Solution properties of an α-(1→3)-d-glucan from Lentinus edodes and its sulfated derivatives Original Research Article

A water-insoluble α-(1→3)-d-glucan (A) from Lentinus edodes was fractionated into 13 fractions in dimethyl sulfoxide containing 0.25 M lithium chloride (0.25 M LiCl–Me2SO). Five fractions were treated with sulfur trioxide–pyridine complex at 25 °C to synthesize water-soluble sulfated derivatives (S-A). The weight-average molecular weights, Mw, and intrinsic viscosities [η], of the samples A and S-A were determined by multi-angler laser light scattering (MALLS), and viscosity. The Mw dependence of [η] and of the radius of gyration 〈S2〉z1/2, was found to be represented approximately by [η]=4.9×10−2 Mw0.67 (cm3 g−1), and 〈S2〉z1/2=4.8×10−2 Mw0.54 (nm) for the α-glucan in 0.25 M LiCl–Me2SO in the Mw range from 7.24×104 to 4.21×105, and by [η]=6.8×10−4 Mw 1.06 (cm3 g−1), and 〈S2〉z1/2=9.4×10−4 Mw0.92 (nm) for the sulfated α-glucan in aqueous 0.5 M NaCl in the Mw range from 5.92×104 to 1.42×105 at 25 °C. The results indicate that the α-(1→3)-d-glucan exists as a flexible chain in 0.25 M LiCl–Me2SO, and its sulfated derivative in 0.5 M NaCl aqueous has stiffer chains than the original. 13C NMR indicated that intramolecular hydrogen bonding occurred in the sulfated α-glucan, causing the observed chain stiffness.