Vesicles Composed of the Single-Chain Amphiphile Sodium Monododecylphosphate: A Model of Protocell Compartment

Abstract The phase behavior of sodium monododecylphosphate (SDP), a typical primitive single-chain amphiphile, in n-butanol (NBT)/H2O mixed solvent was investigated. An isotropic phase was observed in the SDP/NBT/H2O ternary system. Three aggregation structures, namely, vesicles, dendritic aggregates, and micelles, were identified in the isotropic phase. The SDP vesicles were characterized by transmission electron microscopy, dynamic light scattering, atomic force microscopy, and small-angle X-ray scattering. Their stability and permeability were determined. In addition, two kinds of enzyme-loaded vesicles were established to support a cascade reaction, to explore the possibility for chemical signaling. The results showed that the critical vesicle concentration of SDP in the solvent is ∼0.30 mM. The size and shell thickness of the vesicles are ∼80 and 3.81 nm, respectively. The vesicle formation probably arises from the synergistic effect of the solubilization of NBT for SDP and the H-bonding between SDP species. The SDP vesicles exhibit long-term and freeze-thawing stabilities and a size-selective permeability. In particular, the SDP vesicles can host a cascade reaction to mimic a chemical-signaling communication scenario, which may be a suitable alternative to protocell models.