Thermodynamic properties of amphiphilic drugs in aqueous solution

Abstract

Osmotic and activity coefficients and excess free energies have been derived as functions of concentration from vapour pressure measurements on aqueous solution of the amphiphilic drugs, chlorpromazine, promethazine and imipramine at 308 and 313 K. The concentration dependence of the osmotic coefficient could be described using a mass-action model of association. Aggregation numbers and the degree of micellar ionisation have been predicted from the osmotic data and compared with values derived by time-averaged light-scattering methods. A temperature increase increased the critical micelle concentration but had no measurable influence on the aggregation number.