Thermodynamics at the cloud point of phenothiazine drug chlorpromazine hydrochloride-additive systems

Abstract

An amphiphilic drug chlorpromazine hydrochloride (CPZ), a phenothiazine with neuroleptic activity, undergoes clouding phenomena, which depend upon the physicochemical conditions (e.g., concentration, pH, temperature, etc.). The clouding components release their solvated water and separate out from the solution. Therefore, the cloud point (CP) of an amphiphile can be considered as the limit of its solubility. Herein, we report the energetics of clouding in CPZ in the presence of additives (viz., alcohols, surfactants, and polymers). The standard Gibbs energy change of solubilization (ΔG⁰_s) for all of the additives is found to be positive. However, the standard enthalpy change (ΔH⁰_s) and the product of the temperature and the standard entropy change (TΔS⁰_s) values are negative as well as positive, depending upon the type and nature of the additive, and the results are discussed on the basis of these factors.