|French, Alfred - Al|
Submitted to: European Carbohydrate Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 8/29/2003
Publication Date: N/A
Technical Abstract: The molecular geometries from crystal structures of 23 small molecules such as cellobiose were extrapolated to give model cellulose chains. Within a given model, all monosaccharide units and their linkages are identical so the models are regular helices. Despite fairly large ranges for the glycosidic linkage torsion angles f and y, 29 and 58, respectively, there is little variation in the n and h parameters of the model helices. They are extended, with h values (the advance per residue along the helix axis) of 5.04-5.27A. Some models had slightly right-handed twists, with n values up to 2.12 residues per helix turn. Left-handed models were in the majority, and n values were as large as -2.91. These results are consistent with known structure of cellulose and its derivatives. An exception comes from a heavily derivatized cellobiose molecule. It yields right-handed helices with n 4.5 and h 3A. Because one half turn of that helix reverses the direction of the chain in a compact region, that linkage geometry is a model for chain-folding. Other derivatives that were unable to form the 03...05' hydrogen bond gave left-handed helices. The puckering of the glucose rings was also surveyed. A number of rings in small molecular structure are puckered to a degree that is similar to the puckering determined for methyl cellotrioside, cellotetraose, cellulose lb and cellulose ll.