Effect of low levels of hydrotropes on micellization of phenothiazine drug

Interactions within mixtures of the phenothiazine drug promethazine hydrochloride (PMH) and cationic hydrotropes ortho -toluidine hydrochloride ( o -TDH) and para -toluidine hydrochloride ( p -TDH) were investigated at different ratios and temperatures via conductometry to understand various physicochemical properties. Critical micelle concentration ( cmc ) was less than values of cmc id ( cmc in ideal mixed system), indicating significant interaction among the studied constituents in solution mixtures. The cmc of pure PMH was also determined by measuring the surface tension for comparison. A variety of micellization thermodynamic parameters (Gibbs free energy [ΔG m 0 ], change in standard enthalpy [ΔG m 0 ], and change in entropy [ΔG m 0 ]) were computed using conductometry. The micellar mole fraction (X 1 Rb , X 1 Rod , and X 1 id ) of hydrotropes estimated by various theoretical models (Rubingh, Rodenas, and Motomura) was assessed, and the results showed a greater contribution of hydrotropes in mixed micelles along with their values increasing via an increase in mole fraction ( α 1 ) of hydrotropes ( o -TDH/ p -TDH). Negative β values suggest extremely favorable attractive interaction/synergism, as declines occurred in the whole quantity of amphiphile used for the desired purpose, leading to a drop of expenditure along with ecological concern. Obtained activity coefficients (f 1 and f 2 ) were always beneath unity, meaning nonideality was found between PMH and o -TDH/ p -TDH. Like the conductivity method, the UV-visible and FT-IR techniques also demonstrate the interaction between the PMH and o -TDH /p -TDH.