Crystal structure cellulose

Stout has written a detailed review on jute and kenaf. X-ray diffraction patterns show the basic cellulose crystal structure, although in jute and kenaf the crystalline orientation is high and the degree of lateral order is lower than in flax. Batra" in a comprehensive review has highlighted the morphological structures and physical, mechanical and chemical properties of other long vegetable fibers. 

Like this, the decomposition of cellulose crystal structure initiated and finished at lower temperatures in C, grafted cellulose, and stannic chloride treated cellulose than those in M. 

Fig. 1. Transformation pathways between cellulose and Na-cellulose crystal structures. (Reproduced with permission from ref. 1. Copyright 1986 John Wiley Sons, Inc.)...

In the case of grinding, the cellulose fibers go over a state of fine fibrillation into a more or less powdery substance. This mechanical severance of cellulose may break main valence bonds and will, therefore, decrease its degree of polymerization. In addition, the crystal structure of cellulose fibers is nearly lost [32]. Grinding of the cellulose fibers also, appreciably increases its surface area. 

Crystal structure (type of cellulose and defects) Supramolecular structure (e.g., degree of crystallinity)... 

When Herman Mark first evaluated the crystal structure of rubber (with E. A. Hauser) and cellulose (with J. R. Katz) in 1924 and 1925, it was generally accepted that these materials were low molecular weight or monomeric. The unusual properties of these substances, now known to be related to high molecular weight, were then attributed to aggolomeration or "association" of the low molecular weight precursors. A common explanation for the associations were secondary forces such as Johannes Thiele s partial valences. 

Figure 9 shows a spectrum of the hydrolyzed membrane, and peaks appeared at 11, 20, and 22 degrees. The crystal structure changed to that of cellulose II type. 

How modeling has been useful in the crystal structure analysis of polysaccharides—and how it could lead to a better understanding of other condensed j)hase states—can be illustrated with structural worK done on cellulose. It is one of the world s most important and widely used raw materials whose structure, properties, derivatives, and transformations remain under continuous study. Some of the results, problems, and indications of future directions resulting from the study of its crystalline structure—and the attendant roles for molecular modeling—are briefly described in the following. 

Figure 2. Two projections of the ramie cellulose I crystal structure on a-b plane (topT on b-c plane (bottom). Hydrogen atoms are omitted hydrofifeu bonds, ar who warfe dashed lines.

As the above results show, the gross features of the cellulose I crystal structure predicted by various methods do not differ appreciably, but the accompanying deviations in the R -factors are significant. When these predictions are used to assess, for example, whether the cellulose I crystal structure is based on parallel- or antmarallel-chains, the range in the R"-factors seen for the parallel models (cf. Table II) is comparable to that between the two different polarity models. As shown in Fig. 5, the most probable parallel- and antiparallel-chain structures of cellulose I, refined by minimizing the function O, differ in R -factors by approximately the same extent as the three predictions for the parallel model shown in Fig. 4 and Table II. 

Figure 3. Isolated chain conformations of cellulose predicted by MM2(85) (left) and PS79 (middle). The conformation on the right is that of the crystal structure of cellulose I (3). Hydrogen bonds are shown by dashed lines.

Divne, C., Stahlberg, J., Teeri, T. and Jones, T. (1998) High-resolution crystal structures reveal how a cellulose chain is bound in the 50 Angstrom long tuimel of cellobiohydrolase I from Trichoderma reesei. J. Mol. Biol., 275, 309-325. 

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