Aggregation Behavior of Triple Helical Polysaccharide with Low Molecular Weight in Diluted Aqueous Solution

Abstract

It has been proven in our previous work that the lentinan triple helical chains with high weight-average molecular weight (M(w) = 1.71 x 10(6)) formed easily a self-entangle one, and no ordered aggregates were detected. In the present work, we used the ultrasonic method to degrade the lentinan triple helical chains to obtain a sample with a mean value of M(w) approximately 5.0 x 10(5) g/mol. Subsequently, its dilute aqueous solution properties were studied by dynamic light scattering (DLS). The relaxation time distributions exhibited two modes (fast and slow) with different relaxation time scales. The fast mode was attributed to the relaxation of an individual triple helical lentinan, whereas the slow mode indicated the formation of large aggregates. On the basis of the scattering wave vector dependencies for the scattering intensity and for the amplitudes and characteristic times associated with the relaxation modes, the molecular parameters were calculated by combing static LS with DLS. The values of the radius of gyration for individuals (R(g)(indi)) and aggregates (R(g)(agg)) were 48.2 and 75.4 nm, and those of the hydrodynamic radius for individuals (R(h)(indi)) and aggregates (R(h)(agg)) were 14.9 and 98.4 nm, respectively. Furthermore, the structure-sensitive dimensionless parameter of individuals (rho(indi) = 3.23) and aggregates (rho(agg) = 0.766) indicated that the individual triple helical chains were stiff, whereas the aggregates existed as compact clusters. The aggregates consisted of short triple helical chains by packing close to form "faggot-like" assembly, and the ordered aggregates (near 10%) coexisted with the predominant triple helical chain in the aqueous solution. Atomic force microscopy provided straightforward evidence on the shape of the triple helical chains and their aggregates in water.