Extraction Of Tryptophan Research Articles

Extraction of Tryptophan with Ionic Liquids Studied with Molecular Dynamics Simulations

Extraction of amino acids from aqueous solutions with ionic liquids (ILs) in biphasic systems is analyzed with molecular dynamics (MD) simulations. Extraction of tryptophan (TRP) with the imidazolium-based ILs [C(4)mim][PF(6)], [C(8)mim][PF(6)], and [C(8)mim][BF(4)] are considered as model cases. Solvation free energies of TRP are calculated with MD simulations and thermodynamic integration in combination with an empirical force field, whose parametrization is based on the liquid-phase charge distribution of the ILs. Calculated solvation free energies reproduce successfully all observed experimental trends according to the previously reported partition of TRP between water and IL phases. Water is present in ILs as a cosolvent, due to direct contact with the aqueous phase during extraction, and is found to play a major role in the extraction of TRP. Water improves solvation of cationic TRP by 7.8 and 5.1 kcal/mol in [C(4)mim][PF(6)] and [C(8)mim][PF(6)], respectively, which is in the case of [C(4)mim][PF(6)] sufficient to extract TRP. Extraction in [C(8)mim][PF(6)] is not feasible, since the hydrophobic octyl groups of the cations limit the water concentration in the IL. The solvation of cationic TRP is 2.4 kcal/mol less favorable in [C(8)mim][PF(6)] than in [C(4)mim][PF(6)]. Water improves the solvation of TRP in ILs mostly through dipole-dipole interactions with the polar backbone of TRP. Extraction is most efficient with [C(8)mim][BF(4)], where hydrophilic BF(4)(-) anions substantially increase the water concentration in the IL. Additionally, stronger direct electrostatic interactions of TRP with BF(4)(-) anions improve its solvation in the IL further. The solvation of cationic TRP in [C(8)mim][BF(4)] is 3.4 kcal/mol more favorable than in [C(8)mim][PF(6)]. Overall, the extractive power of the ILs correlates with the water saturation concentration of the IL phase, which in turn is determined by the hydrophilicity of the constituting ions. The results of this work identify relations between the extraction performance of ILs and the basic chemical properties of the ions, which provide guidelines that could contribute to the design of improved novel ILs for amino acid extraction.

Characteristics of Solute Transfer in Sodium Dioleyl Phosphate/Sodium Bis(2-Ethylhexyl) Sulfosuccinate Microemulsion Systems.

The behavior of solute transfer in sodium dioleylphosphate (SDOLP)/n-heptane and SDOLP-AOT/n-heptane systems was elucidated by focussing on the extraction process in Winsor II and the solute-exchange process between microemulsion droplets. The extraction of tryptophan (Trp) between the organic and aqueous phases is rather fast for the simultaneous extraction of water and Trp in the SDOLP and SDOLP/AOT systems, whereas in the extraction of Trp without water transfer between the microemulsion droplet and the aqueous phase, the rate slows down significantly with the addition of SDOLP in the AOT system. The rate of the interdroplet exchange process is insensitive to the presence of SDOLP. The reason for the difference in these two processes is discussed with the help of a model of the exchange processes.