Vesicle formation by ultrashort alkyl-phosphonic acids and serine in aqueous solutions

Vesicles possess unique biofilm structures and offer biomimetic advantages for drug and gene delivery. Herein, we report the spontaneous vesicle formation from ultrashort alkyl-phosphonic acids in the presence of amino acids. The aggregation characteristics and self-assembly structures of vesicles in aqueous solution were investigated by using dynamic light scattering, zeta potential, and cryo-transmission electron microscopy. We combined low-field nuclear magnetic resonance and Fourier transform infrared spectroscopy to study the H-proton-induced multilamellar vesicle formation. When we increased the molar fraction of serine, stable and closed spherical vesicles were formed at relatively low critical micelle concentrations. This transition of the self-assembled structure indicates that vesicle formation occurs when the chain length and the magnitude of the surface charge cause a fluctuation in the volume of the vesicle. Density functional theory reveals the critical role of the mixed alkyl-phosphonic acid/amino acid-enhanced electrostatic attraction between the head groups and hydrogen bonds associated with the aggregated states.