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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 1187-1197 
    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 have developed a method for building up accurate electrostatic models for polypeptides, based on a distributed multipole representation of the SCF charge densities for the dipeptides (CH3.CO.NH.CHR.CO.NH.CH3) of the naturally occurring amino acids. It is based on the observation that each peptide residue has almost the correct formal charge (0, ±1). We find that the variations in the backbone charge distributions (excluding proline) with sidechain have a negligible effect on the predicted electrostatic potential around the residue. However changes in the atomic multipoles with the torsion angles (φ, ψ, χ) are more significant, and may need to be taken into account if electrostatic potential close to the residue is required to high accuracy. This type of DMA peptide library provides more accurate, more theoretically based, estimates of the electrostatic potential around polypeptides than current models.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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