Effects of urea and sodium hydroxide on the molecular weight and conformation of α-(1→3)-d-glucan from Lentinus edodes in aqueous solution Original Research Article

The weight-average molecular weight (Mw) and intrinsic viscosity ([η]) of the α-(1→3)-d-glucan (L-FV-II) from Lentinus edodes in 0.5 and 1.0 M NaOH aqueous solution containing urea, were studied by light scattering and viscometry. The Mw value of the glucan decreased with increase of the urea and NaOH concentration. A strong intermolecular hydrogen bonding confers water-insolubility on the glucan, but NaOH and especially urea, broke this hydrogen bonding leading to enhanced water-solubility. Use of 1.0 M urea–1.0 M NaOH as solvent broke not only intermolecular hydrogen bonds but also partial covalent bonds of the α-glucan in aqueous solution, resulting in a decrease of Mw and [η]. The urea and NaOH concentrations, storage time with stirring, and mode of preparation of the polysaccharide in aqueous solution significantly affected the determination of Mw and [η]. The dependences of specific rotation and fluorescence emission ratio of a probe on urea concentration showed that a change in the molecular conformation of the α-glucan in 0.5 M NaOH aqueous solution containing urea occurred in the range 0.4–0.6 M urea. The 0.5 M urea–0.5 M NaOH aqueous solution is a suitable solvent for the glucan, and the Mw and [η] values obtained were 5.21×105 and 148 cm3 g−1, respectively. Degradation of the glucan was obvious after storage for 15 months.