Chain conformation of sulfated derivatives of β-glucan from sclerotia of Pleurotus tuber-regium

Abstract

Six water-insoluble (1→3)-β- d-glucan fractions TM8-1 to TM8-6 with weight-average molecular mass M w ranging from 5.76 to 77.4×10 4 obtained from the sclerotia of Pleurotus tuber-regium were sulfated to produce the water-soluble fractions S-TM8-1 to S-TM8-6 with M w from 6.0 to 64.8×10 4. The degree of substitution (DS) of S-TM8 fractions was analyzed by elemental analysis (EA) to be 1.14–1.74. The 13C NMR results indicated that the C-6 was fully substituted, and C-2, C-4 were partially substituted by the sulfo-groups. The M w and the intrinsic viscosity [ η] of the S-TM8 fractions were measured, respectively, by size-exclusion chromatography combined with laser light scattering (SEC-LLS), LLS and viscometry in phosphate buffer solution (PBS) at 37 °C. The dependences of [ η] and radius of gyration 〈 s 2〉 z 1/2 on M w for the S-TM8 samples were found to be [ η]=1.89×10 −2 M w 0.70 (cm 3/g) and 〈 s 2〉 z 1/2=1.12×10 −4 M w 0.81 (nm) in the M w range tested. Based on current theories for a wormlike chain model, the molar mass per unit contour length M L and persistence length q of the S-TM8 were calculated to be 990 nm −1 and 8.5 nm, respectively. The relatively higher q value suggested a more expanded flexible chain of S-TM8 in PBS. The water-solubility and relatively expanded chain conformation of the STM8 fractions were considered to be significant to their antiviral activity.