Three-Dimensional Crystalline Structure of Cellulose Triacetate II

Two‐dimensional magic angle spinning NMR investigation of naturally occurring chitins: Precise 1H and 13C resonance assignment of α‐ and β‐chitin

“…This finding supported different hydrogen-bonding patterns associated with the hydroxyl group at the C6 site in ␣-and ␤-chitin and the prior hypothesis of hydrogen bonding at position 6 of ␣-chitin. 42 Although 2D NMR techniques used in this study have been principally developed for the structural analysis of 13 C-labeled compounds in the solid-state, 13 C- 13 C correlations of naturally occurring chitin specimens could be clearly obtained, given a sufficiently long experiment time. The usefulness of these techniques for collecting structural data on carbohydrate polymers would be significantly enhanced by using a much higher magnetic field.…”

“…In the case of ␣␥;-chitin, it is considered that structure of this allomorph crystallizes into a unit cell of the space group P2 1 2 1 2 1 , which involves two antiparallel chitin chains. 10 In the relationship between carbon backbone structures and 13 C-NMR spectra of chitin allomorphs, the structures of two kinds of cellulose triacetate (CTA) allomorphs, namely, CTA I and CTA II, proposed by diffraction analyses 41,42 are interesting since the structures of CTA I and CTA II are considered very close to the structures of ␤-and ␣-chitin, respectively. The model structure of CTA I is described with a one-chain unit cell and a P2 1 space group with the chain axis on one of the 2 1 screw axes of the cells, 41 while the unit cell of CTA II is considered to be orthorhombic with space group P2 1 2 1 2 1 .…”

“…The model structure of CTA I is described with a one-chain unit cell and a P2 1 space group with the chain axis on one of the 2 1 screw axes of the cells, 41 while the unit cell of CTA II is considered to be orthorhombic with space group P2 1 2 1 2 1 . 42 The structural model of CTA II is the antiparallel packing. This indicated that all 2,3,6-triacetyl-anhydroglucopyranose monomer units in CTA I are equivalent in conformation and that CTA II has at least an nonequivalent site in the unit cell of this allomorph.…”

Estimation of Miscibility and Interaction for Cellulose Acetate and Butyrate Blends with N‐Vinylpyrrolidone Copolymers

“…As is generally accepted, CA having a DS value of approximately 3, which is so-called cellulose triacetate (CTA), would be crystallizable from solution or melt in a stable CTA II form. [20,21] In accordance with the expectation, the CA (DS ¼ 2.95) sample exhibited an exothermic peak and an endothermic peak, ascribable to the cold-crystallization and the melting of the CTA crystal, respectively, after onset of a clear baseline gap reflecting the glass transition; a T g value of 173 8C was obtained from the midpoint of the baseline shift, and the coldcrystallization and melting temperatures were evaluated as 208 and 296 8C, respectively, from the peak-top positions of the exo-and endotherms. In DSC data of CA (DS ¼ 2.95) blends with PMMA, two T g s of both components and the cold-crystallization exotherm and melting endotherm of the CA component, were detected at every blend composition, with no applicable shift in their temperature locations, as demonstrated in Figure 1b.…”

The crystal and molecular structure of a trisaccharide, β-cellotriose undecaacetate: 1,2,3,6-tetra-O-acetyl-4-O-[2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-β-D-glucopyranosyl]-β-D-glucopyranose

“…Although the exact nature of the chain symmetry of the polymer has not yet been established, the observed fibre repeat is 10.54 (2) A (Roche & Chanzy, 1977). It is therefore very probable that the solid-state conformation of cellulose triacetate II will involve glycosidic torsion angles with values very Fig.…”