Cellulose glycosidic torsion angles

FIGURE 7-19 Conformation at the glycosidic bonds of cellulose, amylose, and dextran. The polymers are depicted as rigid pyranose rings joined by glycosidic bonds, with free rotation about these bonds. Note that in dextran there is also free rotation about the bond between C-5 and C-6 (torsion angle [Pg.251]

Our recent CP/MAS 3c NMR work(l, 2) on native and regenerated celluloses has shown that the resonance lines can be analyzed in terms of the contribution from the crystalline and noncrystalline components. The chemical shifts of Cl, C4, and C6 carbons thus ascribed to the respective components could be correlated to the torsion angles i(> and Tp, which define the conformation about the 3-1,4-glycosidic linkage, and x about the exo-cyclic C5-C6 bond,... 

The second topic reviewed is a quantitative analysis of DD MAS NMR spectra of native celluloses. The resonant lines of Cl, C4 and C6 carbon species for these samples are deconvolved into the crystalline and non-crystalline components using the difference in the spin-lattice relaxation time between both components. The chemical shifts of these lines are determined separately for the both components of samples, and correlated to the torsion angles (f and ip about -1,4-glycosidic linkage and x> about the exocyclic C5-C6 bond, respectively. On the basis of these results, the characteristic chain conformations of the crystalline and non-crystalline components of native and regenerative cellulose are discussed. 

Next, we have examined the relationship between the chemical shifts and the molecular chain conformation. The versatility of chain conformation of cellulose molecules is expressed in three torsion angles as shown in Fig. 14 (j> and xp, rotations around the /3-l,4-glycosidic linkages and the rotation of methylol side groups around the C5-C6 bonds. In order to find out the relationship between the chemical shifts of cellulose samples and the torsion angles, the... 

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