Library

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 [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 608-619 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The study of the qualitative and quantitative product distribution in a chemical reaction, in particular regioselectivity, is of fundamental importance. Recently, it has been shown that the regioselectivity of some Diels-Alder cycloadditions can be explained by analyzing the interrelations between electron density contours and molecular electrostatic potentials. This problem is related to a central topic of modern theoretical chemistry and biochemistry: the analysis of molecular shape. This work deals with a rigorous, algebraic method to analyze these surfaces. The procedure is based on the computation of the shape groups (symmetry-independent homology groups of algebraic topology) of the molecular surface, using either a fully analytical algorithm requiring no visual inspection, or a precise method for processing pictorial information if the latter is available. The method provides a concise description of the molecular contour surface, that can replace the usually intuitive, and somewhat subjective, visual characterization of density and electrostatic potential contours. The method is illustrated for the case of Diels-Alder reactions by considering a number of monosubstituted dienes. Extensions of the analysis to dienophiles, as well as other types of reactions are also discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 185-196 
    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: Local coordinate systems are introduced into open sets of topological spaces, defined for the nuclear configuration space R of polyatomic nuclear systems. The open sets are directly related to common chemical concepts, such as chemical structure, reaction mechanism, and stability of reaction paths. A topological model of molecules and chemical reactions is a generalization of the geometrical model, and is particularly suitable to account for the nonrigid nature of chemical structures. The coordinate neighborhoods defined on R and on its submanifolds represent the extent and natural limits for partial analyses of multidimensional potential surfaces.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 24 (1983), S. 523-526 
    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: Boundaries of electronic energy level sets in the nuclear charge space wZ can be parametrized as single valued functionals for any nuclear geometry of molecules, which property, combined with the general convexity of such level sets, leads to various electronic energy inequalities.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 267-272 
    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 a previous study an energy criterion has been applied for the simplification of the enumeration problem of various conformers of biomolecules. In the present note, the above energy criterion is combined with a spatial criterion that in general leads to a reduction in the size of those domains of biomolecule potential surfaces within which the search for chemically important conformers is warranted. The above model and the conformational domains of primary interest can be formulated in a hyperspherical representation. Advantages and disadvantages of representing biomolecule potential surfaces in terms of hyperspherical coordinates are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 675-681 
    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: Current computer hardware developments, in particular, vector processing and parallel processing, are likely to open the door for new applications in quantum chemistry. One applied field that is expected to evolve is a computer-based approach to quantum-chemical synthesis design. Whereas some of the computational difficulties still appear formidable, there are reasons to be optimistic: besides the direct impact of computer hardware developments on existing methods, new theoretical approaches such as density functional theory and numerical molecular wave functions may also become feasible. The topological model of energy hypersurfaces, reaction topology, and quantumchemical manifold theory of reacting systems form a possible framework for a global analysis of a set of all reactions involving a fixed set of nuclei and a fixed number of electrons. The apparent bottleneck for the application of the topological method is the actual computation of the catchment regions (open sets) of reaction topology Tc. In this study some properties of catchment region boundaries are described which lead to computational simplifications. Whereas the ultimate goal of the proposed analysis is to serve as an aid in future quantum-chemical synthesis planning, nonetheless, the boundary networks and sum rules developed in this study may also be of some immediate interest in local surface analysis.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 191-198 
    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: Chemical reactions and conformational changes of N-atom systems can be described as displacements in a (3N-6)-dimensional metric configuration space M provided with a global metric. Although space M has a metric, it is not in general a vector space; it is a topological space. In contrast to the commonly used internal configuration spaces based on bond length/bond angle internal coordinates, and having no global metrics, within space M each internal configuration of the nuclei of the molecule corresponds to one and only one point of the space. This property of M is advantageous when analyzing chemical reactions. The global metric of M ensures that differences between any two internal configurations can be interpreted as a distance in this space that allows one to provide M with coordinate systems by turning M into a manifold with boundary. Certain formal reaction paths show some counterintuitive behavior within this space: they may undergo a formal reflection at some points of M. A condition, the tangent criterion, is used for the diagnosis of such reaction paths and for the determination of special nuclear configurations where such reflections occur.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 847-853 
    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: Methyl substitutents located peri to bay-region benzo rings of polycyclic aromatic hydrocarbons generally reduce or eliminate carcinogenic activity, most likely because such substituents force the hydroxyl groups of dihydrodiol intermediates to adopt preferentially pseudodiaxial, rather than pseudodiequatorial, conformations. Empirical force field calculations have been employed to examine the influences of peri and other positional substituents on hydroxyl conformation, taking naphthalene, anthracene, and phenanthrene as model compounds. For the unsubstituted naphthalene and anthracene dihydrodiols, the pseudodiequatorial conformation is preferred. This preference is reduced by adjacent methyl substitution and reversed by peri methyl substitution. Because of steric crowding the phenanthrene bay-region dihydrodiol preferentially adopts a pseudodiaxial conformation. The results are discussed in relation to recent experimental evidence.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year 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. 127-132 
    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: Most of the important conformations of biomolecules possess only trivial symmetry. Consequently, symmetry groups have no roles in the characterization of the shapes of such conformations. However, an alternative group theoretical model, based on homology groups of algebraic topology, provides a detailed description of shapes for all conformations. These shape groups are useful for precise comparison of molecular shapes and are proposed as a computational tool for QSAR. A new computational method for the determination of various shape groups is described which is suitable for the simultaneous analysis of a pair or a family of molecular properties. In this note a general method is described and applied to the shape of electronic charge distribution along van der Waals surfaces.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...