Abstract
The modifying effects of polyoxyethylene lauryl ether, sodium lauryl sulfate, cetyltrimethylammonium bromide and N-dodecyl betaine micelles on the rate of base-catalyzed hydrolysis of procaine were investigated. The retardation effect for the hydrolysis was observed in any surfactant solutions. Partition coefficients (K) to the micelles were calculated from kobs and the partial molar volume based on the phase separation model. The order of K was found to be SLS>CTAB>NDB>PLE for the free base. In the cationic surfactant system, the corresponding p-nitro substituted of procaine was also retarded in hydrolysis rate. These observations are contrary to the electrostatic theory. It could be considered that the effect of diethylaminoethyl moiety rather than p-substituents was predominant in the solubilization mechanism. The determination of partition coefficients by the potentiometric method was made for PLE and CTAB systems and a fairly good agreement with the values from kinetics data was obtained. Nuclear magnetic resonance studies suggested that in the case of SLS and PLE the solubilization of procaine was related as far as the center portion of the micelle whereas the drug molecule was located at the outer layer for CTAB and NDB micelles.
