Ramie cellulose packing

Using the two-chain unit-cell,3 with a = 0.817 nm, b = 0.785 nm, c = 1.034 nm, andy = 96.38°, the modified intensity-data of Mann and coworkers,37 and several residue-geometries, the structure of native ramie cellulose was refined. The resulting R factors were 15.8%, 18.5%, and 17.5% for, the antiparallel, parallel-up, and parallel-down models, respectively. A temperature factor of 0.23 nm2 was necessary in order to obtain a good fit with the observed data. It was suggested that the antiparallel packing of the chains cannot be discounted for cotton and ramie celluloses. 

Woodcock C, Sarko A (1980) Packing analysis of carbohydrates and polysaccharides, II. Molecular and crystal structure of native ramie cellulose. Macromolecules 13 1183-1187... 

Fractionation of the cellulose from the alga Valonia afforded a component of weight-average DP 4.4 x 10, which is thought to determine the size of the template required for the simthesis of the polysaccharide. The synthesis of cellulose molecules takes place on a flat template and leads directly to a folded-chain structure. Cellulose I crystallizes after it becomes detached from the site of synthesis. The crystal structure of native Ramie cellulose has been shown to be similar to that recently reported for Valonia cellulose. The R values, 0.158, 0.185, and 0.175, were obtained for anti-parallel, parallel-up, and parallel-down alignments respectively. Anti-parallel chain packing must still continue to receive consideration for cotton and Ramie cellulose despite contrary reports. 

Other workers (19-20) have interpreted these differences in the NMR spectra and other data in alternative ways. They believe that celluloses I and II have the same skeletal conformation but are packed in different lattices. In this theory, the differences within the cellulose I family are derived from the size of the unit cells. Valonia contains a larger 8 chain unit cell, whereas ramie contains a mixture of the 8 chain unit cell and the smaller Meyer and Misch unit cell. Therefore the interpretation of the NMR spectra remains controversial. 

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