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 H-1 and C-13 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-alpha-D-GlcpA-(1 --> 2)][3-O-Ac]-beta-D-XylP-(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. (C) 2002 Elsevier Science Ltd. All rights reserved.