Keiichi Noguchi

Strain-induced crystal modification in poly(tetramethylene succinate)

Abstract A new crystal modification induced by strain was found in uniaxially oriented fibres of poly(tetramethylene succinate). This new modification (β form) had a planar zigzag conformation of T10 (all trans) and a fibre identity period of 11.90 A, while the conventional α form had a T7GTḠ conformation and fibre identity period of 10.90 A. The solid-state crystal transition between α and β forms was reversible with respect to the successive application and release of strain.

Structural study of anhydrous tendon chitosan obtained via chitosan/acetic acid complex

The molecular structure and packing arrangement of anhydrous tendon chitosan was determined by the X-ray fibre diffraction method together with the linked-atom least-squares refinement technique. The specimen was prepared from chitosan/acetic acid complex which was obtained by exposing tendon chitosan to acetic acid vapour at room temperature for several days. There is high degree of orientation and crystallinity compared with the specimen obtained by the annealing method. Two chitosan chains are present in an orthorhombic unit cell of dimensions a = 8.26(2), b = 8.50(1), c (fibre axis) = 10.43(2) A and space group P2(1)2(1)2(1). The 2-fold helical chain is stabilised by O3 triple bond O5 hydrogen bond with the gt orientation of O6. There are direct hydrogen bonds (N2 triple bond O6) between adjacent chains along the a-axis, which makes a sheet structure parallel to the ac-plane. On the other hand, no hydrogen bond is found between the sheets.

Two different molecular conformations found in chitosan type II salts.

The type II structure of chitosan acidic salts prepared from crab tendon in solid state was studied using an X-ray fiber diffraction technique together with the linked-atom least-squares (LALS) technique. The cylindrical Patterson method was applied to confirm the molecular conformation of the chitosan. It was shown that there are two different helical conformations for type II salts. One is the relaxed twofold helix having a tetrasaccharide as an asymmetric unit as found in chitosan.HCl salt, which was previously reported as a conformation of chitosan.HCOOH salt. The other is the fourfold helix having a disaccharide as an asymmetric unit newly found in chitosan.HI salt.

Single helical structure of curdlan triacetate

The molecular and crystal structure of curdlan triacetate, acetylated (1 → 3)β-D-glucan, was analyzed by means of an x-ray diffraction technique with the help of the linked-atom least-squares method. Unit cell dimensions are a = b = 11.00(1), c(fiber axis) = 22.91 (9) A, and γ = 120°. The space group is P61. The unit cell contains six chemical repeating units related by 6/I-helical symmetry, which is essentially the same as the backbone conformation of one of the modifications (form I) of curdlan. During the refinement calculation, the terminal methyl in every acetyl moiety was elastically restrained to the trans conformation commonly observed in related oligosaccharide structures. The difference Fourier map, the observed and calculated densities, and the thermogravimetric measurement indicated one water molecule per glucose residue. The water oxygen is linked to two carbonyl oxygens in adjacent molecules by hydrogen bonds. The conformation of the primary acetyl moiety is a (skew, -gauche, trans). So far, no skew conformation was observed for the primary acetyl and hydroxyl moieties except in α, β-panose. In both cases, the unusual eclipsed orientation of the primary group is attributed to the hydrogen bond and this conformation is quite different from that of pachyman triacetate.

Molecular and Crystal Structures of Dodecyltrimethylammonium Bromide and its Complex with p-Phenylphenol

Abstract The crystal structures of dodecyltrimethylammonium bromide (Space group of P21, a = 5.638(2), b = 7.244(1), c = 21.554(2)A, β = 93.06(2)°, R = 0.083 for 1425 reflections) and its complex with p-phenylphenol (Space group of P21/m, a = 11.191(2), b = 7.462(1), c = 27.413(1)A, β = 96.738(7)°, R = 0.076 for 3679 reflections) were determined by the X-ray diffraction method. Both crystals have the smectic layer structure stacked along the c-axis and the molecular plane layer structures stacked along the b-axis. In the crystal of the complex, the guest molecules (p-phenylphenol) are included between the host (dodecyltrimethylammonium bromide) molecules to form many interactions with them. The arrangement of the host molecules along the c-axis is affected by the guest molecules. but the arrangement of them along the a- and b-axis are almost conserved through the inclusion of guest molecules.

Structures of Complex Crystals of Alkylammonium Salts with Aromatic Molecules

Abstract The complex crystal structures of dodecyltrimethylammonium chloride (DTAC) with catechol and hydroquinone were analysed by an X-ray diffraction method. Both complexes have isomorphous layered structures. The guest molecules locate between the interdigitated host molecules. Crystal structures are stabilized by mainly hydrogen bonds including water molecules. A cross-section balance between hydrophilic and hydrophobic parts is important for an energetically stable packing. DTAC can form the crystalline complexes with catechol and hydroquinone by both crystallizing from the solution and mixing host and guest powders in a mortar. In addition, DTAC can also make a complex with resorcinol. Powder diffraction pattern indicates that this complex has similar layered structure with complexes of DTAC / catechol and DTAC / hydroquinone. However, it is unstable in atmospheric condition.

Structural Studies of Cetyltrimethylammonium Chloride and its Complex with p-Phenylphenol

Abstract According to the temperature-composition phase diagram of Cetyltrimethylammonium chloride (CTAC) and p-phenylphenol (p-PP), which was obtained by DTA measurement of powder mixtures at various composition ratios, it was found that only one complex with a 1/1 molar ratio was available for the CTAC/p-PP system. The single crystal structure of this complex, together with the crystal structure of CTAC, was determined by the X-ray diffraction method. Both crystals have a smectic layer structure stacked along the c-axis. The CTAC (and p-PP) molecules are arranged almost perpendicular to the layer surface. Within the smectic layer of the host (CTAC) crystal, long alkyl chains from both sides of layer surfaces are interdigitated mutually, which makes a hydrophobic region in the middle of the layer. In complex (CTAC/p-PP) crystals, guest (p-PP) molecules were accommodated in the space formed by loosening their interdigitation. The arrangement of p-PP molecules found in the complex crystal is very similar t...

The molecular complexes of monoalkylammonium bromide salts with (R)-(+)-1,1'-bi-2-naphthol and rac-1,1'-bi-2-naphthol

Abstract The crystal structures of hexyltrimethylammonium bromide (6TAB) adduct of (R)-(+)-1,1′-bi-2-naphthol (RBNP) and decyltrimethylammonium bromide (10TAB) adduct of rac-1,1′-bi-2-naphthol (BNP) have been determined by the X-ray diffraction method. The molecules of the 6TAB/RBNP complex are held in their aggregates by O1…Br [3.228(4)Å], O2…Br [3.225(6)Å] intermolecular hydrogen bonds and C-H…π interactions between the alkyl chain, methyl groups and aromatic rings of the naphthol moieties. It was observed in the crystal structure of 10TAB adduct of BNP that the crystal structure formation was mainly stabilized by the intermolecular hydrogen bonds between the bromide anion and OH group of BNP (01…Brl [3.241(4)Å], O2…Br2 [3.172(3)Å]). In both complexes, the packing arrangement of the monoalkylammonium bromide salts with non-planar aromatic molecules are different from those observed in complexes of monoalkylammonium bromide salts with planar aromatic guest molecules. X-ray powder diffraction studies on both complexes showed that the crystals complex can be obtained by crystallization from solution and also by mixing powdered samples in a mortar. This study has shown that a non-chiral host amphiphile can form a complex with either a chiral or racemic aromatic guest compound.

Molecular and crystal structures of 2,3,4,6,1′,3′,4′,6′-octa-O-acetyl-β-sophorose, methyl 2,3,4,6,3′,4′,6′-hepta-O-acetyl-β-sophoroside, and methyl 2,3,4,6,3′,4′-hexa-O-acetyl-6′-deoxy-β-sophoroside

The molecular and crystal structures of 2,3,4,6,1′,3′,4′,6′-octa-O-acetyl-β-sophorose (β-sophorose octaacetate), methyl 2,3,4,6,3′,4′,6′-hepta-O-acetyl-β-sophoroside (methyl β-sophoroside heptaacetate), and methyl 2,3,4,6,3′,4′-hexa-O-acetyl-6′-deoxy-β-sophoroside (methyl 6′-deoxy-β-sophoroside heptaacetate) were determined by X-ray diffraction. All structures were obtained by the direct method and refined by the full-matrix least-squares procedure. The crystal data and final R values are as follows: (β-sophorose octaacetate, C28O19H38, monoclinic, P21, a = 15.529(4), b = 10.958(2), c = 10.804(2) A, β = 107.73(3)°, Dobsd = 1.285 g cm−3, Dcalcd = 1.288 g cm−3, Z = 2, R = 0.052, RW = 0.052; methyl β-sophoroside heptaacetate, C27O18H38, orthorhombic, P212121, a = 20.992(5), b = 27.642(7), c = 5.730(2) A, Dobsd = 1.305 g cm−3, Dcalcd = 1.295 g cm−3, Z = 4, R = 0.064, RW = 0.066; methyl 6′-deoxy-β-sophoroside hexaacetate, C25O16H36, hexagonal, P65, a = b = 15.136(2), c = 23.534(4) A, Dcalcd = 1.264 g cm−3, Z = 6, R = 0.079, RW = 0.064. All the d-glucose residues have the 4C1 pyranose conformation. These three molecules interact with their surrounding molecules by van der Waals forces, only. Conformational angles of φ and ω at the β (1 → 2) glycosidic linkage of these compounds are similar to each other and close to the energetically minimum positions. All the primary acetate substituents at C-6 take a gauche-gauche conformation.

Bilayered Super-Structures of Antiferroelectric Mesogens

Abstract Crystal structures of two antiferroelectric mesogens, TFMHPBC and MHPBC-10, were analysed by an X-ray diffraction method. In both crystals, mesogen molecules formed a herringbone structure which was essentially the same as that proposed for the antiferroelectric liquid crystal phase. Because of the crystallographic 21-symmetry along the b-axis, only the b-axis component of the dipole moment remains in a smectic layer. Since the dipole moment in the next layer has the same magnitude but the opposite direction, both crystals show no dipole moment as a whole. These structural features observed in their crystal states seem to be conserved in their antiferroelectric liquid crystal phases which are just above their crystal phases.