The Hydrogen Bonding in Polysaccharide Fiber Structures Is Poorly Defined

7 The Hydrogen Bonding in Polysaccharide Fiber Structures Is Poorly Defined 

The most advanced interpretative methods combine a least-squares fitting to the experimental structure amplitudes with energy minimization calculations by means of molecular mechanics. Since the limited amount of observations places severe constraints on the number of parameters that can be varied, it is common practice to use standard geometries for the monomer units [508], at least until the final stages of the refinement calculations. 

In order to discuss the hydrogen bonding in polysaccharide crystal structures, two interrelated problems have to be resolved. One is to determine the intrachain hydrogen bonding, which may be inter- or intramonomer residue. This bonding must be consistent with fitting the polymer repeat unit to the length of the fiber axis, which is usually a well-defined quantity. When the fiber axis coincides with the axis of the polymer, the conformation of the polymer repeat unit must fit the symmetry of the fiber axis. 

The favored polymer chain model for cellulose I places the crystallographic 2X axis through the polymer chain (Fig. 13.60). This permits the formation of two in- 

The cellulose II structure is more complex to unravel, since it involves two symmetry-independent chains. Polymer chain structures have been proposed that involve six different intrachain hydrogen-bond arrangements [344]  

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