Investigation
of Amino Acid–Polymer Aqueous Biphasic Systems
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Abstract
Aiming at gathering further information
to evaluate the recently proposed, mechanism of
the salt effect in aqueous polymer solutions, experimental vapor–liquid
equilibria (VLE), liquid–liquid equilibria (LLE), and volumetric-compressibility
measurements were carried out for several polymer–amino acid
aqueous systems. The constant water activity lines (obtained through
the isopiestic method at 298.15 K) of aqueous polypropylene glycol
400 (PPG400) + alanine or glycine systems, which form aqueous biphasic
systems (salting-out effect), have a concave and convex slope, respectively,
in the one-phase and two-phase regions. However, all the investigated
polyethylene glycols (PEG400, PEG2000, PEG6000, and PEG10000) do not
form aqueous biphasic systems with alanine or glycine (salting-in
effect) and their constant water activity lines have a convex slope.
In the second part of this work, the apparent molar volume and isentropic
compressibility of transfer of alanine and glycine from water to aqueous
solutions of PEG200, PEG2000, PEG10000, and PPG400 were studied at
different temperatures. The third part of this work is concerned with
the determination of LLE phase diagrams for several ternary polymer–amino
acid aqueous systems containing polymers PPG400 and PPG725 and amino
acids alanine, glycine, serine, and proline at different temperatures.
On the basis of the obtained cloud point values of aqueous solutions
of PPG725 in the absence and presence of various amino acids, it was
found that all the investigated amino acids have a salting-out effect
on PPG725 in aqueous solutions and entropy is the driving force for
biphasic formation