Valonia, cellulose

Valonia, cellulose, 326, 329-330 Vitamin B6, biosynthesis, 1-deoxy-D-threo-pentulose in, 287 Vitamin C... 

Baker AA, Helbert W. Sugiyama J, Miles MJ. High-resolution atomic force microscopy of native Valonia cellulose I. Microcrystals. J Struct Biol 1997 119 129-138. 

T ine structural studies on woody cell walls attacked by ectoenzymes of fungi in situ are numerous (cf. 1,2). In contrast, investigations on the selective degradation of cell walls by enzymes isolated from fungi are few. Jutte and Wardrop (3) attempted the use of crude commercial cellu-lase preparations to determine the degradation pattern of Valonia cellulose and beechwood fibers. Similar use of commercial preparations of enzymes was made by Reis and Roland (4) to evaluate the nature of diverse cell walls and to show the distribution of polysaccharides. An endo-/ -l,4-xylanase with specific xylanolytic activities was isolated from a commercial cellulase preparation using chromatographic methods and... 

High quality electron diffraction patterns of Valonia cellulose fibrils were first obtained by Honjo and Watanabe.(17) These patterns contain a large number of reflections and this technique promises a significant increase in the possible... 

Sarko A, Muggli R (1974) Packing analysis of carbohydrates and polysaccharides, III. Valonia cellulose and cellulose II. Macromolecules 7 486-494... 

Claffey W, Blackwell J (1976) Electron diffraction of Valonia cellulose. A quantitative interpretation. Biopolymers 15 1903-1915... 

Another AFM study of Valonia cellulose I showed 06 to be in thegt orientation [213]. Work with NMR spectrometry has gone further. Difference spectra show that the surfaces have extensively disordered regions as well as gt and gg 06 orientations [214]. When cellulose I is in water, NMR studies have indicated that its surface hydroxyl groups are also iagt positions [215]. 

Valonia cellulose I was peracetylated under nonswelling conditions. The observations made by electron microscopy and electron diffraction on the fibrous tri-O-acetylcellulose I (CTA I) and the cellulose I obtained by deacetylation thereof led to the conclusion that the chains in CTA I are parallel-packed, as in cellulose I. Similar experiments showed that CTA II and cellulose II have the same antiparallel polarity of the chains in the lattice. 

Fig. 7.—Schematic Diagram Showing the Interrelationship of Base-plane Packing for Three Unit cells of Native Cellulose. (The one in heaviest outline is the Meyer-Misch cell. The cell proposed for Valonia cellulose is twice as large in the base-plane dimensions. The third cell, having a angle of 93°14 is another proposal. )...

It is important at this point to address the need for a new paradigm that was not recognized in the early work of Atalla and VanderHart. The title of the early articles was still defined in terms of the classical approach to cellulose structure in that the two forms of cellulose, and 1,3, were referred to as two distinct crystalline forms. Note was not taken at that point of the rapidly developing evidence that the lateral dimensions of most native cellulose fibrils were very limited and that cellulose nanofibrils have an inherent tendency to develop a right-handed twist when cellulose chain molecules aggregate. While this important development had shed some light on the controversies associated with many of the prior interpretations of diffractometric characterizations of native celluloses, it had not yet provided conclusive evidence that the interpretations based on the symmetry of the P2i space group for crystalline cellulose cannot be valid for native celluloses. It was the acquisition of the Raman spectra of Tunicate and Valonia celluloses that provided the conclusive evidence. 

A similar study has been made with Valonia cellulose this showed a constant d.p. of 16,500, regardless of the conditions of growth. Furthermore, the distribution curve indicated that almost 80% of the cellulose was monodisperse, with a d.p. of 18,500. 

The assumptions concerning the symmetry of the unit cell noted above have been the basis of recent refinements of the structure of cellulose I. In one such refinement (17) the forbidden reflections were simply assimed negligible, and the intensity data from Valonia cellulose were used to arrive at a final structure. In another study, the inadequate informational content of the diffractometric data was complemented with analyses of lattice packing energies (29) the final structures were constrained to minimize the packing energy as well as optimizing the fit to the diffractometric data. 

Similar recording of the respective spectra were possible for other native celluloses such as ramie, bacterial, and valonia celluloses as well as regenerated celluloses. 

Fig. 1 X-ray diffractograms of the allomorphs in cellulose I family by the reflection method (the reflection plane is parallel to the membrane surface). A I, valonia cellulose, B IVj prepared from A through IIIi(C), C IIIi prepared from valonia.

Fig. 5 IR spectra of the deuterated allomorphs in OD stretching region. A I, valonia cellulose, B IV prepared from IHi (C), C IHi from A, D II, ophane, E Hn from D, F IVxi E.

In the low frequency region (Figure 7), there are only minor differences between the spectra of native ramie and Valonia. The peaks in the Valonia spectra are narrower and better resolved. The reason for this is probably the larger size of the crystallites in Valonia cellulose (38-39). When the crystallites are larger, the environment of the molecules is more homogeneous. Therefore, the vibrational energy of the molecules is more uniform, resulting in narrower bands. 

In the 0-H stretching region (3200-3600 cm ), however, significant differences are observed between all three celluloses. These differences are most prominent in the spectra recorded with the electric vector parallel to the fiber axis (Figure 8a-c). The frequency as well as the broadness of the peaks varies in this region. The spectra of Valonia cellulose have a peak at 3231 cm that is not observed in the ramie spectra. The spectra of native ramie on the other hand, have a peak at 3429 cm that is not observed in Valonia. The spectrum of mercerized ramie recorded with the elec-... 

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. 

In the present paper we extend the range of scattering angles as far as five degrees and combine SAXS measurement with wide-angle x-ray diffraction measurements. Me report what we believe to be the first complete SAXS curves for cotton and Valonia cellulose. We also demonstrate how the fractal concept can be applied to explain the microcrystallite structure in 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. " ... 

The discovery of the crystalhne dimorphism of cellulose and the existence of two famihes of native cellulose explained the number of inconsistencies that have characterized fifty years of crystallographic studies of cellulose. Thus the eight-chain unit ccll can be explained as an artifact arising from the superposition of the diffraction diagrams of the phases la and ip, which are both present in Valonia cellulose. 

These characteristics confer very interesting mechanical properties on microfibrils. Transmission electron-diffraction methods have made a contribution to the quantification of the degree of crystalhnity. Thus, using the technique of image reconsfruction it was shown that, in the microfibril of Valonia cellulose, which has a diameter of about 200 A, there could be more than 1000 cellulose chains, all aligned parallel in an almost perfect crystalline array. 

Fig. 19. Molecular model of a microfibril of cellulose, projected along the fibril axes compared with the typical morphologies observed for Valonia cellulose and tunicin, along with the CPK (Corey-PauUng-Koltun) representation of the main crystalline faces for cellulose 1. (See Color Plate 12.)...

Under partial acetylation, the size of Valonia cellulose crystals diminished in diameter such decrease is not homogeneous and corresponds to the loss of discrete fragments. At the beginning of the acetylation, the la phase is more susceptible to acetylation than the ip phase the latter appears more resistant. The missing fragments correspond to la domains, which are solubilized initially. These domains, which are more susceptible to acetylation, are acetylated first leaving behind exposed surfaces somewhat depleted in the la phase (Fig. 39). This confirms that in Valonia cellulose the la and Ip phases occur as discrete phases within the same microfibril. 

Fig. 39. Electron-diffraction diagrams of microciystals of cellulose at different states of acetylation and after removal of cellulose acetate by selective hydrolysis A, initial B, sample of DS 2.41 C, sample of DS 2.81. Schematic drawing describing the onset of acetylation of a typical crystalline cellulose, showing how chains that are sufficiently acetylated are partially lifted from the crystal. Schematic representation of the change in cross section of the cellulose crystals from Valonia during partial acetylation. CP/MAS C-NMR spectra of the fraction of cellrtlose remaining as insoluble at increasing acetylation ratio, showing disappearance of the la component. Schematic representation of the localization of one part of the la phase in Valonia cellulose...

A prerequisite for this model of stmetural interconversion is the existence of arrays of parallel-packed chains in a single microfibril, the arrays being oriented in up and down directions. The occurrence of such an arrangement was demonstrated in the highly crystalline and well-organized cell-wall of Valonia. Cellulose microfibrils are statistically distributed in opposite polarities wifltin given arrays, where they are packed side by... 

---