Cellobiose units

A monoclinic unit-cell with a = 8.2 A (820 pm), b(fiber axis) = 10.30 A (1.030 nm), c — 7.90 A (790 pm), and /3 = 83.3° is used. The distance between the terminal oxygen atoms in the cellobiose unit is taken to be 10.3912 A (1.03912 nm). A left-handed, helical structure, with seven cellobiose residues in a pitch of 72.1 A (7.21 nm) was proposed. The packing arrangement involves the central reversed and comer chains, and a relative shift between them of 0.25 repeat length along the b axis. 

Cellobiohydrolase I (CBH I, 1,4-jS-D-glucan-cellobiohydrolase, E.C. 3.2.1.91) is the main protein (ca. 60%) of the cellulase complex produced by T. reesei strains. CBH I hydrolyses crystalline cellulose, acid swollen cellulose and 4-methylumbelliferyl-cellodex-trins by cleaving off the terminal cellobiose unit from the non reducing end of the chain. It operates with retention of configuration in the reaction products 19,20. The abundance of this enzyme and its stability has facihtated its purification to homogeneity... 

TGA analysis shows that polymer degradation starts at about 235°C which corresponds to the temperature of decomposition of the cellobiose monomer (m.p. 239°C with decom.). Torsion Braid analysis and differential scanning calorimetry measurements show that this polymer is very rigid and does not exhibit any transition in the range of -100 to +250 C, e.g. the polymer decomposition occurs below any transition temperature. This result is expected since both of the monomers, cellobiose and MDI, have rigid molecules and because cellobiose units of the polymer form intermolecular hydrogen bondings. Cellobiose polyurethanes based on aliphatic diisocyanates, e.g. HMDI, are expected to be more flexible. 

The considerations involving comparisons of the structures of cellobiose and / -methylcellobioside with the structures of mercerized and native cellulose, respectively, when taken together with the additional observation that the basic repeat unit derived from the diffractometric studies is 10.3 A rather than 5.15 A, require that data relating to the structure of cellulose be reexamined with the constraint that the anhydro-cellobiose unit, rather than the anhydroglucose unit, is the basic repeat unit. To the author s knowledge, no efforts have been made to interpret... 

The primary structure of the extracellular polysaccharide from X. aampestris was recently reinvestigated by Jansson et al. (2), and by Melton et al. (8). The chemical repeat unit is a pentasaccharide. The backbone is a 8-1,4 glucan like cellulose and chitin (9,10) with a trisaccharide side-chain on each cellobiose unit (I). 

The enzyme preparations were provided by Novo Nordisk. Cellulase (Celluclast) possessed 115 filter paper units (FPU)/mL P-glucosidase (Novozym 188) had 570 cellobiose units (CBU)/mL. 

It may be concluded that the low field envelope in the C4 carbon peak can be assigned to cellobiose units having fewer intramolecular hydrogen bonds (i.e., the region around such cellobiose units in cellulose molecules has a very disordered conformation). We cannot simply conclude that in the absence of any intramolecular hydrogen bonds, the peak would narrow significantly, since cellobiose units in cellulose molecules in the solid state can take on a large number of conformations. 

The hydrogen bonding in cellobiose and methyl cellobioside as models for that in the celluloses. In the absence of crystal structure analyses of higher oligomers of 1 - 4-linked /5-glucopyranose, cellobiose is frequently used as a model for interpreting the X-ray fiber diffraction patterns of the celluloses, especially since the cellobiose unit is considered to be the repeating unit of the polysaccharide chain. 

Karl-Erik Eriksson (42) reported that he had prepared an enzyme from Chrysosporium lignorum which, when combined with each of three CM-cellulase enzymes, increased the hydrolysis rate of cotton tenfold. When he incubated this enzyme, which he believed to be of the Ci type, with cellohexaose and observed cellobiose as the only product, he concluded that it was an exo-glucanase which split off cellobiose units. Later (27) Eriksson and Rzedowski reported that the three CM-cellulase enzymes from C. lignorum contained 13, 10, and 7% carbohydrate and catalyzed the hydrolysis of cotton and cellodextrins to produce cellobiose and glucose in the approximate ratio of 3 1. 

The PL method has been used to investigate the IMM of the maaomolecules of carboxymethylcellulose (CMC) Anthrylacyloxymethane luminescent groups were used as LM. It was found that the presence of the cellobiose units in the main chain or the formation of intramolecular hydrogen bonds leads to a marked decrease in IMM. The value of r for CMC in water is 57 ns. As Tables 11,12 show, these high values of t are characteristic of the IMM of macromolecules with the elements of the internal structure such as polyfmethacrylic acid) (PM AA) in water. For non-ionized PMAA in water, is ca. 77 ns for LM in the side chain 9-anthrylmethyl-oxycarbonyl groups). 

In the crystalline part, the cellobiose units are closely packed to form Cellulose I in native cellulose fibres and Cellulose II in regenerated cellulose fibres. In Cellulose I the chain molecules are parallel to one another [16]. The folded chain occurs at Cellulose II, in the crystalline regions the chain molecules are antiparallel. Thus, the basis for helical structure for Cellulose I is preferably extended to the structure of Cellulose II [17]. 

Cellulose is the main constituents of flax fibre (Fig. 1-14). The unretted flax contains about 16.7% hemicellulose, 1.8% pectins, 2% lignin and 1.5% fats and waxes. The polymer of flax consists with a degree of polymerisation of about 18000 cellobiose units. Flax is an assembly of ultimates cemented together within the fibres and an assembly of these fibres into bundles. These assemblies are prone... 

Polymer Approx, no. of cellobiose units Approx. Approx, polymer polymer length (mm) thickness (nm) Approx, degree of polymesisation... 

When cellulose is treated with a mixture of nitric and sulphuric acids, nitrates of cellulose are formed, the composition of which depends upon the conditions of the reaction. Thus with two molecules of nitric acid for each cellobiose unit a dinitrate is obtained in accordance with the following... 

For several years a mechanism involving simultaneous transfer of two glucose residues (I. M Saxena, R. M. Brown, M. Fevre, R. A. Geremia and B. Henrissat, J. Bacterial. 1995, 177, 1419) to form a cellobiose unit was favoured, but can now be discounted because of the absence of more than one nucleotide sugar binding domain in cellulose synthases. 

GH 7. The active site tunnel of the CBH 1 of T. reesei is 50 A long, and can accommodate ten monosaccharide residues, in accord with the proc-essivity of the enzyme (it releases around 44 cellobiose units per encounter with... 

C. Cellulose Cellulose is a polymerized polysaccharide characterized by the cellobiose unit. The presence of free OH groups in cellulose permits hydrogen bonding with low-molecular-weight liquids such as alcohols or water. Cellulose is useful for the separation of hydrophilic substances primarily by the mechanism of normal-phase partition chromatography. For a discussion of separation mechanisms and the cellulose-water complex , see Ref. 176. 

Figure 1.44 Allowed values cp and ip angles for 0-glycosidic link of cellobiose (a) or maltose (b). In (a) black squares or circles indicate positions of observed conformational angles in cellobiose or cellobiose units found in larger polysaccharide systems. In (b) black triangle or circles indicate position of observed conformational angles in maltose or maltose units found in a larger polysaccharide systems (adapted from Rees Smith, 1995, Figs. 7 5).

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