Effect of Electrolytes on the Cloud Point and Dye Solubilization of Promazine Hydrochloride Solutions

The effect of electrolytes on the micellar behavior of amphiphilic drug, promazine hydrochloride (PMZ)a phenothiazine tranquillizer, has been investigated using cloud point (CP) and dye solubilization techniques. An increase in the pH of the PMZ solutions decreased the CP in the absence as well as presence of additives (NaCl, NaBr, KBr) due to deprotonation of the drug molecules. At constant pH (6.67), addition of sodium halides (NaF, NaCl, NaBr) and alkali metal bromides (LiBr, NaBr, KBr) caused an increase in CP and UV visible absorbance of the dye Sudan III. The behavior is explained on the basis of the ions' position in Hofmeister series and their hydrated radii. The CP increased with the addition of quaternary ammonium bromides due to adsorption/mixed-micelle formation; the order being: BuPrEtMe. The experimental results have been interpreted in terms of electrostatic effect and interactions between additives and PMZ head groups.