Solubilization of hydrocortisone, dexamethasone, testosterone and progesterone by long-chain polyoxyethylene surfactants.

Solubility and dialysis methods were used to study the solubilization of hydrocortisone, dexamethasone, testosterone and progesterone in aqueous long-chain polyoxyethylene non-ionic surfactant solutions. Partition coefficients, Km, between micellar and aqueous phases were calculated between 10-50 degrees. Km decreased with temperature and polyoxyethylene chain length but increased with decrease in steroid polarity. The standard free energy change, deltaGOS, for the solubilization of the steroids decreased with decrease in steroid polarity and surfactant hydrophilic chain length but was essentially independent of temperature. The enthalpies and entropies for the process were determined from the variation of Km with temperature. deltaHOS and deltaSOS increased with decreasing steroid polarity but were essentially independent of temperature and polyoxyethylene chain length.