High-field, C-N.M.R. spectroscopy of β-d-glucans, amylopectin, and glycogen

¹³C-N.m.r. spectra of several d-glucans, recorded at 100 MHz, have afforded information about structural detail not previously accessible at lower frequencies. Spectra of (1→4)- and (1→3)-linked β-d-glucans of oats, barley, and lichenan of Iceland moss demonstrate the presence, in each, of three, non-equivalent, 4-O-substituted residues, that the ratio of these to 3-O-substituted residues averages 2.4–2.5, and hence that the patterns of repeating sequences in the three polymers are essentially the same. A comparison of wheat amylopectin with a minor, amylopectin-like fraction of wheat starch indicates that they are strictly analogous in basic structure, and differ only in that the average length of branches in the minor fraction is 20–25% shorter. By combining the advantages of high-field operation with the use of dimethyl sulfoxide as solvent, a large number of distinctive resonances have been observed, representing end-units, branch-points, and residues adjacent to branch-points. Accordingly, these signals are even more prominent in the spectrum of glycogen, reflecting the higher incidence of branching in this polymer. At 100 MHz, the excellent resolution and sensitivity afforded constitute a potent basis for assessing the purity of polysaccharide preparations, as illustrated with wheat amylose and barley β-d-glucans.