Hydration Properties of Anionically-Modified Phytoglycogen Nanoparticles

Phytoglycogen (PG) is a glucose-based polymer with a tree-like or dendritic architecture that is produced as compact nanoparticles in the kernels of sweet corn. The particles take up a significant amount of water,¹ and the nanoconfinement of the hydration water inside the dense PG particles results in water ordering that is significantly larger than for other polysaccharides.² Chemical modification of the PG particles with charged groups (both cationic and anionic) significantly increases the amount of water uptake with a corresponding decrease in the water ordering and the bulk modulus.³ For PG particles modified with carboxymethyl groups (anionic, CM-PG), we have measured the effect of adding salts of different valencies on water uptake and water structuring in thin films of CM-PG particles. We find that the addition of Ca²⁺ reduces the swelling of the films, as measured using ellipsometry, and results in a shift in the carboxylate peak to lower frequency measured in infrared experiments. These results are consistent with bridging between different CM groups on the CM-PG particles and provide insight into the tunability of the hydration properties of PG.

[1] Nickels, J.D. et al. (2016) Biomacromolecules 17 (3), 735-743.

[2] Grossutti, M., Dutcher, J. R. (2016) Biomacromolecules 17 (3), 1198-1204.

[3] Grossutti, M., Dutcher, J. R. (2020) Biomacromolecules 21 (12), 4871-4877.