resumo
Ion specific effects on the mutual solubilities between hydrophobic ionic liquids (ELs) and water are complex and not fully understood. The aim of this work is to obtain further evidence about the molecular mechanism behind this phenomenon by evaluating the effect of a large series of inorganic and organic salts on the mutual solubilities of water and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(4)mim][Tf(2)N]. The magnitudes of the salting-in and salting-out effects were assessed by changing either the cation or the anion, in a series of salts, as well as the salt concentration. It was observed that the influence of the ions on the solubility followed the Hofmeister series. Both salting-in and salting-out effects were observed and they showed to be dependent on both the nature of the salt and its concentration, while the pH had only a marginal effect on the studied solubilities. On the basis of the solubility changes of the ionic liquid in water in the presence of salts and on NMR spectroscopic data, it will be shown that salting-out inducing ions (high charge density) and salting-in inducing ions (low charge density) act through different mechanisms. While the former act mainly through an entropic effect resulting from the formation of water-ion hydration complexes which cause the dehydration of the solute and the increase of the surface tension of the cavity, the salting-in results from a direct ion binding of the low charge density ions to the hydrophobic moieties of the solute.
palavras-chave
AQUEOUS BIPHASIC SYSTEMS; HYDROGEN-BOND STRUCTURE; LIQUID/ORGANIC MIXTURES; HOFMEISTER SERIES; PHASE-BEHAVIOR; SALTING-OUT; MECHANISM; MACROMOLECULES; PRECIPITATION; EXTRACTION
categoria
Chemistry
autores
Freire, MG; Carvalho, PJ; Silva, AMS; Santos, LMNBF; Rebelo, LPN; Marrucho, IM; Coutinho, JAP
nossos autores
Isabel Maria Delgado Jana Marrucho Ferreira
Professor Catedrático
Mara Guadalupe Freire Martins
Investigador Coordenador
Pedro J. Carvalho
Professor AuxiliarGrupos
G4 - Materiais Renováveis e Economia Circular
G5 - Materiais Biomiméticos, Biológicos e Vivos
agradecimentos
Acknowledgment. The authors thank financial support from Fundacao para a Ciencia e a Tecnologia for Project POCI/EQU/58152/2004 and Ph.D. Grant SFRH/BD/41562/2007 of P.J.C. and post-doctoral Grant SFRH/BPD/41781/2007 of M.G.F.