Ramie cellulose crystal structure

Figure 2. Two projections of the ramie cellulose I crystal structure on a-b plane (topT on b-c plane (bottom). Hydrogen atoms are omitted hydrofifeu bonds, ar who warfe dashed lines.

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

Nishiyama Y, Sugiyama 1, Chanzy H and Langan P (2003) Crystal structure and hydrogenbonding system in cellulose la from synchrotron x-ray and neutron fiber diffraction. Journal of the American Chemical Society, 125(47) 14300-6 Nishiyama Y, Kim U-1, Kim D-Y, Katsumata KS, May RP and Langan P (2003) Periodic disorder along ramie cellulose microfibrils. Biomacromolecules, 4 1013-7 NIST (1995) Voluntary product standard PS 1-95. Construction and industrial plywood. US Department of Commerce, National Institute of Standards and Technology, Gaithersburg, Maryland... 

Cellulose, which Is one of the most abundant organic substances found In nature, has been extensively studied by various techniques such as x-ray scattering, electron microscopy, IR and Raman spectroscopy, NMR spectroscopy etc. However, the crystal structure and noncrystalline state are not yet solved for cotton, ramie, bacterial and valonla celluloses which can be easily obtained in pure form. Cross-polarization/magic angle spinning(CP/MAS) C NMR spectroscopy is a promising new method to study these unsolved problems of cellulose, because this method is very sensitive to local molecular conformations and dynamics. 

The crystalline component of ramie and cotton differs In chemical shift and line splittings from that of valonia and bacterial cellulose. This suggests that there Is some difference in crystal structure among these samples, although the crystalline form Is generally assumed to be cellulose I for all these materials. 

Current fiber x-ray diffraction studies, including new calculations by the authors, are reviewed. Because of different conventions used to describe the crystal structure of native cellulose, the preferred parallel structure described as "up by Gardner and Blackwell for Valonia corresponds to the "down" structure that was strongly rejected for ramie by Woodcock and Sarko. 

It was observed In earlier studies of controlled alkall-mercerlzatlon of ramie cellulose that the crystal structure of native cellulose Is transformed to cellulose II through a series of crystalline alkali-cellulose complexes (1,2). The relationships between these "Na-celluloses" and their pathways of transformation are Illustrated In Fig. 1. It has further been observed that all of the transformations are crystal-to-crystal phase changes, not Involving Intermediate amorphous phases. All of the experimental evidence has suggested... 

The use of synchrotron X-ray data collected from ramie fibers after ad hoc treatment in NaOH provided a revised crystal-structure determination of mercerized cellulose II at 1 A resolution." The unit-cell dimensions of the P2i monochnic space group are a = 8.10 A, h = 9.04 k,c= 10.36 k,y= 117.1°. As with the regenerated cellulose, the chains are located on the 2i axes of the cell. This indicates that the different ways of preparing cellulose II result in similar crystal and molecular structures. The crystal structure consists of antiparallel chains having different conformations, but with the... 

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. 

Fig. 3 Approximate structure of a cellulose crystal In ramie wood (according to Nishiyama et al. 2002, 2003a, b)...

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