Abstract
The current study investigated the mixed micellization of a phenothiazine drug, promethazine hydrochloride (PMT), with the anionic hydrotrope sodium benzoate (NaB) using a conductometric method in three different solvent media: water, 50 mmol.kg−1 sodium chloride (NaCl), and 300 mmol.kg−1 urea (U). Five different temperatures, ranging from 293.15 to 313.15 K, were chosen for the current study of both pure and mixed systems. PMT belongs to a class of drugs known as antihistamines, which are used to treat allergy symptoms. Various physicochemical parameters of both pure and mixed systems (PMT+NaB) were evaluated at different compositions and temperatures, using numerous theoretical models associated with mixed micellization. The attained critical micelle concentration (cmc) and ideal cmc (cmcid) values indicated the formation of mixed micelles due to interactions between the components. The evaluated cmc value for PMT, the minimum hydrotropic concentration (mhc) of NaB, and the cmc value for the PMT+NaB mixture decreased in the NaCl system and increased in the U system compared with these values in the aqueous solution. The cmc values of the studied mixed systems decrease due to an upsurge in the mole fraction (α1) of NaB, indicating the non-ideality of the evaluated solution mixtures. The interaction parameter (β) was negative, revealing that the interaction between the constituents increased with the increasing α1 of NaB in aqueous solution. In the NaCl solution, the β value increased, whereas, in the U solution, the value decreased. The degree of dissociation (g) values decreased by increasing the α1 of NaB in the solution mixture. Various thermodynamic parameters were also evaluated in detail. The activity coefficient values in all cases were below unity, which further indicated the non-ideality of the system. The assessed excess free energy (∆GexRb) of the system was found to be negative in all cases, displaying the stability of the formed mixed micelles. Across the different solvents, their magnitudes were observed in the following order: ∆GexRb in NaCl > ∆GexRb in water >∆GexRb in U. An ultraviolet (UV)-visible study showed a clear interaction between NaB and PMT in the aqueous system. A Fourier-transform-infrared (FT-IR) spectroscopy investigation revealed a shift in the frequency bands of the components due to the interactions between them.
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•Interaction of PMT drug and sodium benzoate mixtures were examined.•Various physicochemical parameters at different composition/temperature were evaluated.•In NaCl, the interaction between components enhanced while decreased in urea.•UV-visible investigation also showed the interaction between drug and hydrotrope.•FT-IR study depicted the shift in frequency band of components owing to interaction.