Cellobiose angles

The torsion angles predicted by conformational analysis agree closely with those of crystalline cellobiose as measured by X-ray diffraction, the conformation of which is restricted by two chain-stabilising intramolecular hydrogen bonds between 0(3 )-H and 0(5) and also between 0(2 )-H and 0(6) (Figure 4.3). These are also found in cellulose and they assist in maintaining the highly extended conformation which allows it to function as a structural polymer. 

Figure 2. A contour diagram of the conformational energy of p-cellobiose computed from eqn. (6) holfing constant all variables except < ), v see ref. 5 for details. The rigid glucose residue geometry was taken from ref. 23, and the valence angle p at 04 was chosen as 116 in accordance with the results of pertinent crystal structure determinations. Contours are drawn at 2,4, 6, 8,10,25, and 50 kcal/mol above the absolute minimum located near ( ), v = -20 , -30 higher energy contours are omitted.

Figure 8. Trajectory of the < ) (top) and i (bottom) angles of cellobiose during 500 ps simulation, at 400 K. (MM2(85) functions).

Unlike maltose, cellobiose is a /3-glycoside. (The aglycone unit is turned 180° to permit a reasonable bond angle for the glycosidic linkage.)... 

All of the likely conformations of cellobiose, cellulose, and xylan are explored systematically assuming the ring conformations and IC-D-O-IC-4 ) angle for each pair of residues to be fixed and derivable from known crystal structures. The absolute van der Waals energies, but not the relative energies of different conformations, are sensitive to the choice of energy functions and atomic coordinates. The results lead to possible explanations of the known conformational stiffness of cellulose and Its solubility properties in alkali. The characteristics of xylan conformations are compared with cellulose. 

Cellobiose octaacetate and 1,6-Anhydro-p-cellobiose hexaacetate are compared with respect to their glycosidic conformation [93, 94], For cellobiose octaacetate it was concluded that the conformation in solution is close to that one determined by X-ray crystal structure analysis to cp = 45° and i / = 16° (Fig. 5) whereas the 1,6-anhydro derivative is demonstrated by use of NOEs, relaxation data, and coupling constants 3JC>H to adopt torsional angles of = 25° and ]c = 45° respectively. 

From the analysis of 13C NMR chemical shifts the / angle in chitobiose should exhibit a value of approximately 10° more positive than that of cellobiose and thus resulting in r = 0° [136],... 

The 2-D energy contour map illustrating the potential energy barriers to rotation around two dihedral angles, O and of cellobiose. (Adopted from Kajiwara and Miyamoto [34)... 

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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