Screening Ionic Solvents for Enhancing the Solubility of Water-Insoluble Natural Dyes

Abstract

One strategy to promote the use of natural dyes consists of developing solvents capable of increasing their solubility. Herein, in silico predictions of activity coefficients based on the conductor-like screening model COSMO-SAC were used to screen the most promising ionic solventsionic liquids or eutectic mixturesfor the dissolution of three natural dyes, namely, indigo, alizarin, and curcumin. The predicted logarithmic activity coefficients at infinite dilution, lnγ∞, indicate that small ions having high charge density and capable of establishing strong hydrogen bonds appear to be the best candidates. Anions such as acetate, methanesulfonate, chloride, bromide, and methyl- or ethyl-sulfate combined with small tetraalkylammonium-based, pyrrolidinium-based, and imidazolium-based cations seem to be the best candidates for the interaction and thus possible dissolution of the natural dyes. The eutectic mixture of such small cation–anion combinations with primary amines, small carboxylic acids, and zwitterions such as betaine and carnitine can lead to ionic solvents that are liquids at room temperature. The chosen potential ionic solvents were prepared, and the experimental solubility of the three natural dyes was measured and compared with that in water.

A water-soluble type II photosensitizer for selective photooxidation reactions of hydroazaobenzenes, olefins, and hydrosilanes in water

“…[32][33][34][35][36] and organic dyes. 37 Although organic dye photocatalysts possess environmentfriendly properties, their solubility and activity in water are rather low, 38 which limits the potential uses of photocatalytic reactions in aqueous environments. Hence, there is a pressing demand for water-soluble organic photocatalysts.…”