Effect of Aqueous Two-Phase System Constituents in Different Poly(ethylene glycol)–Salt Phase Diagrams

Abstract

Eight different poly(ethylene glycol) (PEG)/salt aqueous two-phase systems (ATPS's) were characterized at 23 °C. PEGs with different molecular weights (1500 and 8000) were combined with different salts (sodium or potassium citrates and formates) to study the effect of each ATPS constituent in the phase diagram. The binodal curve and several tie-lines were determined for each system using common analytical techniques described in the literature for ATPS's (cloud point method, conductivity, and gravimetric analysis after lyophilization). According to the results, it was found that each ATPS constituent produced a particular effect in the phase diagram. For the salts, changes in the anion produced larger variations in the heterogeneous region size than changes of the cation. Thus, the effect of salt type seems to be largely dependent on the anion, which makes the dominant contribution. The ability to form ATPS's is connected with the Gibbs energy of hydration, ΔG hyd , of the anions: more negative ΔG hyd values facilitate ATPS formation. Changes in the PEG molecular weight affected also the phase diagram: the size of the heterogeneous region increases with the increase in the polymer molecular weight.

(Liquid+liquid) equilibria of polymer-salt aqueous two-phase systems for laccase partitioning: UCON 50-HB-5100 with potassium citrate and (sodium or potassium) formate at 23°C

“…In fact, the largest heterogeneous region was obtained with the bivalent anion HPO 4 2À . A similar behavior was found when UCON is replaced by PEG8000 (or PEG6000, found as similar to PEG8000 for several PEG-salt ATPS [16,28,29]) and combined with Na 3-C 6 H 5 O 7 [16], Na 2 SO 4 [30], Na 2 HPO 4 [31], NaH 2 PO 4 [31], and NaHCO 2 [16] (Figure 6). In this case, the tendency found was: HPO 4 2À % , as expected from anion valence or DG hyd .…”

“…The phase diagrams for the ATPS obtained in this work can be compared with previous results for PEG-salt ATPS [16], as presented in figure 7. Inspection of this figure shows that less salt and polymer are required for phase splitting in the UCON-salt ATPS compared to ATPS with PEG.…”

“…Effect of salt type on the binodal curves of UCON-sodium salt ATPS: Na 3 C 6 H 5 O 7 (-)[17]; Na 2 SO 4 (-Á Á Á-)[20]; Na 2 HPO 4 ()[24]; NaH 2 PO 4 (-Á -)[24] and NaHCO 2 (--), this work; Effect of salt type on the binodal curves of UCON-potassium salt ATPS: K 3 C 6 H 5 O 7 (-), this work; K 2 HPO 4 ()[24]; KH 2 PO 4 (-Á -)[24] and KHCO 2 (--Effect of salt type on the binodal curves of PEG (8000 or 6000, see text)-sodium salt ATPS: Na 3 C 6 H 5 O 7 (-)[16]; Na 2 SO 4 (-Á Á Á-)[30]; Na 2 HPO 4 ()[31]; NaH 2 PO 4 (-Á Á-)[31] and NaHCO 2 (--)[16].…”

“…Formate is also biodegradable and nontoxic and could be discharge into biological wastewater treatment plants. In this respect, the liquid-liquid aqueous twophase systems containing PEG and (potassium or sodium) citrate and (potassium or sodium) formate has been studied [13][14][15][16]. However, only a very limited amount of research has been reported using EOPO copolymers with citrate or formate salts [17].…”

An aqueous two-phase system to pre-purify a heterologously produced siderophore

“…Increasing PEG molecular weight will increase interfacial tension between the resulting two phases which provides a stronger barrier to the transport of solute molecules from the upper PEG phase to the lower salt phase and, thus, prompting higher K d values 7 . However, PEG chains with a higher molecular weight will also increase repulsive interactions with solute and potentially decrease K d values 6,8 . Positive partitioning trends are refl ected in Fig.…”