Chain conformation of carboxymethylated derivatives of (1 → 3)-β- d-glucan from Poria cocos sclerotium

Abstract

A water-insoluble (1 → 3)-β- d-glucan (PCSG) isolated from the fresh sclerotium of Poria cocos was carboxymethylated to afford a water-soluble derivative coded as C-PCSG. The carboxymethylated (1 → 3)-β- d-glucan was fractionated to obtain eight fractions according to the nonsolvent addition method. The weight-average molecular mass ( M w), radius of gyration ( 〈 s 2 〉 z 1 / 2 ) and intrinsic viscosity ([ η]) of the fractions were determined by size-exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry in 0.2 M NaCl aqueous solution at 25 °C. The dependences of [ η] and 〈 s 2 〉 z 1 / 2 on M w for C-PCSG were found to be [ η ] = 1.49 × 10 - 2 M w 0.75 ( mL g - 1 ) , and 〈 s 2 〉 z 1 / 2 = 3.65 × 10 - 2 M w 0.56 (nm), respectively. Analysis of M w and [ η] in terms of the known theories for wormlike chain model yielded 633 nm −1 for molar mass per unit contour length ( M L), 5.5 nm for persistence length ( q), and 20.2 for characteristic ratio ( C ∞). These results indicated that C-PCSG exists as a relatively extended flexible chain in 0.2 M NaCl aqueous solution. Therefore, the introduction of the carboxymethyl groups into the β-glucan improved significantly the water solubility and enhanced the stiffness of the chains.