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

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 (Mw), radius of gyration (〈s2〉z1/2) 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 〈s2〉z1/2 on Mw for C-PCSG were found to be [η]=1.49×10-2Mw0.75(mLg-1), and 〈s2〉z1/2=3.65×10-2Mw0.56 (nm), respectively. Analysis of Mw and [η] in terms of the known theories for wormlike chain model yielded 633 nm−1 for molar mass per unit contour length (ML), 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.