STRUCTURAL FEATURES OF A WATER-SOLUBLE ARABINOXYLAN FROM THE ENDOSPERM OF WHEAT

A cold-water-soluble wheat-endosperm arabinoxylan consisting of a backbone of (1 --> 4)-linked beta-D-xylopyranosyl residues that are variously unsubstituted, and 3- or 2,3-substituted single alpha-L-arabinofuranosyl groups, was subjected to H-1-n.m.r. spectroscopy. The results of 2D homonuclear Hartmann-Hahn and 1D H-1-n.m.r. spectroscopy allowed the identification of 3- and 2,3-substituted xylose residues, each with adjacent unsubstituted xylose residues, and also substituted xylose residues with a substituted xylose residue as a neighbour. The H-1-n.m.r. data were correlated with C-13-n.m.r. data by means of a C-13-H-1 2D proton-detected heteronuclear multiple-quantum correlation experiment, which showed that only different types of branching (i.e., 3- and 2,3-) can be identified by the C-13-n.m.r. data.