Partitioning of biomolecules in aqueous two-phase systems of polyethylene glycol and nonionic surfactant

Abstract

The partitioning of various hydrophobic or hydrophilic amino acids was investigated in aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) and nonionic surfactant (Triton X-100 and Tween 80), respectively. The influences of amino acids side chain group, tie line length (TLL) of ATPS, nonionic surfactant type and PEG molecular weight on the partitioning coefficients of amino acids were extensively studied. The results displayed that the hydrophilic amino acid preferred to partition in the top PEG-rich phase, and the hydrophobic amino acid preferred to the bottom surfactant-rich phase. These distribution trends of amino acids in PEG/nonionic surfactant ATPS were more obvious with increasing TLL, while the PEG molecular weight had no significant effect on the amino acids partitioning in ATPS. Moreover, the estimated hydrophobic factor (HF) values of PEG/nonionic surfactant ATPS should be about −10−2mol/kJ according to the amino acids partitioning, which demonstrated that the bottom surfactant-rich phase was generally more hydrophobic than the top PEG-rich phase. PEG20000/Triton X-100 ATPS had more extensive HF values scope (−0.0038 to −0.0496mol/kJ) than PEG20000/Tween 80 ATPS (HF −0.0162 to −0.0306mol/kJ) in the investigated TLL due to the different micelles size and number. The partitioning of model protein lysozyme was predicted in PEG/nonionic surfactant ATPS based on ATPS HF and lysozyme hydrophobicity. The experimental and predicted partitioning coefficients of lysozyme displayed a good consistency in the PEG/nonionic surfactant ATPS. It was shown that the hydrophobic interaction played an important role in both the partitioning of amino acids and the partitioning of the small model protein in PEG/nonionic surfactant ATPS.