Exploring the impact of sodium salts on hydrotropic solubilization

abstract

Some ionic liquids (ILs) were shown to display a strong ability to enhance the solubility of phenolic compounds through hydrotropy. However, evidence shows that salt ions in hydrotropic aqueous solutions may change the behavior of molecules by promoting possible interactions between the components of the system, thus causing changes in solubility. Herein, we study the impact of sodium salt anions on the hydrotropic dissolution of syringic acid using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) as a hydrotrope, with a focus on dicyanamide Na[N(CN)2] and thiocyanate Na[SCN] salts. Dynamic light scattering, Raman spectroscopy, and nuclear magnetic resonance spectroscopy were used to investigate how the mixture of IL-salts affects the solvation. The results obtained show that [C4mim]Cl is able to increase the solubility of syringic acid 80-fold. Despite their structural similarities, the presence of Na[N(CN)2] or Na[SCN] in an aqueous solution of [C4mim]Cl induced opposite solubility trends. The addition of Na[N(CN)2] promotes a higher ability to solubilize syringic acid than in the corresponding IL system due to a pH buffering effect, resulting in the deprotonation of the solute. The addition of Na[SCN], on the other hand, induces a relative decrease in syringic acid solubilization at higher concentrations of ILs due to the negative contribution of the NaCl formed by anion-exchange. These results emphasise the often overlooked pH contribution provided by ILs for biomolecule solubilisation whilst providing experimental insights into the structure of aqueous solutions of ionic liquids and the role it plays in the formation of IL-salt aggregates. The influence of salts, in the presence of an ionic liquid, on the aqueous solubility of syringic acid was assessed by determining the respective contribution of pH and hydrotropy.

keywords

IONIC LIQUIDS; MICELLE FORMATION; AQUEOUS-SOLUTIONS; WATER; AGGREGATION; BEHAVIOR; CATIONS; ANIONS; PHASE; ACIDS

subject category

Chemistry; Physics

authors

Benfica, J; Martins, AC; Peréz-Sanchéz, G; Schaeffer, N; Coutinho, JAP

Groups

G4 - Renewable Materials and Circular Economy
G6 - Virtual Materials and Artificial Intelligence

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & amp; LA/P/0006/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. J. B. S. acknowledges FCT for her PhD grant 2020.05802.BD. N. Schaeffer and G. Perez-Sanchez acknowledge the national funds (OE), through FCT (Fundac & atilde;o para a Ciencia e a Tecnologia), in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.