Methylglucuronic acid side-groups

The xylan obtained was studied by NMR spectroscopy. One major and two minor signals were observed in the anomeric proton region between 4.4 and 5.5 ppm in the H NMR spectrum (Fig. 3). The chemical shifts and three-bond coupling constants in the H NMR spectrum indicate that the major structural element in the xylan was a P-(l->4)-D-xylopyranosyl residue and that a 4-0-methylglucuronic acid side-group and a disubstituted xylopyranosyl residue were minor structural elements. The spectrum resembles the spectrum for alkali-extracted 4-0-methylglucuronoxylan from aspen described earlier. It can thus be concluded that the isolated... 

The xylan was commercial birch xylan (4-0-methylglucuronoxylan fix>m Roth, 14 400 g/mol, DP 100). It contains 7.8 % a-D-methylglucuronic acid side groups and is alkali soluble. NaCl, NaOH and HCl were all of analytical grade. Solutions were prepared in doubly distilled water (Millipore). The mica was muscovite mica (Electron Microscopy Sciences, FT.Washington). 

The distribution of the acid side-chains in softwood xylans is not known. No oligosaccharides containing more than one 4-0-methylglucuronic acid residue were liberated on partial hydrolysis of a hemlock xylan, suggesting that few of the acid groups occur on contiguous D-xylose residues. 

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