Homoxylans

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 

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Homoxylans are linear polysaccharides common in some seaweeds. 

Hemicelluloses are non-cellulosic low molecular weight polysaccharides that are found together with cellulose in plant tissues 1311. In the cell walls of land plants, xylan is the most common hemicellulosic polysaccharide, representing more than 30% of the dry weight 1321. Most xylans are heteropolysaccharides which are composed of 1,4-linked (3-D-xylopyranosyl residues 133, 134, 135). This backbone chain is substituted with acetyl, arabinosyl, and glucuronosyl residues 133. Homoxylans, on the other hand, consist of xylosyl residues exclusively and have been isolated from esparto grass 136, tobacco stalks 137, and guar seed husk 138. ... 

Xylans can thus be categorized as linear homoxylan, arabinoxylan, glucuronoxylan and glucuronoarabinoxylan. 

The reaction of beech wood xylan in N2O4/DMF with SO2 or SO3 yields sulfuric acid half esters of low DS (0.17-0.55) compared with the sulfation of cellulose due to the absence of reactive primary hydroxyl groups in the xylan structure (10). Moreover, algal cell wall microfibril homoxylan (P-l->3-xyIan) was sulfated with S03-pyridine under mild conditions and investigated with regard to the sulfation regioselectivity by means of different NMR techniques... 

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