Effects of acetylation on thermodynamic properties of seaweed alginate in sodium chloride solutions

Abstract

Alginates are polysaccharides consisting of mannuronate and guluronate units. While bacterial alginate is acetylated, seaweed alginate does not contain acetyl groups. This is one of the main differences between algal and bacterial alginates. The acetyl groups play an important role in the physical–chemical properties of the alginates. To determine the influence of acetyl groups on the properties of alginates in solutions, seaweed alginates were acetylated according to a procedure described by Skjak-Braek et al. Effects of the acetylation on the size, the interactions and the shape of the macromolecules were investigated amongst other methods with analytical ultracentrifugation. Though the molar mass of the alginate hardly increases after acetylation, a size-increasing effect on the alginate spheres is observed. In very dilute solutions positive second virial coefficients are observed for acetylated and nonacetylated alginate. Acetylation increases the second virial coefficients of alginate solutions, indicating better interaction of acetylated alginate with the water molecules than nonacetylated alginates.

Acknowledgements. The authors are participants of the research group Physical Chemistry of Biofilms and thank the Deutsche Forschungsgemeinschaft for financial support.