Cellotetraose

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. 

Carbon, ring oxygen replacement by, 141-143 2-Carboxy-5-(2-hydroxymethyl)-4-methylthiazole, synthesis and transformations, 284-286 Carrageenans, 366-368,418-419 Cellotetraose hemihydrate, 331 Cellulose, 326, 329-332 alternate unit cells, 329-330 derivatives, 332... 

It now appears that cellulose I is not exclusively the native polymorph present in all organisms. The results reported originally by Sisson (61), which provided evidence that cellulose II was the native polymorph present in Halicystis (Ulvophyceae) cell walls, were recently reinvestigated and confirmed (62). Additionally, cellulose II producing mutants of Aceiobacier have been isolated and analyzed with x-ray and low-dose electron diffraction (63). When cellotetraose is induced to crystallize in solution it forms a structure which has been used as a model compound approximating the crystallographic nature of cellulose II based on x-ray diffraction, electron diffraction and CP-MAS 13C NMR evidence (64). Significantly, in all cases where Aceiobacier cellulose synthase in vitro activity has been reported,... 

Figure 13. Taper chromatogram of the hydrolysis products from cello-oligosaccharides by Ex-1. Developed by the descending technique for 72 hr at room temperature on Whatman No. 1 paper, using 1-butanol pyridine water (6 4 3, v/v) as a solvent (S) standard, (Gt) glucose, (Ge) cellobiose, (Gs) cellotriose, (Gu) cellotetraose, (G5) cellopentaose, (G6) cellohexaose final enzyme concentration 3.0 X 10 2%.

The mechanism of thermal endwise peeling of cellotetraose can be summarized as in Eq. 5, with the Eqs. 1-4 describing the consecutive, stepwise character of furan formation ... 

A final conformation of the computationally predicted mechanism was provided by the use of isotopically labeled material. N,N-Dimethylaceto-acetamide-2-13C was used to produce a snapshot of the reaction intermediates present during reaction with cellotetraose as a model compound, taken by 13C NMR. A series of consecutive spectra produced a kinetic record how the positions with isotopic enrichment were distributed among different intermediates. From the prominent resonance in the starting material, the... 

Hydrolysis of 1,4-linkages in 1,4-/3-D-glucans, to remove successive glucose units Hydrolysis of l,4-/3-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the nonreducing ends of the chains... 

Longer cellulose oligomers have been modeled with MD as well. Two studies have attempted to discuss the molecular shapes in aqueous solution as well as the solvent llo-dextrin and cellodextrin llodextrin interactions [191,192]. The first of these studies showed that chains were heavily solvated and not fully extended or in contact with other cellulose fragments. The simulation was proposed as a model for freshly prepared cellophane. The latter study was more in agreement regarding chain shapes with the results in Figure 5.16. In addition, that work showed, unlike the simulated cellotetraose molecules in the same study. 

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]. 

None of the six enzymes cleaved cellobiose, but in comparing the products released from swollen Avicel by hydrocellulase C with those from cellulodextrin by the Cellulases, further evidence of contamination of cellulases II and III was found. For the latter cases both glucose and cellobiose are produced whereas both hydrocellulase C and Cellulase IV yield predominantly cellobiose. Cellulase IV produced much more cellobiose than glucose from cellotetraose whereas the other Cellulases yielded only slightly more cellobiose than glucose. 

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