Glucuronoxylans residues

Most of the glucuronoxylans have single 4-0-methyl-o -D-glucopyranosyl uronic acid residues (MeGlcA) attached always at position 2 of the main chain Xylp units (Fig. 2). This structural type is usually named as 4-0-methyl-D-glucurono-D-xylan (MGX). However, the glucuronic acid side chain may be present in both the 4-0-methylated and non-methylated forms (GlcA). 

Species Common name Total extractives Lignin Cellulose Glucomannan6 Glucuronoxylane Other polysaccharides Residual constituents... 

Glucuronoxylans D-Xyl D-GlcpA P-(1 4)-linked D-Xylp residues with... 

In hardwood, the xylan, or glucuronoxylan, consists mainly of D-xylose residues, most of which are acetylated, and 4-0-methyl-D-glucuronic acid residues (Fig. 2). Minor amounts of other constituents, such as L-rhamnose and D-galacturonic acid, can also be found. The molar ratio of 4-0-methyl-a-D-glu-curonic acid, acetyl groups, and xylose has been estimated to be 1 7 10 [59]. Hardwood also contains small amounts (2-5% dry weight (DW)) of gluco-mannan, composed of D-glucose and o-mannose. 

The degree of polymerization of wood arabinoglucuronoxylan is about 100 and that of glucuronoxylan is about 200 [11]. Seven out of ten xylose residues of... 

The glucuronoxylans are composed of linear chains of p-(l->4) xylopyranosyl residues branched with a-(l->2)-linked 4-0-methylglucuronopyranosyl residues (4-0-MeGlcA). The 4-0-MeGlcA-to-xylose ratio is -1 6 for softwood and -1 10 for hardwood xylans. (7-acetyl-(4-D-methylglucurono)-xylan is the major hemicellulose present in hardwood, whereas arabino-(4-6>-methylglucurono)-xylan is present in softwood. 

Figure 4. MALDI-MS spectrum (negative-ion mode) of a 4-0-methyl-glucuronoxylan from a sulfite pulp (spruce). The mass peaks correspond to xylooligosaccharides of increasing lengths containing an odd (o) or even (x) number of4-0-methylglucuronic acid residues. Reproduced from Reference 3, Copyright 2001 American Chemical Society,...

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