TEMPERATURE-INDUCED PHASE PARTITIONING OF PEPTIDES IN WATER SOLUTIONSOF ETHYLENE-OXIDE AND PROPYLENE-OXIDE RANDOM COPOLYMERS

A thermoseparating random copolymer (Ucon 50-HB-5100) composed of (50% ) ethylene oxide and (50%) propylene oxide has been used to form an aq ueous two-phase system by heating the polymer-water solution above the cloud point of the copolymer. In the formed two-phase system a water rich top phase is in equilibrium with an aqueous polymer rich bottom p hase. The partitioning of amino acids and peptides in this aqueous two -phase system has been studied. Hydrophobic peptides (containing aroma tic amino acids) were strongly partitioned to the polymer rich phase, while hydrophilic peptides were enriched in the water rich phase. The effect of temperature on the partitioning was investigated and a decre ased partitioning to the polymer rich phase was obtained upon temperat ure increase. The effect of two salts (NaClO4 and Na2SO4) on the parti tioning of a positively charged polypeptide, poly(Lys, Trp), was very strong. With NaClO4 the polypeptide was quantitatively partitioned to the polymer rich phase while with Na2SO4 the polypeptide was partition ed to the water rich phase. Model calculations based on a modified Flo ry-Huggins theory have been performed to better understand the experim ental behavior.