Cellulose conformational stability

The seemingly small difference in structure between starch and cellulose allows the linear chains of cellulose to pack together side-by-side in an antiparallel extended conformation, stabilized by hydrogen bonds, to produce an insoluble structure of high mechanical strength. 

Evidence for the involvement of salt links in the stabilization of bakers yeast jS-o-fructofuranosidase has been obtained from studies of immobilization of the enzyme on cellulose, derivatives of Sephadex and insolubilized con-canavalin A, and modification with citraconic anhydride, methyl acetimidate, or ethylene diamine. The general stability to such treatments was offered as the evidence, since modification of either amino- or carboxy-groups would result in loss of conformational stability, unless the stabilizing salt linkages were present. 

Naturally occurring cellulose is extremely mechanically stable and is highly resistant to chemical and enzymatic hydrolysis. These properties are due to the conformation of the molecules and their supramolecular organization. The unbranched pi 4 linkage results in linear chains that are stabilized by hydrogen bonds within the chain and between neighboring chains (1). Already during biosynthesis, 50-100 cellulose molecules associate to form an elementary fibril with a diameter of 4 nm. About 20 such elementary fibrils then form a microfibril (2), which is readily visible with the electron microscope. 

The chemical transformations that lead to the conversion of cellulose to mixed polysaccharides differing from cellulose in the conformation of the pyranose ring and the number and configuration of the hydroxyl groups of the repeating unit of the macromolecule, may exert a considerable effect on the structure of the material as well as on its important chemical properties (rate of acetylation and O-alkylation of OH groups, stability of the acetal linkage) and physicochemical indices (solubility of modified preparations of cellulose and cellulose ethers and esters). 

Application of this approach to cellulose has confirmed31 that the Hermans conformation is the only possibility that is free from strong steric clashes while fitting the usual interpretation of the x-ray evidence by having two fold screw symmetry and a projected residue height of 5.15 A. It is also stabilized by a hydrogen bond between successive residues, as in the crystal structures of cellobiose and... 

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