Shrinking factors of hyperbranched polysaccharide from fungus

Abstract

The branched structure properties of hyperbranched polysaccharides (TM3a and TM3b), extracted from sclerotia of Pleurotus tuber-regium, were studied by using laser light scattering and viscometry. The configurational shrinking factor ( g) and viscometric shrinking factor ( g′) of TM3a and TM3b were discussed, where curdlan and pullulan were taken as the linear references for derivation of g and g′. The dependences of g factor, g′ factor, and Flory factor ( Φ branched) on weight average molecular weight ( M w) were established to be g = 1.07 × 10 2 M w - 0.48 ± 0.09 , g′ = 3.63 × 10 1 M w - 0.43 ± 0.01 , and Φ branched = 7.08 × 10 20 M w 0.39 ± 0.1 for TM3a in 0.25 M LiCl/DMSO at 25 °C, when curdlan acted as the linear reference. A power law relationship g′ = 2.71 × 10 −1 g −0.61±0.1 for TM3a was found, and the exponent was approximately same to 0.60 established by Kurata et al. for polystyrene star molecules. The dependence of g factor on M w for TM3b was found to be g = 1.99 × 10 2 M w - 0.53 ± 0.02 , when pullulan was used as the linear reference. On the basis of Zimm–Stockmayer equation for tetrafunctional units, molecular weight of branching unit ( M 0) deduced from nonlinear curve fitting of g versus M w was 8739 ± 564 g/mol and 3961 ± 1245 g/mol for TM3a and TM3b, respectively. The effect of different linear reference curves and polydispersity was discussed. This work gave valuable information on branched structure characterization and insights into the biosynthetic pathways of the hyperbranched polysaccharide from fungus.