Structure Properties of Dextran. 2. Dilute Solution

Abstract

Dilute solution properties of 13 dextrans with different molar masses in water and 0.5 M NaOH were investigated. Seven of these samples were products of Sigma prepared by bacteria from Leuconostoc mesenteroides, one was obtained by fractionation of the dextran with the highest molar mass, and five samples were obtained by degradation via controlled acid hydrolysis. Static and dynamic light scattering, viscometry and analysis of the reducing end group were applied. The molar mass dependencies of the radius of gyration R g, the hydrodynamic radius R h, the second virial coefficient A 2 and the intrinsic viscosity [ η ] for the nonfractionated samples were determined. The results are compared with data from the literature. Size exclusion chromatography in on-line combination with multiple-angle laser light scattering and viscosity detection revealed different calibration curves M i vs V e for the studied samples. The molar mass dependencies of the radii and intrinsic viscosities could be measured. The data of the radii of gyration from four fractionated samples were found to form one common curve. The intrinsic viscosities, on the other hand, gave two curves, one for the Sigma sample and another one for the acid-degraded samples. These findings are discussed in comparison with the nonfractionated samples. The polydispersity of dextrans, like those for other hyperbranched polysaccharides, increased strongly with M w but weaker than predicted by theory. Generalized ratios ρ = R g / R h and V r = A 2 M w/ [ η ] are considered and discussed in comparison with data from other laboratories and compared with predicted values. The coil−coil interpenetration function Ψ and the solvent-coil draining function Φ were found to increase with the molar mass as a result of increasing branching density.