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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 4910-4918 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2859-2868 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The minima in the electrostatic energy, for accessible orientations, have been located for the s-tetrazine and benzene dimers and the 1:1 complexes of s-tetrazine with hydrogen chloride, water, acetylene, and benzene, and of benzene with acetylene, anthracene, and perylene. The minima give reasonably successful predictions of the structures of these van der Waals molecules, demonstrating the importance of the electrostatic interactions in these systems. The electrostatic energy was calculated using sets of distributed multipoles obtained from ab initio wave functions of the monomers. This method is contrasted with empirical point charge and central multipole models for the electrostatic energy. It is shown that the simple models for the electrostatic interactions can give qualitatively misleading results for aromatic systems.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 3325-3335 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 42 (1986), S. 388-401 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 95 (1996), S. 151-163 
    ISSN: 1432-2234
    Keywords: β-lactam compounds ; β-lactamase class A ; Binding orientations ; Electrostatic forces ; Distributed Multipole Analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The electrostatic forces within the active site of theβ-lactamaseStaphylococcus aureus PC1 have been used to predict structures for the precatalytic complex with ampicillin, methicillin, clavulanate and imipenem. There are significant differences in the orientation of theseβ-lactams within the binding site, which explains the differences in their resistance to the lactamase. The electrostatic forces were calculated using a distributed multipole analysis ofab initio wave functions for both the lactams and the binding site residues, to ensure a good representation of the orientation dependence of this dominant contribution. The predicted binding orientations are contrasted with those predicted by overlaying the electrostatic extrema around the ligands. The accuracy of the ligand-only-based predictions is limited in some cases because of the subtle steric requirements of the lactamase binding site.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 10 (1996), S. 107-122 
    ISSN: 1573-4951
    Keywords: Electrostatic similarity ; Molecular electrostatic potential ; β-Lactam compounds ; γ-Lactam compounds ; Distributed multipoles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Electrostatic and structural properties of a set of β-lactam, γ-lactam and nonlactam compounds have been analyzed and compared with those of a model of the natural substrate d-alanyl-d-alanine for the carboxy- and transpeptidase enzymes. This first comparison of the electrostatic properties has been based on a distributed multipole analysis of high-quality ab initio wave functions of the substrate and potential antibiotics. The electrostatic similarity of the substrate and active compounds is apparent, and contrasts with the electrostatic properties of the noninhibitors. This has been quantified to give a reasonable correlation with the MIC (Minimum Concentration for Inhibition) and with kinetic data (k2/K) in accordance with the model for interaction of the lactam compounds with dd-peptidase. These correlations provide a better prediction of antibacterial activity than purely structural criteria.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0040-5744
    Keywords: Key words: β-lactam compounds ; β-lactamase class A ; Binding orientations ; Electrostatic forces ; Distributed Multipole Analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The electrostatic forces within the active site of the β-lactamase Staphylococcus aureus PC1 have been used to predict structures for the precatalytic complex with ampicillin, methicillin, clavulanate and imipenem. There are significant differences in the orientation of these β-lactams within the binding site, which explains the differences in their resistance to the lactamase. The electrostatic forces were calculated using a distributed multipole analysis of ab initio wave functions for both the lactams and the binding site residues, to ensure a good representation of the orientation dependence of this dominant contribution. The predicted binding orientations are contrasted with those predicted by overlaying the electrostatic extrema around the ligands. The accuracy of the ligand-only-based predictions is limited in some cases because of the subtle steric requirements of the lactamase binding site.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An SCF calculation has been performed on C63H113N11O12, a derivative of the immuno-suppressive drug cyclosporin, using a 3-21G basis set and a Direct SCF method. A distributed multipole analysis has been performed on the resulting charge density to give a set of multipoles at each atomic site, which are used to calculate the electrostatic potential around the molecule. The potential maxima and minima on the accessible surface of the molecule are compared with those predicted using the corresponding Mulliken charges, and also using a potential-derived point-charge model based on the force-field of Kollman et al. The Mulliken charges give a misleading picture of the electrostatic potential around this peptide. The potential-derived charges give results which are in far better agreement with the ab initio distributed multipole model, despite being derived from calculations on smaller molecules with different basis sets and geometries. The limitations of point-charge models for describing the electrostatic interactions of polypeptides are discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 2060-2074 
    ISSN: 0192-8651
    Keywords: hydrogen bond ; Cambridge Structural Database (CSD) ; distributed multipole analysis (DMA) ; intermolecular perturbation theory (IMPT) ; heterocycle ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The directionality and relative strengths of hydrogen bonds to monocyclic aromatic heterocycles were investigated using crystal structure data and theoretical calculations. Surveys of the Cambridge Structural Database for hydrogen bonds between C(sp3)(SINGLE BOND)O(SINGLE BOND)H and aromatic fragments containing one or more nitrogen and/or oxygen heteroatoms showed that hydrogen bonds to nitrogen atoms are much more abundant than to oxygen. Distinct preferred orientations were also revealed in these surveys. Theoretical calculations were performed on the interaction of methanol with pyridine, pyrimidine, pyrazine, pyridazine, oxazole, isoxazole, 1,2,4-oxadiazole, and furan as models for the heterocyclic fragments. The intermolecular potential surface was thoroughly scanned using a model potential that accurately described the electrostatic forces (derived from distributed multipole analysis) with empirical parameters for the repulsion and dispersion terms. Minima on this surface agreed well with the observed orientations in the data base and they were typically deeper for nitrogen than for oxygen acceptors, although the hydrogen bond strength and geometry was influenced by other heteroatoms in the ring. These results were confirmed by highly accurate intermolecular perturbation theory calculations, which also estimated the deviations from hydrogen bonding in the traditional nitrogen lone pair direction that could occur with negligible reduction in the interaction energy.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 2060-2074, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 628-647 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We describe a method for minimizing the lattice energy of molecular crystal structures, using a realistic anisotropic atom-atom model for the intermolecular forces. Molecules are assumed to be rigid, and the structure is described by the center of mass positions and orientational parameters for each molecule in the unit cell, as well as external strain parameters used to optimize the cell geometry. The resulting program uses a distributed multipole description of the electrostatic forces, which consists of sets of atomic multipoles (charge, dipole, quadrupole, etc.) to represent the lone pair, π electron density, and other nonspherical features in the atomic charge distribution. Such ab initio based, electrostatic models are essential for describing the orientation dependence of the intermolecular forces, including hydrogen bonding, between polar molecules. Studies on a range of organic crystals containing hydrogen bonds are used to illustrate the use of this new crystal structure relaxation program, DMAREL, and show that it provides a promising new approach to studying the crystal packing of polar molecules. © 1995 by John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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