Microwave-assisted solubilization and solution properties of hyperbranched polysaccharide

A water-insoluble hyperbranched β-d-glucan (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was treated by microwave exposure to improve its solubility in water. This method led to complete dissolution of the TM3a polysaccharide in 0.02 wt % aqueous NaN3. Various treatment periods were tested, and optimal conditions corresponded to 35 s at 765 W. The solution properties of TM3a in water were studied systematically by using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering at 25 °C. The dependences of intrinsic viscosity ([η  ]), radius of gyration (〈S2〉z1/2), and hydrodynamic radius (Rh) on weight average molecular weight (Mw) for TM3a in 0.02 wt % aqueous NaN3 at 25 °C were found to be [η]=3.02×10-2Mw0.44±0.1(cm3g-1), 〈S2〉z1/2=8.32×10-2Mw0.38±0.2(nm), and Rh=4.37×10-2Mw0.46±0.08(nm) in the Mw range from 8.20 × 105 to 4.88 × 106. The fractal dimension, ratio of ρ=〈S2〉z1/2Rh, and the o/Mw value of TM3a were calculated and discussed. The results indicated that TM3a existed in a sphere-like conformation in 0.02 wt % aqueous NaN3. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules of TM3a. This work gave valuable information on improvement of solubility and chain conformation characterization of the water-insoluble polysaccharide in water.

Graphical abstractA water-insoluble hyperbranched polysaccharide was treated by microwave heating to produce an aqueous solution. The effect of microwave exposure time upon the molecular weight and molecular weight distribution was determined in order to ascertain an appropriate treatment regime. Furthermore, we attempted to study the chain conformation of hyperbranched polysaccharide in aqueous solution using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering.Modified Stockmayer–Fixman plot for hyperbranched polymers with the data for TM3a in 0.02 wt % aqueous NaN3 at 25 °C (●), in comparison with TM3a in 0.25 M LiCl/DMSO at 25 °C (○).Figure optionsDownload full-size imageDownload as PowerPoint slide