Fredrik Joabsson

Partitioning of hydrophobic amino acids and oligopeptides in aqueous two-phase system containing self-aggregating block copolymer - Effects of temperature, salts and surfactants

Abstract The partitioning of hydrophobic amino acids and oligopeptides in the Pluronic P105-dextran-water system has been studied. Pluronic P105 is a member of a family of triblock copolymers with the structure PEO-PPO-PEO, where PEO is poly(ethylene oxide) and PPO poly(propylene oxide). The partitioning was studied for tryptophan, phenylalanine and di- and tri-peptides composed of these amino acids at 5 and 40°C. These temperatures correspond to a unimeric (5°C) and a micellar (40°C) state of the P105 molecule. Partitioning depend strongly on the temperature which is attributed to the increased hydrophobicity of Pluronic P105 with increasing temperature. However, it appears that the presence of the micelles plays no major direct role. The effect of different pH, salts and surfactants (both cationic and anionic) on partitioning has also been investigated.

Phase separation induced by dilution in a system of a hydrophobically modified polymer

Abstract A phase map of a nonionic cellulose ether, and an anionic surfactant (SDS), in aqueous solution has been determined. The influence of hydrophobic modification of the polymer has been investigated. In the system containing the hydrophobically modified polymer, a phase separation is induced by dilution. We suggest that the mechanism is related to a ‘bridging flocculation’. The polymer concentration in the polymer rich bottom phase is determined by association strength, preferred distance between the ‘tie points’, and, in the case of charged surfactant, electrostatic swelling. At higher surfactant concentrations the two polymer systems behave similar, and the effect of hydrophobic modification is lost.