Studies of Reactions and Dissolution of Polysaccharides in Quaternary Ammonium Salt-Based Deep Eutectic Solvents

Polysaccharides are essential biopolymers composed of long chains of monosaccharide units linked by glycosidic bonds, serving both structural and storage functions in biological systems. Representative polysaccharides such as cellulose, chitin, chitosan, and alginate possess distinct physicochemical properties and industrial relevance. Cellulose, a β-D-glucose polymer, forms rigid plant cell walls and is resistant to dissolution due to extensive hydrogen bonding. Chitin, present in arthropod exoskeletons and fungal cell walls, and its derivative chitosan offer broad biomedical applications. Alginate, derived from brown seaweed, is appreciated for its gel-forming capacity and biocompatibility. However, the strong hydrogen bonding networks in these polysaccharides hinder their solubility in conventional solvents, necessitating harsh chemical or physical treatment, which is often environmentally and economically unsustainable. Deep eutectic solvents (DES), formed by mixing a hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), have emerged as a green and cost-effective alternative for polysaccharide processing. These solvents disrupt internal hydrogen bonding through intermolecular interactions, enhancing solubility while preserving structural integrity. This study investigates the dissolution behavior of various polysaccharides in DES systems based on choline chloride combined with urea (CCU) or oxalic acid (COA), with a focus on optimizing parameters such as temperature, component ratio, and HBD type. Dissolution efficiency was evaluated gravimetrically, and ATR-FTIR spectroscopy was used to assess structural changes and interactions. Results revealed that cellulose dissolution in CCU is optimal at temperatures below 90 °C, while temperatures above 100 °C promote carbamation, inhibiting dissolution. Conversely, the COA system induced structural modifications even below 100 °C, suggesting stronger reactivity. Overall, ChCl/urea showed more favorable, non-destructive interactions, indicating its potential as a more suitable DES for polysaccharide dissolution.