Effects of excluded volume and polydispersity on solution properties of lentinan in 0.1 M NaOH solution

Seven lentinan fractions of various weight‐average molecular weights ( M w ), ranging from 1.45 × 10 5 to 1.13 × 10 6 g mol −1 were investigated by static light scattering and viscometry in 0.1 M NaOH solution at 25°C. The intrinsic viscosity [η] − M w and radius of gyration 〈 s 2 〉   z 1/2− M w relationships for lentinan in 0.1 M NaOH solution were found to be represented by [η] = 5.1 × 10 −3 M   w 0.81cm 3 g −1 and 〈 s 2 〉   z 1/2= 2.3 × 10 −1 M   w 0.58nm, respectively. Focusing on the effects of the M w polydispersity with the Schulz–Zimm distribution function, the data of M w , 〈 s 2 〉   z 1/2 , and [η] was analyzed on the basis of the Yoshizaki–Nitta–Yamakawa theory for the unperturbed helical wormlike chain combined with the quasi‐two‐parameter (QTP) theory for excluded‐volume effects. The persistence length, molecular weight per unit contour length, and the excluded‐volume strength were determined roughly to be 6.2 nm, 980 nm −1 , and 0.1, respectively. Compared with the theoretical value calculated by the Monte Carlo model, the persistence length is longer than that of the single (1 → 3)‐β‐ D ‐glucan chain. The results revealed that lentinan exists as single‐stranded flexible chains in 0.1 M NaOH solution with a certain degree of expansion due to the electrostatic repulsion from the interaction between the OH − anions and lentinan molecules. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 187–196, 2005