Static light scattering of high amylopectin waxy maize starch gently dispersed in 90% dimethyl sulfoxidewater yielded a weight average molecular weight Mw and radius of gyration Rg 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 Rh was calculated from this diffusion constant using the StokesEinstein equation and found to be 348 nm. The structure-related parameter =Rg/Rh 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.
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