PhD Thesis Presentation: Hydration Properties of Chemically Modified Phytoglycogen Nanoparticles

PhD Candidate

Carley Miki

Abstract

Phytoglycogen (PG) is a naturally occurring, soft, compact glucose-polysaccharide nanoparticle with an underlying dendritic chain architecture. Not only is it desirable for applications in personal care, nutrition and biomedicine, but it also provides a model system for fundamental studies of soft nanoparticles. For example, its hydration properties are unique, with a high level of ordering of the water within the particles. In this thesis, we study the effect of chemical modification of PG on its hydration properties. We use carboxymethylation to create anionically-modified carboxymethyl-phytoglycogen (CM-PG), in which a hydroxyl group on the glucose monomer is substituted with a negatively charged carboxymethyl group. We developed a procedure to produce CM-PG at the scale of 10 g, and we used a variety of techniques to characterize this material. The diameter, molar mass and zeta potential were measured using dynamic light scattering and multi-angle light scattering, and the water uptake and water structuring in CM-PG thin films were measured as a function of relative humidity using ellipsometry and infrared spectroscopy. We compared the hydration properties of CM-PG to those measured for native PG, a cationically-modified PG (GTAC-PG), and a base hydrolyzed PG (BH-PG) to distinguish between the effects of chemical substitution and structural changes that occur during synthesis. The water uptake was similar for CM-PG and GTAC-PG, and considerably larger than that for native PG and BH-PG. Despite the similarity of their water uptake, CM-PG and GTAC-PG had large differences in their water structuring, which we interpreted in terms of the ability of the substituted functional groups to participate in a hydrogen bonding network. We also studied changes to the hydration properties of CM-PG with exposure to both monovalent and divalent cations. We found that interaction of CM-PG with Ca2+ resulted in a dramatic decrease in film swelling, possibly due to the formation of bridging complexes within the CM-PG particles. Collectively, our results demonstrate how the hydration properties of PG can be tuned through chemical modification, revealing the potential for new applications for this sustainable nanotechnology.

Examination Committee

• Dr. Leonid Brown, Chair
• Dr. John Dutcher, Advisor
• Dr. Robert Wickham, Advisory Committee
• Dr. Ian Tetlow, Graduate Faculty
• Dr. Eugenia Kumacheva, External Examiner (University of Toronto)