Spontaneous Vesicle Formation of Monododecenyl Phosphonic Acid in Water

We report the synthesis of amphiphilic dodecenyl phosphonic acid PC₁₂ from vinylphosphonic acid, a reactive phosphonic acid intermediate. The trans-P-C=C moiety enabled PC₁₂ to disperse well in water. Surface tension and dynamic light scattering measurements revealed that PC₁₂ exhibited high surface activity and reduced the surface tension of water from 72.0 to 23.6 mN/m, thereby resulting in the spontaneous formation of aggregates even in a dilute aqueous solution (critical aggregation concentration (CAC) = 4.8 × 10^-4 M). In contrast to modern lipids with double-tailed structures, the PC₁₂ of simple singletailed structure spontaneously formed bilayered vesicles, without an external energy supply. Compared with the strength of hydrogen bonds formed by the long, saturated alkyl chain of dodecyl phosphonic acid (DPA), the strength of PC₁₂ intermolecular hydrogen bonds was weaker. The melting point of PC₁₂ was approximately 20°C lower than that of DPA. These results indicate that the trans-P-C=C moiety was considerably important for spontaneous vesicle formation in water. Preliminary modeling of the morphological transitions of the closed bilayer structures in the vesicles was then conducted, by varying the pH and adding an α-helical peptide scaffold.