Investigation of molecular masses and aggregation of beta-D-glucan from Poria cocos sclerotium by size-exclusion chromatography

beta-D-Glucan PC3 (weight-average molecular mass = 9.15. 10(4), polydispers ity = 1.6), a linear glucan from Poria cocos sclerotium, was fractionated b y a preparative size-exclusion chromatography (SEC) column packed with rege nerated cellulose gels using dimethyl sulfoxide (DMSO) as mobile phase. The molecular masses and aggregation of the fractions were investigated by usi ng analytical SEC, viscometry and membrane osmometry under different condit ions. The results of SEC analysis proved that glucan PC3 forms partial aggr egates in 0.25 M LiCl/DMSO (namely, 0.25 M LiCl in DMSO) at 40 degrees C, s howing a new shoulder peak of a higher-molecular-mass component in the chro matogram, and dissolves as a single-stranded chain at 80 degrees C, giving a sharper peak. The mean apparent aggregation number (N-ap) of the fraction s in 0.25 M LiCl/DMSO at 40 degrees C was 1.9, and much smaller than that o f glucan PC3 in 20% cadoxen. It is indicated that the analytical SEC is mor e sensitive and direct in detection of the aggregates than other methods, a nd aggregation can be avoided by carrying out SEC measurement at 80 degrees C. The Mark-Houwink equation for glucan PC3 in DMSO at 25 degrees C was es tablished as [eta] = 0.107M(w)(0.50) in the M-w range of 7-11 . 10(4), sugg esting that it behaves as a flexible coil. (C) 1999 Elsevier Science B.V. A ll rights reserved.