Order cellulosics

As indicated earlier, clear cellulose solutions are not necessarily molec-ularly dispersed they may contain aggregates of still ordered cellulose molecules [107]. The structure of these aggregates has been described in terms of a fringed micellar structure. Figure 2a shows a schematic possi-... 

With the discovery in the last few years that the Ci component is associated with exoglucanase activity (5-10), the debate has been resolved to some extent, at least to the satisfaction of some, but there are still many unanswered questions regarding the synergistic action between Ci and Cx in solubilizing highly ordered cellulose. It is hoped that the results presented in this chapter will go some way toward providing some of the answers at worst they will help to formulate the questions that need answering. 

On the basis of all this evidence, the possibility must be remote that Ci and cellobiohydrolase activities do not reside in the same protein. The separation of so many different components all with Ci/cellobiohydrolase activity must be good evidence that Ci can be identified with cellobiohydrolase. Clearly, there are good grounds for questioning the basic tenet of Reese s hypothesis, namely, that the function of Ci is to produce some disorder between the cellulose chains only the prediction that two components are required for hydrolysis of highly ordered cellulose is confirmed. 

Solid-state cellulose can also be noncrystalline, sometimes called amorphous. Intermediate situations are also likely to be important but not well characterized. One example, nematic ordered cellulose has been described [230]. In most treatments that produce amorphous cellulose, the whole fiber is severely degraded. For example, decrystallization can be effected by ball milling, which leaves the cellulose as a fine dust. In this case, some crystalline structure can be recreated by placing the sample in a humid environment. Another approach uses phosphoric acid, which can dissolve the cellulose. Precipitation by dilution with water results in a material with very little crystallinity. There is some chance that the chain may adopt a different shape (a collapsed, sixfold helix) after phosphoric acid treatment. This was concluded because the cellulose stains blue with iodine (see Figure 5.12), similar to the sixfold amylose helix in the starch-iodine complex. 

Consistent with the behavior of simple glycosides (Table 2), the homogeneous hydrolysis rate of B-(l-4)-linked polysaccharides, as BeMiller summarized [255, 256], increased in the order cellulose (1) < mannan (2-2.5) < xylan (60-80) < galactan (300). This further demonstrates the significant role of accessibility in acidic degradation reactions. 

By increasing the pretreatment temperature and the amount of the acid the content of chemically bound phosphorus increased for both celluloses. At 200 °C the less ordered cellulose Taircell binds practically all phosphorous (92.5 to 97.2%), For the more ordered microcrystalline Munktell cellulose the amount of chemically bound phosphorus was lower compared to Taircell and reached after thermal treatment at 200 C 81 % of the amount introduced. 

Three more recent models of the microfibril are shown in Figure 4 (47). According to the concept shown at a in Figure 4, the microfibril is about 50 X 100 A. in cross section and consists of a "crystalline core of highly ordered cellulose molecules arranged in a flat ribbon, rectangular in cross section. This crystalline core is surrounded by a "paracrystalline sheath that in cotton contains mainly cellulose molecules but in wood also contains hemicellulose and lignin molecules. The crystalline... 

The length of the cellulose molecules, especially its relation to the length of the elementary crystals or fused fibrillar aggregations. Recent studies favour the idea that the cellulosic material is dispersed in a matrix of non-cellulosic material. The ordered cellulosic fibres are organized in a pseudo-liquid crystalline form. This type of model is consistent with many physical properties of these materials (Figure 12.6b). 

Hiraishi, M., Igarashi, K., Kimura, S., Wada, M., Kitaoka, M., Samejima, M., 2009. Synthesis of highly ordered cellulose II in vitro using ceUodextrin phosphorylase. Carbohydrate Research 344, 2468—2473. 

The structure of cellulose is closely tied to its synthesis, and although many of the chapters discuss the synthesis of cellulose, the nature of the cellulose product is always kept in mind. A comprehensive account of the structure of cellulose and its polymorphism is provided by French and Johnson, and the structure and properties of a novel form of cellulose (nematic-ordered cellulose) is described by Kondo. Cellulose is the most abundant biomacromolecule in nature, and it is used in a variety of applications. In almost all cases, the applications of cellulose as an industrial material are dependent on its physical and chemical properties. Two chapters discuss novel applications of cellulose. Czaja et al. describe the use of microbial cellulose for applications in wound care and Kim discusses the usefulness of cellulose as a smart material, specifically the production of cellulose-based electroactive paper. 

Current data suggest that cellulose biosynthesis is a bacterial invention and that eukaryotes acquired the process via multiple lateral gene transfers. Bacteria and eukaryota have independently evolved regulatory mechanisms and molecular structures to utilize the p-1,4-homopolymer synthesized by the catalytic activity of homologous cellulose synthase enzymes. The differences in accessory enzymes probably reflect not only convergent evolution to produce a cellulose I crystalline allomorph, but also inventions of alternative products such as cellulose II, noncrystalline cellulose, or nematic ordered cellulose. 

Not all cellulose is crystalline. Less-ordered cellulose is more chemically reactive and has different physical properties. Therefore, it is necessary to understand both the crystalline and noncrystalline phases. Various treatments can be applied to destroy the crystallinity, but less-ordered cellulose also occurs naturally. For example, a given cellulose molecule will often pass through several crystallites, as in ramie (a bast fiber). In ramie, crystallites are long enough to accommodate approximately 300 glucose units (Nishiyama et al. 2003b), but the cellulose molecules in ramie are much longer than that. 

The authors developed a unique form of i-glucan association, nematic ordered cellulose (NOC) that is molecularly ordered, yet noncrystalline. NOC has unique characteristics in particular, its surface properties provide with a function of tracks or scaffolds for regulated movements and fiber production of Acetobacter xylinum (=Gluconacetobacter xylinus), which produces cellulose ribbon-like nanofibers with 40-60 nm in width and moves due to the inverse force of the secretion of the fibers (Kondo et al. 2002). This review attempts to reveal the exclusive superstructure-property relationship in order to extend the usage of this nematic-ordered cellulose film as a functional template. In addition, this describes the other carbohydrate polymers with a variety of hierarchical nematic-ordered states at various scales, the so-called nano/micro hierarchical structures, which would allow development of new functional-ordered scaffolds. 

STRUCTURE OF NEMATIC ORDERED CELLULOSE 2.1 What is nematic ordered cellulose NOC ... 

Figure 16-5. Atomic force micrographs showing the surface of the nematic ordered cellulose (NOC) template with a schematic representation...

Another type of nematic ordered cellulose honeycomb-patterned cellulose... 

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