The hydrodynamic characterization of waxy maize amylopectin in 90% dimethyl sulfoxide–water by analytical ultracentrifugation, dynamic, and static light scattering

Static light scattering of high amylopectin waxy maize starch gently dispersed in 90% dimethyl sulfoxide–water yielded a weight average molecular weight M_w and radius of gyration R_g of 560×10⁶ g/mol and 342 nm, respectively. To obtain an independent hydrodynamic characterization of these solutions, we measured the sedimentation coefficient for the main component in an analytical ultracentrifuge. The value of s⁰, the infinite dilution sedimentation coefficient, was 199 S. The translational diffusion coefficient D⁰ in very dilute solutions was measured by dynamic light scattering at 90° and found to be 2.33×10⁻⁹ cm²/s. An effective hydrodynamic radius R_h was calculated from this diffusion constant using the Stokes–Einstein equation and found to be 348 nm. The structure-related parameter ρ=R_g/R_h was calculated to be 0.98. The weight average molecular weight calculated from the Svedberg equation using the values measured for s⁰ and D⁰ was 593×10⁶ g/mol. This result is in reasonable agreement with the light scattering results. As light scattering results are subject to experimental errors due to the possibility of dust contamination, the presence of microgel or aggregates, and the questionable applicability of light scattering theory to interpret results for macromolecular sizes approaching the wave length of light used as a source for scattering, it is advisable to have corroborating hydrodynamic data when possible to further validate light scattering results in this very high molecular weight range.