Valonia cellulose fibrils

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... 

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. 

High-resolution images of cellulose I microcrystals [155] demonstrated the application of CM-AFM to the study of large biopolymers. Here, the 0.52 nm repeat along the chains of the cellulose from Valonia ventricosa (a dark-green balloon-Uke marine alga) was observed. AFM has also been used to study the polysaccharides present in wheat straw cell walls [156], where clear differences can be seen both before and after de-waxing. Cellulose appeared to form microfibrils which were orientated in one direction. These fibrils measured some 20 nm in diameter and are believed to contain as many as 60-80 cellulose molecular chains. 

The diameter of cellulose fibers is about 12 pm, which is similar to glass fiber (and probably inspired the latter). Cellulose fibers consist of fibrils. The individual diameters of cellulose fibrils are in range of 4 to 35 nm, depending on the cellulose source including bacterial cellulose (0.004 to 0.007 pm), cotton (inters (0.007 to 0.009 pm),ramie (O.OlOtoO.015 pm), pulp (0.010 to 0.030 pm), and valonia cellulose (0.010 to 0.035 pm). 

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. 

Cellulose is insoluble in water because of the high affinity of the polymer chains for one another. Its individual polymeric chains have molecular weights of 50,000 or greater. The molecular chains of cellulose interact in parallel bundles of about 2,000 chains. Each bundle constitutes a single microfibril. Many microfibrils arranged in parallel constitute a macrofibril, which can be seen under the light microscope. Figure 12.10 shows the inner cell walls of the plant Valonia the fibrils in the wall are almost pure cellulose. 

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. 

Eleven cotton celluloses and one of Valonia were studied. Among the twelve samples, the first nine cotton samples are in a randomly oriented fibril state (cotton sliver), EHC I and Hydrocellulose II are powders, and Valonia is in membrane pieces. They are listed and described below. 

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.)...

Lattice images of algal, bacterial, and ramie cellulose have been obtained. These images show the individual molecular chains and the sizes of microfibrils, which vary in size and shape according to the source of cellulose [242,243]. There is also some variation within a given source. For example, microfibrils of Valonia ranged from 150 to 250 A (15 to 25 nm). No evidence of elementary fibrils was seen. 

The lateral size of elementary nanofibrils varies in a wide range, from 3-4 nm for natural cellulose of herbaceous plants and woods to 10-15 nm for Valonia cellulose (Table 7.6). Length of the elementary fibrils reaches several microns. Thus, the elementary fibril has thread-like shape (Fig. 7.19). 

In cellulose, crystalline regions coexist with non-ciystalline, amorphous domains statistically alternated along the fibril. Amount of amorphous phase in plant depends on the sample origin and, e.g., for Valonia it is 11%, while for primary walls of plants it reaches more than 70% [5,14]. 

---