POPC and EPL (composition: 67.0% phosphatidylethanolamine, 23.2% phosphatidylglycerol, 9.8% cardiolipin) lipids were dissolved in cyclohexane and transferred into a glass vial. Cyclohexane was evaporated under a gentle N 2 stream. The dried lipid film was flash frozen in liquid N 2 and further freezedried for five hours. Lipids were resuspended (5 mg/mL) in 10 mM potassium phosphate buffer (pH 7.0) under gentle agitation for 1 hour, followed by sonication for 1 hour. Fos-choline-12 (5 mg/mL) was solubilized in solvent A. Before injection, lipids were diluted to the appropriate concentration and finally added to ice-cold 100 mM potassium phosphate buffer, pH 2.3 (1:1 vol/vol; final pH 2.5).