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  • Articles  (11)
  • Atomic, Molecular and Optical Physics  (11)
  • 1980-1984  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Active-site α-helix in papain and the stability of the ion pair RS- ··· ImH+. Ab initio molecular orbital study (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 17 (1980), S. 651-671 
    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 MO calculations, using both minimal (STO-3G) and extended (Roos-Siegbahn) basis sets are reported for the systems methanethiol-imidazole, methanethiol-imidazole-formaldehyde, and methanethiol-imidazole-formamide, which, together with a point-change representation of a long α-helix, form models for the active site of papain. It is shown that the large electric field exerted by the helix in the active-site region is responsible for the presence of the essential residues Cys 25 and His 159 in the form of an ion pair RS- ··· ImH+, which is crucial for a recently proposed mechanism for the catalytic action of the enzyme. Also, an explanation is given for the anomalies in measured pK values for these residues. Detailed studies on the (sub)systems show that minimal basis sets lack the flexibility necessary for describing the type of proton transfer involved. We conclude that α-helices are essential parts of enzymes and that they play a significant role in the catalytic process.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560170407
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic states near dislocations in transition metals: An application of quantum chemistry in technology (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 575-582 
    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: This paper outlines a model for calculating the localized states of a 〈 100 〈 edge dislocation in α-Fe. The model used for the calculations is based on the multiple-scattering model (SCF-X α-SW). The purpose of this research is twofold: (1) To determine changes in electronic structure of the lattice near the core region of defects in α-Fe. (2) The variations of hydrostatic pressure about an edge dislocation produce a rearrangement of the conduction electrons. The question is what electrical interaction might be expected between a dislocation and a charged solute atom. The calculations show that the electrons tend to flow away from the compression side toward the dilated regions. The electrical contribution to the binding energy of a solute atom and a dislocation in α-Fe is of the order of 0.01 Ry/electronic unit charge of the atom.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180229
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of periodic molecular systems with perturbed periodicity within the PCILO framework. I. Method (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 21 (1982), S. 711-716 
    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 method within the PCILO framework for the study of periodic molecular systems involving impurities is described regarding a one-dimensional chain. The calculation of the whole system is reduced to the calculation of subsystem pairs only. By use of the first-neighbor approximation only one or two subsystem pairs must be considered for subsystems with identical or differing surroundings, respectively. The procedure described yields the ground state energies and charge distributions of the subsystems.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560210405
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  • 4
    Electronic Resource
    Electronic Resource
    Hindered internal rotations in Van der Waals molecules and molecular crystals (1983)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 1091-1100 
    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: The quantum dynamical behavior of the Van der Waals molecule (N2)2 and that of the ordered α and γ phases of solid N2 have recently been calculated, starting from the same ab initio N2—N2 potential. By interpreting the results of these calculations we try to improve our understanding of the libration/internal rotation motions of the N2 monomers and the orientational order-disorder (α-β) phase transition. Some new results are presented and further (mean-field and libron-model) calculations are proposed which assess explicitly the intermolecular pair correlation effects caused by the anisotropic interaction potential.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560230333
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  • 5
    Electronic Resource
    Electronic Resource
    A modified PCILO framework using the CNDO/Boyd-Whitehead parametrization (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 1055-1060 
    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: The CNDO/BW modification of the CNDO/2 approximation was used within the PCILO framework. It was shown on some significant examples that all the good results of the original PCILO-CNDO/2 method can be reproduced by the modified version PCILO-CNDO/BW at least. Thus, preserving the quality of its results a computer-expense-reduced PCILO method is proposed for calculations on large molecular systems.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250610
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  • 6
    Electronic Resource
    Electronic Resource
    Calculation of periodic molecular systems with perturbed periodicity within the PCILO framework. II. Model systems (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 1061-1067 
    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: The energetic behavior of one-dimensional (HF)n and (H2O)n chains with added or inserted H2O or HF was studied by means of the PCILOPSI method presented in Part I. The results were compared with the ones by the original PCILO method. The stabilization energies are in good qualitative agreement; energy differences due to impurity effects even quantitatively agree. The results show that the PCILOPSI method is well suited for the study of perturbed periodic molecular systems.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250611
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  • 7
    Electronic Resource
    Electronic Resource
    Combination of pseudopotentials and density functionals (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 113-130 
    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: Semilocal pseudopotentials have been determined for first-row (Li to Ne), second row (Na to Ar), and third-row atoms (K, Ca). Core-valence correlation is included by adjusting the pseudopotentials to experimental energies of ions with a single valence electron. Correlation within the valence shell is taken into account by using the spin-density functional formalism. The approximations involved in this approach are tested for atomic ionization energies as well as binding energies of monohydrides and alkali diatomics, agreement with experiment is usually satisfactory, but in certain applications density functionals should be already included in the fitting of the local part of the pseudopotential. In addition, 3s/3p and 3s/2p basis sets (for first and second row, respectively), designed for use in connection with our pseudopotentials, are given; it is shown that they yield reasonable results for both SCF and correlation energies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190111
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  • 8
    Electronic Resource
    Electronic Resource
    Steady states and quasienergies of a system in an oscillating field within the perturbation configuration interaction method (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 163-170 
    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 perturbation configuration interaction method is formulated for a system in an external oscillating field (PCILOSC). It is closely connected with the static PCILO method and can be used for the conformational analysis of molecules and molecular crystals with localized bonds in external fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190114
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  • 9
    Electronic Resource
    Electronic Resource
    Semiempirical studies on 1,2- and 1,3-tetrathiofulvalenes (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 369-371 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200208
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  • 10
    Electronic Resource
    Electronic Resource
    Calculation of systems involving strong delocalized bonds within a modified PCILO framework. I. Valence-bond PCILO method (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 475-481 
    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: In describing mesomer structures by the original PCILO method several problems may occur because of the use of localized bonds. A so-called VB-PCILO including a superposition of several mesomer boundary structures in the CI perturbation treatment will be proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250303
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