Dissolution behaviour of sulphonamides into sodium dodecyl sulfate micelles: a thermodynamic approach.

The surface energies of four sulfonamides have been assessed from contact angle data, using the Lewis acid-base approach. From these data the free energy of adhesion between the drugs and sodium dodecyl sulfate (SDS) head groups and tails has been calculated. The most favored interaction was for adhesion to the SDS tails, rather than the head groups. The initial rotating disk dissolution rate (hereafter termed dissolution 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 relationships exist between the enthalpy of transfer between water and SDS micelles and the free energy of adhesion between the drugs and both SDS head groups and SDS tails. The most nonpolar drugs had the most favored free energy of adhesion and the most favored enthalpy of transfer. The most polar drug had a disfavoured free energy of adhesion to the SDS head and a disfavoured enthalpy of transfer. This response demonstrates that the most important barrier to the passage from the aqueous fluid 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 solubilization and offers the prospect of understanding even more complex partitioning behavior.