Abstract
Considering to the importance of choline amino acid ionic liquids, [Ch][AA]-ILs, as green biocompatible and biodegradable solvents utilized for separation of proteins through inducing aqueous biphasic systems in the presence of some water soluble polymers, it is vital to elucidate the solute-solute and solute-solvents interactions in water media which may be responsible for phase separation. In this respect, density, sound speed and viscosity of choline L-histidine, [Ch][L-His], in water and aqueous solutions of three polymers containing polyethylene glycol dimethyl ether 250, PEGDME250, polypropylene glycol 400, PPG400, and polyethylene glycol 400, PEG400, have been measured experimentally at T = (288.15 to 318.15) K and 298.15 K under atmospheric pressure, respectively. The obtained data from these measurements were employed for computing the limiting values for apparent molar volume (Vφ0), molar isentropic compressibility (κφ0), transfer molar volume (ΔtransVφ0) and isentropic compressibility (Δtransκφ0) for transferring [Ch][L-His] from water to aqueous polymer solutions, viscosity B-coefficient, transfer viscosity B-coefficient (ΔtransB), free energies of activation per mole of solvent (Δμ10≠) and solute (Δμ20≠). These quantities provide some useful information about [Ch][L-His]-polymer and [Ch][L-His]-water interactions, soluting-out ability of IL and capability of above ternary solutions for separation into two-phases. The results showed that the ΔtransVφ0 values for PPG and PEGDME are negative which indicates that IL-water interactions become stronger in the presence of these polymers. But, in the case of PEG, a positive value of ΔtransVφ0 shows that the IL-water interactions are weaker in the presence of this polymer.
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