The partition of charged liposomes in aqueous two-phase systems.

Surface charge has been conveyed upon phosphatidylcholine liposomes by incorporation of varying amounts of stearic acid and stearylamine. The partition behaviour of these charged liposomes in several aqueous two-phase polymer systems containing a range of potential differences across the interface was investigated. Changes in partition were observed that were dependent on the stearylamine concentration of the liposomes. Incorporation of stearic acid produced no major changes in partition. Identical changes in partition were detected for stearic acid and stearylamine containing liposomes in a phase system with little or no potential difference. These changes in partition therefore represent the effect of the 'non-charged' portion of the lipid molecule. The use of aqueous two-phase partition as a method for detecting liposome surface charge is discussed.