Ramie cellulose unit cell

The second choice is a simpler solution. According to Sarko and Muggli,66 all 39 observed reflections in the Valonia X-ray pattern are indexable by a two-chain triclinic unit cell with a = 9.41, b =8.15 and c = 10.34 A, a = 90°, 3 = 57.5°, and y = 96.2°. Ramie cellulose, on the other hand, is completely consistent with the two-chain monoclinic unit cell. Also, there are significant differences between their high-resolution solid-state l3C NMR spectra, indicating that Valonia and ramie celluloses, the two most crystalline forms, reflect two distinct families of biosynthesis. On this basis, the Valonia triclinic and the ramie monoclinic forms are classified69 as Ia and Ip, respectively. It has been shown from a systematic analysis of the NMR spectra by these authors, and from electron-dif-... 

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. 

The N,N -dimethyl-l,3-propanediamine complex of cellulose, prepared from ramie, requires a large unit-cell, with a - 3.364 nm, b (chain axis) = 1.026 nm, c = 3.040 nm, and /3 = 32.74°. One diamine molecule per two /3-D-Glcp residues exists in the complex. 

Work with electron microscopes showed that there is preferential enzymatic activity at only one end of the native microfibrils. This indicates that the reducing ends are all at one end of the microfibril and thus the chains are parallel, not antiparallel [240]. Electron microscopy and diffraction work on algal and bacterial cellulose confirmed the parallel-up nature of the chain orientation in the unit cell and the addition of new glucose residues to the cellulose chain at the nonreducing end [241]. Similar attempts with ramie fibers were not successful. 

It has been known for some time that the more crystalline native celluloses from algae and from Acetobacter xylinum produce diffraction patterns that have many features in common with those of the crystalline celluloses from the higher plants, such as ramie, but that cannot be indexed as simply or on the basis of the same unit cell. The new information from the CP-MAS UMR spectra, together with that from the Raman spectra, suggests some bases for understanding these differences, and directions for further explora-t ions. 

Chaln unit cell. They argued that algal celluloses consist of pure 8-chaln unit cells, whereas higher plant celluloses, like ramie, are mixtures of 2-chain and 8-chain unit cells. 

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. 

As can be seen in table 2, a number of unit cells have been proposed for cellulose I-hydrazlne complexes over the years. Some of this diversity is almost certainly due to poor quality data, which can be Indexed in different ways. Nevertheless, visual comparison shows that our patterns are significantly different from those published previously, which probably reflects the fact that we used hydrazine containing no more than 3% water, as compared to up to 40% in earlier work. So far we have prepared three different cellulose Il-hydrazlne complexes, two for Fortisan (designated A and B) and one for Mercerized ramie. There may be some rationale for this complex A has only been obtained using anhydrous hydrazine, and the Fortisan and Mercerized ramie have different morphologies. However, it seems likely that all three complexes can be formed by both specimens once the preparation conditions are better understood. 

Some 39 independent reflections are observed in the fiber diagram of ramie cellulose I-ethylenediamine complex, and there are a further 36 that are predicted within the range of these data, but which are too weak to detect. Elemental analysis indicates the presence of one ethylenedlamlne per glucose residue and density considerations require dlsaccharlde units of two chains per unit cell. 

The ramie cellulose I-l,3-diaminopropane complex structure is the most crystalline of the diaminopropane complexes so far examined, and has a (metrically) orthorhombic unit cell that can contain only one chain which dictates a parallel chain structure. Elemental analysis and density measurements point to one molecule of 1,3-diamlnopropane per glucose residue. Refinement proceeded in a manner similar to that described above for the ethylenedlamlne complex, based on Intensity data for 24 observed and 12 unobserved reflections. 

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... 

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