SEC−MALLS and SANS Studies Applied to Solution Behavior of Linear α-Glucans

Abstract

Both size-exclusion chromatography coupled on-line with multiangle-laser-light-scattering (SEC−MALLS) and small-angle neutron scattering (SANS) demonstrate that linear α-glucan chains adopt the conformation of random coils with a higher dimension in alkaline conditions than in water. For amylose, the mass per unit length, ML ∼ 410 g/mol/nm, obtained from the SEC−MALLS results, shows that the α(1,4)-glucan chain has an overall flexible character in H2O. An insignificant difference is obtained by SANS using KOD as solvent, but when D2O is used, ML decreases with the molar mass. This effect is explained by a decrease in solvent quality. Then, when the radius of gyration vs the molar mass and the logarithm of the molar mass vs the elution volume relationships are considered, it is found that pullulans can be used to replace the linear amylose standards for chromatographic calibration purposes in 0.1 M KOH; the same cannot be done using water as solvent. On the contrary, the hydrodynamic radius vs elution volume calibration curve is found to be independent of the solvent and the polymer used.