Dextrans are polysaccharides with molecular weights ≥1000 Dalton, which have a linear backbone of α-linked D-glucopyranosyl repeating units. Three classes of dextrans can be differentiated by their structural features:
Class 1 dextrans contain the α(1→6)-linked D-glucopyranosyl backbone modified with small side chains of D-glucose branches with α(1→2), α(1→3), and α(1→4)-linkage. The class 1 dextrans vary in their molecular weight, spatial arrangement, type and degree of branching, and length of branch chains, depending on the microbial producing strains and cultivation conditions. Isomaltose and isomaltotriose are oligosaccharides with the class 1 dextran backbone structure.
Class 2 dextrans (alternans) contain a backbone structure of alternating α(1→3) and α(1→6)-linked D-glucopyranosyl units with α(1→3)-linked branches.
Class 3 dextrans (mutans) have a backbone structure of consecutive α(1→3)-linked D-glucopyranosyl units with α(1→6)-linked branches. One and two-dimensional NMR spectroscopy techniques have been utilized for the structural analysis of dextrans.
The physical and chemical properties of purified dextrans vary depending on the microbial strains from which they are produced and by the production method. Dextrans have high water solubility and the solutions behave as Newtonian fluids. Solution viscosity depends on concentration, temperature, and molecular weight, which have a characteristic distribution. The hydroxyl groups present in dextran offer many sites for derivatization, and these functionalized glycoconjugates represent a largely unexplored class of biocompatible and environmentally safe compounds.
Sigma Life Sciences offers a large variety of dextrans with high polydispersity and dextran molecular weight standards with low polydispersity (Mw/Mn values close to 1.0). Dextran sulfate from Leuconostoc spp. and fluorophore-dextran conjugates are also available in a range of polymer sizes.