Screening of ionic liquids for the dissolution of chitosan using COSMO-RS

Abstract

The dissolution of chitosan is a tedious and time-consuming process. Herein, we select the best Ionic Liquids (ILs) for chitosan dissolution through the application of Conductor-like Screening Model for Real Solvents (COSMO-RS), which allowed the screening of 640 ILs based on 32 cations based on amino acids, imidazolium, pyridinium, and pyrrolidinium, and 20 selected anions such as [C₂H₃O₂], [Cl], [NO₃], [BF₄], and others. Thermodynamic properties such as logarithmic activity coefficient at infinite dilution (ln γ) and excess enthalpy (H^E) were used to evaluate the dissolution potential of ILs towards chitosan, whereby low values of ln γ and H^E indicated better engagement between the solute and the solvent, thus resulting in a higher solute being dissolved. A preliminary screening of chitosan dissolution was carried out in all 5 synthesized ILs to validate the results obtained by COSMO-RS. It was observed that ILs with [BF₄⁻] as the anion and cations such as [Ser], [Gly], [Phe], [Cys], and [Asn] have the lowest ln γ values, hence better interaction with chitosan. The values of H^E indicated that the molecular interactions between chitosan and ILs were governed by hydrogen bonding (ranging from 37 to 50%), followed by misfit interactions (ranging from 21 to 31%) and van der Waals forces (ranging from 22 to 32%) due to the abundance of hydroxyl (–OH) groups present in the intermolecular and intramolecular chitosan structures. These proved the great ability of COSMO-RS to accurately predict the dissolution of chitosan in ILs.