Salt effect on the (polyethylene glycol 8000+sodium sulfate) aqueous two-phase system: Relative hydrophobicity of the equilibrium phases

Abstract

Salt effect Relative hydrophobicity Gibbs free energy of transfer a b s t r a c tThe relative hydrophobicity of the phases of several {polyethylene glycol (PEG) 8000 + sodium sulfate (Na 2 SO 4 )} aqueous two-phase systems (ATPSs), all containing 0.01 mol Á L À1 sodium phosphate buffer (NaPB, pH 7.4) and increasing concentration of a salt additive, NaCl or KCl, up to 1.0 mol Á L À1 , was measured by the free energy of transfer of a methylene group between the phases, DG(CH 2 ). The DG(CH 2 ) of the systems was determined by partitioning of a homologous series of five sodium salts of dinitrophenylated (DNP) -amino acids with aliphatic side chains in three different tie-lines of each biphasic system. The relative hydrophobicity of the phases ranged from À0.125 to À0.183 kcal Á mol À1 , being the NaCl salt the one to provide the more effective changes. The results show that, within each system, there is a linear relationship between the DG(CH 2 ) and the tie-line length (TLL), and biphasic systems with high salt additive concentration present the most negative DG(CH 2 ) values. Therefore, the feasibility of establishing a relationship between the relative hydrophobicity of the phases in a given TLL and the ionic strength of the salt additive was investigated and a satisfactory correlation was found for each salt.

Partitioning of DNP-Amino Acids in New Biodegradable Choline Amino Acid/Ionic Liquid-Based Aqueous Two-Phase Systems

“…This result is the same for the four DNP-amino acids in the two studied ATPS. Higher values of the K (and ln K ) for the DNP-amino acids for the APTS containing K 3 PO 4 were obtained. The partition coefficient values of DNP-amino acids for the {[Ch]­[Ala] (1) + K 3 PO 4 or K 2 HPO 4 (2) + water (3)} ATPS follow the trend: K leucine > K valine > K alanine > K glycine . This tendency is in agreement with previously studied ATPS. − …”

“…The partition coefficient values of DNP-amino acids for the {[Ch]­[Ala] (1) + K 3 PO 4 or K 2 HPO 4 (2) + water (3)} ATPS follow the trend: K leucine > K valine > K alanine > K glycine . This tendency is in agreement with previously studied ATPS. − …”

“…A comparison of the partition coefficients presented in this work and those found in literature for the same studied DNP-amino acids on different ATPS was carried out. − It should be noted that only those data that allow the representation of distribution coefficients versus tie-line length were considered in Figures and . Nevertheless, all data found in literature were taken into account to elucidate the conclusions reached.…”

“…Logarithm of the distribution coefficients of the DNP-amino acids: (a) DNP- l -leucine, (b) DNP- l -valine, (c) DNP- l -alanine, and (d) DNP-glycine versus tie-line length for the ATPS: (★) {[Ch]­[Ala] (1) + K 3 PO 4 (2) + water (3)} (this work), (×) {[Ch]­[Ala] (1) + K 2 HPO 4 (2) + water (3)} (this work), (□) {PEG 4000 (1) + Na 3 C 6 H 5 O 7 (2) + water (3)}, (■) {PEG 6000 (1) + Na 3 C 6 H 5 O 7 (2) + water (3)}, (■) {PEG 8000 (1) + Na 3 C 6 H 5 O 7 (2) + water (3)}, (○) {PEG 8000 (1) + Na 3 C 6 H 5 O 7 (2) + water (3)} at T = 296.15 K, (●) {PEG 8000 (1) + K 3 C 6 H 5 O 7 (2) + water (3)} at T = 296.15 K, (△) {PEG 4000 (1) + K 3 C 6 H 5 O 7 (2) + water (3)}, (▲) {PEG 6000 (1) + K 3 C 6 H 5 O 7 (2) + water (3)}, (▲) {PEG 8000 (1) + K 3 C 6 H 5 O 7 (2) + water (3)}, (◊) {PEG 4000 (1) + KNaC 4 H 4 O 6 (2) + water (3)}, (⧫) {PEG 6000 (1) + KNaC 4 H 4 O 6 (2) + water (3)}, (⧫) {PEG 8000 (1) + KNaC 4 H 4 O 6 (2) + water (3)}, (−) {PEG 8000 (1) + Na 2 SO 4 (2) + water (3)}, (|) {PEG 8000 (1) + Mg 2 SO 4 (2) + water (3)}, (×) {PEG 8000 (1) + Na 2 SO 4 (2) + water (3)} at T = 296.15 K, (+) {PEG 8000 (1) + Na 2 SO 4 (2) + water (3)} . Note: All represented values were determined at T = 298.15 K and p = 101.3 kPa, except those indicated.…”

“…With these systems, it is possible to evaluate the effect of the salt in the partition coefficient values of the four DNP-amino acids. Further, the experimental data were compared with those found in literature for the same studied DNP-amino acids on other ATPS. − To our knowledge, no data for the partitioning of these four amino acids on the ATPS involving [Ch]­[Ala] are available in the literature. It is worth mentioning that the experimental data for the binodal curve and the tie-lines of the studied ATPS were reported in a previous work .…”