Structural characterization of the acetylated heteroxylan from the natural hybrid Paulownia elongata/Paulownia fortunei

The heteroxylan from the hybrid Paulownia elongata / Paulownia fortunei is an O -acetyl-(4- O -methylglucurono)xylan with an acetylation degree (DS) of 0.59 and a molecular weight ( M w ) of 29 kDa. The heteroxylan backbone is composed by (1→4)-linked β- d -xylopyranosyl units (Xyl p ) partially ramified with terminal (1→2)-linked 4- O -methyl-α- d -glucuronosyl (MeGlc p A) and a small proportion of α- d -glucuronosyl (Glc p A) residues in a molar ratio of Xyl p :(MeGlc p A+Glc p A) of 20:1. Roughly half of the β- d -xylopyranosyl units in the backbone are acetylated: 3-O-acetylated (22 mol %), 2-O-acetylated (23 mol %) or 2,3-di-O-acetylated (7 mol %). ESI-MS and MALDI-MS studies of partially hydrolyzed heteroxylan revealed a random distribution of O -Ac and MeGlc p A within the backbone. However, the frequency of substitution with O -Ac along the backbone is not uniform and the molecular regions that did not contain MeGlc p A substituents possessed an acetylation degree significantly lower than the average DS of the xylan.