Characterization of O-acetyl-(4- O-methylglucurono)xylan isolated from birch and beech

The structures of water-soluble birch and beech xylans, extracted from holocellulose using dimethyl sulfoxide, were determined employing 1H and 13C NMR spectroscopy together with chemical analysis. These polysaccharides were found to be O-acetyl-(4- O-methylglucurono)xylans containing one 4- O-methylglucuronic acid substituent for approximately every 15 d-xylose residues. The average degree of acetylation of the xylose residues in these polymers was 0.4. The presence of the structural element →4)[4- O-Me-α- d-Glc pA-(1→2)][3- O-Ac]-β- d-Xyl p-(1→ was demonstrated. Additional acetyl groups were present as substituents at C-2 and/or C-3 of the xylopyranosyl residues. Utilizing size-exclusion chromatography in combination with mass spectroscopy, the weight-average molar masses (and polydispersities) were shown to be 8000 (1.09) and 11,100 (1.08) for birch and beech xylan, respectively. The structural element depicted at the right is common to xylans isolated from different hardwood species, such as aspen, beech and birch.