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  • 1
    Electronic Resource
    Electronic Resource
    Intramolecular-catalyzed sulfonamide hydrolysis. VII. The Thorpe-Ingold effect in the intramolecular carboxyl-catalyzed hydrolysis of sulfonamides (1984)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 106 (1984), S. 139-143 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00313a029
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  • 2
    Electronic Resource
    Electronic Resource
    Interlayer Porosity in Montmorillonite Intercalated with Keggin-like Cation Studied by Molecular Mechanics Simulation (1997)
    Springer
    Journal of molecular modeling 3 (1997), S. 467-472 
    Details
    ISSN: 0948-5023
    Keywords: Keywords: Molecular mechanics ; Intercalated clays ; Keggin cation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics simulation using Cerius2 modeling environment have been used to investigate the structure of montmorillonite, intercalated with Keggin-like cation7+. Present work is focused to the strategy of modelling in case of intercalated layered structures and to investigation of structure parameters characterizing the interlayer porosity, that means: the interlayer distance, the position, orientation and distribution of Keggin cations in the interlayer space and the stacking of layers. Molecular simulations revealed the structure of the interlayer and led to the following conclusions: In the most stable configuration the 3-fold axis of Keggin cation is perpendicular to the silicate layer. This orientation of Keggin cations leads to the basal spacing 19.51 (10-10 m). Energy minimization during the translation of Keggin cation along the silicate layer gives only small fluctuations of basal spacing and no correlation has been found between the shift of cation along the layers and the value of basal spacing. No systematic relationship has been found between the shift of cation and crystal energy and no systematic relationship exists between the mutual shift of two successive layers and the values of basal spacing and crystal energy. Consequently, no two-dimensional ordering of Keggin cations in the interlayer and no regular stacking of layers can be expected. X-ray diffraction diagrams obtained for montmorillonites, intercalated with Keggin cation, confirm present conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050064
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular Mechanics Simulations in Structure Analysis of Intercalate VOPO4·2CH3CH2OH (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 150-157 
    Details
    ISSN: 0948-5023
    Keywords: Molecular mechanics ; Structure of intercalates ; Vanadyl phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics simulations using Cerius2 combined with X-ray diffraction and supported with vibrational spectroscopy have been used to investigate the layered structure of vanadyl phosphate VOPO4 intercalated with ethanol. This intercalated structure exhibits certain degree of disorder, which affects the diffraction diagram and obstructs the conventional structure analysis based on diffraction methods only. Present structure analysis is focused to the crystal packing in the interlayer space and layer stacking in the intercalate. The bilayer arrangement of ethanol molecules in the interlayer has been found, giving the basal spacing d = 13.21 Å, experimental d-value obtained from X-ray diffraction is 13.17 Å. One half from the total number of CH3CH2OH molecules is anchored with their oxygens to VOPO4 layers to complete vanadium octahedra and their orientation is not very strictly defined. The second half of ethanoles is linked with hydrogen bridges to the anchored etahanoles and sometimes also to the layer oxygens. Positions and orientations of these unachored ethanoles with respect to VOPO4 layers exhibit certain degree of disorder, resulting in the disorder in layer stacking. Molecular mechanics simulations revealed the character of this displacement disorder in layer stacking and enabled to determine the components of the displacement vector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089480040150
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  • 4
    Electronic Resource
    Electronic Resource
    Host-guest Interactions in Intercalates Zr(HPO4)2·2C2H5OH and VOPO4·2C2H5OH (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 284-293 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Vanadyl phosphate ; Zirconium phosphate ; Molecular mechanics ; Vibrational spectroscopy ; Host-guest interaction ; Intercalates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics simulations using Cerius2 modelling environment combined with vibrational spectroscopy (IR and Raman) have been used to study the host-guest interactions in zirconium and vanadyl phosphate intercalated with ethanole. The strategy of investigation is based on the comparison of vibrational spectra for the host compound, intercalate and guest species. This comparison confirmed the rigidity of VOPO4- and Zr(HPO4)2-layers during the intercalation and provided us with the basis for the strategy of modelling. Molecular mechanics simulations revealed the structure of intercalates and enabled to analyse the host-guest interaction energy and bonding geometry. The bilayer arrangement of ethanole molecules in the interlayer space with two differently bonded ethanole molecules has been found in both intercalates. The average interaction energy ethanole-layer for two differently bonded ethanole molecules is : 127.5 and 135.7 kcal·mol-1 in Zr(HPO4)2·2C2H5OH, respectively 94.0 and 104.4 kcal·mol-1 in VOPO4·2C2H5OH. The Coulombic contribution to the ethanole-layer interaction energy is predominant in all cases, but the hydrogen bonding contribution is much higher in Zr(HPO4)2·2C2H5OH than in VOPO4·2C2H5OH. Present results of modelling enabled the interpretation of vibrational spectra and explanation of small changes in positions and shapes of spectral bands, in infrared and Raman spectra, proceeding from the host structure to intercalates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050086
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling in Structure Analysis of Vanadyl Phosphate Intercalated with 1-Alkanols (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 9-15 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Vanadyl phosphate-alkanol intercalates, Molecular mechanics, Structure analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics simulations supported by X-ray powder diffraction measurements have been used to investigate the structure of vanadyl phosphate intercalated with 1-alkanols CnH2n+1OH for n = 2, 3, 4. Modeling revealed the specific features and differences in arrangement of alkanol molecules with different chain length, depending on the relation between the parameters of active sites network and size of guest molecules. This result enabled us to explain the irregularities in dependence of basal spacing on the chain length. The comparison of experimental dexp and calculated dcalc values of basal spacing showed the good agreement of modeling with x-ray powder diffraction. While we obtained dcalc(Univ) = 13.05 Å for vanadyl phosphate-ethanol using the Universal force field (dexp=13.17 Å), for vanadyl phosphate-propanol and vanadyl phosphate-butanol better agreement with experiment was obtained using the Tripos force field. In the case of vanadyl phosphate-propanol the calculated basal spacing dcalc(Tripos) = 14.49 Å, compared with an experimental value of dexp=14.36 Å. For vanadyl phosphate-butanol dcalc(Tripos) = 17.71 Å and dexp=17.90 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010722
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  • 6
    Electronic Resource
    Electronic Resource
    Modelling of Aniline-Vermiculite and Tetramethylammonium-Vermiculite; Test of Force Fields (1999)
    Springer
    Journal of molecular modeling 5 (1999), S. 8-16 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Vermiculite ; Intercalate ; Aniline ; Tetramethylammonium ; Molecular mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics simulations in Cerius2 have been used for modelling vermiculite intercalated with tetramethylammonium and aniline cations. The published structure data obtained for these intercalated structures from X-ray single crystal diffraction have been used to test the force fields and modelling strategy for organo-clays. The strategy of modelling was based on the nonbond host-guest interactions and on rigid silicate layers and rigid guest species. The rigidity of silicate layers requires that the cell parameters a, b andγare kept fixed during the energy minimisation. The energy term was set up using the nonbond interaction terms only and the Crystal Packer module in Cerius2 has been used for the energy minimisation. In Crystal Packer the rigid units, i.e. the silicate layers and guest species can be translated and rotated during energy minimisation and the cell parameters c, α, and β have been varied. Three sets of Van derWaals (VDW) parameters available in Crystal Packer: Tripos, Universal and Dreiding have been used in present molecular simulations. Ab initio MP2 calculations were performed to justify the application of the force field. The best agreement of molecular mechanics simulations with both: experimental and ab initio data was obtained with the Tripos VDW parameters for both intercalates. The results of modelling are in good agreement with the experimental data as to the cell parameters and the interlayer packing. The cell parameters reported by Vahedi-Faridi and Guggenheim (1997) for tetramethylammonium-vermiculite are: c = 13.616 Å, α = 90°, β = 97.68° ; from the present modelling we obtained: c = 13.609 Å, α = 90.19°, β = 97.56°. Tetramethylammonium-cations are arranged in one layer in the interlayer space. One C-C edge of NC4 tetrahedra is perpendicular to the silicate layers. The deep immersion of the methyl groups into the ditrigonal cavities suggested by Vahedi-Faridi and Guggenheim was not confirmed by modelling. Slade and Stone (1984) presented the measured cell parameters for aniline vermiculite: c = 14.89 Å, α = 90°, β = 97°; present result is: c = 14.81 Å, α = 90.72°, β = 96.70° for partially exchanged vermiculite and c = 14.84 Å, α = 90.53°, β = 97.17° for fully exchanged vermiculite. The aniline cations are positioned over the ditrigonal cavities alternating in their anchoring to lower and upper silicate layer. The C-N bonds are perpendicular to layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050101
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  • 7
    Electronic Resource
    Electronic Resource
    1-[(2-Nitrophenyl)hydrazono]-1H-naphthalen-2-one (Pigment Orange 2) from powder data (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. o1152-o1153 
    Details
    ISSN: 1600-5368
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of the title compound, C16H11N3O3, has been determined from X-ray powder data. The molecule is slightly non-planar. The structure adopts a stacking arrangement, with the stacks extended along [001]. The AM1 calculations of the crystal electrostatic potential show that the crystal environment causes only a moderate (23%) increase in the molecular dipole moment of the title compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S1600536801018268
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  • 8
    Electronic Resource
    Electronic Resource
    Crystal structure analysis of two crystalline bis(ω-hydroxyalkoxy)biphenyls using a combination of powder diffraction, IR spectroscopy and molecular simulation (1999)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 6 (1999), S. 1035-1043 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Synchrotron and standard X-ray powder diffraction (XRD) combined with IR spectroscopy and molecular simulations have been used to investigate the crystal structure of two crystalline mesogenic diols: 4,4′-bis(6-hydroxy-1-hexyloxy)biphenyl (D-I) and 4,4′-bis(11-hydroxy-1-undecyloxy)biphenyl (D-II). The crystal structure of D-I has been determined from high-resolution synchrotron powder-diffraction data collected at BM16 of the ESRF. The methods of grid search and Rietveld refinement have been used to determine this structure. The space group is Cc, with unit-cell parameters a = 44.392 (3), b = 7.221 (1), c = 6.631 (1) Å and β = 91.09 (1)°. The structure of D-II has a small degree of disorder. This structure was analyzed with a combination of experimental methods, conventional XRD, IR spectroscopy and molecular mechanics simulations, revealing the character of the structural disorder. Both the structures of D-I and D-II are lamellar-packed and layered. The hydrogen-bonding system between two adjacent layers in the structure of D-II is distorted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599007840
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  • 9
    Electronic Resource
    Electronic Resource
    Structure Analysis of Intercalated Zirconium Phosphate Using Molecular Simulation (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 845-850 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Molecular simulation supported by X-ray diffraction and IR spectroscopy has been used to analyse the structure of α-zirconium phosphate intercalated by ethanol, Zr(HPO4)2.2C2H5OH. Molecular-mechanics simulations using the Crystal Packer module in the Cerius2 modelling environment revealed the crystal packing in the interlayer, i.e. the positions of ethanol with respect to the Zr(HPO4)2 layers and the layer stacking in the intercalated structure. The average interlayer distance d\,=\,14.03 (13) Å obtained by modelling is in agreement with the experimental d value of 14.05 (4) Å obtained from the X-ray diffraction analysis. The disorder in the Zr(HPO4)2.2C2H5OH structure found by molecular simulation has been confirmed by the character of the X-ray diffraction pattern.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889898006773
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  • 10
    Electronic Resource
    Electronic Resource
    Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 1186-1190 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal structures of [1,2-bis(2,6-diisopropylphenylimino)acenaphthene-N,N′]carbonylchlororhodium(I) (1) and [N,N′-ethylene-bis(3-methylsalicylideneiminato)-O,N,N′,O′](tetrahydrofurfuryl)-cobalt(II) (2) have been determined from high-resolution synchrotron X-ray powder diffraction data. Compound 1 is the first neutral Rh complex, in contrast with findings in the literature, containing a bidentate nitrogen ligand, and compound 2 is the first three-dimensional structure of a (five-coordinated) tetrahydrofurfurylcobalt(III) complex. Grid-search and Rietveld refinement have been used to determine and refine the structures, respectively. Crystals of 1 are orthorhombic, space group Pbca, Z = 8, with cell parameters a = 21.729 (2), b = 27.376 (3), c = 11.580 (1) Å. Crystals of 2 are monoclinic, space group P21/n, Z = 4, a = 16.6701 (6), b = 9.4170 (4), c = 13.7088 (7) Å and β = 96.520 (3)°. Chemical diagrams for the two compounds are given. Soft restraints were applied during Rietveld refinement; for 1 converging to Rp = 8.4%, Rw = 11.0%, GoF = 2.3, and for 2 converging to Rp = 8.5%, Rw = 11.4%, GoF = 7.6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049501013784
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