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  • 101
    Electronic Resource
    Electronic Resource
    Modified MINDO/3 13C chemical shift calculations for simple hydrocarbons (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 416-423 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Calculations of 13C chemical shifts in some simple hydrocarbons have been carried out using the GIAO approach in the MINDO/3 semiempirical formalism. In order to achieve reasonable agreement with experiment it is necessary to modify (increase) the vacant orbital energies in the MINDO/3 calculation in order to reduce the magnitude of the paramagnetic contribution, and to also modify this dominant term by generally reducing it as a function of the number of hydrogen and carbon atoms bonded to the resonant nucleus in question. For a set of 34 resonant nuclei of the simpler hydrocarbons, agreement with experiment of the order of 7.8 ppm is attained; however, pathological cases such as cyclopropane and some simple allenes continue to cause problems, increasing the standard deviation of the full set to 12.5 ppm. Our results indicate that the MINDO/3 approach is as viable for 13C chemical shift calculations as other semiempirical approaches, all of which seem currently to be limited to a standard deviation of the order of 10 ppm.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090417
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  • 102
    Electronic Resource
    Electronic Resource
    Ab initio calculations on large molecules: The multiplicative integral approximation (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 620-626 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In the multiplicative integral approximation (MIA), two-electron integrals are evaluated using an expansion of a product of two Gaussians in terms of auxiliary functions. An estimator of the error introduced by the approximation is incorporated in the self-consistent field (SCF) calculations and the integrals for which the error estimate is larger than a preset value are systematically corrected. In this way the results of a MIA-assisted calculation have the same accuracy as a conventional calculation. The full exploitation of the expansion technique while constructing the Fock-matrix allows important time savings. Results are presented for a number of test cases.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090607
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  • 103
    Electronic Resource
    Electronic Resource
    Computer assisted structure-taste studies on sulfamates by pattern recognition method using graph theoretical invariants (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 636-646 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Structure-taste relationships for 25 acyclic and 20 cyclic carbosulfamates were investigated by means of pattern recognition using different graph theoretical invariants as molecular substituent descriptors. The SIMCA method was used to classify the compounds into sweet and nonsweet classes. All selected graph theoretical invariants that are related to the “rooted” vertex were found to give promising results. Using the weighted path numbers and self-returning walks for the rooted atom as descriptors of substituents, we found 87% of acyclic compounds were correctly classified. Using the atomic path numbers for the rooted atom as descriptors of substituents, we found 81% of cyclic compounds were correctly classified. These results are better than previously used shape and size substituent descriptors. It may be concluded that the graph theoretical descriptors have great potential in encoding structure components in structure-activity studies (SAR) studies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090609
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  • 104
    Electronic Resource
    Electronic Resource
    Structure and properties of small silicon and aluminum clusters (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 803-809 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Small Sin and Aln clusters (n = 3-10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For each n, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with available ab initio calculations d orbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three-dimensional structures rather than two- or one-dimensional structures, except for n = 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most-stable structures. Ionization potentials, HOMO-LUMO energy differences, binding energies per atom, and average atomic valencies are presented.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090802
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  • 105
    Electronic Resource
    Electronic Resource
    Hydration of Fe+: A Monte Carlo simulation of water clusters and of a dilute aqueous solution (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 819-826 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Monte Carlo statistical thermodynamic computer simulations are reported for several clusters Fe+ (H2O)n at different temperatures and for a dilute aqueous solution of Fe+ at 298 K. The energy of each configuration has been calculated in the pairwise additivity approximation using the MCY potential for the water-water interaction and an ab initio analytical potential built by us for the Fe+-H2O interaction. Energy and structural analysis of the generated configurations lead to the prediction of a coordination number of six for the first hydration shell of the Fe+ ion, both in clusters and in dilute solution. Finally, the variation in the distance to the Fe+ ion of the energy and orientation of water molecules in the solution are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090804
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  • 106
    Electronic Resource
    Electronic Resource
    Molecular mechanics of peroxides. I. Parametrization and conformational analysis of linear compounds (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 851-860 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A force field has been developed for use in MM2 calculations of geometric and energy data for linear peroxides R1—O—O—R2 and tested in some of them (R1, R2 = H, Me, Et, Pri, But). The field obtained yield results that agree considerably better with experimental and ab initio data than those afforded by the only set of estimated parameters hitherto available.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090808
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  • 107
    Electronic Resource
    Electronic Resource
    On testing difference equations for the diatomic eigenvalue problem (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 844-850 
    Details
    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 determination of the vibration-rotation eigenvalues (for an electronic state of a diatomic molecule) is done using various algorithms, where the differential equation y″ + f(r)y = 0 (with given initial values yo and y′o at an origin ro) is to be integrated, that is, to be replaced by a “convenient” difference equation (DE). The best known are those of: Numerov (N), Runge-Kutta (RK), and the Taylor series expansion (TS). Each algorithm is commonly associated with an “appropriate” DE, and the conventional comparisons of algorithms and/or DE are often misleading. This work compares different DE used in the same algorithm for the same potential and with the same tests. It considers the mentioned conventional DE, and three nonconventional ones: Hajj et al. (HKN) [J. Comp. Phys., 16, 150 (1974)], Cash and Raptis (CR) [Comput. Phys. Commun., 32, 299 (1984)], and Kobeissi “integrals superposition” (IS) [J. Phys. B, 15, 693 (1982)]. A convenient test of these DE is presented and applied. It is shown that: (i) if ∊ is the average error by using Numerov DE, it is of 4∊ for RK, 2∊ for TS, ∊ × 10-3 for HKN, 4∊ × 10-4 for CR and ∊ × 10-6 for IS; (ii) if τ is the average computing time by using Numerov DE, it is of 2.9τ for RK, 3.4τ for TS, 1.5τ for HKN, 2.7τ for CR and 0.9τ for IS.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090807
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  • 108
    Electronic Resource
    Electronic Resource
    Doublet instability and the molecular structure of AlO2A contribution from the “Grup Química Quàntica de Catalunya, Institut de'Estudis Catalans.” (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 836-843 
    Details
    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 possible Cs, C2v, and C∞v structures of AlO2 corresponding to the two lowest electronic states which dissociate into the neutral Al(2P) and O2(3Σg-) fragments have been investigated at the ab initio self-consistent field (SCF) and CI levels using nonempirical pseudopotentials. The most stable structure corresponds to a C2v symmetry in the 2A2 electronic state. However, this structure presents the three-center three-electron Hartree-Fock instability and CASSCF calculations were necessary to unequivocally characterize it as true minimum. Moreover, only another stable structure, of C2v geometry, was found to be a minimum, corresponding to a low-lying excited state of 2A1 symmetry. The optimized C∞v structures were not minima on the corresponding potential energy surfaces and no evidence of any stable Cs structure was found. Calculating values are compared with the different experimental data obtained from the reaction of Al and O2 in frozen gas inert matrices.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090806
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  • 109
    Electronic Resource
    Electronic Resource
    Application of the higher order finite-element method to one-dimensional Schrödinger equation (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 827-835 
    Details
    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 accuracy and applicability of the finite-element method of the higher order interpolation functions to the one-dimensional Schrödinger equation were examined. When the fifth-order Lagrange and Hermite interpolation functions were used as the basis functions, practically exact solutions were obtained for all eigenvalues of several model potential energy functions. It was demonstrated that the appropriate analytical integration over the potential energy function within each element is important in the matrix element evaluation. The accuracy of the method was examined for the potential functions with a double minimum, which has a large classically forbidden region. The method was also applied to evaluate the Franck-Condon factors of the transitions between the 1 1Σg+ and 2 1Σu+ states of Na2; the latter state having a double minimum in its potential energy function.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090805
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  • 110
    Electronic Resource
    Electronic Resource
    The MT-MSXα(R) method: Applications to Li2, F2, and N2 molecules (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 890-892 
    Details
    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 multiple scattering Xα(R) method with the scaling parameter α expressed as a function of the internuclear distance is applied to the Li2, N2, and F2 molecules. Compared with the results obtained by the Xα method, the calculated Xα(R) equilibrium distances are smaller, the total energies are lower, and the dissociation energies are larger.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090810
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  • 111
    Electronic Resource
    Electronic Resource
    Response of immature chicken meniscus to strenuous exercise: Biochemical studies of proteoglycan and collagen (1988)
    Hoboken, NJ [u.a.] : Wiley-Blackwell
    Journal of Orthopaedic Research 6 (1988), S. 196-204 
    Details
    ISSN: 0736-0266
    Keywords: Meniscus ; Exercise ; Proteoglycan ; Collagen ; Biochemistry ; Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Male white Leghorn chickens were exercised on a treadmill at 70-80% of their maximal oxygen consumption starting at 4 weeks and continuing up to 20 weeks of age. The effect of the strenuous exercise regime on the extracellular matrix of menisci was followed through studies of proteoglycans and collagen. Avian menisci contain type I collagen, chondroitin sulfate proteoglycans, which increase with age in amount and degree of aggregation, and dermatan sulfate proteoglycans, which decrease with age. Five weeks of exercise cause a premature decrease of dermatan sulfate proteoglycans, while the chondroitin sulfate-containing molecules become significantly more aggregrated than those of the tissue of age-matched controls. Strenuous exercise also causes a significant decrease in the number of pyridinoline crosslinks per mole of collagen in the menisci of young runners. The exercise-induced changes of proteoglycan and collagen occur only during the period of active growth, and all parameters return to normal when the animals reach skeletal maturity. The early proteoglycan aggregation and dermatan sulfate decrease induced by exercise are probably an adaption to the increased loading. Although the mechanism by which strenuous exercise reduces or delays the formation of collagen pyridinoline crosslinks in menisci of skeletally immature animals is unknown, their decrease could negatively affect the mechanical properties of the tissue during the period of active growth.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jor.1100060206
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