Rigid cellobiose

Figure 8. The mean directional correlation F(x) of virtual bond x with the initial virtual bond in the chain.25 Closed circles correspond to a calculation based on the "rigid" cellobiose map of Fig. 2 open circles refer to the relaxed cellobiose surface of Fig. 6.

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 9. Same as Fig. 7 except based on the rigid p-cellobiose map of Fig. 2. 

French has recently presented comparisons of rigid and relaxed conformational maps for cellobiose and maltose obtained with the MMP2(1985), which includes ano-meric effects. The fully relaxed maps show interesting details. 

Figure 5. a) The starting model of cellobiose (gtgtRR) after rigid rotation to -80, 0 -100. b) The result of attenpted optimization by MM2, c) The same linkage conformation, but the structure was taken from the study that produced the map in Figure 4. 

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. 

Cellulose is composed of D-glucose units linked by j8-l,4 glycosidic bonds. This bonding arrangement (like that in cellobiose) is rather rigid and very stable, giving cellulose desirable properties for a structural material. Figure 23-17 shows a partial structure of cellulose. 

Cellobiose phenylosazone when treated by Diels method yielded a monoanhydride in the form of a hydrate. The same product was also obtained from cellobiose phenylosazone heptaacetate by deacetylation. The anhydride gave a pentaacetate proving that an oxide ring system was present, and structure XXXIII was proposed although the possibility of 1,3-anhydro- (1,5-oxide), 1,3-anhydro- (2,6-oxide) and 1,3-anhydro- (2,5-oxide) structures could not be rigidly excluded. 

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