[Structure and characteristics of glucomannans from Eremurus iae and E.zangezuricus: detection of acetyl group...

Water-soluble glucomannans from roots of Eremurus iae and E. zangezuricus were studied. These polysaccharides were shown to contain 28.8; 69.0, and 2.2% (E. iae) and 22.6; 74.8, and 2.6% (E. zangezuricus) of D-glucose, D-mannose and acetyl groups, respectively. Their IR spectra were identical and revealed the presence of 1,4-beta-glycosidic bonds and ester carbonyl groups. 13C-NMR spectroscopy revealed both polysaccharides to be linear partially acetylated 1,4-beta-D-glucomannans. Acetyl groups substituted C-2- and C-3-hydroxyls of mannopyranose residues. Comparison of 13C-NMR data and the results of correlation analysis enables a conclusion to be made that acetyl groups can substitute no more than one OH-group in the mannopyranosyl residue. [alpha]D = -34.0 degrees, [eta] and molecular weights (MW) for E. iae polysaccharide were determined to be -34.0, 6.5 dl/g, and 265.5 kDa, respectively, and for E. zangezuricus polysaccharide -38.2, 5.4 dl/g, and 233.5 kDa, respectively. A correlation between intrinsic viscosities of polysaccharides and their molecular masses determined by HPLC was revealed.