APPARENT MOLAR VOLUMES AND ADIABATIC COMPRESSIBILITIES OF AQUEOUS-SOLUTIONS OF AMPHIPHILIC DRUGS

The apparent molar volumes and adiabatic compressibilities of aqueous solutions of the amphiphilic tricyclic drugs, chlorpromazine, promethazine, promazine and imipramine have been determined from measurements of density and ultrasound velocity. Positive deviations of the apparent molar volume from the Debye-Huckel limiting law in dilute solution indicate possible premicellar association. The changes of molar volume and compressibility accompanying aggregate formation were appreciably smaller than those of typical surfactants, suggesting a more tightly packed aggregate. The magnitude of the increase in molar compressibility on micellisation of imipramine decreased with temperature rise between 20 and 35 degrees C. The results are discussed in terms of the structure and hydration of the drug aggregates.