Effects of urea and sodium hydroxide on the molecular weight and conformation of alpha-(1-->3)-D-glucan from Lentinus edodes in aqueous solution.
The weight-average molecular weight (Mw) and intrinsic viscosity ([eta]) of the alpha-(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 alpha-glucan in aqueous solution, resulting in a decrease of Mw and [eta]. 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 [eta]. 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 alpha-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 [eta] values obtained were 5.21 x 10(5) and 148 cm3 g(-1), respectively. Degradation of the glucan was obvious after storage for 15 months.
Zhang
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P
Department of Chemistry, Wuhan University, PR China.
Zhang
L
L
Cheng
S
S
D004305:Dose-Response Relationship, Drug; D005936:Glucans / Q000737:chemistry*; D006860:Hydrogen Bonding / Q000187:drug effects; D008027:Light; D008968:Molecular Conformation; D008970:Molecular Weight; D012542:Scattering, Radiation; D020942:Shiitake Mushrooms / Q000737:chemistry*; D012972:Sodium Hydroxide / Q000494:pharmacology*; D012995:Solubility / Q000187:drug effects; D012996:Solutions; D014508:Urea / Q000494:pharmacology*; D014783:Viscosity / Q000187:drug effects; D014867:Water / Q000378:metabolism
D005936:Glucans; D012996:Solutions; D014867:Water; D012972:Sodium Hydroxide; D014508:Urea; C045788:alpha-1,3-glucan