Preparation and Characterization of Vesicles from Mono- n -alkyl Phosphates and Phosphonates (original) (raw)

The aggregation properties of different linear, single-chain alkyl phosphates and phosphonates in water were investigated at concentrations of up to 50 mM as a function of pH, focusing in particular on spontaneous vesicle formation. Under conditions where about half the molecules are monoionic and half the molecules are completely protonated (pH ≈ 2), n-dodecylphosphoric acid, n-decylphosphonic acid, and n-dodecylphosphonic acid spontaneously form vesicles at room temperature. For n-hexadecylphosphoric acid, stable vesicles only form above ∼40°C. The presence of vesicles was evidenced by light and electron microscopy and in the case of n-dodecylphosphoric acid by entrapment experiments using as water soluble probes glucose, dextran, and pepsin. The phase-transition temperature of vesicles of n-dodecylphosphoric acid was 2.3°C, as determined by differential scanning calorimetry. For n-hexadecylphosphoryladenosine evidence for micelle formation has been obtained with a cmc of 20-50 µM at 25°C. In an experimental extension of the vesicle selfreproduction principles to phosphoamphiphiles, results are also presented on the alkaline hydrolysis of the water-insoluble din -decyl-4-nitrophenyl phosphate, which led to the formation of 4-nitrophenol and di-ndecyl phosphate, the latter being a known vesicle-forming amphiphile.