AUTOPOIETIC SELF-REPRODUCTION OF FATTY-ACID VESICLES

Conditions are described under which vesicles formed by caprylic acid and oleic acid in water are able to undergo autopoietic self-reproduct ion-namely an increase of their population number due to a reaction wh ich takes place within the spherical boundary of tile vesicles themsel ves. This is achieved by letting a certain amount of the neat water-in soluble caprylic or oleic anhydride hydrolyze at alkaline pH: the init ial increase of the concentration of the released acid/carboxylate is extremely slow (several days to reach the conditions for spontaneous v esicle formation), but afterwards, the presence of vesicles brings abo ut a rapid second phase leading to more and more vesicles being formed in an overall autocatalytic process. The catalytic power of the capry lic acid and oleic acid vesicles toward the hydrolysis of the correspo nding anhydride is documented in a set of independent experiments. In these experiments, the hydrolysis was carried out in the presence of v esicles at a pH corresponding approximately to the pK of the acid in t he vesicles. The process of autopoietic self-reproduction of caprylic acid and oleic acid vesicles is studied as a function of temperature: by increasing temperature (up to 70 degrees C), the exponential time p rogress of vesicle formation tends to become steeper while the long in itial slow phase is significantly shortened. The caprylic acid and ole ic acid vesicles are characterized by electron microscopy and by deter mining their internal volume. The question whether and to what extent these vesicles form a classic chemical equilibrium system-in which nam ely the free surfactant is in equilibrium with the aggregates-is also investigated.