Author
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French, Alfred - Al |
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Johnson, Glenn |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 11/9/2007 Publication Date: 4/5/2008 Citation: French, A.D., Johnson, G.P. 2008. Stability of two-fold screw axis structures for cellulose. Meeting Abstract.CARB 42. Interpretive Summary: Technical Abstract: Diffraction crystallography indicates that most forms of crystalline cellulose have two-fold screw axis symmetry. Even if exact symmetry is absent, the degree of pseudo symmetry is very high. On the other hand, this symmetry leads to short contacts between H4 and H1' across the glycosidic linkage. Therefore, modeling studies of cellobiose often show high energies for two-fold structures, and model cellulose crystallites have an overall twist as well as twisted individual chains. In the present work, we used B3LYP/6-31+G* modeling and surveys of crystal structures of small molecules. The starting cellobiose models had their primary and secondary hydroxyl groups in numerous orientations and the linkage torsion angles set so that they were distant in two directions from the two-fold symmetry line. A significant number, with varied energy, minimized to have strong two-fold symmetry. Similarly, a number of molecules in experimental crystal structures have pseudo symmetry. While all of the cellobiose models with two-fold symmetry retained an inter-residue hydrogen bond, an exception was found in the experimental studies. A two-fold structures was also found despite configurational differences in a mannose disaccharide. Thus, two-fold screw structures have little intrinsic strain. |
