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  • Computational Chemistry and Molecular Modeling  (22)
  • 1995-1999  (22)
  • 1965-1969
  • 1
    Electronic Resource
    Electronic Resource
    A semiempirical study of pyrazole acylhydrazones as potential antimalarial agents (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1835-1843 
    Details
    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 evaluated structural and electronic similarities between a new class of acylhydrazones, recently presented as effective inhibitors of a Plasmodium falciparum cysteine protease, and a series of pyrazole arylacylhydrazones with analgesic and antiaggregating (antithrombotic) properties, using AM1. The calculated results suggest that at least one of the pyrazole compounds is similar enough to the active compounds to be considered as a candidate for a future antimalarial series. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular modeling on platelet-activating factor (PAF) and new proposed PAF antagonistsPresented at the 1995 Sanibel Conference. (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1069-1080 
    Details
    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: Platelet-activating factor (PAF) is an autacoid derived from cellular membrane phospholipids in response to chemical or physical stimuli. It has been identified as 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine; the alkyl group is composed of 16 or 18 carbon atoms in human cells. PAF can cause a series of pathophysiological effects, related to inflammatory and allergic diseases such as asthma, gastric ulcerations, transplant rejections, psoriasis, cerebral, renal, and myocardial ischemia. As PAF biological action is a result of interactions with specific receptors on target cells, several specific PAF receptor antagonists have been proposed for therapeutic control of the pathological states in which PAF is implicated. In this work we have calculated at AM1 level 16 conformations of a model (alkyl = octyl) of (R)-PAF. We have used these conformations and calculated structures of two hetrazepines (WEB 2086 and E 6123), FR 128998 and RP 59227, known antagonists of PAF activity currently under development, to test a recently proposed pharmacophore map. Our results suggest that the model is too rigid. Having this in mind, we used the pharmacophore model to evaluate the potential activity of a new series of proposed PAF receptor antagonists based on bicyclo[3.3.0]-2-oxaoctane. The results were used to decide which compounds should receive priority in synthesis. The synthetic results and pharmacological profiles of the new derivatives will be published elsewhere. © 1996 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Stability and structure of rare-gas ionic clusters using density functional methods: A study of helium clustersThis is a contribution to a symposium on “The Quantum Theory and the Chemical Bond” published in honor of Professor Roy McWeeney. The authors wish to affectionately dedicate this work to a great scientist and a long-standing friend. (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 593-608 
    Details
    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 modelings of exchange and correlation forces which can be carried out using density functional theory (DFT) methods have been analyzed to study their efficiency and reliability when evaluating possible competing structures of helium ionic clusters of increasing size. This study examines Hen+systems with n from 1 to 7 and compares the present calculations with earlier evaluations that used more conventional, and more computationally intensive, methods with configuration interaction (CI) approaches. The present results indicate that it is indeed possible to strike a fruitful balance between reduction of computational times and quality of the ensuing structural information. © 1996 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Power series with rational coefficients for two-electron atom energies (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 63 (1997), S. 1079-1089 
    Details
    ISSN: 0020-7608
    Keywords: large-order perturbation theory ; lie algebra ; three-body problem ; symbolic computations ; helium atom ; Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The method of o(4, 2) operator replacements is generalized. As a result, the series whose limiting values when the variable goes to  +∞ should correspond to the two-electron atom energies now have rational coefficients. This generalization allows one also to compute the series for the case of singlet S symmetry, a case which could not be considered in the previous original formulation of the method. Series with rational coefficients for the helium singlet and triplet S ground-state energy are calculated up to order 41 and 45, respectively. Moreover, symbolic computations also allow one to give the first few coefficients of these series for arbitrary values of the nuclear charge Z. Finally, a new method for analytic continuation to the limit  +∞ is presented for the energies of the helium singlet and triplet ground states.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1079-1089, 1997
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  • 5
    Electronic Resource
    Electronic Resource
    Extension of the Coulomb-Hole-Hartree-Fock theory to molecules (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 131-147 
    Details
    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 Coulomb-Hole-Hartree-Fock method introduced by E. Clementi in the early 1960s and reparametrized more recently by S. Chakraworty and E. Clementi to compute the correlated electronic energy in atomic systems, is here extended to compute molecules. The new parametrization is obtained empirically by fitting first and second atomic ionization potentials from He to Ca and a few diatomic molecules. The present formulation makes use of either one or more determinants in order to ensure proper dissociation products, following the early proposal of G.C. Lie and E. Clementi in the context of density functional computations for molecular systems. The new formulation is tested against the dissociation energies of a large number of molecules and it is found satisfactory. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560530202
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical studies on nonsteroidal anti inflammatory drugs. Benoxaprofen, chlorpromazine, and piroxicam (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 123-136 
    Details
    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 report quantum chemical semi-empirical calculations of the geometries and the electronic structures (at AM1 and INDO/s levels) of three nonsteroidal antiinflammatory drugs (NSAIDs), namely, benoxaprofen, chlorpromazine and piroxicam, and a piroxicam metabolite, that have undesirable phototoxic effects. Our calculated electronic spectra in gas phase and in water fit reasonably well the observed spectral data. The wavelength of the absorption maxima are not significantly affected by changing from gas phase to water (at the SCRF level). We were able to assign the observed bands to the calculated transitions. We found also that the spectrum of the piroxicam metabolite actually responsible for the phototoxicity cannot be understood on the sole basis of one of the tautomers. We hope that these finding will be useful for the understanding of the photochemical events that lead ultimately to the biological effects. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560713
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  • 7
    Electronic Resource
    Electronic Resource
    Utopia dielectrica (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 523-531 
    Details
    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 dielectric constant of a material is a macroscopic property that measures the reduction of the electrostatic forces between charged plates separated by the material, compared to a vacuum as intermediate material. It is next encountered as a scaling parameter in Coulomb's law for interacting charges, not only in the force, but also in the energy. In deriving the theory for dielectrics, the macroscopic nature is essential: Only then is the basic assumption that the dielectric material is homogeneous and isotropic a valid one. The appearance of the dielectric constant as a simple scaling factor in Coulomb's law has tempted many computational chemists to forget about the macroscopic nature of the dielectric and to apply the screened Coulomb's law between charges, supposedly in a low-dielectric medium such as proteins, in microscopic force fields. Optimization of force fields even led to distance-dependent “dielectric constants.” Another use of the dielectric constant appears in the dielectric continuum reaction field approaches for the computations of solvation energies and solvent effects. The solute is embedded in a cavity surrounded by the dielectric. Specific interactions between solvent molecules and solute are thus neglected. The cavity size and dielectric constants of interior and exterior are optimized for the model. The aim of this article is to show, by means of calculations on interacting point charges embedded in cavities surrounded by dielectrics and microscopic models of “low-dielectric” materials by explicit polarizabilities, that as far as the dielectric “constant” is concerned anything can happen, depending on the nature of the charges, the distance to the cavity boundary, the spatial arrangement of charges, and polarizabilities. Thus, a warning is issued to injudicious use of dielectric models in microscopic calculations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560855
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  • 8
    Electronic Resource
    Electronic Resource
    Acidity of first- and second-row hydrides: Effects of electronegativity and hardness (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 459-468 
    Details
    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 study is made on the influence of the electronegativity and hardness of a group X on the gas-phase acidities of the first- and second-row hydrides HX. It is shown that these two density functional theory (DFT)-based global properties are sufficient for the correct description of the gas-phase acidity sequences, the group hardness being the more important factor and describing the influence of polarizability effects in the charged forms of the acid-base equilibrium. Various calculated properties of the traditional quantum chemical type (Mulliken charges and the MEP) and DFT-based (local softness), associated with the neutral form of the acid, were found to contain a certain periodicity in their description of the gas-phases acidities. The gas-phase acidities (Δ Hacid and ΔGacid values) were also obtained theoretically via quantum statistical thermodynamical calculations at the Hartree-Fock level with the 6-31 + G* basis set; these calculated acidities were in fair agreement with the experimental ones. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560550604
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical studies on the elimination of hydrogen fluoride from alkyl fluoride and its substituent effect (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 715-719 
    Details
    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 reaction mechanism of the α, α and α, β elimination of hydrogen fluorides from alkyl fluorides has been studied theoretically. For fluoroethane as a reactant, the transition state (TS) optimized at the level of the 6-31G** basis set shows that the α, β elimination proceeds via a four membered-ring TS with a barrier height 64.6 kcal/mol, while the α, α elimination, via a three-membered ring TS with a 83.7 kcal/mol barrier. Four substituents, CH3, CN, F, and NH2, were used to investigate the substituent effect of elimination by using the 3-21G basis set. The calculated barriers show that NH2-substituted alkyl fluorides favor both the α, α and α, β elimination and these two reactions would be expected to proceed simultaneously. © 1996 John Wiley & Sons, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    Design of new potential 5-lipoxygenase inhibitors, dual thromboxane synthase inhibitors, and thromboxane a2 receptor antagonists by AM1 (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 181-190 
    Details
    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: Leukotrienes and thromboxane A 2 are autacoids derived from arachidonic acid (5, 8, 11, 14-icosatretraenoic acid). They are synthesized in cells by 5-lipoxygenase and thromboxane synthase, respectively. Leukotrienes are related to inflammatory and allergic diseases, while thromboxane A2 is a potent platelet aggregating and vasoconstrictor agent involved in cardiovascular pathologies. In this article we have calculated partial potential energy surfaces at the AM1 level for some 5-lipoxygenase inhibitors, thromboxane synthase inhibitors, thromboxane A2 receptor antagonists, and a dual blocker which inhibits thromboxane synthase and antagonizes thromboxane A2 receptor. Our objective was to identify stereoelectronic properties and topographical requirements for these compounds that could be related to their biological activities. Based on our results and on molecular mechanisms of pharmacological action, we were able to propose new potential 5-lipoxygenase inhibitors and dual blockers derived from pyrazole, pyrrole, 1, 2, 3-triazole, and 1, 2, 4-triazole. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560719
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