Valonia cellulose electron diffraction studies

The existence of an ordered structure in cellulose is shown conclusively by wide-angle x-ray diffraction (WAXD) and electron diffraction studies (3). The diffraction patterns exhibit reasonably well-definid reflections for which unit cells have been defined. There are four basic recognized crystalline modifications, namely, cellulose I, II, III and IV. By the WAXD method as proposed by Hermans (4,5) it has been found that native celluloses of different biological origin vary in crystallinity over wide limits, from A0% in bacterial cellulose to 60 in cotton cellulose and 70 in Valonia cellulose. 

Studies on highly crystalline algal cellulose led to a reopening of the question of the unit cell and space group proposed by Meyer and Misch. In particular, electron diffraction studies, made at low temperature on Valonia cellulose, produced results that were incompatible with both fire unit-cell dimensions and the space-group symmetry proposed previously. The results, confirmed by independent studies, contradicted the two-fold symmetry of the ehain, and suggested that Valonia cellulose had the space group Pi and a triclinic unit cell. " ... 

Lamellar, single crystals of ivory-nut mannan were studied by electron diffraction. The base-plane dimensions of the unit cell are a = 0.722 nm and b = 0.892 nm. The systematic absences confirmed the space group P212121. The diffraction pattern did not change with the crystallization temperature. Oriented crystallization ofD-mannan with its chain axis parallel to the microfibril substrates, Valonia ventricosa and bacterial cellulose, was discovered ( hetero-shish-kebabs ). 

Why an organism should produce more than one kind of crystalline cellulose is not obvious. Moreover, if two crystalline forms coexist, the morphological expressions of each form are not yet recognized, nor have electron diffraction patterns from, say, individual Valonia fibrils yet shown any obvious difference from fibril to fibril (20-21). Therefore, we thought it desirable to examine further the evidence supporting the composite model since the hypothesis has important implications for both biosynthetic etnd morphological studies. 

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