Aqueous biphasic systems formed by nonionic polymers I. Effects of inorganic salts on phase separation

Abstract

The effect of salts KSCN, KI, KBr, KCI, KC104, KF, K2SO4 and NH4CI, LiC1, NaC1, KC1, CsC1 on the binodials of the phase diagrams for aqueous biphasic dextranpolyvinylpyrrolidone, dextran-polyvinyl alcohol, dextran-ficoll and dextran-polyethylene glycol systems was studied. It is established that the K-salts present at the concentrations of 0.1 and 0.5 mol/kg alter the binodials of the phase diagrams for the above systems. The effect of a salt is found to be related to the lyotropy of the salt quantified by the salt molal surface tension increment. It is assumed that phase separation in an aqueous polymer biphasic system is affected by the presence of a salt mainly due to the effect of the salt on the structure and/or state of water in the system.

Effect of Polymer Size and Cosolutes on Phase Separation of Poly(Vinylpyrrolidone) (PVP) and Dextran in Frozen Solutions

“…Sodium chloride would be expected to increase the miscibility of PVP and dextran in frozen solutions by two main mechanisms: shifting the binodal of the aqueous polymer system, and diluting the nonice phase 24,25,35. Various salts alter the miscibility of nonionic polymers in aqueous solutions by changing the water structure and/or molecular interactions.…”

“…Various salts alter the miscibility of nonionic polymers in aqueous solutions by changing the water structure and/or molecular interactions. Salting‐in salts (e.g., NaSCN, KI) in Hofmeister's lyotropic series increase polymer miscibility and raise the polymer concentrations required for the aqueous two‐phase separation 35. These salts also show a large effect in merging the PVP and dextran phases in frozen solutions 8.…”

“…These salts also show a large effect in merging the PVP and dextran phases in frozen solutions 8. Addition of NaCl, which is an “intermediate” salt in the lyotropic series, slightly increases PVP and dextran miscibility in aqueous solutions, and prevents phase separation of the polymer combinations in frozen solutions 8,25,35. Salts and surrounding water molecules dilute other solutes in the nonice phase, which would provide the polymer combinations larger chances to remain in the single‐phase region of the phase diagrams.…”

The synergic effect of water and biomolecules in intracellular phase separation

“…For FUS family proteins, interactions between Tyr residues of PLDs and Arg residues of RBDs function as stickers, allowing the prediction of their critical concentration for phase separation 171 The aim of this Perspective is to compare the relatively well-studied ATPSs with MLOs in order to better understand the molecular mechanisms by which the latter form. The discussion will focus on two well-known models of phase separation: the Flory-Huggins (FH) theory [51][52][53] and the theory of H2O structure alteration originally formulated by Zaslavsky 54,55 . In view of the importance of H2O ordering, we propose here that intracellular LLPS is driven by a balance of enthalpically favourable intermolecular interactions and the increase of solvent entropy on moving to a solute surface to the bulk.…”

“…None of these newer theories account for the influence of H2O-mediated polymer-polymer or protein-protein interactions. These effects were considered by Zaslavsky and co-workers, who proposed that phase separation occurs because polymers alter the structure of H2O to the point that it forms two different and mutually incompatible H2O structures 54,55,85 . This proposal was developed in order to explain previous experimental studies suggesting that H2O-mediated structural changes induced either by the ATPS components (polymers, salts, ionic liquids) [86][87][88][89][90] or factors such as temperature and urea concentration 54 modulated phase separation.…”