Dimer cellobiose

Cellulose is the 1,4-p-D anomer of starch. It has a repeating cellobiose dimer that exists in vivo as closely packed 2-30-nm-long microfibrils embedded in a noncellulose matrix. The microfibrils are thoroughly hydrated in succulent fruits and vegetables in which moisture can be as high as 95%. 

Our initial, small models of an isolated cellulose chain ranged from the dimer (cellobiose) to the octamer. The dynamics of these fragments have thus far been simulated only in vacuum, using different potential energy functions such as those of MM2(85) (9) and AMBER (10), with and without contributions from electrostatic terms and hydrogen bonds, etc. (The program DISCOVER, customized for carbohydrates and for operation on the Alliant FX/80 computer, has been used (12).) Generally, the time span for the simulations has been of the order of several hundred picoseconds to 1 nanosecond. 

Cellobiose, a dimer of /3-1,4-linked glucose, is reported to be a cellulase inducer in T. reesei as well as in several other fungi (20,28,33, 34). But whether cellobiose is a true inducer is questionable since Reese et al. (35) reported that cellobiose could induce as well as inhibit cellulase biosynthesis. The same is also true for glucose. Whether glucose or cellobiose is an inducer or inhibitor depends on the concentration of sugars in the environment. 

Cellulose is a strictly nonbranched p(1 4)-linked glu-can formed by the repeating dimer cellobiose (Fig. 7A). It forms microfibrils with a length of lOO-xO 000 nm and a diameter between 2 and 20 nm. Cellulose fibers contain highly ordered (crystalline) and minor regular (amorphous) domains and, hence, form stiff construction material with limited flexibility. 

In terms of the carbon source, glucose is a catabolite repressor, but many oligomers and polymers of glucose induce enzyme production. Lactose, cellobiose, and sophorose are all dimeric sugars that induce cellulase production. Cellulose is also an inducer. A list of the performance of several carbon sources is found in Table 5 [37]. 

Cellulose itself is a polymer built from glucose, although the repeat unit is generally taken as the dimer, cellobiose (l,4- 3-D-glucopyranosyl-D-glucose see Figure 3). 

The only other enzymes which could yield glucose from dimer and tetramer are the phosphorylases (cellobiose phosphorylase, etc.). 

Fig. 4 (a) Normalized force curves of NC obtained in octane, (b) Comparison of a force curve of NC obtained in octane and the QM-FJC fitting curve, (c) Comparison of force curves of PAAm and NC obtained in octane, (d) Molecular structure of the dimer (cellobiose) used in QM calculations and the QM results. The arrows indicate the atoms defining the constrained distance. Figure reproduced with permission from [42]... 

Table 6.3 lists the results of the one-pot synthesis of HMF from three disaccharides. Sucrose consists of glucose and fructose cellobiose is a glucose dimer linked... 

Many polymers have a natural origin (mineral, vegetal or animal). Some of these have been used for centuries. In the vegetal kingdom, cellulose is the most abundant macromolecule. Cellulose is a polysaccharide composed of repeating units of cellobiose, i.e. it is a dimer of glucose. 

Among many of these natural fibers, eellulose and its derivatives have attracted a lot of attention due to their high flexibility and elasticity properties, which enable them to uphold their high aspect ratio (Prone et al., 2011). Cellulose was first discovered and named by a French Chemist called Anselme Payen in 1838, when he snggested that the cell walls of almost all plants are made of similar material. In 1921, Haworth discovered the dimer of cellnlose known as cellobiose. Five years later (1926), Sponsler and Dore became the first gronp to propose its molecular structure (Kontturi, 2005). 

Chemicai Structure. The raw cotton fiber produced in the bolls of the cotton plant is composed almost entirely of the polysaccharide cellulose (see Cellulose). Evidence from degradation of cellulose by hydrolysis, oxidation, and other chemical reactions shows that it is a 1 4 linked linear polymer of j8-D-glucopyranose (Fig. 6). If degradation is extensive, cellobiose (the dimer) or glucose is produced. 

---