TA Instruments -Applications Note Thermodynamics of Micelle Formation

Abstract Micelles are organized molecular assemblies of surfactants. In aqueous solution, the hydrophilic head of the surfactant is in contact with solvent, and the hydrophobic tail is sequestered within the center of the micelle. Micelles are usually spherical in shape, and can be cationic, anionic, ampholitic (zwitterionic), or nonionic depending on the chemical structure of the surfactant. Knowledge of the micellar phases of naturally occurring molecules or drugs is essential for determining how they may influence biological events. Mixed micelle formations that include amphipathic drug molecules, may result in decreased biological activity, and hence decreased therapeutic response. The propensity of drug molecules to aggregate is of great biological importance, and identifying the chemical details of the aggregation process could enhance control of micelle-encapsulated drugs. Enthalpies of micelle formation and critical micelle concentration were determined with isothermal titration calorimetry (ITC) for two model micelle systems, sodiumdodecylsulphate (SDS) and cetyltrimethylammonium bromide (CTAB)