Correlation of the structure of dextrans to their 1H-n.m.r. Spectra

Abstract

Dextran fractions from NRRL strains Leuconostoc mesenteroides B-742, B-1299, B-1355, and B-1501, Streptobacterium dextranicum B-1254, Streptococcus sp. B-1526, and also the native dextrans from L. mesenteroides B-1142, B-1191, B-1402, and L. dextranicum B-1420 were examined in aqueous solution at 90° by Fourier-transform, 1H-n.m.r. spectroscopy. Branching of dextrans through the 2,6-, 3,6-, and 4,6-di- O-substituted α- d-glucopyranosyl residues was correlated to changes in spectral patterns. The major, spectral differences for these dextrans were in the anomeric (4-6-p.p.m.) region. In general, the degree of branching of a dextran can be determined by comparing anomeric-peak integrals; however, the integrals of the displaced, nonlinear, anomeric resonances are also dependent on the type of branching residues present in the dextran. Although the 1H-n.m.r. resonances for the anomeric region identify the presence of non-6-mono- O-substituted α- d-glucopyranosyl residues, these additional resonances provide little discrimination between other residue types, the exception being the 2,6-di- O-substituted residue, which has a clearly displaced resonance. Techniques for the suppression of the interfering resonance of deuterium hydroxide are also discussed.