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41.
Toledano P Figueiredo Neto AM de Sant'Ana ZA 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(1):486-492
Experimental investigations of lyotropic cholesterics fluids are presented which show that changes in the shape anisotropy and chirality of the micellar population determine the topology of the temperature-concentration phase diagrams. For given amounts of the substances which induce the chirality and modify the shape anisotropy of the micelles, two distinct biaxial cholesteric phases are disclosed in the phase diagrams. This is interpreted in the framework of the catastrophe theory of phase transitions. 相似文献
42.
43.
The crystal structure of C6H11N3O22+·2F2− is reported. The structure contains a fluoride ion strongly H-bonded to a carboxylic O atom, a rare, very strong, hydrogen bond. The donor-acceptor distance is 2.3818(10) Å, the shortest value reported to date, considerably less than the sum of the van der Waals radii of the atoms implicated, as expected from a very strong hydrogen bond. The di-cation has an open conformation. There is an extensive H-bonding network between anions and cations assembling rings on the ac plane and chains in several directions. Two extra intermolecular interactions of the type CH?π are found, exhausting the aromatic π electron system ability to act as a proton acceptor. 相似文献
44.
J. A. Paixo A. Matos Beja M. Ramos Silva L. Alte da Veiga A. C. Serra 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1348-1350
The title compound, C7H6O2, forms infinite chains where the molecules are hydrogen bonded via the hydroxyl and aldehyde groups, with an O?O distance of 2.719 (3) Å. Interchain interactions are weak. The geometry of the ring differs from the ideal form due to the effect of the substituents. Abinitio (Hartree–Fock self‐consistent field–molecular orbital and density functional theory) calculations for the free molecule reproduce well the observed small distortions of the ring. In the crystal, the geometry deviates from the ideal Cs symmetry of the free molecule, as given by the ab initio calculations. The aldehyde and hydroxyl groups are twisted around the single bonds which join them to the ring as a result of the intermolecular hydrogen‐bond interactions. These are also responsible for an elongation of the hydroxy C—OH bond compared with that calculated for the free molecule. 相似文献
45.
Fonseca AC Jarmelo S Silva MR Beja AM Fausto R Gil MH Simões PN 《The Journal of chemical physics》2011,134(12):124505
Poly(ester amide)s (PEAs) are lacking in structural and spectroscopic information. This paper reports a structural and spectroscopic characterization of N(α)-benzoyl-L-argininate ethyl ester chloride (BAEEH(+)·Cl(-)), an important amino acid derivative and an adequate PEAs' model compound. Crystals of BAEEH(+)·Cl(-) obtained by slow evaporation in an ethanol∕water mixture were studied by different complementary techniques. X-ray analysis shows that BAEEH(+)·Cl(-) crystallizes in the chiral space group P2(1). There are two symmetry independent cations (and anions) in the unit cell. The two cations have different conformations: in one of them, the angle between the least-squares planes of the phenyl ring and the guanidyl group is 5.1(2)°, and in the other the corresponding angle is 13.3(2)°. There is an extensive network of H-bonds that assembles the ions in layers parallel to the ab plane. Experimental FT-IR and Raman spectra of BAEEH(+)·Cl(-) were recorded at room temperature in the 3750-600 cm(-1) and 3380-100 cm(-1) regions, respectively, and fully assigned. Both structural and spectroscopic analysis were supported by quantum chemistry calculations based on different models (in vacuo and solid-state DFT simulations). 相似文献
46.
47.
P. L. Almeida S. Kundu D. Beja J. Fonseca J. L. Figueirinhas M. H. Godinho 《Cellulose (London, England)》2009,16(3):427-434
In this work we study the strain-induced deformation of both isotropic and anisotropic liquid droplets dispersed in a liquid
crystalline cellulose matrix. We have produced two types of acetoxypropylcellulose (APC) solid films one with a droplet dispersion
of the commercial liquid crystal E7 from Merck, and another with a droplet dispersion of silicone oil. To produce the solid
films a solution of APC (60%wt) in dimethylacetamide (DMAc) with 15%wt of either the commercial nematic liquid crystal E7
or the silicone oil was prepared. After homogenization the phase separated solutions were submitted to a shear flow mechanical
field and casted onto a Teflon plate. We performed mechanical uniaxial stress-strain tests in the free standing films recording
continuously the strain and images of the deformed droplets. The mechanical tests were carried out using a mini stress-strain
testing machine apparatus and an Olympus optical polarizing microscope with an attached CCD camera. The images obtained from
the mechanical tests for each value of the imposed strain were then analyzed comparing the images of deformed droplets with
those of the undeformed ones, extracting in this way the local strain field. The droplet deformation data obtained show, as
expected, significant differences in the local strain field when stretching parallel and perpendicular to the initial shear
direction. No significant differences were found in the local strain fields obtained from the silicone oil and the E7 droplets
films. The local strain fields variation with the imposed strain are compared with the predictions of the theory developed
for nematic elastomers by Warner and Terentjev (Liquid crystal elastomers. Clarendon Oxford Press, Oxford, 2003). 相似文献
48.
Ana T. Marques Joana A. Silva Manuela Ramos Silva Ana Matos Beja Licinia L. G. Justino Abilio J. F. N. Sobral 《Journal of chemical crystallography》2008,38(4):295-299
Abstract 2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction
at two temperatures: orthorhombic, space group P212121, Z = 12 with a = 5.9900(2) ?, b = 20.4873(6) ?, c = 26.3727(8) ? and R = 0.0868 for 293(2) K and a = 5.8337(9) ?, b = 20.4428(31) ?, c = 26.0773(40) ? and R = 0.0669 for 120(2) K. There are three independent molecules in the unit cell. One of them is approximately planar, the other
two have the phenyl rings rotated. At room temperature the two latter molecules are joined in dimers through H-bonds and at
low temperature the same molecules are joined in columns that run along the a-axis.
Index Abstract
X-ray Diffraction and DFT Studies of 2-Methoxy-5-phenylaniline
Ana T. Marques, Joana A. Silva, Manuela Ramos Silva, Ana Matos Beja, Licinia L. G. Justino, Abilio J. F. N. Sobral
2-Methoxy-5-phenylaniline, a promissor monomer for PANI studies, has been characterized by single-crystal X-ray diffraction
at 293(2) K and 120(2) K. The three independent molecules in the unit cell show different conformations and establish distinct
intermolecular H-bonds.
相似文献
49.
50.
M. Ramos Silva J. A. Paixão A. Matos Beja L. Alte da Veiga 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(1):7-8
The title compound, [CuCl2(C3H7N3O2)2], is a new copper(II) complex with glycocyamine [(diaminomethyleneamino)acetic acid], the first complex ever reported with this organic molecule. It is composed of discrete centrosymmetric coordinated CuII monomers, the Cu atoms being located at inversion centers. Each metal ion is square-planar coordinated by two Cl atoms and two glycocyamine O atoms. The coordinating glycocyamine molecule exists as a zwitterion, the H atom from the carboxyl group being transferred to the guanidinium group. A three-dimensional network of hydrogen bonds links the monomers and stabilizes the structure. 相似文献