Monomeric geometry

However, representing allowed shapes on a t-Y grid has fundamental limits. These limits arise when one converts from the linking conformation, expressed in terms of and Y, to the polymer conformation, described by the values of ji and h. The limits result because calculation of n and values depends on the exact monomeric geometry and linking bond angle used for the stereochemical calculations. 

Figure 3. Stereochemically allowed zones, drawing adapted from Ref. 10. These zones vary somewhat, depending on the chosen monomeric geometry as well as...

Figure 4. Combination of stereochemically allowed zones (Figure 3) and contours of iso-n and iso-h values. Adapted from Ref. 11. The positions of the contour lines vary substantially with different monomeric geometries.

Each n- h point could be examined for feasibility by a variety of methods. Although we discuss below several techniques for these examinations, our primary point is not an evaluation of these various methods. Our main point is that the ranges of polymeric shape must be reported only after a thorough test of the important variables monomeric geometry and linking bond angle. 

We have developed a new representation of conformational space and a computer program to prepare it U). This representation, the n-h map, allows many combinations of monomeric geometry and glycosidic linkage angle to be considered. A bonus in our method is that representations for the various polymers are quite different, whereas the Phi-Psi maps (without the iso-n and iso-h contours) are all very similar (3 ). Some polymers are characterized by n-b maps that have large, continuous allowed areas, while others have small or multiple, disconnected areas. 

Monomeric Geometry. Previous work (21) showed that the overall conclusions are not substantially affected by small differences In coordinates for the glucose ring used in the Starting model. We have reexamined this point since the WS and RMF data sets have become available for ramie cellulose, along with the WS monomeric geometry that was internally adjusted to best agree with the WS diffraction and stereochemical analysis of ramie. 

Comparison of Che Effect of Different Monomeric Geometries in Rigid Models... 

Figure 4. R factors (Rtot, R , and R"wt) for 100 Increments of shifts of the center chain along the z axis (RMF data, parallel up model, WS monomeric geometry). R"wt, preferred by statisticians, provides little Indication of the best value of the shift.

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