ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 133-147 
    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 the course of conformational motions of molecules the changes in shapes of electronic charge distributions follow that of the nuclear framework. However, this coupling between the changes in the nuclear geometry and electron density may depend on the actual nuclear displacement; the coupling may be weak or strong for a given conformational motion. It is of some interest to analyze how faithfully the charge density variations follow the nuclear displacements in a family of conformational rearrangements. In certain cases small conformational changes may induce large changes in the shape of charge density distributions, while in other cases large and qualitatively important conformational changes may involve qualitatively inessential distortions in the shape of electron distributions. In this article we describe a new classification of conformations based on those domains of nuclear configuration space within which the „shape groups“ (symmetry independent homology groups) of the electric charge density remain invariant. Such an analysis might be valuable when seeking correlations between molecular structure and certain biological or biochemical activities.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 269-288 
    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 assessment of molecular similarity between molecules is a fundamental task in computer-aided drug design. In this work, we have applied a combined analysis of steric and electrostatic properties of a series of inhibitors of liver alcohol dehydrogenase (LADH) to rationalize their action. The methodology is based on a topological characterization of the distribution of molecular electrostatic potential (MEP) on the fused-sphere van der Waals surface of a molecule. The topological description can be rendered in the form of two-dimensional diagrams that allow a quick visual or algorithmic analysis of the most relevant shape features of a molecule. By using the representations mentioned above (topological information as a function of the MEP), one can correlate this “structural” information with the values of inhibition constants KI for compounds with different levels of inhibitory activity. This approach allows one to have quantitative measures of similarity for related molecules and to eventually propose compounds that may exhibit a desired activity. The compounds analyzed in this work are a series of substituted derivatives of pyrazole, which span a relatively wide range of inhibitory powers. We have studied the role of the nature of the substituent, as well as its substitutional position, on the molecular shape and correlated these findings with the activity of each compound. Some consequences on the mechanism of inhibition of LADH are also discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 335-345 
    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 this work we analyze the interrelations between potential energy changes and molecular shape changes along the reaction paths for a series of ring-opening reactions. The processes studied correspond to the opening of the four-member rings of 1,2-dioxete, 2H-oxete, 2H-thiete, and 1,2-dithiete, which recently have been given considerable attention in the literature. We describe the molecular shape in terms of a continuum of fused-sphere surfaces, which are characterized by using molecular topological methods. The four processes cover a range of reaction enthalpies from largely exothermic to almost thermoneutral. The similarity between the configurations found along the reaction path is assessed quantitatively in terms of parameters associated with the molecular shape and the path itself. We find a correlation between the value of the energy barriers (and reaction enthalpies) and the similarity parameters. The correlation is comparable to that found in the case of various other processes, such as torsional changes, collisions, and intramolecular atom displacements or shifts. The results are in line with the intuitive correlations expected from the Hammond postulate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 459-474 
    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: An analysis of molecular shape has been performed along an ab initio reaction path of the PPO → OPP isomerization. In a first approximation, we have used the fused-sphere (van der Waals) model to represent shape. The results show that there is no one-to-one correspondence between the species defined in terms of shape and those based on an energy criterion. In contrast to the cases of most other isomerizations in triatomic molecules (e.g., the HCN isomerization), for the PPO isomerization there exists a stable intermediate. For the elementary reaction from the linear PPO (C∞v, reactant) to the cyclic P2O (C2v, intermediate), we found no distinct molecular shape type for the transition structure (between the reactant and the intermediate). In terms of shape, the nuclear configuration of the transition structure is more similar to that of the intermediate than that of the reactant. Using the PPO → OPP reaction as an example, in this work we discuss the implications of this result regarding possible measures of shape similarity and shape stability along reaction paths. We have performed a molecular-shape analysis of the electron density contour surfaces to test the reliability of the fused-sphere approximation. A comparison between the van der Waals and electron isodensity surface models at critical points shows that the former model can be qualitatively correct for molecular-shape descriptions along some reaction paths.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 713-726 
    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 this work, a detailed discussion and illustrative example are given for a new conceptual approach to the notion of similarity between nuclear configurations. We analyze the changes in molecular shape, as described by a topological characterization of molecular envelope surfaces, along reaction paths. This approach provides an independent definition of formal species along the path, defined in terms of molecular shape, rather than based on the curvature properties of the potential energy function. The two approaches are compared in this work, using the [1,3] hydrogen-shift in formic acid as an illustrative example. The reaction is studied at SCF and MP2 ab initio levels. Although the actual reaction paths are different, the molecular shape changes encountered along them are similar, indicating that the essential shape changes provide chemical information on a more fundamental level than do detailed reaction paths.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 405-423 
    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 numerical method is developed to obtain sequences of functions converging to the eigenfunctions of a Schrödinger operator in the Hilbert space L2(-∞, ∞), whose norm is used to introduce the criterion of convergence in the norm and we show that it guarantees the accurate computation of expected values of a symmetric operator. The method consists in solving the Dirichlet problem associated to the eigenvalue problem in the interval [-n, n] by the Ritz method, whose convergence to both eigenvalues and eigenfunctions is guaranteed by the compactness criterion. Using the asymptotic perturbation theory in L2(-∞, ∞), we prove the convergence of both eigenvalues and eigenfunctions of the Dirichlet problem to those of the unbounded system when the interval [-n, n] is expanded. The method is applied to the harmonic oscillator, the Mitra potential, as well as to the potential V(r) = r and the Coulomb and Yukawa potentials; in each case, the convergence of eigenvalues and eigenfunctions is shown. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 433-450 
    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 methodology to characterize large-scale shape of macromolecular conformations is generalized and applied to a simple model of branched polymers. The standard global analysis of polymer configurations uses geometric shape descriptors, such as the mean radius of gyration. However, geometric descriptors alone do not depict well the intrincate folding features found in many macromolecules. For a more complete characterization, we employ here a new class of shape descriptors which convey the degree and complexity of the “entanglements” in a branched chain. Recently, the methodology has been applied to study statistical properties of linear polymer chains. In the present work, we extend the technique to branched polymers and analyze the configurational and long-chain behavior of their entanglement descriptors. A family of “stars” (polymers with a single branchpoint) with excluded volume interaction is studied, and the results are contrasted with those for linear chains. The relation between changes in geometric and shape descriptors within the polymer conformational space is presented. The complexity of entanglements for large chains and large stars are compared. The results suggest a similar scaling behavior of the entanglement descriptors for the two polymer architectures. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    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: Several approximate analytical formulas for the multidimensional isotropic bounded oscillators and the bounded hydrogen atom are compared. Numerical results show that the coth z method is in both cases better than the Padé approximants method. Perturbational polynomials, necessary in order to build the approximate eigenvalues, are obtained through the hypervirial perturbative method.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 1039-1049 
    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: Hartree-Fock equations are viewed as nonlinear algebraic equations that can be solved iteratively. Provided we assume the existence of a solution, valuable properties of convergence may be assessed. The close connection between convergence of the SCF procedure and stability properties of the solution is shown from a nonapproximate standpoint. The convergence features of level-shifting convergence-forcing techniques are analyzed. The connection between this nonlinear algebraic approach and the related gap equation is displayed and the example of the restricted Hartree-Fock hydrogen molecule is discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 475-485 
    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: We present a coupled-cluster polarization propagator method based on a coupled cluster singles and doubles reference state. Applications to the Be atom show that we may calculate electronic excitation energies with an average absolute error of about 0.08 eV using this method. We have also calculated the nuclear spin-spin coupling constant of 1H19F to be 524.4 cps, in good agreement with experiment. For Be there is a large effect of using coupled-cluster rather than a low-order Rayleigh-Schrödinger expansion, whereas the coupling constant of HF is less sensitive to this improvement in the reference state.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...