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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of vicinal proton-proton coupling constants in polypropylene chains (1981)
    s.l. : American Chemical Society
    Macromolecules 14 (1981), S. 1830-1831 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma50007a044
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation between carbon-13 NMR chemical shifts and conformation of polymers. 4. Solid-state spectra of poly(3-methyl-1-pentene) (1984)
    s.l. : American Chemical Society
    Macromolecules 17 (1984), S. 485-490 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00133a042
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of .beta.-Isotactic Polypropylene: A Long-Standing Structural Puzzle (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 2615-2622 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00087a034
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  • 4
    Electronic Resource
    Electronic Resource
    Evidence for conformational equilibrium of the sulfated L-iduronate residue in heparin and in synthetic heparin mono- and oligo-saccharides: NMR and force-field studies (1986)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 6773-6778 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00281a052
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  • 5
    Electronic Resource
    Electronic Resource
    Tetrahexylsexithiophene: crystal structure and molecular mechanics calculations (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1973-1979 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis, crystal structure and detatiled molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    An improved force field for conformational analysis of sulfated polysaccharides (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 351-367 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A force field to be used in molecular mechanics studies of sulfated polysaccharides with explicit account of water and counterion interactions was derived from the analysis of six crystal structures of sulfated monosaccharide salts. The force field is based on Allinger's MM2, and was developed starting from the parameters used in previous studies of heparin and related oligosaccharides. While the novel parameters have been derived empirically, use of the atomic charge distribution obtained from ab initio quantum-mechanical computations, at the 6-31 + G** level, improves the quality of structural fitting significantly. The overall discrepancy between the positions of the nonhydrogen atoms determined by X-ray diffractometry and those corresponding to the minimum-energy structure is 0.21 Å. While most geometrical features of both carbohydrate and sulfate moieties are reproduced satisfactorily, in some cases (particularly in the case of the Na+ salt of α-methyl-4-O-sulfogalactopyranoside) the hydrogen bond pattern is altered by energy minimization, probably due to errors in the balance of the strong electrostatic forces. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    A force-field study of the conformational characteristics of the iduronate ring (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 7 (1986), S. 105-112 
    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: Methods of molecular mechanics were applied to investigate the conformation of the (methyl 2-O-sulfate-4-methyl-α-L-idopyranose) uronic acid (DMIS), in order to correlate the peculiar vicinal proton coupling constants observed in polysaccharides containing the iduronate ring to the conformational characteristics of this sugar ring. We found three conformers with comparable energies, namely the two chair forms 1C4 and 4C1 and the skew-boat form 2S0(L); the latter is separated from each chair form by a barrier of about 9 kcal/mol. Along the pseudorotational path three additional minima (3S1, 1S3, and 1S5) were found, yet at least 4 kcal/mol higher than 2S0. The results obtained for the relative energies of the three conformers and the conformation of the side groups were affected by the inclusion of the electrostatic term and, in particular, by the charge assigned to the ionic groups of DMIS. However, the conformational properties of the idopyranosidic ring in DMIS (and in related compounds) should still be interpreted in terms of equilibrium among these three conformers only.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540070203
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  • 8
    Electronic Resource
    Electronic Resource
    Semiempirical energy calculations on model compounds of polypeptides. Crystal structures of DL-acetylleucine N-methylamide and DL-acetyl-amino-n-butyric acid N-methylamide (1972)
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 105-117 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sum E of the packing and conformation energies of the crystals of DL-acetylleucine N-methylamide (ALNMA) and DL-acetyl-α-amino-n-butyric acid N-methylamide (ABAMA) is calculated as a function of the crystallographic parameters and the conformational angles. The intermolecular energy is assumed to be the pairwise sum of nonbonded and electrostatic atomic interactions, while both these terms and intrinsic terms describing barriers of internal rotation contribute to the intramolecular energy. For ALNMA E is minimized with respect to 18 parameters: the minimum found when starting from the experimental structure agrees with this within 0.07 Å and 3°, except for one angle which deviates by 6° the average deviations of the atomic coordinates are \documentclass{article}\pagestyle{empty}\begin{document}$ |\overline {\Delta x|} = 0.02,|\overline {\Delta y|} = 0.07,|\overline {\Delta z|} = 0.08 $\end{document} Å. Another minimum with about the same energy shows slightly worse agreement. A comparison between different sets of nonbonded functions is made. The prediction of conformation and intermolecular packing of ABAMA is attempted on the basis of the knowledge of the unit cell and the space group. In agreement with available experimental data it is found that only one-di-mensional arrays of molecules linked by pairs of hydrogen bonds are compatible with the unit cell. The more stable of two possible conformations of the main chain agrees approximately with the experimental conformation. The calculation is not conclusive with regard to the side-chain conformation and the packing of non-hydrogen-bonded molecules.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1972.360110108
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  • 9
    Electronic Resource
    Electronic Resource
    The peculiar conformational characteristics of cis-poly(tert-butlacetylene) (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 5 (1996), S. 231-254 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular mechanics was applied to investigate the conformational structure of cis-poly(tert-butylacetylene) (c-PTBA). The program CHAMP, adopting a MM2-based force field, was used for a thorough search of the minimum-energy conformers of oligomers, helices and long segments of the c-PTBA chain. The results show that short oligomers are not good models of the polymer, as their preferred conformations are not allowed inside the chain. Segments of 83 and 85 helices appear as the most probable feature. Junctions between right- and left-handed helices can occur at the cost of 1,7 kcal/mol: such defects may run through the chain, the barrier to their shift being 7,8 kcal/mol. Other conformational defects, having energies in the range of 1-3 kcal/mol above the minimum, form knuckle-joints in the helix, changing the axial direction by 70-80°. The present calculations suggest a disordered model of c-PTBA in solution, made of rather stiff helical segments. Such a picture corresponds to a chain less rigid than proposed by previous computations on substituted polyacetylenes, and seems consistent with the observed physical aging of c-PTBA films. Preliminary packing calculations of right- and left-handed helices lead to density values not much higher than observed, indicating rather low degrees of disorder and free volume in the solid state.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1996.040050206
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  • 10
    Electronic Resource
    Electronic Resource
    Application of molecular mechanics to refine and understand the crystal structure of polythiophene and its oligomers (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 713-727 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A molecular mechanics computational procedure, previously used for the refinement and the analysis of several crystalline polymers, was applied to investigate the crystal structures of the tetramer (T4) and hexamer (T6) of thiophene, as well as the crystal structure of polythiophene (PT). Simultaneous minimization of intra- and intermolecular energies of the T4 and T6 structures, obtained by Rietveld analysis of powder X-ray diffraction profiles, leads to molecular conformations showing smaller deviations from the ring co-planarity than the original models. For both oligomers the calculations confirm that the molecular centre of inversion is not a crystallographic centre of symmetry, as also revealed by X-ray diffraction of the T6 single crystal. This surprising effect appears to arise from intermolecular interactions between the terminal residues, hence is not relevant with respect to the PT polymer structure. The small energy cost for constraining the molecules at the crystallographic centre of symmetry is in agreement with experimental findings that reveal the existence of polymorphs for both T4 and T6. The calculations on the T6 single crystal were used to upgrade the MM2-like force field, which was then used to determine the minimum-energy model of the monoclinic crystal structure of polythiophene.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1997.040060403
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