Physicochemical studies of pyridinium gemini surfactants with promethazine hydrochloride in aqueous solution

The mixed micellization and interfacial behavior of pyridinium gemini surfactants, 1,1′-(1,1′-(ethane-1,2-diylbis-(sulfanediyl))bis(alkane-2,1-diyl))dipyridinium bromide, i.e., [12-(S-2-S)-12], [14-(S-2-S)-14], [16-(S-2-S)-16] with a phenothiazine tranquilizer drug, promethazine hydrochloride (PMT), has been investigated by conductivity, surface tension and steady state fluorescence measurements. Different spectroscopic techniques like fluorescence, UV-visible and NMR were also employed to understand the nature of interactions between the pyridinium gemini surfactants and PMT. The various micellar, interfacial and associated thermodynamic parameters for different mole fractions of PMT–pyridinium gemini surfactant mixtures have been evaluated. Synergism was observed in the mixed micelle as well as the monolayer formed by these mixtures. The fluorescence quenching experiment indicates that the interactions between PMT and surfactants are hydrophobic in nature. The UV-visible measurements reveal the distinct formation of a drug–surfactant complex. The detailed mechanism for the type of interactions was further studied by NMR titrations which show cation–π interactions between PMT and pyridinium gemini surfactant molecules.