Work

Developing a fast estimation method for the pH in aqueous solutions made of ILs with protic constituents: The case of choline with amino acid and peptide anions

Year: 2025

Type: article

Abstract: This work aims to provide simple and fast estimations for the pH of protic Ionic Liquids (ILs) solutions, particularly for those constituted with choline cation ([Ch] + ) and Amino Acid (AA) or Peptide (Pep) -based anions. pH calculation based on the pK a of pILs are typically carried-out with a posteriori , after synthesis and measurement, or a priori procedures, through quantum chemical calculations. Here, we adapt the isoelectric point (p I ) concept to perform a straightforward pH estimation for an aqueous solution of pILs using the pK a from their parental ions. Moreover, a library of pH values for 1 M aqueous solution of 14 different in-house synthetized ILs based on AA and Pep is presented, including the first (pH, FTIR and TGA) characterization of some of those solvents. Following the p I approach and using the pK a of the parental ions, the pH of a 1 M aqueous solution of these ILs has been predicted with suitable accuracy ( RMSD ≈ 0.5 units of pH), fulfilling the main estimation purposes of this work. Despite the tabulated pK a of each molecule being a more suitable input, software able to deploy fast pK a predictions may be used as well, especially when no experimental values are available, but one must be aware that some systematic errors may appear. In summary, we present a fast and straightforward method able to simplify the pH prediction of pIL aqueous solutions, a matter that can be key in the design of IL-based technologies.

Source: Fluid Phase Equilibria

DOI: 10.1016/j.fluid.2025.114477