The mechanism of hydrotropy is experimentally proven in this work. Apolarity is shown to be the driving force of hydrotropy.

The efficiency of an ionic hydrotrope is shown to increase with the hydrophobicity of its counterion, challenging the common view that ionic hydrotropes should possess a small, densely charged counterion...

Cyrene is an emerging bio-based green solvent that has been shown to have the ability to increase the solubility of hydrophobic substances in water. Even though the water-Cyrene system is an attractive solvent, its applications are hampered by difficulties in the understanding of its solvation mechanism, caused by a delicate chemical equilibrium established between water and Cyrene. This work aims to rationalize the solvent capability of the water-Cyrene system and to establish the mechanisms of solvation through which hydrophobic solutes are dissolved in it.Using the cooperative model of hydrotropy, it is shown that hydrotropy is the solubilization mechanism of hydrophobic solutes in the water-Cyrene system, in most of its concentration range. Furthermore, the ketone form of Cyrene is revealed to be the principal hydrotrope of the system, with the diol form acting as a hydrotrope only at low Cyrene concentration. The parameters of the cooperative model, namely the number of hydrotrope molecules aggregated around the solute and the maximum solubility increase, are shown to be correlated with the hydrophobicity of the solutes quantified by their octanol-water partition coefficient. This result not only supports recent studies on the mechanism of hydrotropy but also adds a predictive ability to the cooperative model, which is then explored to successfully predict the solubility curves of phthalic acid, aspirin, gallic acid and vanillin in water-Cyrene mixtures.

No abstract

Levodopa (l-dopa) is an amino acid precursor of catecholamines dopamine, norepinephrine, and epinephrine, which can be used in the treatment of Parkinson’s disease. Levodopa is present in several vegetable sources, such as Mucuna pruriens seeds. However, the extraction of levodopa from vegetable matrices is usually carried out with volatile organic solvents (methanol, hexane, and chloroform). In this work, we demonstrate that aqueous solutions of eutectic solvents (ES) can be used as alternative solvents for the extraction of levodopa. ES based on carboxylic acids or polyols combined with cholinium chloride ([Ch]­Cl) were studied. Experimental conditions such as the temperature, solid–liquid (solvent/biomass) ratio, and ES concentration in aqueous solutions were optimized by a response surface methodology, with the aim of maximizing the levodopa extraction yield. Extraction yields of up to 9.9 ± 1.0 wt % (levodopa per dry weight of M. pruriens seeds) were obtained at a temperature of 56 °C, a solid–liquid ratio of 1:7, and an ES concentration close to 35 wt %. The recovery of levodopa from the ES aqueous solutions was achieved by a subsequent solid-phase extraction step, allowing the recovery of 87% of the extracted levodopa with high purity. This step further allowed solvent recovery and reuse, demonstrating that the solvent can be reused at least three times without compromising the extraction yield of levodopa. This work shows the remarkable capacity of ES aqueous solutions to extract the value-added compound levodopa from biomass and the possibility of applying reusable solvents, paving the way for their use as alternative solvents to extract bioactive compounds from natural sources.