Xylan

Type I: (→3)-β-D-xylan(1→). Xylan is a hemicellulose. Only a portion of the xylose units are substituted, and the substitution is not regular.

Type II: (→4)-β-D-xylan(1→). Short side chains of one or more types as in arabinoxylans and (4-O-methyl)-glucoronoxylans. Different sidechains may be attached to the main chain (1→4)-β-D-xylopyranosyl. These sidechains are α-D-glucopyranosyluronic acid (or the 4-methyl ether) and/or α-L-arabinofuranosyl residues attached at O(2) and O(3), respectively. Only a portion of the xylose units are substituted, and the substitution is not regular [4]. The highest number of consecutive substitutions is 6 [4].

Type I: Crystallographic data [6].

Type II: The xylan chain is normally linear, but occationally it may be branched. Degree of polymerization: 70-130 [1].