The Structure and Characteristics of Glucomannans from Eremurus iae and E. zangezuricus: Assignment of Acetyl Group Localization in Macromolecules

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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) D-glucose, D-mannose and acetyl groups, respectively. Their IR spectra were identical and revealed the presence of 1,4-β-glycosidic bonds and ester carbonyl groups. 13C-NMR spectroscopy revealed both polysaccharides to be linear partially acetylated 1,4-β-D-glucomannans. Acetyl groups substituted C2- and C3-hydroxyls of mannopyranose residues. A comparison of 13C-NMR data and the results of correlation analysis suggested that acetyl groups can substitute no more than one OH-group in the mannopyranosyl residue. The estimated values of [α]D, [η], and molecular weights (MW) were –34.0°, 6.05 dl/g, and 265.5 kDa, respectively, for E. iae polysaccharide, and –38.2°, 5.4 dl/g, and 233.5 kDa, respectively, for E. zangezuricus polysaccharide. A correlation between the intrinsic viscosities of polysaccharides and their molecular weight determined by HPLC was revealed.

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