Cellulose cellotetraose similarity

According to a recent report, the unit cell of cellotetraose hemihydrate in single crystals contains two antiparallel chains, which are conformationally distinct—especially in the sugar geometries.74 However, all hydroxymethyl groups adopt similar gt orientations. Whether this oligosaccharide morphology can be implemented for cellulose II in fibers remains to be seen. 

The cellulose oligomers, beginning with methyl cellotrioside, yield powder diffraction patterns that are very similar to those of cellulose II. The NMR studies of the cellulose oligomers further establish the extensive analogy between cellotetraose and cellulose II. Work by both Gessler et al. [222] and Raymond et al. [223] has shown that the 06 atoms in cellotetraose and methyl cellotrioside [224] all take the gt position, consistent with the diffraction and NMR results for cellulose II. Because the chains in the methyl cellotrioside and cellotetraose are antiparallel, this work adds support to the above results on cellulose II. On the other hand, molecules in crystalline a-lactose, a related disaccharide, have parallel packing [225]. 

Characteristics of macromolecules are often preserved In oligomeric model compounds. As one example, X-ray powder diffraction patterns (1) and the infrared spectra (2) of the oellodextrins beginning with cellotetraose are very similar to those of cellulose II. Such a similarity implies a close relationship in their molecular structures. While these model compounds should permit more accurate characterization because of their macroscopic, single-crystal domains (3), oellodextrins form non-centrosymmetric crystals and analysis of their diffraction data is a serious challenge. 

Very short cellulose chains, such as cellotetraose (Gessler et al. 1995), with four glucose residues, and methyl cellotrioside (Raymond et al. 1995), with just three glucose residues and a terminal methyl group on 01, have been crystallized and their structures determined. Based on their powder diffraction patterns, which are sharper but otherwise nearly identical to those of cellulose II, their structures (see Figure 15-4) should be similar to cellulose II. This is another observation that supports antiparallel cellulose II, as the short chains in these structures are also antiparallel. 

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