Cellulose electron diffraction pattern

Treatment of the algal cellulose (mixture of la—IP) from Valonia in ethylenediamine to give Cellulose IIIj simultaneously induced sub fibrillation in the initial microfihril (75). Thus crystallites 20 nm wide were spHt into subunits only 3—5 nm wide, even though the length was retained. Conversion of this IIIj back to I gave a material with an electron diffraction pattern and nmr spectmm similar to that of cotton Cellulose ip. 

Electron diffraction patterns from the primary wall of 15-day-old cotton fiber showed sharp, meridional reflections, with d spacings of 0.517 nin and 0.258 nm. Broad maxima on the equator, with spacings of 0.416 nm and 0.570 nm were also observed. On this basis, it was suggested that the primary wall of cotton contains the cellulose IVi polymorph, which is simply a laterally disordered structure of cellulose I. A discussion of the morphology of cellulose in the primary wall was given. 

Three diffraction patterns and one micrograph are thus recorded on the same plate or film. In some cases, we tried to evaluate the degradation of the crystalline patterns during one exposure this is analogous to an idea of a previous work of Dobb (9) who has studied the kinetics of the disappearance of the main interferences in the electron diffraction pattern of cellulose under constant irradiation rate by a method of "time-lapse series". Our aim was to try to determine a "true" crystallinity by an extrapolation to zero dose. In such a mode, the "crystalline" pattern of the same selected area is recorded three times (on the same emulsion) the irradiation rate corresponding to an exposure being set only during the exposure time. 

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... 

FIGURE 5.17 Cellulose diffraction patterns. Top left synchrotron radiation x-ray diffraction pattern for cotton fiber bundle. The fiber was vertical and the white circle and line correspond to a shadow from the main beam catcher and its support. (Credit to Zakhia Ford.) Top right electron diffraction pattern of fragments of cotton secondary wall. The much shorter arcs in the top right figure are due to the good alignment and small number of crystallites in the electron beam. (Credit to Richard J. Schmidt.) Bottom a synthesized powder pattern for cellulose, based on the unit cell dimensions and crystalline coordinates of Nishiyama et al. [209]. (Credit to Zakhia Ford.) Also shown are the hkl values for the Miller indices. The 2-theta values are for molybdenum radiation instead of the more commonly used copper radiation. 

In addition to the disallowed reflections in the electron diffraction patterns that placed the crystallographic models in question, new spectral evidence was developed pointing to the need for further refinement of structural models, particularly for native celluloses. The models derived from the crystallographic studies could not rationalize many features of the spectral data known to be quite sensitive to structural variations. 

Later studies by Sugiyama et were based on electron diffraction and were directed at addressing questions concerning the nature of the differences between the Iq, and I forms of cellulose. In a landmark study, electron diffraction patterns were recorded from V. macrophysa both in its native state, wherein the Iq, and Ifj forms occur in their natural relative proportions, and after annealing using the process first reported by Horii and coworkers, which converts the Iq, form into the I form. The native material, which is predominantly the Iq, form, was shown to produce a complex electron diffraction pattern similar to that which had earlier led Honjo and Watanabe to propose an eight-chain unit cell. In sharp contrast, the annealed sample, which is essentially all of the I form, produced a more simple and symmetric pattern that could be indexed approximately in terms of a two-chain monoclinic unit cell. 

Colvin as a glucolipid. The source of the enzyme was the supernatant solution of an active Acetobacter culture, freed from cells and cellulose by ultrafiltration. The product obtained on mixing the substrate with the enzyme preparation was identified as cellulose by the following criteria insolubility in hot alkali or in lipid solvents, appearance of the fibrils under the electron microscope, x-ray and electron diffraction-patterns, and appearance of D-glucose on hydrolysis of the product followed by chromatography. 

Figure 2. Dark- and bright-field TEM images and electron diffraction patterns of CGO, Cu-CGO cermet and SFA (F) powders prepared by cellulose-precursor technique.

The key conclusion that is relevant here is that the native celluloses are composites of more than one crystaline form, but that the difference between the two forms lies not in the molecular conformation but in the hydrogen bonding patterns. Thus, it is possible that the native celluloses have unit cells with very similar atomic coordinates for the heavy atoms, but with different coordinates for the hydrogens. The similarities in the heavy atom locations could account for the many comonalities in the diffraction patterns, while the differences in the coordinates of the hydrogen atoms could be responsible for the differences between the patterns. This would account for the greater incidence of nonallowed reflections in the electron diffraction patterns. 

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. 

Fig. 17. Cellulose triacetate (CTA) 11. (A) Transmission electron microscopy of a polymeric single crystal of CTA 11. (B) Projections of the chains in the a-b plane. (C) Electron diffraction pattern of a tip of a single crystal of CTA 11 in the a-b plane. (See Color Plate 10.)...

The process of the artificial cellulose was visually analyzed by using transmission electron microscopy (24). Cellulose formation was detected as early as 30 s after the initial stage of the reaction in the aqueous acetonitrile. The electron diffraction pattern of the product showed the typical pattern of the crystal structure of thermodsmamically stable cellulose II with antiparallel orientation between each glucan chains. When the purified cellulase (39 kDa) was used, cellulose microfibrils with an electron diffraction pattern characteristic of metastable cellulose I with parallel orientation, an allomorph of natural cellulose, were first observed in an artificial process (25). Based on these results, a new concept of choroselectivity, selectivity concerning the relative ordering of the polymer chain direction, in polsrmerization chemistry has been proposed (26-28). 

Figures 12-13 to 12-15. Electron diffraction patterns of cellulose microfibrils isolated from the tunicate Halocynthia as a standard cellulose sample (13), microfibrils isolated from thecal plates (14), and pellicles (15) of Scrippsiella hexapraecingula. Note the typical equatorial (110, iTO, 200) and meridional (004) reflections of cellulose I.

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 ). 

Cellulosic materials usually form crystal structures in part, and water cannot penetrate the inside of crystalline domains at room temperature. Native celluloses form crystalline microfibrils or bundles of cellulose chains 2-5 nm in width for higher plant celluloses and 15-30 nm for algal celluloses, which are observable by electron microscope. Almost all native celluloses have X-ray diffraction patterns of cellulose I with crystallinity indexes (Cl) 13] of about 40-95 %. 

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... 

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. 

Fig. 12. X-Ray and neutron fiber-diffraction patterns recorded from native cellulose (OH) and frilly deuterated (OD) cellulose samples. The difference in the scattering properties of hydrogen and deuterium (indicated by the red circles) allows the precise location of the electron density (shown in blue), which corresponds to the position of hydrogen atoms in the crystalline lattice. (See Color Plate 5.)...

PSt and PMMA formed by electron beam irradiation have no effect on the crystallinity of cellulose insofar as the blackness in the X-ray diffraction patterns of both WPC (irradiation) systems taken at room temperature are concerned. However, the high temperature feature of the E,p pattern of the PSt-WPC (irradiation) system indicates the enhancement of band (c) at ca. 190°C and the lowering of bands (a) and (b) (Figure 9). Therefore, it seems likely that grafted PSt somewhat perturbs the crystallites and increases the amorphous portion in wood by thermal shear at high temperatures. 

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