# MSc Thesis Presentation: Exploring the Binding Properties of Phytoglycogen in its Native and Acid-Hydrolyzed States

Videoconference

## MSc Candidate

Nicholas van Heijst

## Abstract

Phytoglycogen (PG) is a polysaccharide made up of anhydroglucose units that occurs in nature as compact, highly branched nanoparticles. In this thesis, I investigate interactions of native and acid-hydrolyzed PG with bioactive compounds using different experimental techniques. In the first project, I explored the binding between acid-hydrolyzed PG and concanavalin A (ConA) in the surface plasmon resonance imaging (SPRi) experiment developed by K. Charlesworth. In the second project, I investigated the ability of PG to enhance the solubility of astaxanthin (ASX) in water and quantified this interaction using SPRi.

To study the interaction between acid-hydrolyzed PG and ConA, SPR sensors were functionalized with acid-hydrolyzed PG using an intermediate monolayer of 4-mercaptophenylboronic acid (4-MPBA). The kinetics studies revealed that ConA binds to acid-hydrolyzed PG with an equilibrium association constant $K= 2.31 \pm 1.38 \times 10^5 M^{-1}$ that is very close to that for ConA and native PG: $K= 2.87 \pm 0.44 \times 10^5 M^{-1.}$ This result demonstrates that morphological changes to PG caused by acid hydrolysis do not significantly affect its ability to bind ConA.

I also investigated the effect of PG to enhance the solubility of the water-insoluble carotenoid ASX in water. To explore this, I evaluated different protocols: emulsification through sonication, and complexing using hydrated organic solvents, including roto-evaporation of the organic solvent, lyophilization and redispersion in water. The effectiveness of each protocol was evaluated using UV-vis spectroscopy, and the most promising protocol was used to evaluate the binding between ASX-PG complexes and PG immobilized on SPR sensor surfaces. We obtained evidence for binding of ASX-PG complexes to the PG-functionalized sensor surface due to the presence of the ASX in the ASX-PG complexes.