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

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 (Mw) for the native glucan and the sulfated derivatives were found to be [η]=9.92×10−3 Mw0.77 (cm3 g−1) in the range of Mw from 1.08 to 23.1×104 and [η]=2.92×10−4 Mw1.09 (cm3 g−1) in the range of Mw from 0.74 to 5.80×104, 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 (ML), 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.