Galactose moieties have been introduced on the uronic groups of alginates from different sources via an
N-glycosidic bond, thus affecting the net charge on the polymer chain. The modified polymers have been
analyzed by means of viscosity and of high-performance size-exclusion chromatography combined with
refractive index multiple angle laser light scattering (HPSEC-RI-MALLS) measurements. The latter technique
enabled us to determine the molecular weight of the modified polymers, proving that the synthetic procedure
did not affect the chemical integrity of the chain. The intrinsic viscosity and the radius of gyration data
showed that the hydrodynamic properties of the polymer chain varied with the degree and the pattern of
substitution. In the presence of a relatively low galactose content (up to 19%), a decrease of the hydrodynamic
dimensions of the coil was experienced, while on increasing the degree of substitution (especially on GG
diads) a re-extension of the chain was discovered. Measurements of intrinsic viscosity at different values of
the degree of dissociation have demonstrated that this effect cannot be solely explained by the reduction of
the charge density of the polymer. Rather, it implies the occurrence of conformational changes of the chain
that are specific to the chemical nature of the site of substitution. These data have been supported by the
values of the persistence length of the natural and modified polymers obtained with the Doty-Benoit equation.
The chiro-optical properties of the modified polymers studied by means of circular dichroism (CD)
spectroscopy confirmed that conformational variations occurred to the polymeric chain upon introduction
of galactose residues.
