Order-disorder conformation change of succinoglycan in aqueous sodium chloride as studied by static and dynamic light scattering

Static and dynamic light scattering measurements have been made on a sodium salt sample of succinoglycan in 0.01 M aqueous NaCl at different temperatu res between 25 and 75 degreesC where the polysaccharide undergoes a thermal ly induced change from an ordered (helical) to disordered conformation with raising temperature T. The weight-average molecular weight M-W the z-avera ge radius of gyration, and the hydrodynamic radius sharply decrease in a re latively narrow T range (around 55 degreesC) in which the specific rotation was previously found to change sigmoidally with T. In particular, the valu e of M-W (4.55 x 10(5)) in the ordered state at 25 degreesC is twice as lar ge as that (2.27 x 10(5)) in the disordered state at 75 degreesC, giving de cisive evidence that the helical structure of the polysaccharide in aqueous NaCl is composed of paired chains. It is concluded that this structure is a double-stranded helix and breaks directly into two disordered chains with increasing T.