Solubilization of aqueous-insoluble phenothiazine drug in TX-100 micellar solution and interactions of cationic/anionic surfactants with phenothiazine–TX-100 system

Abstract

This article discusses the interaction of surfactants such as tetradecyltrimethylammonium bromide (TTAB), hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC), cetylpyridinium bromide (CPB) and sodium dodecylsulphate (SDS) in presence of poorly soluble drug phenothiazine (PTZ) in triton X-100 (TX-100) micellar aqueous media through the investigation of different physicochemical parameters. The interaction of surfactants in PTZ–TX-100 media has been studied using conductometric technique at pH 7.4 (SP buffer) and at three temperatures. The conductometric results reveal the sequence of critical micelle concentration (CMC) values of surfactants as SDS > TTAB > CPC > CPB > CTAB. UV–vis spectroscopy studies were used to learn the interactions of surfactants with the drug PTZ in TX-100 aqueous media (at 303.15 K and pH 7.4) which suggest the interactions are highly feasible (change of Gibbs energy; ΔGb < 0) and greatly improve beyond the CMC values of corresponding surfactants. The estimated parameters using the Benesi–Hildebrand equation indicate higher binding constant (Kb) for cetylpyridinium surfactants and least for SDS and the drug–surfactant complex formations are found to be in 1:2 stoichiometric ratios. Fluorescence technique has also been employed to study the aggregation number (Nagg), Stern-Volmer constant (KSV) and micro-polarity of TTAB/CTAB/SDS in PTZ–TX-100 systems at 303.15 K. The evaluated thermodynamic parameters such as change in Gibbs energy (ΔGm0), enthalpy (ΔHm0) and entropy (ΔSm0) of micellization show the process of micellization of all studied surfactants in PTZ–TX-100 aqueous media are spontaneous and exothermic.