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  • Cell & Developmental Biology  (29)
  • Photochemistry  (7)
  • Atomic, Molecular and Optical Physics  (6)
  • 1
    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 summary is given of our recently developed semiempirical pseudopotentials and their applications, and new results are presented on the K2 molecule.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 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
    Notes: Computational studies are reported of Stieltjes orbitals for Hilbert-space descriptions of discrete and continuum molecular electronic eigenstates. Particular attention is focused on the identification of N → V π(π → π*) and N → Vσ(σ → σ*) intravalence contributions to photoexcitation and ionization spectra in CO and H2CO molecules. Three-dimensional graphical representations of appropriate Stielties orbitals serve to identify the σ → σ* transitions of Mulliken as photoionization resonances above threshold in these compounds, whereas the corresponding π → π* contributions are spectrally localized as familiar discrete excited states. The development illustrates the nature and properties of Stieltjes orbitals, and demonstrates their utility in studies of both discrete and continuum excitation spectra on a common basis.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 2 (1968), S. 165-177 
    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
    Description / Table of Contents: Deux méthodes MO - la méthode Hückel généralisée et la méthode CNDO/2 - ont été employées pour estimer les réactivités électrophiles relatives des positions alpha et béta dans les composés suivants: pyrrole, indole, furan, et benzofuran. Ces résultats-ci ont été obtenus d'une comparaison des énergies totales des états de transition. On a prédit l'ordre des basicités de trois positions de l'indole et du pyrrole. On a calculé aussi des densités de charge et on les a correlées aux données sur le déplacement chimique en r.m.n.
    Abstract: Zwei MO-Methoden - die verallgemeinerte Hückelmethode und die Methode CNDO/2 - sind für die Abschätzung der relativen elektrophilen Reaktivitäten der Alpha- und Betalagen in den folgenden Verbindungen: Pyrrol, Indol, Furan, and Benzofuran angewendet worden. Diese Resultate wurden vom Vergleich der Gesamtenergien der Übergangszustände erhalten. Die Ordnung der Basizitäten von drei Lagen im Indol and Pyrrol wurden vorhergesagt. Ladungsdichten wurden auch berechnet, und mit der chemischen Verschiebungen in k.m.r. korreliert.
    Notes: Two molecular-orbital methods - extended Hückel theory and CNDO/2 - have been used to estimate the relative electrophilic reactivities of the alpha and beta positions in the nonalternant heterocyclic compounds pyrrole, indole, furan, and benzofuran by comparing total transition-state energies. The order of basicities of three positions of indole and pyrrole are predicted. Charge densities are also calculated and evaluated in the light of n.m.r. chemical shift data.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 125-141 
    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: As is known, the Schrödinger equation for a particle in the ring-shaped potential V(r,v) = ησ2(2a0/r-a02/r2 sin2v)ε0, defined in the whole space, has been solved exactly. Here the eigenfunctions are represented in a form which is advantageous for concrete evaluations. The spin-orbit interaction energy ELS in quasirelativistic approximation is determined analytically, for the first time with a nonspherically symmetric potential. The influence of spin-orbit interaction on the eigenvalues of the spin-free problem and on the selection rules for electrical dipole transitions are investigated as well as the dependence of ELS on the position and depth of the potential minimum. The model can be useful for investigations of axial symmetric subjects like the benzene molecule or related problems and may be easily extended to a many-electron theory.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 1491-1503 
    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 certain type of classical nonlinear field theory of chemical bonding has been proposed. The interaction between two neighboring atoms is assumed to be nonlinear. The coupled field equations are decoupled applying the methods of parametrization. The field energy associated with the coupled field has been determined perturbation theoretically. The chemical bonding energy equivalent to the change of field energy due to the coupling has been expressed in a closed form. The bonding energies of the molecules Li2, Na2, and K2 are evaluated.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 135-146 
    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: Methods are reported for construction of closed-form optical potentials that provide useful L2-basis-set approximations to the discrete and continuum Schrödinger states of self-adjoint Hamiltonian operators. The potentials are obtained employing information from a finite (Lanczos) reference space only, but nevertheless correspond to explicit summation over an infinite-dimensional remainder space. Connections are indicated between the Stieltjes-Tchebycheff orbital solutions of the resulting optical-potential Schrödinger problem and previously described corresponding moment-theory approximations to spectral densities and distributions. Use of a Lanczos basis insures that the orbital eigenvalues are generalized Gaussian or Radau quadrature points of the spectral density, and that their (reciprocal) norms provide the associated quadrature weights. Convergence of the orbitals in the limit of high order is obtained to Schrödinger eigenstates of finite norm in the discrete spectral region, and to scattering states of improper (infinite) norm in the essential portion of the spectrum. In finite orders the spatial characteristics of the Stieltjes-Tchebycheff orbitals correspond to spectral averages in the neighborhoods of the quadrature points over the correct Schrödinger states. Explicit closed-form expressions are obtained for the spectral content of individual orbitals in terms of orthogonal polynomials without reference to the correct Schrödinger states. A computational application to regular Coulomb l waves illustrates the nature and convergence of the development.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 889-892 
    ISSN: 0009-2940
    Keywords: Wittig reaction ; Siegrist reaction ; Azo compounds ; Photochemistry ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4,4′-Distyrylazobenzene as Chromophore4,4′-Distyrylazobenzenes are prepared from 4,4′-dimethylazobenzene. Whereas the Siegrist method furnishes stereoselectively the (E,E,E) configuration, a Wittig olefination leads to a mixture of (Z,E,Z), (Z,E,E) and (E,E,E) isomers which can be easily separated. Irradiation of the intense absorption at λ ≈ 400 nm causes a selective (E) → (Z) isomerization of the N = N bond of all three isomers. The reverse reaction takes part in the photochemical equilibration, moreover, it is a thermal process with a relatively low activation barrier.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The density of intramembranous protein particles was studied by freeze-fracture. Particle density on the fracture faces of the plasmalemma and the rough endoplasmic reticulum (RER), as well as the outer and inner membranes of the nucleus and the mitochondria in rat hepatocytes were quantified. Comparison among different age groups sampled days postcoitum (dpc), days postpartum (dpp), and months postpartum (mpp) shows age-related changes in particle density in each membrane system. With the exception of the RER, particle densities increased after the 16th dpc, reached a maximum at birth, and then decreased with increasing age. Simultaneously, the number nuclear pores shows a positive correlation with the particle density of the nuclear membranes. The particle density on the membranes of the RER shows a maximum on the 16th dpc, and on the 6th dpp. Thereafter, the density of the RER decreases slightly. In all membrane systems, the density of the particles on the external fracture faces is more variable than the density of the particles on the protoplasmic fracture faces.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1434-193X
    Keywords: Crystal engineering ; Diynes ; Photochemistry ; Solid-state chemistry ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diynes 4a-c were obtained from the corresponding 2,5-dimethoxybenzenes 1 by bromination followed by a copper-catalyzed Grignard reaction with 3-bromoprop-1-yne. Catalyzed coupling of the resulting 3-(2,5-dimethoxyphenyl)prop-1-ynes 3 under Hay conditions gave the hexa-2,4-diynes 4a-c in good yields. The molecular structures of the diynes 4a and 4b were determined by X-ray diffraction analysis. In each crystal structure, an unusual 1,6-synperiplanar conformation of the hexa-2,4-diyne unit is observed, with the 1,6-diphenyl substituents arranged in a coplanar orientation. According to the crystal structure data obtained, irradiation of diynes 4a and 4b afforded the deeply-colored, highly-ordered polymers 5a and 5b under topochemical control. Oxidation of 4a and 4b with cerium(IV) ammonium nitrate gave the corresponding 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diyne-1,6-diones 6a and 6b.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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