title: Competition of hydrophobic steroids with sodium dodecyl sulfate, dodecyltrimethylammonium bromide, or dodecyl β-D-maltoside for the dodecane/water interface.
abstract: The surface tension lowering abilities of insoluble steroids, progesterone and testosterone, were examined at the dodecane/water interface in the presence and absence of surfactants, sodium dodecyl sulfate, dodecyltrimethylammonium bromide, and dodecyl maltoside. In the absence of these surfactants, the steroids significantly lowered the interfacial tension while exhibiting no activity at the air/water and air/dodecane surfaces. Further, in mixtures of surfactants and steroids, significant enhancement of interfacial tension lowering was observed. At a sufficiently high concentration of surfactant, no further lowering of tension was observed in the presence of the steroids. The synergistic effects on interfacial tension of steroids and surfactants were characterized by the free energy of transfer to the interface of each solute based on a two-dimensional solution equation of state. Assuming no significant interaction between the steroids and the surfactants in the interface, predictions of interfacial tensions were made based on the calculated free energies of transfer and interfacial area occupied. Good agreement was found between the predicted values and experimental values for interfacial tension. The results of these studies show that progesterone and testosterone, molecules not normally thought of as surface active, exhibit significant interfacial activity and can successfully compete with surfactants for the dodecane/water interface.
authors.affiliation: College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536, USA.
authors.forename: Shaoxin
authors.initials: S
authors.lastname: Feng
authors.forename: Paul M
authors.initials: PM
authors.lastname: Bummer
mesh_terms: D000327:Adsorption; D000388:Air; D000473:Alkanes / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D019999:Pharmaceutical Solutions; D011374:Progesterone / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D012996:Solutions; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013739:Testosterone / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water
chemical_list: D000473:Alkanes; D005960:Glucosides; D019999:Pharmaceutical Solutions; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D013501:Surface-Active Agents; D014867:Water; C007548:n-dodecane; D012967:Sodium Dodecyl Sulfate; D013739:Testosterone; D011374:Progesterone; C040358:dodecyl maltoside; C022806:dodecyltrimethylammonium