Evaluation of thermodynamic parameters of some amphiphilic drugs in presence of sugars at the cloud point.

In the present investigation, we report the thermodynamics of clouding in four amphiphilic drugs viz., two tricyclic antidepressants: amitriptyline hydrochloride (AMT) and imipramine hydrochloride (IMP) and two phenothiazines: chlorpromazine hydrochloride (CPZ) and promethazine hydrochloride (PMT) in the absence and presence of sugars. For an amphiphile, cloud point (CP) can be considered as the limit of its solubility as the phase separates at temperatures above the CP. The clouding components release their solvated water and separate out from the solution. For all the cases, the standard Gibbs energy change of solubilization (ΔGs(0)) is evaluated, and found to be positive. However, the standard enthalpy change of solubilization (ΔHs(0)), and the product of standard entropy change of solubilization and temperature (TΔSs(0)) values are found negative as well as positive.