DISSOLUTION BEHAVIOR OF SULFONAMIDES INTO SODIUM DODECYL-SULFATE MICELLES - A THERMODYNAMIC APPROACH

The surface energies of four sulfonamides have been assessed from cont act angle data, using the Lewis acid-base approach. From these data th e free energy of adhesion between the drugs and sodium dodecyl sulfate (SDS) head groups and tails has been calculated. The most favored int eraction was for adhesion to the SDS tails, rather than the head group s. The initial rotating disk dissolution rate (hereafter termed dissol ution rate) of drug compacts has been measured in water and water with SDS micelles at a range of temperatures. The thermodynamic parameters of activation have been calculated from the rate data. Linear relatio nships exist between the enthalpy of transfer between water and SDS mi celles and the free energy of adhesion between the drugs and both SDS head groups and SDS tails. The most nonpolar drugs had the most favore d free energy of adhesion and the most favored enthalpy of transfer. T he most polar drug had a disfavoured free energy of adhesion to the SD S head and a disfavoured enthalpy of transfer. This response demonstra tes that the most important barrier to the passage from the aqueous fl uid to the hydrophobic core of the micelle is the monopolar repulsion between the polar forces of the drug and head group surface energies. This provides a new insight into a possible mechanism of solubilizatio n and offers the prospect of understanding even more complex partition ing behavior.