A heteroxylan and hemicellulosic materials from bamboo leaves,and a reconsideration of the general nature of commonly occurring xylans and other hemicelluloses

The molecular structures of water-soluble and -insoluble hemicelluloses of bamboo leaf, and of a hemicellulosic xylan from the former, have been examined. It is concluded that all the materials have the same structural features on their main xylan chain, namely, the side-chains or residues (a) l-arabinofuranose, (b) O-galactopyranosyl-(1→5)-l-arabinofuranose, (c) O-galactopyranosyl-(1→4)-O-d-xylopyranosyl-(1→2)-l-arabinofuranose, (d) O-d-xylopyranosyl-(1→2)-O-l-arabinofuranosyl-(1→2)-l-arabinofuranose, (e) O-(d-glucopyranosyluronic acid)-(1→4)-O-d-xylopyranosyl-(1→4)-galactopyranose, and (f) d-glucopyranuronic acid and its 4-methyl ether. Feature (d) is proposed for the first time, but it may have been present in xylans studied by others. The main xylose chain in the soluble, insoluble, and xylan materials have, respectively, 1 in every 2.8, 4.0, and 7.6 xylan residues substituted by side residues or chains (a)–(e). It is concluded that the polysaccharide product recovered after methylation of the three hemicellulosic materials does not fully represent the quantitative composition of the materials subjected to methylation, although structural features (a), (d), and (e) are not much altered. When the soluble material was treated with dilute acid under mild conditions, most of (a) was removed, while (d) and other substituents, including those with l-arabinofuranose residues, were not removed to the same extent.