RESUMO
Critical micelle concentration (cmc) values were determined for the mixed zwitterionic/cationic gemini systems of N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/ N, N'-bis(dimethyldodecyl)-α,ω-alkanediammonium dibromide (12-s-12) systems. The cmc values for the mixed systems were determined through conductivity measurements. The degree of nonideality of the interaction in the mixed micelle (ßm), for each system, was determined according to Rubingh's nonideal solution theory. In most cases, the systems exhibited negative deviations (-ßm values) at high surfactant mole fractions of zwittergent (αZW3-12). Specifically, the ZW3-12/12-4-12 system displayed -ßm values at αZW3-12 ≥ 0.5, while both the ZW3-12/12-5-12 and the ZW3-12/12-6-12 systems displayed -ßm values over the entire mole fraction range. Except for the low mole fraction range in the 12-4-12 system, these mixed surfactant systems demonstrated almost identical behavior to the n-dodecyltrimethylammonium bromide/12-2-12 system studied by Bakshi et al. providing further evidence that ZW3-12 tends to behave as a cationic surfactant in mixed surfactant systems. The manner in which the cosurfactants aggregate in the micelles was determined via two-dimensional (2D) NOESY spectroscopy. In the case of both the ZW3-12/12-5-12 and the ZW3-12/12-6-12 systems, the 2D NOESY spectra exhibited strong cross peaks between the gemini and zwitterionic surfactants over the entire micellar composition range. In the case of the ZW3-12/12-4-12 system, little cross peak intensity was observed between the gemini and the zwitterionic surfactant at low micellar compositions of the zwittergent. The results suggest some micelle demixing is occurring between the gemini and the zwittergent certain micellar composition ranges, a phenomenon rarely associated with hydrocarbon surfactants.
RESUMO
Ibuprofen (IBF), 2-(4-isobutylphenyl) propionic acid, is a surface-active, common nonsteroidal anti-inflammatory drug (NSAID), and it possesses a high critical micelle concentration (cmc) compared to that of conventional surfactants. The interactions of this common NSAID with an anionic surfactant, sodium octyl sulfosuccinate, were studied by tensiometric, fluorimetric, and calorimetric measurements to investigate this system as a possible model drug-delivery system for an NSAID like IBF, particularly in a high-dose regime for IBF. The interactions between the drug and the surfactant were modeled using a regular solution theory approach in the presence and absence of a model electrolyte (sodium iodide) and a novel nonaromatic, gemini hydrotrope, tetramethylene-1,4-bis( N, N-dimethyl- N-butylammonium)bromide (4-4-4). Both the simple and the hydrotropic electrolyte were shown to have an effect on the solution properties (aggregation parameters, interfacial properties, and thermodynamics of aggregate formation) of the drug-surfactant mixtures and on the interaction between the drug and the surfactant. Surface charges of all self-assembled systems were estimated from ζ-potential measurements, whereas density functional theory calculations showed the interaction energy comparison among all of the binary and ternary combinations. All of these results were interpreted in terms of how altering the subtle balance of hydrophobic and electrostatic forces can significantly improve the ability of these self-assembled systems to transport drug molecules.