Xylan seaweed

Xylan-type polysaccharides are the main hemicellulose components of secondary cell walls constituting about 20-30% of the biomass of dicotyl plants (hardwoods and herbaceous plants). In some tissues of monocotyl plants (grasses and cereals) xylans occur up to 50% [6j. Xylans are thus available in huge and replenishable amoimts as by-products from forestry, the agriculture, wood, and pulp and paper industries. Nowadays, xylans of some seaweed represent a novel biopolymer resource [4j. The diversity and complexity of xylans suggest that many useful by-products can be potentially produced and, therefore, these polysaccharides are considered as possible biopolymer raw materials for various exploitations. As a renewable resource, xylans are... 

Xylans as true homopolymers occur in seaweeds of the Palmariales and Nemaliales, however, their backbone consists of Xylp residues linked by -(1 3) (Type X3, Fig. la) or mixed -(1 3, 1 -> 4)-glycosidic linkages (Type Xmy Fig. lb). They are assumed mainly to have a structural function in the cell-wall architecture, but a reserve function cannot be ruled out [4]. From the microfibrils of green algae (Siphonales) such as Caulerpa and Bryop-sis sp., X3 was isolated and the structure confirmed by methylation analysis, C-NMR spectroscopy [7], as well as by mass spectrometry of enzymically released linear oligosaccharides up to a degree of polymerization (DP) of... 

Xylans Green plants Brown seaweed D-Xylose (31,3 ... 

H. Bjomdal, K. E. Eriksson, P. J. Garegg, B. Lindberg, and B. Swan, Studies on the xylan from the red seaweed Rhodymenia palmata, Acta Chem. Scand., 19 (1965) 2309-2315. 

A. I. Usov and I. M. Dobkina, Polysaccharides of algae. 43. Neutral xylan and sulfated xylomannan from the red seaweed Liagora valida, Sov. J. Bioorg. Chem., 17 (1991) 596-603 (English translation from Bioorg. Khim., 17 (1991) 1051-1058). 

The sole Nano-probe paper published in 2004 of which the author is aware was the study by Claeyssens and co-workers220 of the enzymatic hydrolysis products of Nothogenia erinacea seaweed xylan, which is a linear homopolymer with mixed / — (1 —3)// — (1 —4) linkages. The sequence of the residues was determined from a combination of nuclear overhauser effect spectroscopy (NOESY) correlations between the anomeric protons and a proton of the residue to which it is glycosidically linked and gHMBC data, that were acquired using Nano-probe capabilities. Finally, in early 2005, Bradley et al.221 compared the ability of cryogenic, Nano- and conventional NMR probes to acquire diffusion-ordered spectroscopy (DOSY) spectra of dilute mixtures of compounds. 

An unusual (1— 3)- 3-D-xylan appears to be the skeletal material for a number of seaweeds, and occurs with microfibrillar morphology, just as for cellulose. However, the birefringence of the fibrils is n ative, whereas for cellulose it is positive, and this observation suggests a helical structure, seen, by examination of molecular models, to be quite plausible. An x-ray fiber diagram for the material conditioned at 98% relative humidity is shown in Fig. 19. The principal characteristic of this diagram is that the most intense reflections are not on the equator this is a feature of molecules of the helical type, such as those of nucleotides or proteins. From an analysis of the x-ray data, Frei and Preston concluded that a double... 

Although reaction in JV,N-dimethyIformamide greatly facilitates methylation, the method suffers from the limitation that it often gives low recoveries of methylated polysaccharides, and the effectiveness of the methylation appears to depend on the volume of N,M-dimethylformamide used. Even with monosaccharides, incomplete methylation has been reported. D. A. Rees and coworkers have given detaUs of a modified Kuhn methylation for carrageenan, and they also described the methylation of dextran and of a xylan from red seaweed in N-methyl-2-pyr-rolidinone. A micro Kuhn method suitable for oligosaccharides has been described by Perila and Bishop. ... 

Xylan in hemicellulose of plants and some marine edgae consists of D-Xyl in P-1—)4 with branched chain at P-1—>3. Rhodymenan (green seaweed) is a linear xylan with P-1—>3 linkage. Xyl also occurs in plant gums and mucilages. D-Xyl is attached to threonine in glycoproteins. 

Skeletal polysaccharides based on pl,4-Dj-mannan and P 1,4-D -xylan backbones exist in the cell walls of red seaweeds which contain agarose or carrageenan in the intracellular matrix. It therefore seems reasonable to suggest that the associations described mimic the natural associations which may exist between the components of the cell wall and the matrix. 

A xylan from esparto grass 63, 64) is a singly branched chain of about 76 D-xylopyranose units linked jS-D-1— 4 in the main chain but with a 1—>3 link at the point of branching. From the cell wall of pear wood, another similarly single-branched xylan is obtained which has about 115 D-xylo-pyranose units, but it contains, in addition, a terminal D-glucopyranosyl-uronic acid unit at one point 65), The xylan from the red seaweed 57,58) Rhodymenia palmata seems to be composed only of D-xylopyranose units... 

True xylans have been found in algae. The xylan from the red seaweed Rhodymenia palmata contains 80% of u-(i -> 4) links and 20% of fi-v-(i - 3) links, while the green seaweed Caulerpa filiformis contains a xylan with only p-v-(i -> 3) links. 

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