Investigating the Deep Eutectic-Water Binary Solvents Association by Vibrational Spectroscopy and Chemometrics methods

solvent interactions are important for probing chemical, industrial, environmental and biological processes in the liquid phase [1]. Therefore, investigating the behaviour of newly introduced solvents in the presence of other solvents such as water is essential. Deep eutectic solvents (DESs), introduced as novel green solvents by Abbott at 2003, are defined as eutectic mixtures of two or three non-toxic natural components that are able to generate intermolecular hydrogen bonds [2]. Choline chloride-glycerol deep eutectic solvent (GDES) was selected as a common DESs to study its behaviour in the presence of water. Combinations of vibrational spectroscopy (Raman and FTIR) and MCR-ALS were used to explore the association of solvents in the binary mixture of GDES and water. Preservation of intermolecular hydrogen binding between constituents of GDES during solvation with water was another aim of this study. Therefore, the behaviour of DESs and its components was compared. The binary mixture of glycerol (Gly), one of the liquid constituents of GDES, and water has been explored under the same conditions. This work utilizes the power of multi-technique (Raman and FTIR) and multi-experiment (GDES and Gly) data analysis for the proper description of complex processes of water and GDES interaction. Two binary solvent systems of GDES-water and Gly-water were studied. For each solvent system, a total of 20 binary solvent mixtures with different mole fractions of co-solvent varied from 0% to 100% (in 5% intervals) were prepared by mixing the proper weights of the pure solvents. The ATR-FTIR and Raman spectra of each prepared binary mixtures were recorded and the digitized spectra of each solvent system were collected in different data matrices. For each solvent system, two data matrices were provided; a data matrix of Raman intensities and a data matrix of IR absorbancies. MCR-ALS was utilized to analyze the obtained IR and Raman data matrices. As a result, five species were obtained for GDES-water interaction. Pure water, GDES, GDES-water association, Gly and Gly-water association were components that were achieved from MCR-ALS analysis of the GDES-water binary mixture. The stoichiometry of GDES-water association was 0.1 of mole fraction of GDES. It exhibits the considerable role of GDES even in very low mole fractions in the presence of water. In addition, concerning both GDES and Gly interaction in the presence of water by multi-technique and multi-experimental technique, identified GDES as a distinct solvent from its constituent (Gly).