Penicillin G solubilisation into AOT reverse micelles

Extraction of penicillin G from an aqueous phase into an organic phase containing AOT reverse micelles has been investigated. The extraction is influenced by the initial penicillin G concentration, the salt type and concentration in the aqueous phase, pH, and surfactant concentration. The results show that penicillin is an interfacially active compound that interacts with AOT, with the interfacial association being dependent on both pH and surfactant concentration. When the concentration ratio [P]aq/[S] is high precipitation of the penicillin occurs. The distribution coefficient favours transfer of the penicillin into the reverse micelles at moderate AOT concentrations. The distribution coefficient at infinite dilution, K∞, is shown to be a function of both pH and surfactant concentration; similar trends in the value of K∞ were observed at different pH values; K∞ decreases as the surfactant concentration is increased. Reverse micelle formation affects the volume of water transferred into the organic phase; from measurements of the water transferred, the size of the reverse micelles was estimated to be about 3 nm and the number of AOT molecules per reverse micelle about 360.