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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1775-1787 
    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: Estimation of brain uptake of solutes and drugs would be useful in designing novel therapeutic agents. Given the problems associated with fragment-based models, including the need for strict additivity, we used AM1-derived molecular parameters in attempting to generate an equation for predicting the log of the brain-to-blood concentration ratios (log B:B) for a collection of compounds. Sequential fitting of the data using 10 AM1-derived variables indicated that dipole generated the most predictive one-term equation, dipole and log P, the best two-parameter system, dipole, log P, and molecular weight produced the optimal three-term model, and dipole, log P, molecular weight, and HOMO energy resulted in the best four-parameter paradigm. These systems were statistically similar to those generated using general solvation equations, but with the use of fewer parameters. An expanded parameter set may generated models of even better predictability. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1147-1154 
    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 peculiar properties of the three-membered ring in cyclopropane are partially due to characteristic relaxation effects of the carbon orbitals in the molecule. AO contraction in the two strongly C—C bonding MO's of A'1 type is essential for the stability of the C3 ring, whereas AO expansion in the E'-type HOMO contributes to the π character of the peripheral C—C bonds.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 441-450 
    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: Variational calculations have been carried out on the ammonia molecule using two-dimensional potential energy functions. The two dimensions used are the inversion and symmetrical stretching coordinates. If the potential function includes a term to describe the interaction between these two coordinates, the results are as good as those obtained in other studies using a six-dimensional potential function. The barrier height for the new potential function is 1857.5 cm-1.
    Additional Material: 10 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 403-409 
    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 paper, the reactions of HNCO or CH3NCO with methanol have been studied using the ab initio MO method. The geometries of the reactants and products have been optimized by the energy gradient method. The calculated results are in accordance with experiment. Using Powell's method, by the minimization of the Euclidean norm σ of the gradient, the structures of the transition state (TS) for the two reactions were obtained. The structures have been further confirmed as TS by finding that there is one and only one negative eigenvalue for their force constant matrix. The imaginary vibration mode corresponding to the TS was also discussed. The calculated activation barriers of these two reactions are 96.02 and 95.13 kJ/mol, respectively. It can be concluded that the alcoholysis reaction of isocyanate is a nucleophilic addition reaction with methanol as an electronic donor and isocyanate as an acceptor and that the hydroxyl hydrogen of CH3OH plays an important role in the reaction.
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 81-89 
    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: Closely related structures, like esters and lactones, have vastly different physical properties. This is apparently due to differences in the intermolecular interactions. The intermolecular interactions of methyl acetate, β-propiolactone, ethyl acetate, and γ-butyrolactone have been studied using the AM1 semiempirical method. Some of the “arranged clusters” were also compared to possible covalently bound trimers and tetramers of β-propiolactone and γ-butyrolactone. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 701-709 
    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: Semiempirical molecular orbital calculations for the porphyrins tetrakis(4-N-methyl pyridyl)porphine (H2TMpyP-4) and tetrakis(2-N-methyl pyridyl)porphine using the MNDO and AM-1 Hamiltonians suggest that twisting one or more of the pyridinium rings results, at considerable energy expense, in highly nonplanar macrocycle configurations as the exocyclic ring(s) approach coplanarity. The results imply that the mechanism of intercalation of H2TMpyP-4 into DNA cannot require twisting the exocyclic rings anywhere close to coplanarity with the central porphine core, but involves, instead, the inherent flexibility of DNA itself. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 49-58 
    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 present paper, the electronic energy-band structures of the LnBa2Cu3O7 (Ln = Pr, Nd, Gd, and Dy) were investigated employing the EHMO approach based on the tight-binding method. The results show that the substitution of Nd, Gd, and Dy for Y in YBa2Cu3O7 complicates the shape of the Fermi surface and results in an increase in the number of energy bands crossing the Fermi level, Ef. Compared with those of YBa2Cu3O7, the electronic densities of states at Ef, N(Ef), for NdBa2Cu3O7, GdBa2Cu3O7, and DyBa2Cu3O7 increase greatly, whereas those of PrBa2Cu3O7 are very small. The results given by the present calculations explain why the substitution of Nd, Gd, and Dy for Y in YBa2Cu3O7 can still maintain the high transition temperature Tc, while PrBa2Cu3O7 is a semiconductor rather than a superconductor. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 7-15 
    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: Hydroxyl-stretching frequencies (vOH) were estimated for a number of 4-substituted and 2,6-disubstituted phenols using the AM1 all-valence electron molecular orbital approximation. There was significant correlation between calculated and experimentally observed frequencies with better correlation observed with the gas phase as compared with dilute solution-phase values. Significant Hammett sigma-rho relationships were recorded for the 4-substituted phenols, consistent with experimental observations. The vOH stretching frequency associated with the equilibrium structure of 2,6-di-t-butylphenol was calculated to be 15 cm-1 higher than that of phenol and this increase was attributed to steric interactions that act to effectively shorten the OH bond length. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 233-242 
    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: Based on the EHMO approach, an approximate treatment of electronic energy-band structures is suggested. By employing this treatment, computations of the band structures for the Al-doped superconductors YBa2Cu3-xAlxO7 + δ were carried out. It is shown by analysis of the band structures and the density of states that the 2D Cu-O planes in the Y—Ba-Cu—O superconducting system play a dominant role in superconductivity, whereas the 1D Cu—O ribbons have indirectly an influence on superconductivity through the connection of the O(4) atoms to two Cu—O planes. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 17-24 
    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 dithionite reduction of pyridinium salts results in the preferential formation of the 1,4-dihydropyridines over the other possible (1,2 and 1,6) structural isomers. Theoretical studies performed in the framework of the AM1 molecular orbital approximation both on some simple, model molecules (dihydro-1-methyl-3-nicotinamide, 1, and dihydro-1-methyl-3-methyl-nicotinate, 2) and more complex derivatives (1-methyl-dihydro-pyridine-3-carboxylates of estradiol, 3, and azidothymidine, 4) supported thermodynamic product control. The increased relative thermodynamic stability of the 1,4-dihydropyridine isomers is explained by favorable electronic interactions (homoaromaticity, hyperconjugation) governing in these derivatives. The calculated data support existing experimental evidence for product formation and isomer stability. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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