three directly calculated points. For the charge transfer energy a polynomial expansion of second order was established on the basis of five values, computed with the aid of the perturbation theoretical expression. To get a more detailed insight in the relatively strong hydrogen bonds between the water molecules and the ionic hydrophilic parts of glycineab initio model studies on NH 4 + ·3H2O and HCOO−·3H2O systems are reported.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2234
    Keywords: Protonated cytosine ; Protonated thymine ; Tautomeric forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Proton affinities of several of the tautomeric forms of cytosine and thymine have been calculated using theab initio Hartree-Fock-Roothaan SCF method. Several of the most stable protonated forms may be obtained by direct protonation from one of the two most stable neutral forms. The calculated total energies do not exclude the possibility of the coexistence of several protonated forms in acidic solutions.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2234
    Keywords: Mutually consistent field calculations ; solvation energies ; glycine-water-system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have performed calculations of the glycine zwitterion surrounded by water molecules with the help of the mutually consistent field (MCF) method and perturbation theoretical expressions. Two different models for the hydration shell have been chosen, the glycine·6H2O and glycine·12H2O complexes, representing the most probable first and second solvation shell, respectively. To calculate the exchange and charge transfer energy contributions we have applied approximative expressions derived from perturbation theory for weakly overlapping subunits. For the sake of comparison we also calculated the interaction energy in the supermolecule approach for the smaller of the two solvation complexes. Furthermore, we have investigated the part of the potential energy surface which is determined by varying the lengths of the hydrogen bonds between glycine and water in the complex glycine·12H2O using the electrostatic approach. The exchange energy contribution to the interaction energy for different points on the surface was approximated with the help of an analytical expression fitted to three directly calculated points. For the charge transfer energy a polynomial expansion of second order was established on the basis of five values, computed with the aid of the perturbation theoretical expression. To get a more detailed insight in the relatively strong hydrogen bonds between the water molecules and the ionic hydrophilic parts of glycineab initio model studies on NH 4 + ·3H2O and HCOO−·3H2O systems are reported.
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  • 5
    ISSN: 1432-2234
    Keywords: Adenine tautomers, relative stabilities of ∼ ; Guanine tautomers, relative stabilities of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relative stabilities of a series of adenine and guanine tautomers have been calculated using anab initio Hartree-Fock-Roothaan SCF MO method. The calculated relative stabilities agree in general with the results of earlier semiempirical studies. According to the present study, tautomeric forms with regular Kekulé structure for the six-membered purine ring are the most stable. The amine-imine tautomerization of purine bases is not likely to be responsible for spontaneous mutations in DNA.
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  • 6
    ISSN: 1432-2234
    Keywords: Biopolymer constituents, protonation of ∼ ; Purine bases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Proton affinities of a large number of tautomeric adenine and guanine structures have been calculated using theab initio Hartree-Fock-Roothaan SCF method. For guanine, and to a lesser extent for adenine, it is likely that several protonated forms may co-exist in acidic solutions. Protonation at the “free” adenine and guanine positions in DNA may introduce effective acceptor levels between the energy bands of the polymer that may cause fundamental changes in the conduction properties of DNA.
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  • 7
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: First, several reminiscences are recalled about the author's encounters with such a beautiful person as Professor Jean-Louis Calais. Since Jean-Louis was very much interested - among other things - in the correlation problem of solids, different methods are reviewed for the correlation correction of the energy bands of 1D and 2D periodic systems as well for the levels of 1D nonperiodic chains. The results obtained show a very good agreement with experiment for the fundamental gap and exciton spectra of different polymers, for the mechanical properties of polyethylene, as well for other not-here-described physical properties of different polymeric systems. The coding of these methods for the relativistic case is in progress. © 1997 John Wiley & Sons, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 1073-1081 
    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 negative factor counting method (in its simple and matrix block form) for the determination of the density of states of disordered polymer chains and its applications to different aperiodic organic polymers are reviewed. The problems of the calculation of the correlation energy in large systems like polymers will be discussed. Different ways for the partitioning of an energy band into regions make it possible to perform Møller-Plesset perturbation theoretical calculations on polymers. Applications to hydrogen chains are presented. Finally, possible applications to disordered polymers are also discussed.
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  • 9
    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 new boundary treatment, a Hartree-Fock (HF) surface potential model, is proposed to deal with the surface effect in the solid-state cluster calculations using the LCAO-MO-SCF ab initio method. The surface potential arises from one or more atoms, which have no basis function and are added to the calculated cluster system. These atoms are placed in such sites so that the HF potential field of the calculated system should possess a point-group symmetry. The surface potential could be found by the corresponding HF potential using a symmetry operator. The fact that a rather symmetric electronic structure of the asymmetric cluster YBa2CuZn2O7 is obtained using the HF surface potential shows that the surface effect in the cluster calculations could be neutralized to a great extent. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 10
    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
    Type of Medium: Electronic Resource
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