Synthesis and Properties of Alkyl Phosphorylcholine Amphiphiles with a Linear and an Asymmetrically Branched Alkyl Chain

Alkyl phosphorylcholine amphiphiles bearing one linear chain and one asymmetrically branched alkyl chain were successfully synthesized using 2-chloro-2-oxo-1,3,2-dioxaphospholane in tetrahydrofuran or ethyl acetate. 1H and 31P NMR studies revealed that the linear alkyl phosphorylcholines (Cn-PC) provide aqueous micelles in D2O and reverse micelles in CDCl3, while the branched alkyl phosphorylcholines (ISOFOLn-PC) give vesicles in D2O. The critical micelle concentrations (CMCs) of Cn-PC were measured by fluorescence dye solubilization methods: the CMCs of C12-PC, C14-PC, C16-PC, and C18-PC were 1.6, 0.38, 0.16, and 0.11 mM, respectively, in water at 25 °C. The critical association concentrations (CACs) of ISOFOL16-PC, ISOFOL20-PC, and ISOFOL24-PC were 0.068, 0.005, and 0.077 mM, respectively, in water at 25 °C. The vesicle size of ISOFOLn-PC in aqueous solution was measured by the dynamic light scattering method. The mean diameter of ISOFOLn-PC vesicles was approximately 30 nm and the size distribution was relatively monodisperse. The ISOFOLn-PC vesicles formed were colloidally stable in water over the period of several weeks.