title: DeltaG(CH2) as solvent descriptor in polymer/polymer aqueous two-phase systems.
abstract: Phase diagrams were determined for aqueous two-phase systems (ATPSs) formed by different paired combinations of Dextran (Dex-75), Ficoll-70, polyethylene glycol (PEG-8000), hydroxypropyl starch (PES-100), and Ucon50HB5100 (a random copolymer of ethylene glycol and propylene glycol) all containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4, at 23 degrees C. Partition coefficients of a series of dinitrophenylated (DNP) amino acids with aliphatic side-chains were studied in all the ATPSs at particular polymer concentrations. Free energies of transfer of a methylene group between the coexisting phases, DeltaG(CH(2)), were determined as measures of the difference between the hydrophobic character of the phases. Furthermore, partition coefficients of tryptophan (Trp) and its di- and tri-peptides and a set of p-nitrophenyl (NP)-monosaccharides were measured in all the two-phase systems, and the data obtained compared with the DeltaG(CH(2)) values obtained in the systems. It was established that for eight out of 10 of two-phase systems of different polymer compositions the partition coefficients for Trp peptides correlate well with the DeltaG(CH(2)) values. Similar correlations for NP-monosaccharides were valid for seven out of 10 two-phase systems. These observations indicate that the difference between the hydrophobic characters of the coexisting phases represented by the DeltaG(CH(2)) value cannot be used as a single universal measure for comparison of the ATPSs of different polymer compositions.
authors.affiliation: Laboratory of Separation and Reaction Engineering, Dpt. de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n 4200-465 Porto, Portugal.
authors.forename: Pedro P
authors.initials: PP
authors.lastname: Madeira
authors.forename: José A
authors.initials: JA
authors.lastname: Teixeira
authors.forename: Eugénia A
authors.initials: EA
authors.lastname: Macedo
authors.forename: Larissa M
authors.initials: LM
authors.lastname: Mikheeva
authors.forename: Boris Y
authors.initials: BY
authors.lastname: Zaslavsky
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003911:Dextrans / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D009005:Monosaccharides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D014364:Tryptophan / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D003911:Dextrans; D009005:Monosaccharides; D010455:Peptides; D011108:Polymers; D012997:Solvents; D014867:Water; D011092:Polyethylene Glycols; D014364:Tryptophan; D000255:Adenosine Triphosphate; D000432:Methanol