Structural features of cellulosic

Cowling, E. B., and Brown, W. (1969). Structural features of cellulosic materials in relation to enzymatic hydrolysis. Adv. Chem. Ser. 95,152-187. 

Structural Features of Cellulosic Materials in Relation to Enzymatic Hydrolysis... 

Structural features of cellulosic materials that determine their susceptibility to enzymatic degradation include (1) the moisture content of the fiber (2) the size and diffusibility of the enzyme molecules involved in relation to the size and surface properties of the gross capillaries, and the spaces between microfibrils and the cellulose molecules in the amorphous regions (3) the degree of crystallinity of the cellulose (4) its unit-cell dimensions (5) the conformation and steric rigidity of the anhydroglucose units (6) the degree of polymerization of the cellulose ... 

The authors are indebted to the many eolleagues who have, over the years, contributed to the advaneement of toe seienee of eellulose. They express their most sincere thanks to colleagues at CERMAV who have shared their results. Dr. Henri Chanzy deserves special mention for his enlightening dedication to unraveling the structural features of cellulose, and his willingness to provide illustrations and materials. The authors dedicate tois chapter to the memory of Dr. Jean-Frau9ois Revol for his significant contributions to toe field. 

Fan L, Lee YH, Beardmore DH. (1980). Mechanism of the enzymatic hydrolysis of cellulose effects of major structural features of cellulose on enzymatic hydrolysis. Biotechnol Bioeng, 22, 177-199. 

The structural features of cellulose microfibrils in these pelagic tunicates are quite similar to that of ascidians. This evidence indicates that the cellulose-synthesizing ability is an inherited character common to ascidians and thaliaceans. It is also reported that the basic structures of the tunic and the epidermis of ascidians and thaliaceans are almost the same (Hirose et al. 1999). The timic cellulose in the thaliaceans may be synthesized by TCs on the plasma membrane of epidermal cells similar to the ascidians. 

Within the medicinal field, bacterial cellulose alone was shown to be a versatile material for the construction of artificial blood vessels, an application which clearly benefits from the structural features of cellulose in combination with its chemical stability under physiological conditions [52], Other applications use cellulose for the production of implantable capsules [53], and even sensors [54], Another interesting biomedical application is the use of cellulose in films supporting wound healing, due to the hydrating characteristics of these cellulose-containing films [55], Besides, cellulose and cellulose derivatives are used as haemostatic agents [56], The latter two fields of application for cellulose have just recently been reviewed in the cited literatiu-e, and are thus not discussed in detail here. 

The rate of enzymatic hydrolysis depends on the structural features of cellulose, as well as on the composition of the cellulolytic complex. Sttuctural features such as crystalhnity and accessible surface area determine the... 

At first glance, the HRC scheme appears simple the polymer is activated, dissolved, and then submitted to derivatization. hi a few cases, polymer activation and dissolution is achieved in a single step. This simplicity, however, is deceptive as can be deduced from the following experimental observations In many cases, provided that the ratio of derivatizing agent/AGU employed is stoichiometric, the targeted DS is not achieved the reaction conditions required (especially reaction temperature and time) depend on the structural characteristics of cellulose, especially its DP, purity (in terms of a-cellulose content), and Ic. Therefore, it is relevant to discuss the above-mentioned steps separately in order to understand their relative importance to ester formation, as well as the reasons for dependence of reaction conditions on cellulose structural features. 

Acylation reactions of dextran in combination with NMR spectroscopy are tools for the elucidation of the reactivity of dextran [30,161,167] and for the analysis of structural features of the polymers. The acetyl group distribution in the Glcp units in acetylated amylose, dextran and cellulose was studied by XH and 13 C NMR spectroscopy. It was concluded that the reactivity of OH groups decreased in the order C2 > C3 > C4 for dextran. 

D-Glucose is the most common of the monosaccharides, occurring in the free state in the blood of animals and in the polymerized state, inter alia, as starch and cellulose. Tens of millions of tons of these polysaccharides are made by plants and photosynthetic microbes annually. A detailed study of the structure of glucose is justified on these grounds, and many of the structural features of all monosaccharides can be illustrated using glucose as an example. 

To study the structural features of preparations mixed polysaccharides, we investigated the process of sorptiewi of water vapor on a vacuum sorption setup of the McBain type (Fig. 2). The data show that preparations of mixed polysaccharides sorb a larger amount of moisture than cellulose, even in the case of mixed polysacdiaride (IV) where the number of hydroxyl groups decreases as a result (rf the forma-... 

The cellulase complex diffuses through the pore system to the microfibrils, attacks the cellulose chains and hydrolyses each chain to the end. The diflerences in the efficacy of cellulases on various fibres are dependent on number of factors such as the amounts of non-cellulosic wood pulp-derived matter, the degree ol polymerisation, the type and degree of crystallinity, and the type and number of chemical substitutions to the cellulose [27-30]. Key features for the cellulose substrate are crystallinity, accessible surface area and pore dimensions [31 ]. Variation of any of these factors, e.g., structural changes of cellulose substrate by pre-treatments, will influence the course of the entire degradation process [32, 33]. 

An important feature of cellulose is its crystalline structure [180], which shows highly ordered crystalline domains interspersed by amorphous regions [177]. The high-crystallinity of cellulose fibrils renders the internal surface of the biopolymer inaccessible to hydrolyzing enzymes, as well as water. 

That such features of cellulose as the crystal lattice form are significant determinants of cellulase action has only recently been established (19), although a great deal remains to be learned about the enzymatic importance of cellulose fine structure. It is clearly established, however, that each of the three water-stable crystal forms of cellulose is distinct in the rate at which it is hydrolyzed and in its properties as an inducer of cellulase. For example the Trichoderma viride cellulase from culture extracts exhibits a lower activation energy in attacking the crystal lattice form used in culture growth, than in attacking the other lattice forms (Table I). 

Another example of modeling the structure of this type of CSP is presented by Francotte and Wolf [47]. They prepared benzoylcellulose beads, in a pure polymeric form as a sorbent, for the chromatographic resolution of racemic compounds like benzylic alcohols and acetates of aliphatic alcohols and diols. Their experimental results implicated multiple interaction sites to be involved in the complexation. Rationalizing the interaction mechanism required a more systematic investigation of the factors influencing separations and, to address the structural features of the cellulose tribenzoate, they carried out molecular modeling with molecular mechanics. The key question being addressed is to what extent is the polysaccharide backbone exposed to small molecules when sterically encumbered benzoates are attached ... 

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