Order-Disorder Conformation Change of Succinoglycan in Aqueous Sodium Chloride as Studied by Static and Dynamic Light Scattering

Summary

Static and dynamic light scattering measurements have been made on a sodium salt sample of succinoglycan in 0.01 M aqueous NaCl at different temperatures between 25 and 75°C where the polysaccharide undergoes a thermally induced change from an ordered (helical) to disordered conformation with raising temperature T. The weight-average molecular weight M _w, the z-average radius of gyration, and the hydrodynamic radius sharply decrease in a relatively narrow T range (around 55°C) in which the specific rotation was previously found to change sigmoidally with T. In particular, the value of M _w (4.55 × 10⁵) in the ordered state at 25°C is twice as large as that (2.27 × 10⁵) in the disordered state at 75°C, giving decisive 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.