Micellar Solubilization of Testosterone II

The solubility of testosterone at 25° was determined in aqueous solutions containing varying concentrations of dodecyltrimethylammonium bromide (DTAB), hexadecyl-trimethylammonium bromide (HTAB), and potassium laurate (KL). After the initial stages of solubilization, a linear relationship was observed between the amount of testosterone solubilized and the molar concentration of the surfactant. The order of increasing solubilizing capacity was DTAB < HTAB < KL. The environment of solubilized testosterone, as investigated by the Z-value method, was found to be quite polar in all cases. At low concentrations of DTAB and HTAB the Z value was similar to that in water. As the concentration of the quaternary ammonium bromides increased, a precipitous drop in Z value, corresponding to a sudden decrease in environmental polarity, was observed in the region of the critical micelle concentration. With further increase in the concentration of DTAB and HTAB the Z value remained reasonably constant. In low KL concentrations the Z value of the testosterone environment was higher (more polar) than in water. With increasing concentrations of KL the Z value displayed behavior similar to that in DTAB and HTAB. In general, solutions of ionic surfactants showed higher Z values than those of the nonionic surfactants examined previously.