Unit cell algal cellulose

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. 

On the basis of the results of electron diffraction studies by Sugiyama, Nishiyama et al undertook their very elaborate analyses of the diffraction patterns of the two forms of cellulose using X-ray, synchrotron, and neutron scattering. They also concluded that the two forms of cellulose have different unit cells, which imply that three different conformations coexist in the algal celluloses that are 60-70% of the Iq, form. This not only contradicts the clear evidence from the Raman spectra shown in Figure 9, but even more importantly is in direct conflict with the results of the lattice image studies reported earlier by Sugiyama et alJ that showed the nanofibrils of... 

In this report we present experimental evidence derived from these four approaches. In the end, the hypothesis that unit cell inequivalence alone causes the observed multiplicity for chemically equivalent carbons is supported. Therefore, the crystalline composite hypothesis, although slightly revised, is strongly supported, particularly for the algal celluloses. 

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. 

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. " ... 

As microalgae can also assimilate cellulose as cell wall component, similar unit operations can be used to breakdown algal cellulose to fermentable sugars in order to yield bioethanol. 

Figure 21.6 Parallel up packing of the triclinic unit cell (left-hand) and monoclinic unit cell (right-hand). For monoclinic structure the center chain is moved down by 2.5 A with respect to the corner chains. Reprinted with permission from Sugiyama, )., Vuong, R, and Chan, H., Electron diffraction study on two crystalline phases occurring in native cellulose from an algal cell wall. Macromolecules, 24, 4168-4175. Copyright (1991) American Chemical Society [17].

Cellulose is a major constituent in vascular plants and is generally absent in algal and microbial tissue. Cellulose is fibrous, water insoluble, and usually present in protective cell walls of plants, such as stalks, stems, and all the woody portion of the plant. Cellulose constitutes 45-90% of woody tissue, and 15-30% of herbaceous plant tissue. Cellulose consists of a linear, unbranched polysaccharide of 10,000 or more glucose units connected by P(l, 4) linkages (Figure 5.12). 

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