Characterization of an acetylated heteroxylan from Eucalyptus globulus Labill Original Research Article

A heteroxylan was isolated from Eucalyptus globulus wood by extraction of peracetic acid delignified holocellulose with dimethyl sulfoxide. Besides (1→4)-linked β-d-xylopyranosyl units of the backbone and short side chains of terminal (1→2)-linked 4-O-methyl-α-d-glucuronosyl residues (MeGlcA) in a 1:10 molar ratio, this hemicellulose contained galactosyl and glucosyl units attached at O-2 of MeGlcA originating from rhamnoarabinogalactan and glucan backbones, respectively. About 30% of MeGlcA units were branched at O-2. The O-acetyl-(4-O-methylglucurono)xylan showed an acetylation degree of 0.61, as determined by 1H NMR spectroscopy, and a weight-average molecular weight (Mw) of about 36 kDa (P=1.05) as revealed from size-exclusion chromatography (SEC) analysis. About half of the β-d-xylopyranosyl units of the backbone were found as acetylated moieties at O-3 (34 mol%), O-2 (15 mol%) or O-2,3 (6 mol%). Practically, all β-d-xylopyranosyl units linked at O-2 with MeGlcA residues were 3-O-acetylated (10 mol%).