PREPARATION AND CHARACTERIZATION OF VESICLES FROM MONO-N-ALKYL PHOSPHATES AND PHOSPHONATES

The aggregation properties of different linear, single-chain alkyl pho sphates and phosphonates in water were investigated at concentrations of up to 50 mM as a function of pH, focusing in particular on spontane ous vesicle formation. Under conditions where about half the molecules are monoionic and half the molecules are completely protonated (pH ap proximate to 2), n-dodecylphosphoric acid, n-decylphosphonic acid, and n-dodecylphosphonic acid spontaneously form vesicles at room temperat ure. For n-hexadecylphosphoric acid, stable vesicles only form above s imilar to 40 degrees C. The presence of vesicles was evidenced by ligh t and electron microscopy and in the case of n-dodecylphosphoric acid by entrapment experiments using as water soluble probes glucose, dextr an, and pepsin. The phase-transition temperature of vesicles of n-dode cylphosphoric acid was 2.3 degrees C, as determined by differential sc anning calorimetry. For n-hexadecylphosphoryladenosine evidence for mi celle formation has been obtained with a cmc of 20-50 mu M at 25 degre es C. In an experimental extension of the vesicle self-reproduction pr inciples to phosphoamphiphiles, results are also presented on the alka line hydrolysis of the water-insoluble di-n-decyl-4-nitrophenyl phosph ate, which led to the formation of 4-nitrophenol and di-n-decyl phosph ate, the latter being a known vesicle-forming amphiphile.