Comparison on chain stiffness of a water-insoluble (1→3)-α- d-glucan isolated from Poria cocos mycelia and its sulfated derivative

Abstract

A water-insoluble (1→3)-α- d-glucan (ab-PCM3-I) isolated from the Poria cocos mycelia by extracting with 0.5 sodium hydroxide was fractionated into ten fractions by non-solvent addition method in 0.25 M lithium chloride in dimethylsulfoxide. Seven fractions were treated with chlorosulfonic acid-pyridine complex to synthesis water-soluble sulfated derivatives (S-ab-PCM3-I) with degrees of substitution in the range 0.35–0.81. The solution behaviours of the α- d-glucan and its derivatives were studied by laser light scattering (LLS), size exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry at 25 °C. The dependences of intrinsic viscosity ([ η]) on weight-average molecular mass ( M w) for the native glucan and the sulfated derivatives were found to be [ η]=9.92×10 −3 M w 0.77 (cm 3 g −1) in the range of M w from 1.08 to 23.1×10 4 and [ η]=2.92×10 −4 M w 1.09 (cm 3 g −1) in the range of M w from 0.74 to 5.80×10 4, respectively. On the basis of current theories for a wormlike chain model, the conformation parameters of the samples ab-PCM3-I and S-ab-PCM3-I were calculated to be 584 and 834 nm −1 for the molar mass per unit contour length ( M L), 3.7 and 6.8 nm for the persistence length ( q), 11.6 and 18.1 for characteristic ratio ( C ∝), respectively. The results indicated that the α- d-glucan ab-PCM3-I exists as an extended random coil chain in 0.25 M lithium chloride in dimethylsulfoxide, and that the sulfated derivatives S-ab-PCM3-I has good water-solubility and exist as semi-stiff chains in 0.9% w/v aqueous sodium chloride, owing to the steric hindrance and electrostatic repulsion of the sulfate groups.